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福 井 大 学 工 学 審 査
学位論文[博士(工学)]
A Dissertation Submitted to the University of Fukui
for the Degree of Doctor of Engineering
Immobilization of Natural Macromolecules onto the
Surface of Synthetic Fabrics Impregnated with
Cross-linking Agents Using Supercritical Carbon Dioxide
(超臨界二酸化炭素を用いる合成繊維布への
架橋剤の注入と天然高分子の固定化)
2010 年 9 月
麻 文 效
Contents Chapter 1. General introduction 1 1.1. Surface modification on polymer material 1 1.1.1. Background of polymer material 1
1.1.2. Conventional techniques in surface modification 2 1.1.2.1. Wet chemical 3
1.1.2.2. Ionized gas treatments 4 1.1.2.2.1. Plasma 4 1.1.2.2.2. Corona discharge 5 1.1.2.2.3. Flame treatment 5
1.1.2.3. Electron beam irradiation 6 1.1.2.4. UV irradiation 6 1.1.2.5. Ozone oxidation 7 1.1.2.6. γ-ray irradiation 7 1.1.2.7. Physical curing or coating method 8
1.1.3. Problems and shortages of conventional techniques 8 1.2. Supercritical fluid techniques in the processing of polymer 8 1.2.1. Supercritical fluid 8 1.2.2. Supercritical carbon dioxide 11 1.2.3. Polymer modification in scCO2 12 1.2.3.1. Foaming 12
1.2.3.2. Impregnation 13 1.2.3.2.1. Fiber dyeing 13 1.2.3.2.2. Drugs loading 14 1.2.3.2.3. Monomer impregnation and polymerization 15 1.2.3.2.4. Other applications by impregnation 16
1.3. Synthetic fiber 17 1.3.1. PET fiber 17 1.3.2. PP fiber 18 1.4. Natural macromolecules 19 1.4.1. Sericin 19 1.4.2. Chitosan 19 1.4.3. Polylysine 20 1.4.4. Collagen 20 1.5. Objective of this research 21 1.6. Outline of the thesis 22
References 24
i
Chapter 2. Coating of natural proteins onto synthetic fabric crosslinked with diisocyanate by supercritical dioxide carbon 35
2.1. Introduction 35 2.2. Experimental procedures 36 2.2.1. Reagents and materials 36 2.2.2. Treatment 37 2.2.2.1. Impregnation of TDI into PET and PP fabrics by scCO2 38 2.2.2.2. Immobilization of natural proteins onto TDI-PET and TDI-PP
fabrics by the pad-dry-cure method 39 2.2.3. Analysis 40 2.3. Results and discussion 40 2.3.1. Supercritical impregnating PET and PP fabrics with TDI 40 2.3.2. Immobilization of natural proteins (sericin and polylysine) onto the
surface of TDI-PET and TDI-PP fabrics 43 2.3.3. FT-IR analysis 44 2.3.4. Staining by methylene blue 48 2.3.5. Hydrophilicity effect 49 2.4. Summary 51 References 52
Chapter 3. Impregnation of cyanuric chloride into PET and PP fabrics with the aid of supercritical carbon dioxide, and its application in immobilizing natural biomacromolecules 54
3.1. Introduction 54 3.2. Experimental procedures 57 3.2.1. Materials and reagents 57 3.2.2. Treatment 57
3.2.2.1. Impregnation of CC into PP and PET fabrics by scCO2 57 3.2.2.2. Immobilization of biomacromolecules (sericin or chitosan) onto
CC-PET and CC-PP fabrics 58 3.2.3. Analysis method 59 3.3. Results and discussion 60 3.3.1. Supercritical impregnation with cyanuric chloride 60 3.3.1.1. Impregnation in pure scCO2 60 3.3.1.2. Impregnation in scCO2 with co-solvents 63 3.3.2. Biomacromolecules immobilization 66 3.3.3. XPS spectra analysis 67 3.3.4. FT-IR spectra analysis 69 3.3.5. Surface morphology 72
ii
iii
3.3.6. Hydrophilicity characterization 75 3.3.6.1. Water contact angles 75 3.3.6.2. Wicking properties 76 3.4. Summary 77 References 78
Chapter 4. Modifying poly(ethylene terephthalate) fabric by supercritical carbon dioxide 81 4.1. Introduction 81
4.2. Experimental procedures 83 4.2.1. Materials and reagents 83 4.2.2. Methods 84 4.2.2.1. Impregnation of GPE into PET by scCO2 84 4.2.2.2. Immobilization of functional agents onto PET fabrics 85 4.2.2.2.1. Processing in an aqueous solution 86 4.2.2.2.2. The pad-dry-cure treatment 86 4.2.3. Characterizations 86 4.3. Results and discussion 89 4.3.1. Supercritical treatment of PET fabric 89 4.3.2. Immobilization of functional agents (sericin, collagen, or chitosan) onto
GPE-PET and original PET fabrics 96 4.3.3. Surface wettability and moisture regain of the original and the modified
PET fabrics 100 4.3.4. Antibacterial efficiency of the untreated and the modified PET fabrics 104 4.4. Summary 106 References 107
Chapter 5. General conclusion 111
List of publication 114
Presentations 115 Acknowledgements 116
Chapter 1. General introduction 1.1. Surface modification on polymer material
1.1.1. Background of polymer material
Now, in the 21st century, it is difficult to find an aspect of our lives that is not affected by
polymers. Polymer, in the form of plastics, rubbers and fibers, have for many years played
essential but varied roles in everyday life: as electrical insulation, as tyres, and as packaging
for food, to mention but three. 1 They have been employed in a variety of biomedical
applications ranging from implantable devices to controlled drug delivery. Polymers such as
poly(methyl methacrylate) find application as photoresist materials used in semiconductor
manufacturing and low-k dielectrics for use in high-performance microprocessors. Recently,
polymers have also been employed as flexible substrates in the development of organic
light-emitting diodes for electronic display. One trend in modern civilization is that the
polymer materials are gradual replacing more traditional materials such as metals, ceramics,
and natural polymers such as wood, cotton, natural rubber ect. In general, successful
applications of polymer materials require special properties such as flame retardancy, ageing
resistance, surface affinity, conductivity, lubricity/roughness, and others. However, ordinary
polymers usually do not present the properties needed for special applications. It is essential
to modify the properties of a polymer according to tailor-made specifications designed for
target applications.
Polymer surfaces are the phase boundaries that reside between the bulk polymer and the
outer environment. The performance of polymeric materials relies largely upon the properties
of the boundaries in many applications.2 For instance, the surface of a fabric used in an
underclothing is often the interface between the body and the underclothing. By controlling
the surface properties of the fabric, the underclothing designer can enhance or inhibit various
reaction of body to the clothing. The interaction between the polymer and its environment
depends in large part on surface composition and structure. As most polymeric materials,
however, have a hydrophobic, chemically inert surface, untreated non-polar polymer surfaces
often have adverse problems in adhesion, coating, painting, coloring, lamination, packaging,
- 1 -
colloid stabilization, etc. Biomedical applications of polymeric materials have also faced
many critical obstacles such as undesirable protein adsorption and cell adhesion, due to the
poor biocompatibility of conventional polymer surfaces. Since surface composition and
topography play such a large role in the performance of the polymer, precise surface
characterization can be an important part in the rapid deployment of new materials or
understanding of problems and behavior in existing materials. To solve these problems, an
enormous number of basic and applied research has been devoted to the surface modifications
of polymeric materials.3-6
1.1.2. Conventional techniques in surface modification
Surface modification techniques, which can transform inexpensive natural or synthetic
polymers into highly valuable end products, have become important to the polymer industries.
A polymer surface can be modified by means of various chemical and/or physical processes,
even the so-called non-reactive polymers. The most common techniques include plasma-ion
beam treatment, electric discharge, UV-irradiation, γ-ray irradiation, chemical reaction,
surface coating etc. The schematic presentation of the surface modification is presented in
Figure 1.
PolymerFunctionalized Polymer
Grafted/Coated Polymer
Functional agents
Chemical reaction
Coating/Curing
EB, UV, γ-ray, etc
Plasma treatmentFunctional agents or monomer
Grafting
Wet chemical
Ozone oxidization
Figure 1. Schematic representation of the conventional methods of surface modification
on polymer materials.
- 2 -
1.1.2.1. Wet chemical
In wet chemical surface modification, a material is treated with liquid reagents to generate
reactive functional groups on the surface. The generated functional groups not only improve
the surface properties of materials but can react with new functional molecules for
modification farther. This classical approach to surface modification does not require
specialized equipment and thus can be conducted in most laboratories. It is also more capable
of penetrating porous three-dimensional substrates than plasma and other energy source
surface modification techniques,7 and allows for in situ surface functionalization of
microfluidic devices.
Chromic acid and potassium permanganate in sulfuric acid have been used to introduce
reactive oxygen-containing moieties to PE and PP.8–12 For example, submersion in a 29:42:29
weight ratio solution of chromium trioxide, water, and sulfuric acid at 72°C for 1 min resulted
in 3.3 nmol/cm2 carboxylic acid functionalities on PE.9 Concentrated sodium hydroxide and
sulfuric acid have been used to generate carboxylic acid groups by base and acid hydrolysis of
PMMA.13-15 Specifically, a 16 h treatment in 10M sodium hydroxide at 40°C was reported to
produce 0.66 nmol/cm2 carboxylic acids on PMMA.13 Methyl ester side chains of PMMA also
have been reduced to hydroxyls by treatment in lithium aluminum hydride in ether.16 Primary
amines have been introduced to PMMA, poly(urethane) (PU), PLA, and PLGA by aminolysis
using various diamines including hydrazine hydrate, 1,6-hexanediamine, ethylenediamine,
and N-aminoethyl-1,3-propanediamine, as well as lithiated diamines.14, 17-24 Lastly, PTFE
surfaces have been modified by refluxing with elementary sodium in toluene to generate
double bonds, followed by an 8 h oxidation at 120°C in a 1:1 mixture of trifluoroacetic acid
and hydrogen peroxide (38%) which improved membrane wetting and allowed
immobilization of the enzyme alliinase.25
Unfortunately, these wet chemical methods generate hazardous chemical waste and can
lead to irregular surface etching.26 Many of these techniques require extended treatment in
concentrated corrosive solutions. In addition, those which target modification of polymer side
chains (as in PMMA ester modification) depend on side chain surface orientation. The degree
of surface functionalization may therefore not be repeatable between polymers of different
- 3 -
molecular weight, crystallinity, or tacticity. For these reasons, while useful in the laboratory
environment, these wet chemical processes may not be suitable for larger scale, industrial
applications.
1.1.2.2. Ionized gas treatments
1.1.2.2.1. Plasma
Plasma is a high energy state of matter, in which a gas is partially ionized into charged
particles, electrons, and neutral molecules.27 Plasma can provide modification of the top
nanometer of a polymer surface without using solvents or generating chemical waste and with
less degradation and roughening of the material than many wet chemical treatments.28, 29 The
type of functionalization imparted can be varied by selection of plasma gas (Ar, N2, O2, H2O,
CO2, NH3) and operating parameters (pressure, power, time, gas flow rate).28
Oxygen plasma is often used to impart oxygen containing functional groups to polymer
surfaces such as PCL,30 PE,31 and PET.32 In addition to oxygen, carbon dioxide plasma has
been used to introduce carboxyl groups on PP,33 PS,34 and PE,35 and air plasma has been used
to oxidize PMMA.14 Ammonia and nitrogen plasmas have been used to impart amine groups
to the surface of PTFE36 and PS,34 respectively. Inert gases can be used to introduce radical
sites on the polymer surface for subsequent graft copolymerization. For instance, Kang et al.
pretreated PTFE with Ar plasma in order to graft polymerize acrylic acid,37 as did Ademovic
et al. on PVDF38 and Cheng et al. on PCL.39 Similarly, PE, PET, and PVDF have been
pretreated with Ar plasma in order to graft polymerize poly(ethylene glycol)
monomethacrylate and 4-vinylpyridine.40 In a process called radio frequency glow discharge
(RFGD), plasma can be used to initiate surface graft polymerization of vaporized
monomers.41 Plasma can be used as a precursor to other surface modification techniques, for
example, plasma activation followed by ultraviolet (UV) graft polymerization42 or plasma
activation followed by silanization.43 However, with the exception of a recent development of
an atmospheric plasma system,44 plasma generation requires a vacuum to empty the chamber
of latent gases, which presents complications for continuous operation in a large scale
industrial setting.45 Also, results are difficult to repeat between laboratories as there are many
- 4 -
parameters involved to optimize conditions, including time, temperature, power, gas
composition/flow/pressure, orientation of reactor and distance of substrate from plasma
source.29 It should be noted that in addition to the monomers and gases intentionally
introduced to the plasma chamber, latent chemicals from prior users may be present thus
posing a risk of contamination. The plasma chamber should therefore be adequately cleaned,
for example by oxygen plasma, before introducing polymers for surface modification.
1.1.2.2.2. Corona discharge
Corona discharge is a simple, low cost, continuous process in which an electrically
induced stream of ionized air bombards the polymer surface. It is commercially used to
improve printability and adhesion to inert polymers28 by introducing surface oxidation
products.26, 46 However, these results in a broad range of oxygenated groups and therefore may
be less useful as a technique to introduce specific functionalities for bioconjugation. Because
it does not operate under a vacuum, contamination may also be an issue, and variations in
local temperature and humidity can affect consistency of treatment.26 Finally, it has been
reported that surface polar groups on corona treated polyolefins are particularly unstable.
Materials should therefore be used shortly after treatment.29
1.1.2.2.3. Flame treatment
Like corona discharge, flame treatment is a non-specific surface functionalization method
that bombards the polymer surface with ionized air, generating a broad spectrum of surface
oxidation products to the top several monolayers.26, 28 In this method, the reactive oxygen is
generated by burning an oxygen rich gas mixture. Flame treatment has been shown to impart
hydroxyl, aldehyde, and carboxylic acid functionalities to poly(ethylene) and is utilized to
enhance printability, wettability, and adhesion.46 Although fundamentally simple and
inexpensive, flame treatment can reduce optical clarity to polymers, and there are many
parameters (including flame temperature, contact time and composition) that must be
accurately controlled to maintain consistent treatment and to avoid burning.29
- 5 -
1.1.2.3. Electron beam irradiation
E-beam radiation is a form of ionizing energy that is generally characterized by its low
penetration and high dosage rates. The beam, a concentrated, highly charged stream of
electrons, is generated by the acceleration and conversion of electricity. The electrons are
generated by equipment referred to as accelerators which are capable of producing beams that
are either pulsed or continuous. As the material being sterilized passes beneath or in front of
the electron beam, energy from the electrons is absorbed. This absorption of energy alters
various chemical and biological bonds within the material. Several applications in polymer
industry are well known, as radiation induced degradation, crosslinking, grafting, curing and
polymerization.47-50 For example, functional vinylic monomers along with functional
cross-linkers were spin coated onto the surface of the silicon and exposed to the keV electron
irradiations to obtain long-term hydrophilic surfaces with a cross-linked network of grafted
monomers by Mahapatra et al.51 It was also reported that some synthetic fibers could be easily
grafted with some vinyl monomers by electron beam (EB) irradiation method.52 There are
some limitations or areas of concern associated with electron beam technology, it included
that discoloration may occur on some materials, and short penetration depending on material
density etc.
1.1.2.4. UV irradiation
Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of
visible light, but longer than X-rays. As an ionizing radiation it can cause chemical reactions,
and causes many substances to glow or fluoresce. When exposed to UV light, polymer
surfaces generate reactive sites which can become functional groups upon exposure to gas or
can be used to initiate UV-induced graft polymerization. This technique differs from ionized
gas treatments by the ability to tailor the depth of surface reactivity by varying wavelength
and thus absorption coefficient.5 UV irradiation has been used to introduce carboxylic acid
functionality to PMMA,53 as well as to activate PS surfaces for enzyme immobilization54 and
tissue engineering55 applications. UV irradiation has also been used to initiate radical graft
polymerization of bioactive compounds. For instance, N-vinylpyrrolidone has been
- 6 -
photografted to the surface of PP films to generate antimicrobial materials.56 UV treatment
can affect the optical properties of the polymer, and UV light can also be blocked by particles,
which may affect treatment consistency.
1.1.2.5. Ozone oxidation
Mathieson and Bradley57 modified the surface of PE and a polyetheretherkotone (PEEK),
oxidizing the surface with ozone in addition to UV radiation, namely an ultraviolet–ozone
oxidation process. The pretreated polymer surfaces exhibited significant improvement in
adhesion when tested using an epoxy adhesive. The combination of UV and ozone treatment
was also utilized by Walzak et al.58 to improve surface properties of PP and PET. They also
compared the effect between UV/ozone and ozone alone. Reactions of PET with ozone alone
typically needed longer times to show the same contact angle and O/C atomic ratio as those
obtained by the UV/air and UV/ozone treatments. They demonstrated that the treatment with
ozone alone (without UV light) followed a different reaction pathway, resulting in a slower
treatment with less chain scission. Exposure of isotactic PP to ozone resulted in surface
oxidation and formation of peroxides and hydroperoxides.59 The molecular weight of PP was
dramatically reduced after times as short as 5 min of ozonation. It was possible to graft
copolymerization of 2-hydroxyethyl methacrylate to the ozonated samples, and the graft
copolymer acted as a continuous matrix consequently linked to and reinforced by the PP
crystals.
1.1.2.6. γ-ray irradiation
γ-rays are electromagnetic waves, which are shorter in length than UV waves and higher
in energy. γ-rays do not have any mass or charge but interact with the material by colliding
with the electrons in the shells of the atoms. The rays slowly lose energy in the material while
generally travelling significant distances before being stopped. Irradiation by γ-ray produces
radical sites on the polymer backbone. This is usually achieved by the abstraction of hydrogen
atoms.60 Gamma radiation has been used for many years to alter the molecular structure and
microscopic properties of polymers as well as initiating polymerization.61-63 Irradiating
- 7 -
polymers with γ-ray can lead to a decrease in the molecular weight of the polymer caused by
the breaking of the C–C bond. The molecular weight has also been found to increase where
two radical species on the polymer backbone recombine to form a new bond. γ-radiation can
also lead to the decomposition of polymers resulting in gas evolution or the creation of double
bonds.
1.1.2.7. Physical curing or coating method
Perhaps the easiest and the most strait forward way to modify polymer surface is by
blending functional molecules into the bulk polymer or just coating it on the polymer surface.
Recently, physical blending/curing functional molecules into/onto polymer surface was
significantly developed by appearance of some new techniques, among which includes self
migration,64 self assembly,65, 66 and layer by layer method.67, 68
1.1.3. Problems and shortages of conventional techniques
Although these techniques mentioned can modify polymer materials in varying degrees,
some shortages are always existent and limited in the manufacture scale. Physical coated
product often exhibit peeling problems during the service performance regardless of how mild
or severe the abrasive condition is, because the abrupt interface that frequently formed in the
coating products generates residual stresses in the coated layer, which cause the detachment of
the coated layer from the substrate with a slight application of load.69 Chemical methods, on
the other hand, can permanently modify polymer materials, however, will generate hazardous
chemical waste and can lead to irregular surface etching. Irradiation techniques are also
limited in laboratory scale because they require complicated production equipment, strict
operation requirements and are expensive, while also having a degradation effect on the
substrate polymer. Accordingly, easy-operate, low-cost, environmentally friendly processes
for modifying the polymer surface are always required currently.
1.2. Supercritical fluid techniques in the processing of polymer
1.2.1. Supercritical fluid
- 8 -
A supercritical fluid (SCF) may be defined as a substance for which both temperature and
pressure are above the critical values (Figure 270, Table 171, 72). However, this definition is of
limited use since it gives no information about the density of the substance. Darr and
Poliakoff offer a more practical definition,72 where a supercritical fluid is described as ``any
substance, the temperature and pressure of which are higher than their critical values, and
which has a density close to or higher than its critical density''. With some exceptions, most
applications reported involve CO2 under conditions of temperature and pressure such that the
density frequently exceeds the critical density (0.47 g cm-3). Indeed, many techniques require
densities that are in the range expected for conventional liquid solvents (0.8-1.0 g cm-3). Close
to the critical density, SCFs display properties that are to some extent intermediate between
those of a liquid and a gas.71, 73, 74 For example, a SCF may be relatively dense and dissolve
certain solids while being miscible with permanent gases and exhibiting high diffusivity and
low viscosity. In addition, supercritical fluids are highly compressible and the density (and
therefore solvent properties) can be ``tuned'' over a wide range by varying pressure [Figure.
3(a)].
Figure 2. Schematic pressure-temperature phase diagram for a pure component showing the
supercritical fluid (SCF) region.
- 9 -
Table 1. Critical parameters for selected substances (Tc=critical temperature, Pc=critical
pressure, ρc=critical density).
Substrance Tc/°C Pc/bar ρc/g cm-3
CH4 -82.5 46.4 0.16
C2H4 10 51.2 0.22
C2F6 19.9 30.6 0.62
CHF3 26.2 48.5 0.62
CClF3 28.9 38.6 0.58
CO2 31.1 73.8 0.47
C2H6 32.4 48.8 0.2
SF6 45.6 37.2 0.73
Propylene 91.9 46.1 0.24
Propane 97.2 42.5 0.22
NH3 132.5 112.8 0.24
Pentane 187.1 33.7 0.23
iPrOH 235.4 47.6 0.27
MeOH 240.6 79.9 0.27
EtOH 243.5 63.8 0.28
iBuOH 275.1 43 0.27
Benzene 289 48.9 0.3
Pyridine 347.1 56.3 0.31
H2O 374.2 220.5 0.32
- 10 -
Figure 3. (a) Graph showing the variation in density for pure CO2 at 35°C. At this
temperature (i.e., close to Tc for CO2) there is a rapid but continuous increase in density near
the critical pressure (Pc). (b) Schematic representation of the change from liquid-gas
equilibrium (T<Tc) to supercritical fluid (T>Tc) conditions as a substance is heated above its
critical temperature at a pressure in excess of Pc.
1.2.2. Supercritical carbon dioxide
Carbon dioxide is the most widely used supercritical fluid because it is readily available,
inexpensive, nontoxic, and nonflammable, and it has a relatively low critical temperature
(31.1 °C) and pressure (73.8 bar). It does not threaten the ozone layer as do
chlorofluorocarbons which are used extensively in polymer manufacturing. Moreover, many
polymers become highly swollen and plasticized in the presence of CO2, allowing processing
at low temperatures. The use of supercritical CO2 does not create a problem with respect to
the greenhouse effect as it is recovered during processing. When the process finished, CO2
- 11 -
can also be separated from a system by simple depressurization. Due to these unique
characteristics, scCO2 has been successfully utilized in separation (extraction),75-77 particle
generatation,78 chemical reaction79 and polymer modification.80
1.2.3. Polymer modification in scCO2
1.2.3.1. Foaming
Microcellular polymers (i.e., polymers with cell sizes less than or equal to 10 mm) are
used as separation media, adsorbents, controlled release devices, biomedical devices, and as
lightweight structural materials. Traditional methods for the formation of these materials are
based on a temperature quench (or, less commonly, the addition of an antisolvent) to induce
phase separation of a homogeneous polymer solution.81 Thermal induced phase separation
involves dissolving the polymer in an appropriate hydrocarbon solvent and quenching the
temperature to induce phase separation. This is followed by solvent removal, either by
freeze-drying or by supercritical fluid extraction. Beckman82 has developed an alternative
``solvent free'' approach, whereby a polymer is saturated with scCO2 at moderately elevated
temperatures followed by rapid depressurisation at constant temperature (i.e., a pressure
quench as opposed to a temperature quench). This method takes advantage of the large
depression in Tg found for many polymers in the presence of CO2,83 which means that the
polymer may be kept in the liquid state at relatively low temperatures. By lowering the
pressure at a fixed temperature the amount of diluent absorbed by the polymer is decreased.
Thus, Tg begins to rise, eventually to the point where Tg for the polymer is higher than the
foaming temperature: at this point the cellular structure can grow no further and is locked in.
The sudden reduction in pressure leads to the generation of nuclei due to supersaturation, and
these nuclei grow to form the cellular structure until vitrification occurs. This method has
been used for the generation of PMMA foams consisting of a microcellular core surrounded
by a relatively non-porous skin. More later, the method by utilizing scCO2 have extended to
the generation of microcellular polystyrene,84 polypropylene,85 polycarbonate,86 and PET
foam so on.87 In some cases, the method was also applied for the foaming of biodegradable
polymers such as poly(lactic-co-glycolic acid),88 poly(3-caprolactone)89 and polylactic acid.90
- 12 -
1.2.3.2. Impregnation
The impregnation process with the aid of scCO2 is the base of many applications in
polymer modification. Supercritical impregnation here can be described as the delivery of
solutes to the desired sites inside the polymer matrix (Figure 4). The process is feasible when
the active substance (the solute) is soluble in the scCO2, the polymer is swollen by the
supercritical solution and the partition coefficient is favourable enough to allow the matrix to
be charged with enough solute. Of course the degree of impregnation can be controlled by
adjusting the solubility of the additive with temperature and pressure. Most of these were
done by direct contact of impregnating materials and substrates with or without a liquid
carrier present. In addition, some researchers have pointed out that the insoluble solute in
scCO2 can also be incorporated into a polymer matrix because of the high partition
coefficients between polymer and scCO2 phase.91
Solutes
scCO2 Polymer
dissolving loading
swelling
plasticizing
Figure 4. Interactions between the scCO2-assisted impregnation system.
1.2.3.2.1. Fiber dyeing
Dyeing using scCO2, in which the solutes transported are organic dyes, is perhaps the
most common application of impregnation to date. The conventional fiber dyeing process
discharges much wastewater that is contaminated by various kinds of dispersing agents,
surfactants and unused dye. It is very difficult to design a conventional biological process that
treats the wastewater discharged from a conventional dyeing process. The environmentally
friendly supercritical CO2 process does not require any water, dispersing agents or surfactants
- 13 -
and also does not involve any drying stage after dyeing. This technique is an alternative one
which has been developed widely since early 1990s.
Saus et al.92 reported on dyeing of synthetic fibers by disperse dyes. Gebert et al.93
extended the supercritical dyeing to natural fibers such as cotton and wool. Knittel and
Schollmeyer94 reported on dyeing of PET and polypropylene with different dyes. Shim et al.95
investigated sorption of some disperse dyes (C. I. Disperse Blue 60 (B60), C.I. Disperse Red
60 (R60), C.I. Disperse Yellow 54 (Y54), and C.I. Disperse Orange 30 (O30)) in PET and
PTT fibers as well as difficult-to-dye fibers such as aramid and polypropylene using
supercritical carbon dioxide at pressures between 10 and 33 MPa and temperatures between
35 and 150°C. For dyeing in a co-solvent laden supercritical fluid, ethanol, acetone, or
N-methyl pyrrolidone was also introduced in the dyeing vessel.
Dye molecules are generally large and their diffusion rate is very small. They may
penetrate only into the glassy part and not in the crystalline part of a polymeric matrix. Dye
sorption increased with pressure at the same temperature and increased with temperature at
the same pressure, but this increasing rate was reduced with increasing pressure.
1.2.3.2.2. Drugs loading
In recent years, considerable attention has been focused on the development of drug
delivery systems, which attempt to increase bio-availability, sustain, localize or target drug
action in the body. Polymer microparticles are often employed as supports to deliver drugs,
either as microspheres (monolithic devices) or microcapsules (reservoir devices). In the
preparation of controlled-release drugs, a liquid solvent swelling the polymer matrix and
serving as a carrier for the drug component is used. Because of cost and environmental
regulations associated to the use of organic solvents, the pharmaceutical industry has been
moving away from the use of these solvents, and alternative technologies have been
developed, such as the supercritical fluid technology.96
Polymeric materials have a very limited solubility in scCO2, and this is an interesting
feature for producing monolithic loaded microspheres, obtained by an impregnation process.97
Also, polymer separation using scCO2 is enabling the selection of a pure fraction of a polymer,
- 14 -
thereby allowing a more precise control of drug release from polymeric delivery systems.
Kazarian and Martirosyan investigated the formation of ibuprofen/PVP composites via in situ
ATR-IR and Raman spectroscopy,98 and the impregnation of 5-fluorouracil and β-estradiol
into PLGA has also been reported.99 PMMA, PCL, and PMMA/Poly(q-caprolactone),
microspheres can also be loaded successfully with different amounts of cholesterol by using
scCO2 impregnation.100
1.2.3.2.3. Monomer impregnation and polymerization
Dissolution of CO2 in a polymer facilitates diffusion of monomers and catalysts/initiators
within the polymer matrix. In this case, CO2 is the carrier of active chemical species101 as well
as the swelling agent. Accordingly, chemical modification of polymers can be carried out in
milder conditions than with standard methods of melt modification in extruders or batch
mixers. This is extremely important for polymers, such as poly(tetrafluoroethylene) (PTFE)102
and PP103 for which modification in the melt is always accompanied by degradation.
The polymeric substrates bisphenol A poly(carbonate) (PC), poly(vinyl chloride) (PVC)
and poly(tetrafluoro ethylene) (PTFE) were modified by the impregnation of vinylic
monomers styrene (S), methyl methacrylate (MMA) and methacrylic acid (MAA) under
supercritical conditions.104 The impregnation of styrene and acrylic acid into a series of
polyamide products (nylon1212, nylon1010, nylon66, nylon6) using supercritical CO2 as
additive carrier and substrate-swelling agent was performed by Xu and Chang.105 It was found
that the relative solubility of the additive in the polymer substrate and CO2 is a major factor
governing the incorporated amount; however swelling of the substrate and CO2-induced
crystallization also contribute to the value. Methyl acrylate,106 2-hydroxyethyl
methacrylate,107 methyl methacrylate,108 styrene109 and maleic anhydride110 are reported to be
successfully grafted onto PP film in CO2 assisted processes. In all these cases the presence of
CO2 does not modify the radical grafting mechanism111 but it provides better dispersion of the
reactive species in the PP matrix at low processing temperature. In the studies, a modification
in the thermal properties of PP was observed and attributed not only to the grafting of polar
groups but to the plasticizing action of CO2.112
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Addition reactions have also been carried out on polymeric substrates in order to graft
active chemical groups onto the backbone. Friedmann et al.113 studied the grafting of
isopropyl isocyanate onto ethylene-vinyl alcohol copolymers (EVOH) concluding that the
major advantage of CO2 consists in the selective dispersion and consequent reaction of the
monomer in the amorphous phase of EVOH. A study about to selectively modify the end
groups of polyamide-6 (PA) in supercritical CO2 was also reported.114 Depending on the
reagent used (e.g. diketene or its adduct with acetone), it is possible to selectively modify acid
or basic end groups of a fiber.
1.2.3.2.4. Other applications by impregnation
Besides organic materials, inorganic metal complexes have also been incorporated into
polymers to fulfill specific functions. For instance, the infusion of silver-containing additives
leads to the formation of metalized polymer film with high reflectivity.115, 116 Polymer/metal
composites, even at a nanoscale level, can be produced by infusing proper metal complexes
into a polymer matrix, such as nanoscale platinum clusters into PTFE,117 copper nanoparticles
in polyacrylate,118 and chelate complexes of copper and iron into polyacrylate.119 Zhao et
al.120 recently proposed a pretreatment method whereby palladium
(II)-hexafluoroacetylacetoneate (Pd(hfa)2) was impregnated into Kevlar○R fiber with scCO2
for producing conductive aramid fibers by subsequent electroless copper plating. The research
is further expanded by Adachi et al.121 in the electroless plating on thermoplastic polymer of
polyamide 6.
In addition, surface modification of some polymers by impregnated with surfactant has
been investigated. Xun Ma and David L. Tomasko122 finished a coating study by the
impregnation of N,N-Dimethyldodecylamine N-oxide into a fibrous PE material. The wetting
properties of this highly hydrophobic material are changed dramatically and permanently
compared to dip coating in an aqueous solution. Generally, utilizing the unique properties of
scCO2, impregnating polymer materials with different additives in scCO2 for new frontiers
and designs is an environmentally friendly, challenging, promising direction of polymer
research. There is expansive space and imagination for researchers to explore.
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1.3. Synthetic fiber
Fiber, one of the three types of polymers, is a class of carbohydrate materials that are
continuous filaments or are in discrete elongated pieces, similar to lengths of thread. They can
be spun into filaments, string or rope, used as a component of composite materials, or matted
into sheets to make products such as paper or felt. Fibers are often used in the manufacture of
textile materials such as fabric or other materials. It is divided mainly into three species:
natural fiber, cellulose fiber, and synthetic fiber. Natural fiber is from plant, animal and
mineral sources, such as cotton, silk, and wool etc. Cellulose fibers are regenerated cellulose
used as textile fibers such as rayon, modal, and the more recently developed Lyocell.
Cellulose fibers are manufactured from dissolving pulp. Cellulose-based fibers are of two
types, regenerated or pure cellulose such as from the cupro-ammonium process and modified
cellulose such as the cellulose acetates. Synthetic fibers are the result of extensive research by
scientists to improve upon naturally occurring animal and plant fibers. In general, synthetic
fibers are created by forcing, usually through extrusion, fiber forming materials through holes
(called spinnerets) into the air, forming a thread. Synthetic fibers account for about half of all
fiber usage, with applications in every field of fiber and textile technology. Four of them -
nylon, polyester, acrylic and polyolefin - account for approximately 98 percent by volume of
synthetic fiber production.123 PET and PP are the important synthetic fibers, which have been
expanding from ordinary cloth, covering to high performance application in hygiene and
medical species.124
1.3.1. PET fiber
Poly(ethylene terephthalate) (PET) was invented in the 1940s by Winfield and Dickson,125,
126 and commercialized in the 1950s as DacronTM (EI DuPont de Nemours) and TeryleneTM
(ICI)127 fibers. Of all man-made fibers, PET has become the most dominant, with worldwide
usage exceeding 20 million tons in 2002,128 thus replacing cotton fiber as the number one in
terms of output. The growing production of polyester fibers is projected to reach 33 million
tons by this year.129 The emergence of PET as the most successful man-made fibers is due to
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its useful properties, such as, durability, strength, stability during heat setting, abrasion
resistance, and resistance to sunlight, acids, alkalis, and bleaches. These fibers also have very
good crease recovery and are durable to washing. Along with these characteristics, PET fiber
has many important uses. Fabrics woven from PET thread or yarn are used extensively in
apparel and home furnishings, from shirts and pants to jackets and hats, bed sheets, blankets
and upholstered furniture. Industrial PET fibers, yarns and ropes are used in tyre
reinforcements, fabrics for conveyor belts, safety belts, coated fabrics and plastic
reinforcements with high-energy absorption. PET fiber is used as cushioning and insulating
material in pillows, comforters and upholstery padding. While synthetic clothing in general is
perceived by some as having a less-natural feel compared to fabrics woven from natural fibres
(such as cotton and wool), polyester fabrics can provide specific advantages over natural
fabrics, such as improved wrinkle resistance.
1.3.2. PP fiber
The synthesis of highly crystalline isotactic polypropylene using stereospecific catalysts
was patented in 1954 by Natta.130 Commercial polypropylene production was initially
undertaken by Montecatini and subsequently expanded by ICI Fibers who introduced their
‘Ulstron’ product in late 1950s.131 However, because of patent restrictions associated with
fiber production, fibrous polypropylene often appeared in the market in the form of tapes and
filaments rather than fibers; it was not until the early 1960s that staple fibers started to be seen
on the market.132 Polypropylene was the first synthetic stereo-regular polymer to achieve
industrial importance133 and it is presently the fastest growing fiber for technical end-uses
where high tensile strength coupled with low-cost are essential feature. In addition, PP fiber
has some characteristics including quick drying, abrasion resistant, stain and soil resistant,
comfortable and lightweight, resistant to deterioration from chemicals, mildew, perspiration,
rot and weather so on. As the materials of apparel, PP fiber can be made of sportswear, socks,
thermal underwear, lining fabrics etc. In industries and home furnishings, it works well as
indoor-outdoor carpeting for its hydrophobicity, as filter fabric or bagging because of the
durable ability and corrosion stability, as fishing rope utilizing its lightweight as well as
- 18 -
waterproof. PP fiber can also be used in automotive components, for instances, interior fabrics
used in or on kick panel, package shelf, seat construction, truck liners, load decks, etc.
Nowadays, PP fibers are being extended widely in new fields, such as hygiene, medicine,
electronics, even aeronautics.134
1.4. Natural macromolecules
Natural macromolecules belong to biomolecules with high relative molecular mass, and
derived from living organisms. These macromolecules have some form of biological activity
which is always drawing the attention from human. Many natural macromolecules including
peptides, proteins and carbohydrates have been used in the surface modification of polymer
because of a broad range of application such as specific protein recognition, hydrophilicity,
antimicrobial activity and others, depending on the kind of grafted molecules.135
1.4.1. Sericin
Sericin is a high molecular weight, water-soluble glycoprotein isolated from silk. It is
made of 18 amino acids most of which have strongly polar side groups such as hydroxyl,
carboxyl, and amino groups.136 The high hydroxyl amino acid content of sericin (approx.
46%) is of particular importance for the water-binding capacity which regulates the skin‘s
moisture content. On the other hand, it has a unique carbohydrate moiety and a unique
repetitive amino acid sequence which give it high affinity for proteins resulting in a tightening,
anti-wrinkle effect. Sericin is therefore the ideal multifunctional ingredient for cosmetic skin
care product lines for dry, sensitive and stressed skin and also for sun protective and after-sun
products. In addition, sericin was found to be a strong antioxidant and antibacterial which can
inhibit tyrosinase activity,137 and can kill micrococcus successfully,136 these promote its
applications in modification of biomaterials.138
1.4.2. Chitosan
Chitosan is a polycationic polymer with a specific structure and properties.139 It contains
more than 5000 glucosamine units and is obtained commercially from shrimp and crab shell
- 19 -
chitin (a N-acetylglucosamine polymer) by alkaline deacetylation (NaOH, 40-50%). Chitosan
is insoluble in most solvents including water, but is soluble after the amino groups participate
in reaction in dilute organic acids such as acetic acid. This is due to the main body containing
a mass of hydroxyl groups. Chitosan is inexpensive and nontoxic and possesses reactive
amino groups. It has been shown to be useful in many different areas,140 as an antimicrobial
compound in agriculture, as a potential elicitor of plant defense responses, as a flocculating
agent in wastewater treatment, as an additive in the food industry, as a hydrating agent in
cosmetics, and more recently as a finishing agent in textiles. Chitosan has been covalently
linked to carboxylic acid functionalized PP using water soluble carbodiimide chemistry. The
resulting material showed enhanced wettability and antimicrobial activity against
Pseudomonas aeruginosa.141
1.4.3. Polylysine
Polylysine (ε-poly-L-lysine) is a small polypeptide of the essential amino acid L-lysine
that is produced by bacterial fermentation. ε-Polylysine belongs to the group of cationic
surfactants. In water, ε-polylysine contains a positively charged hydrophilic amino group and
a hydrophobic methylene group. Cationic surface-active compounds have the ability to inhibit
the growth of microorganisms. According to research, ε-polylysine is absorbed
electrostatically to the cell surface of the bacteria, followed by a stripping of the outer
membrane. This eventually leads to the abnormal distribution of the cytoplasm causing
damage to the bacterial cell.142 Literature studies have reported an antimicrobial effect of
ε-polylysine against yeast, fungi, gram-positive bacteria and gram-negative bacteria.143
Polylysine is commercially used as a food preservative,144 is also used a delivery vehicle for
small drugs in chemotherapy.145 Recently, along with the development technology of
bioelectronics, polycationic compounds including polylysine have been used to construct
biochip and integrated circuit.146 Generally, the utilization of this biopolymer is both
economical and environmental, it is valuable to explore new applicable field.
1.4.4. Collagen
- 20 -
Collagen is a triple helical coil of amino acid sequences comprised mainly of repeating
residues of glycine, proline, and hydroxyproline.147 It is the most abundant and ubiquitous
protein in the body of animals, making up about 25% to 35% of the whole-body protein
content. Collagen has good biological compatibility and well characterized low antigenicity. It
can be degraded into physiologically well tolerated compounds. Also, it can also be processed
in aqueous base for enhanced cellular penetration and wound repair. Therefore, collagen has
attracted great interest as a biomaterial for medical use, such as drug delivery,148 and tissue
engineering.149 Collagen possesses characteristics as a biomaterial distinct from those of
synthetic polymers. The most distinct is its mode of interaction with the body. It has be
pointed out that collagen minimizes contractions of facial muscles and can encourage skin
renewal as a cosmetic cream.150 Hydrolyzed collagen has an affinity to water because many
hydrophilic groups will occur, such as hydroxyl, amine.
1.5. Objective of this research
As described in the first section, current techniques on surface modification of polymer
still existed in shortcoming in the limited yield scale or environmental issues. It is always
required that new, easy-operation, low-cost, environmentally friendly processes for modifying
the polymer surface can occur. Supercritical technology, where not only there is no pollution
effect but the operation and treatment are very simple, has received wide attentions. The
impregnation process in scCO2 is particularly valuable for us to consider. Synthetic fabrics
(PET or PP) are necessary in our daily life, are important components in textile industry,
which possess superior strength and resilence. For the application of PET and PP fabrics in
health and comfort related respects, these fabrics have to be modified to improve the surface
wettability and biocompatibility. Some natural macromolecules are nontoxic, inexpensive,
hydrophilic and pharmic functional agents. If these functional agents can be grafted onto the
surface of synthetic fabric, there will be a useful application in textile finishing.
Thus, we proposed the new coating technology where the scCO2 impregnation technology
is to be combined with the regular method. In our research, some active cross-linking agents
will be impregnated into synthetic fabrics by using scCO2, and then the impregnated fabrics
- 21 -
will be treated to attach natural macromolecules by aqueous system or pad-dry-cure method.
In addition, the immobilization of natural macromolecules onto the fabric surface without
impregnation pretreatment in scCO2 will also be done only for a comparison.
For the fabrics impregnated with cross-linking agents in scCO2, the cross-linking agents
will penetrate the surface of fabrics, and active functional groups of cross-linking agents will
present on the surface of fabrics. The results will be investigated by FT-IR or XPS spectra.
After the immobilization of natural macromolecules on the surface of functionalized fabrics,
the surface hydrophilicity of fabrics will be improved, the effects will be investigated by
measurements of water contact angle, moisture regain, as well as the wicking height. The
antibacterial properties of some modified fabrics against S. aureus will also be tested for
investigating the biocompatibility. Finally, the feasibility of this research will be given in a
conclusion.
1.6. Outline of the thesis
In chapter one, the surface modification technologies conventionally used in the polymer
processing were reviewed, as well as the application of supercritical technology in polymer
processing. In addition, synthetic fibers (PET and PP) and some natural macromolecules were
also made an introduction in nature and application. The objection of this research was drawn
out finally.
In chapter two, the coating of natural proteins (sericin or polylysine) onto the surface of
synthetic fabrics (PET and PP) functionalized by the diisocyanate crosslink with scCO2 was
reported. Firstly, the experimental background was introduced, and the coating mechanism
between biopolymers and isocyanate was also presented. Secondly, the analysis methods and
concrete experimental operate were described distinctly. Thirdly, the impregnation results and
the coating results were discussed mainly. Finally, a conclusion was obtained from these
results.
In chapter three, the modification of the synthetic fabrics (PET and PP) was reported by
the method of impregnating PET and PP with cyanuric chloride in scCO2 prior to immobilize
sericin or chitosan. The experimental process and the analysis method were described in detail
- 22 -
in the preceding parts. The rest parts discussed mainly the experimental results and analyzed
the experimental phenomena. During the section of results, the modified PET and PP fabrics
were compared in water contact angle and wicking property.
In chapter four, the immobilization of three functional agents to the surface of PET fabric
impregnated with epoxy compounds in scCO2 were reported. The impregnation process and
the immobilization method was definitely made an introduction, three results on the
immobilization of three functional agents were also compared accordingly. The
hydrophilicities of these modified fabrics were investigated in water contact angle and
moisture regain. The antibacterial effects of these fabrics were given in the results section.
In chapter five, the research results in this study were summarized, and some suggestions
were proposed about the research and the developing direction in new projects.
- 23 -
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Chapter 2. Coating of natural proteins onto synthetic fabrics crosslinked with diisocyanate by supercritical dioxide carbon
2.1. Introduction
Natural proteins derived from living organisms, which is known as polypeptides made of
amino acids arranged in the main chain. Some natural proteins including sericin1 and
polylysine2 showed excellent functional characteristics, such as, hydrophilicity, oxidation
resistance and antimicrobial effect etc. Silk sericin is obtained from silkworm Bombyx mori.
During the various stages of producing raw silk and textile, sericin can be recovered for other
uses. Sericin protein can be cross-linked, copolymerized, and blended with other
macromolecular materials, especially artificial polymers, to produce materials with improved
properties. The protein is also used as an improving reagent or a coating material for natural
and artificial fibers, fabrics, and articles. The materials modified with sericin and sericin
composites are useful as degradable biomaterials, biomedical materials or polymers for
forming articles, functional membranes, fibers, and fabrics. Polylysine is produced by
bacterial fermentation, which is a small polypeptide of the essential amino acid L-lysine.
Polylysine is commercially used as a food preservative,3 is also used a delivery vehicle for
small drugs in chemotherapy.4 Recently, along with the development technology of
bioelectronics, polycationic compounds including polylysine have been used to construct
biochip and integrated circuit.5 Generally, natural macromolecules used to modify the fabrics
by impregnation or coating of them onto the substrate materials have got considerable
progress in textiles industry.6-10 Synthetic fabrics of Poly(ethylene terephthalate) (PET) and
polypropylene (PP) possess good mechanical and low producing cost, thus making them
attractive as substrate for natural proteins to cover.11
With the development of supercritical fluid technology, supercritical carbon dioxide
(scCO2) in impregnation aspects is drawing much attentions in research or application.12
Recently, Free-radical grafting of glycidyl methacrylate (GMA) onto PP films has been
studied using scCO2 as a solvent and a swelling agent.13 Making the introduced regents in
polymer to participate in a chemical reaction is a good elicitation for surface modification of a
- 35 -
fiber. It is well known that the impregnated organic regents can remain on the surface of
polymer after the impregnation in scCO2,14 especially for the fiber materials.15 Thus, once
some active molecules was impregnated into the fiber by scCO2, an immobilization of sericin
or polylysine onto the surface of synthetic fabric can be designed by the reaction of sericin or
polylysine with these active molecules embedded on the fiber surface.
Toluene 2,4-diisocyanate (TDI) is a major isocyanate compound used commercially in
surface coating, adhesives, resins, elastomers (especially in polyurethane foams), binders and
sealants.16 The compound has two isocyanate functional groups attached to a parent toluene.
The functional groups of isocyanate have agility properties to be rapid reaction to alcohol,
water, amine, etc., in the ambient temperature,17 in which a reaction between isocyanate
compound and amine occur, an urea compound will be produced. In addition, TDI is the
compound that is hydrophobic and affinitive to CO2. Some reactions about TDI where the
scCO2 is utilized as a medium system have been reported,18, 19 these applications indicated
that TDI has good solubility in scCO2.
Accordingly, to bridge the synthetic fabrics and natural proteins (sericin or polylysine),
TDI is selected as the cross-linking agents in the design. In this study, the impregnation of
TDI into PET and PP fabrics will be investigated by the scCO2 method, and the
immobilization of sericin or polylysine will also be described. The fabrics of TDI-PET,
TDI-PP, TDI-PET and TDI-PP finished by natural proteins will be analyzed by ATR-IR
measurement. The hydrophilicity of these fabrics will be investigated and discussed. The
proteins immobilization results of fabrics will also be evaluated by the staining test using
methylene blue.
2.2. Experimental procedures
2.2.1. Reagents and materials
The cross-linking agents of toluene 2,4-diisocyanate (TDI, Mw: 174.2, d: 1.214g/ml) used
in the impregnation to synthetic fabrics by supercritical CO2 was purchased from
Sigma-Aldrich Inc. The natural functional agents of sericin (Powder, Mw: ca. 30,000) and
polylysine (Mw: ca. 5000, 25% in water) were supplied by Seiren Co., Ltd. and Chisso Co.,
- 36 -
Ltd., respectively. Figure 1 showed the structural formulas of TDI and polylysine. Sericin is
made of 18 amino acids and is dominated by the presence of hydroxyl (Ser, Thr, and Tyr),
acidic (Asp and Glu), and basic (Lys, His, and Arg) amino acid residues.20 PET fabric (90
g/m2) and PP fabric (224 g/m2) used as synthetic fabric substrates for modification were
supplied by Toyobo Co., Ltd. and Asahi Kasei Ind. Co. Ltd. respectively. Previously, the PET
fabric was washed and stabilised by immersing in acetone at 35°C for 30 min, the PP fabric
was rinsed with tetrahydrofuran (THF) for 30 min at 35°C followed by a rinse with acetone,
both of them was dried in vacuum at 70°C. Dimethylformamide (DMF) used as a component
of dipping solution was purchased from Wako Pure Chemical Industries, Ltd. The water in
polylysine solution was distilled deionized water. The carbon dioxide used in all of the
experiments was purchased from Uno Sanso Co., Ltd. (99.5% pure).
CH3
N=C=O
N=C=O
2,4-TDI
CNH
**
O
NH2 n
ε-poly-L-lysine
Figure 1. Structural formulas of Toluene 2,4-diisocyanate and polylysine.
2.2.2. Treatment
The whole process of treating synthetic fabrics (PET and PP) including impregnation of
diisocyanate and surface immobilization of natural proteins were shown schematically in
Figure 2. The details for each process are described below.
- 37 -
In scCO2
ImmobilizationSynthetic fabric TDI-impregnated fabric
Natural protein-TDI-fabric
Natural protein
TDI
Figure 2. Processing flow on immobilization of natural proteins onto the synthetic fabrics.
2.2.2.1. Impregnation of TDI into PET and PP fabrics by scCO2
A size of cleaned synthetic fabrics (10 cm×16 cm), TDI and corresponding glassy filter
paper used as an insulation layer between the fabric and TDI were set into the scCO2
apparatus. The apparatus is schematically illustrated in Figure 3. The impregnation was
conducted in a 50 ml-vessel equipped with a high-pressure needle valve at the export. The
vessel was heated to the preset temperature, carbon dioxide was then introduced, and the
desired pressure was maintained. The system was treated under agitation for detecting time.
After the impregnation, the system was cooled and depressurized slowly (ca. 0.5 MPa/min)
till the temperature close to ambient condition. The treated fabrics were washed by acetone at
room temperature to remove the cross-linking agents which are cohesive on the surface of
fabrics. The impregnation amounts of TDI to PET and PP fabric using supercritical CO2 was
determined gravimetrically and expressed as a percentage of impregnation by the equation 1
and 2:
G (PET) impregnation (%) = [W (PET) 1 – W (PET) 0] / W (PET) 0 × 100 (1)
G (PP) impregnation (%) = [W (PP) 1 – W (PP) 0] / W (PP) 0 × 100 (2)
where W1 and W0 are the weight (g) of TDI-impregnated PET/PP and untreated PET/PP
fabric, correspondingly.
- 38 -
1:CO2 cylinder 2:cooling pump 3:syringe pump 4,9:pressure gauges
5:thermometer 6:heater 7:high pressure stainless vessel 8:magnetic stirrer
10:manual valve 11:needle valve
Figure 3. Illustration of the supercritical impregnation apparatus.
2.2.2.2. Immobilization of natural proteins onto TDI-PET and TDI-PP fabrics by the
pad-dry-cure method
It has been known that toluene diisocyanate react easily with H2O, but the selected natural
proteins (sericin and polylysine) are water-soluble reagents, in order to avoid much of
diisocyanate react with the medium of H2O, a method of pad-dry-cure was adopted for the
immobilization of the two proteins (sericin and polylysine). In the experiment, to immerse the
hydrophobic fabrics (especially for PP) quite in the dipping solution, the dipping solvent is
made up of H2O and DMF, sericin and polylysine finishing solutions were diluted to 1wt%,
3wt% and 5 wt% respectively in relation to the mass of mixed solvent. The fabric samples
were padded twice to about 110% wet pickup with freshly prepared aqueous solutions of
polylysine. Padded fabrics were dried at 60°C for 90 minutes, cured at 120°C for 20 minutes,
washed, and dried. The immobilization ratio of sericin or polylysine onto TDI-PET and
TDI-PP fabrics are defined by equation (3) and (4):
- 39 -
G (PET) immobilization (%) = [W (PET) 2 – W (PET) 1] / W (PET) 1 × 100 (3)
G (PP) immobilization (%) = [W (PP) 2 – W (PP) 1] / W (PP) 1 × 100 (4)
where W2 represent the weights of the natural proteins-finished TDI-PET and TDI-PP fabrics.
2.2.3. Analysis
Infrared absorption spectra of the samples of PET and PP fabrics (untreated, treated in
each step), sericin, polylysine and TDI were obtained from a Fourier-Transform Infrared
Spectroscopy (FT-IR). The fabrics were executed by the method of attenuated total reflection
(ATR) where a total of 200 scans were accumulated at a resolution of 4 cm-1, and reagents of
TDI, sericin and polylysine were performed with usual method of making pellets (ca.0.5%
w/w) with potassium bromide (KBr) where a total of 16 scans were accumulated at a
resolution of 8 cm-1.
Static water contact angles of the original and modified PET and PP fabrics were
measured with a contact angle measurement apparatus (KRÜSS, DSA20) which is a suitable
instrument for the automatic recording of the surface force tension of liquids. For this
measurement, a droplet of distilled water (5 μl) was placed onto the PET fabric surface from a
fixed height (1cm). Before measurement, the samples were dried at 60°C under vacuum.
More than five measurements were carried out and the resulting values were averaged.
Staining test is often used to temporarily stain bacterial in biology technique. The amine
groups in natural proteins are electron-rich, this made it can be stained by methylene blue. For
the staining test, 0.1wt% of methylene blue solution is prepared with deionized water. The
synthetic fabrics were dipped into the solution for 10 minutes with a shake at room
temperature. Then, the fabrics were taken out, dried for 30 minutes, rinsed with deionized
water.
2.3. Results and discussion
2.3.1. Supercritical impregnating PET and PP fabrics with TDI
The impregnation of dyes into synthetic fibers utilizing scCO2 has been investigated by
- 40 -
many studies.21-23 It was pointed out that 120 -130°C is suitable to the PET dyeing and
100-110°C is suitable to the PP dyeing. Thus, the conditions of impregnating synthetic fabrics
with TDI in scCO2 were selected at 120°C, 25MPa for PET, at 100°C, 25MPa for PP. Because
TDI has good solubility in scCO2, the filling amounts of TDI in vessel need to solve here. In
order to investigate the relation of the filling amounts in vessel and the uptakes in the
synthetic fabrics, a 2-hours impregnation was performed for PET and PP, respectively. The
results were shown in Figure 4. From the curve trend, the uptakes of TDI in synthetic fabrics
is increased with the increase of filling amounts initially, when the filling amount is close to
0.66 ml in 50 ml (0.09 mol/L), the uptake in either fabric of PET and PP nearly attained the
maximal value. This indicated that the filling amount of TDI was sufficient in excess of the
amount required to saturate the CO2 during the entire course of impregnation. The uptake of
TDI in PET is more than it in PP, this result is attributed to the affinity of PET to TDI, which
is higher than the affinity of PP to TDI because PET includes some hydroxyl side chains.
Another reason maybe has a relation with the swelling extent of PET and PP fiber in scCO2.
0.05 0.10 0.15 0.20
1.6
2.0
2.4
2.8
TDI u
ptak
e [w
t%]
C [mol/L]
PET (120oC, 25MPa)
PP (100oC, 25MPa)
Figure 4. Uptake of TDI into PET and PP fabric as a function of the filling concentration of
the cross-linking agent in scCO2 for 2 hours.
- 41 -
The impregnation is later than the swelling of substrate in supercritical phase. The
swelling process usually influences the impregnation amount of an additive into the substrate.
After the filling amount of TDI was confirmed, the relation of impregnation uptake and the
time was investigated. The results of impregnation uptakes for TDI into the PET and PP
fabrics were shown in Figure 5. It can be noted, the impregnation equilibrium on PET fabric
was obtained after 4 hours, and the impregnation equilibrium on PP fabric was faster than that
in PET, the time was about 2 hours. The different equilibrium time is considered for the
materials are not same. This can be explained by the cause that the swelling time on PET and
PP fabrics is different. Besides, the uptake of TDI in PP fabric presented a downward trend
after a treatment over 3 hours. The phenomenon maybe account for the cause that microcells
of crystallization appeared in the amorphous domains which pushed the TDI out of the
substrate of PP when the structure of crystal is destroyed next to melting point after long time.
0 60 120 180 240 300 3600
1
2
3
4
TDI u
ptak
e [w
t%]
Impregnation time [minute]
PET (120oC, 25MPa)
PP (100oC, 25MPa)
Figure 5. Uptake of TDI into PET and PP fabrics as a function of impregnation time in
scCO2.
- 42 -
2.3.2. Immobilization of natural proteins (sericin and polylysine) onto the surface of
TDI-PET and TDI-PP fabrics
The investigation above suggested that the upmost uptakes of TDI in synthetic fabrics
were, 3.54wt% for PET treated in scCO2 for 4h at 120°C and 25MPa, and 2.48wt% for PP
treated in scCO2 for 2h at 100°C and 25MPa. The fabric samples impregnated with the
upmost uptake of TDI were used to immobilize natural proteins. The immobilization results
are shown in Table 1. From the data, it can find that, the immobilization amount to TDI-PET
is always more than the value to TDI-PP in the same concentration of finishing solution. This
is mainly understood as the impregnation amount of TDI in PET fabric is higher than it in PP
fabric. The higher the impregnation amount, the more the functional groups of isocyanate will
bare on the surface of the fabric, which can react with more natural proteins. For the TDI-PET
fabric, either protein immobilization attained maximal value after the treatment in 3wt%
solution, even treating it in the case of 5wt%. This result indicated that a concentration of
3wt% protein solution is adequate to react with those isocyanate groups on the surface of
TDI-PET fabric. Comparatively, the protein immobilization amount to TDI-PP has no biggish
change with its concentration, this can be considered that 1wt% of protein solution has been
ample for the required amount to participate in the reaction with isocyanate because the less
uptake of TDI in PP fabric. Obviously, the whole immobilization results of sericin is higher
than of polylysine to TDI-PET or TDI-PP, this can be explained for the more amino groups of
sericin relating to polylysine facilitated the reaction with isocyanate moieties on the fabric
surfaces.
Table 1. Immobilization amount of natural proteins onto the TDI-PET and TDI-PP fabrics.
Fabric samples Sericin finishing solution Polylysine finishing solution
1wt% 3wt% 5wt% 1wt% 3wt% 5wt%
TDI-PET 0.95 1.22 1.19 0.73 1.07 1.02
TDI-PP 0.78 0.84 0.81 0.63 0.65 0.67
- 43 -
2.3.3. FT-IR analysis
To easily compare the results of impregnation and immobilization, the IR spectra of the
cross-linking agent of TDI, of immobilization protein of sericin and polylysine were
investigated and analyzed in Figure 6, Figure 7 and Figure 8, respectively. The typical bands
of several reagents have been indicated in each spectrum.
3500 3000 2500 2000 1500 10000
1
2
3
4
Abs
orba
nce
Wavenumber [cm-1]
N=C=O STRBenzene ring STR
Out-of-plane CH BEND
In plane CH BEND
CH STR (Methyl and Benzene ring)
Methyl CH BEND
Figure 6. IR spectrum of the cross-linking agent TDI.
- 44 -
3500 3000 2500 2000 1500 1000 5000.0
0.4
0.8
1.2
1.6A
bsor
banc
e
Wavenumber [cm-1]
OH and NH STR
CH STR
AmideⅠ
Amide Ⅱ
Amide Ⅲ
N-CH STR
C-OH
Out-of-plane NH2 BEND
Figure 7. IR spectrum of the immobilization agent sericin.
3500 3000 2500 2000 1500 1000 5000.0
0.5
1.0
1.5
2.0
Out-of-plane NH2 BEND
N-C(=O)-N STR
Amide Ⅲ
Amide Ⅱ
AmideⅠ
Abs
orba
nce
Wavenumber [cm-1]
NH STR
CH2 STR
Figure 8. IR spectrum of the immobilization agent polylysine.
- 45 -
After the whole treatment was finished, the ATR-IR spectra of the untreated,
TDI-impregnated and polylysine-immobilized fabrics of PET and PP were measured, as
shown in Figure 9 and Figure 10, respectively. Compared with the spectra of original fabric,
it is obvious that a new peak appeared at 2260 cm-1 in either fabric impregnated with TDI.
This is a convincing poof that TDI was impregnated into the fabrics of PET and PP,
meanwhile, it also suggested the impregnated agent can penetrate the surface of the fibers.
Having immobilized sericin or polylysine onto the TDI-impregnated PET and PP fabrics, the
functional group of –N=C=O disappeared. Instead of it, a broad band about 3300-3500cm-1
was found, this is a character of amine or hydroxyl absorption in IR spectra. From this result,
it is be deduced that the isocyanate group of TDI bared on the surface of fabrics have
participate in reaction in the main. The spectra of sericin-immobilized TDI-PET and TDI-PP
did not shown because it is similar to the spectra of polylysine-immobilized fabrics. For the
proteins-finished TDI-PET and TDI-PP fabrics, some flaxen stains may be noted. This is
accordant with the result on which the samples of TDI-PET or TDI-PP are laid in air or H2O
for a long time. Accordingly, the reaction of TDI with H2O existed affirmatively in the
pad-dry-cure treatment.
- 46 -
3500 3000 2500 2000 1500 10000.00
0.05
0.10
0.15
0.20
0.25A
bsor
banc
e
Wavenumber [cm-1]
Polylysine-TDI-PET TDI-PET Untreated PET
Figure 9. ATR-IR spectra of PET, TDI-impregnated PET and Polylysine-TDI-PET fabrics.
3500 3000 2500 2000 1500 10000.00
0.05
0.10
0.15
0.20
Abs
orba
nce
Wavenumber [cm-1]
Polylysine-TDI-PP TDI-PP Untreated PP
Figure 10. ATR-IR spectra of PP, TDI-impregnated PP and Polylysine-TDI-PP fabrics.
- 47 -
2.3.4. Staining by methylene blue
Although TDI on the surface of fabrics have participated in chemical reaction during the
course of immobilizing natural proteins, the reaction with proteins is still a suspectable matter
for the isocyanate groups were also easily substituted by water. Once the active groups have
reacted with water, the staining effect will not occur. Thus, the investigation of staining by
methylene blue as a detective means is implemented. The TDI-samples treated in 3wt%
finishing solution were stained here and the images of the stained fabrics are shown in Figure
11. Contrastively, the untreated and the TDI-impregnated fabrics of PET and PP can not be
stained by methylene blue essentially, but, the TDI-PET and TDI-PP fabrics finished by
natural proteins captured the methylene blue successfully, even though the color deeper or
lighter. On the whole, the staining on PET is uniform, the uneven color on PP is possible due
to the immobilization of proteins is non-uniform. In addition, the sericin-TDI-fabrics are
stronger than the polylysine-TDI-fabrics in chroma, there may be two reasons for this, firstly,
the electron-rich groups of sericin is more than that in polylysine; secondly, the
immobilization amount of sericin is higher than the polylysine amount on TDI-PET or
TDI-PP fabrics.
Untreated PET TDI-PET Sericin-TDI-PET Polylysine-TDI-PET
Untreated PP TDI-PP Sericin-TDI-PP Polylysine-TDI-PP
Figure 11. Staining of diverse fabrics of PET and PP by mehtylene blue.
- 48 -
2.3.5. Hydrophilicity effect
The static water contact angle on the untreated and modified fabrics of PET and PP was
measured to evaluate the hydrophilicity of these fabrics. Table 2 gave the data of them. The
natural proteins-immobilized samples were the TDI-PET and TDI-PP fabrics treated in 3wt%
finishing solution. It is evident that all modified fabrics of PET and PP have a decrease in
water contact angle. This means the hydrophilicity of the modified fabrics was improved even
after the impregnation of TDI. Compared with the untreated fabric, PET fabric in the aspect of
hydrophilicity was improved consumedly, and PP fabric also gained some progress from 132
to 107 o. The relevant images of water contact angles on these fabrics were shown in Figure
12. From all results, it indicated that sericin has better hydrophilicity than polylysine, this owe
to that much hydroxyl groups also existed in sericin, but there is only amine groups for
polylysine.
Table 2. Static water contact angle of diverse fabrics of PET and PP.
PET samples Static water contact angle (o) PP samples
Untreated PET 102.6 132.2 Untreated PP
TDI-PET 97.4 118.5 TDI-PP
Sericin-TDI-PET 66 107.7 Sericin-TDI-PP
Polylysine-TDI-PET 85 115 Polylysine-TDI-PP
- 49 -
Figure 12. Images of water contact angle on diverse fabrics of PET and PP.
- 50 -
2.4. Summary
An attempt to coat the synthetic fabrics (PET or PP) with natural proteins (sericin or
polylysine) was designed. The study made a success by impregnating the fabric substrate with
a functional reactive agent of TDI prior to attach the natural proteins.
The impregnation of TDI into synthetic fabrics of PET and PP was performed in scCO2.
During the course of impregnation, to reach an optimal impregnation effect, the filling amount
of TDI in scCO2 vessel was investigated firstly, and then, the equilibrium time of
impregnating PET and PP fabric with TDI were also obtained under the experimental
temperature and pressure, respectively. After the optimization treatment, the impregnation
uptakes of TDI attained 3.54wt% for PET, and 2.48wt% for PP fabric.
The coating of sericin or polylysine onto the TDI-PET and TDI-PP fabrics was treated by
the pad-dry-cure method. It is approved that a concentration of 3wt% protein solution was
adequate to react with those isocyanate groups on the surface of TDI-PET and TDI-PP fabrics.
The coating results got recognitions on the IR spectra of the modified samples and the
staining effects of these fabrics. The water contact angle measurement revealed the
hydrophilicity of the modified fabrics of PET and PP was improved to a certain extent,
especially for the sericin-immobilized fabrics.
- 51 -
References
1. Yu-Qing Zhang, Applications of natural silk protein sericin in biomaterials, Biotechnol. Adv. 20 (2002)
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2. S. Shima, Antimicrobial action of ε-poly-L-lysine, J. Antibiot. 37 (1984) 1449.
3. J. Hiraki, ε-polylysine: Its development and utilization, Fine Chem. 29 (2000) 25.
4. R. Duncan, Drug–polymer conjugates: potential for improved chemotherapy, Anti-Cancer Drugs 3
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5. L. Cai, H. Tabata, T. Kawai, Probing electrical properties of oriented DNA by conducting atomic force
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6. A. Kongdee, S. Okubayashi, I. Tabata, T.Hori, Impregnation of silk sericin into polyester fibers using
supercritical carbon dioxide, J. Appl. Polym. Sci. 105 (2007) 2091.
7. K. F. El-tahlawy, M. A. El-bendary, A. G. Elhendawy, S. M. Hudson, The antimicrobial activity of
cotton fabrics treated with different crosslinking agents and chitosan, Carbohyd. Polym. 60 (2005) 421.
8. A. Hebeish, M.G. Fouda, I.A. Hamdy, S.M. EL-Sawy, F.A. Abdel-Mohdy, Preparation of durable insect
repellent cotton fabric: Limonene as insecticide, Carbohyd. Polym. 74 (2008) 268.
9. N. Blanchemain, S. Haulon, B. Martel, M. Traisnel, M. Morcellet, H. F. Hildebrand. Vascular PET
rostheses Surface Modification with Cyclodextrin Coating: Development of a New Drug Delivery
System, Eur. J. Vasc. Endovasc. Surg. 29 (2005) 628.
10. Y.-C. Tyan, J.-D. Liao, R. Klauser, I.-D. Wu, C.-C. Weng, Assessment and characterization of
degradation effect for the varied degrees of ultra-violet radiation onto the collagen-bonded
polypropylene non-woven fabric surfaces, Biomaterials 23 (2002) 65.
11. M. J. Shenton, M. C. Lovell-Hoare, G. C. Stevens, Adhesion enhancement of polymer surface by
atmospheric plasma treatment, J. Phys. D: Appl. Phys. 34 (2001) 2754.
12. I. Kikic, F. Vecchione, Supercritical impregnation of polymers, Curr. Opin. Solid State Mater. Sci. 7
(2003) 399.
13. M. H. Kunita, A. W. Rinaldi, E. M. Girotto, E. Radovanovic, E. C. Muniz, A. F. Rubira, Grafting of
glycidyl methacrylate onto polypropylene using supercritical carbon dioxide, Eur. Polym. J. 41 (2005)
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14. X. Ma, D. L. Tomasko, Coating and Impregnation of a Nonwoven Fibrous Polyethylene Material with a
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Nonionic Surfactant Using Supercritical Carbon Dioxide, Ind. Eng. Chem. Res. 36 (1997) 1586-1597.
15. Andrew I. Cooper, Polymer synthesis and processing using supercritical carbon dioxide, J. Mater. Chem.
10 (2000) 207.
16. National Institute for Occupational Safety and Health (NIOSH): Determination of Airborne Isocyanate
Exposure, in: M.E. Cassinelli, P.F. O’Connor (Eds.), NIOSH Manual of Analytical Methods (DHHS
[NIOSH] Publication no. 98-119), 4th ed., 2nd suppl., U.S. Department of Health and Human Services,
Public Health Service, Centers for Disease Control and Prevention, NIOSH, Cincinnati, OH, 1998, pp.
115.
17. Y. Shang, Y. Peng, UF membrane of PVA modified with TDI, Desalination 221 (2008) 324.
18. F. Montilla, E. Clara, T. Avile´s, T. Casimiro, A. A. Ricardo, M. N. da Ponte, Transition-metal-mediated
activation of arylisocyanates in supercritical carbon dioxide, J. Organomet. Chem. 626 (2001) 227.
19. P. Chambona, E. Clouteta, H. Cramaila, T. Tassaingb, M. Besnard, Synthesis of core-shell
polyurethane–polydimethylsiloxane particles in cyclohexane and in supercritical carbon dioxide used as
dispersant media: a comparative investigation, Polymer 46 (2005) 1057.
20. J. Huang, R. Valluzzi, E. Bini, B. Vernaglia, D. L. Kaplan, Cloning, expression, and assembly of sericin
-like protein, J. Biol. Chem. 278 (2003) 46117.
21. A. Ehrhardt, I. Tabata, K. Hisada, T. Hori, Imoregnation of Hydroxy-Anthraquinone Compounds into
Polypropylene Fabrics by scCO2 and the Sorption Ability for Metal Ions, Sen’I Gakkaishi 61 (2005)
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- 53 -
Chapter 3. Impregnation of cyanuric chloride into PET and PP fabrics with the aid of supercritical carbon dioxide, and its application in immobilizing
natural biomacromolecules
3.1. Introduction
Multifunctional polymers have seen rapid growth in the past decade in such industries as
biomedicine, microelectronics, food packaging, wastewater treatment and textiles. The
surface modification of low-cost, commodity-shaped polymer materials – by the addition of
functional molecules – is of great interest since it offers an effective method for pre-existing
polymer materials to gain higher added value in application.1-3 PET and PP are by far the most
widely used commercial pre-existing polymers – in the form of film, plastic, fiber and fabric –
due to their excellent physical and mechanical properties, together with their low cost.
The finishing of PET or PP fiber by immobilizing functional molecules onto their
substrates without losing their inherent special effects (fire retarding,
hydrophilicity/hydrophobicity, antibacterial or even medical properties) has been studied,
including physical padding or coating4, 5 and grafting induced by chemical treatment, such as
wet chemical,6 plasma,7 UV irradiation,8 electron beam irradiation9 and γ-ray radiation.10
Physical immobilization techniques do not have a long-term effect on the fiber because the
agents used are only physically adsorbed on the fiber surfaces, yielding a poor washing
fastness. Chemical methods, on the other hand, can permanently immobilize functional
molecules onto the fiber surfaces. Wet chemical methods, however, will generate hazardous
chemical waste and can lead to irregular surface etching. Irradiation techniques are also
limited in laboratory scale because they require complicated production equipment, strict
operation requirements and are expensive, while also having a degradation effect on the
substrate fiber. In addition, during the process of immobilization the functional molecules,
especially bioactive compounds, sometimes lose activity when linked directly to the
hydrophobic polymer surface and so it may be necessary to graft an intermediate
cross-linking agent between the surface and the bioactive compound.1 Considering the inert
nature of PP and PET with no active side chain, a better cross-linking method is required to
- 54 -
introduce intermediate active-linker agents to the surface of PET and PP fibers prior to
coupling a functional molecule.
Recently, supercritical fluids – especially supercritical carbon dioxide (scCO2) – with their
unique mass transport properties, have had a marked effect on polymer processing,11
including impregnation. Basically, the impregnation process consists of three steps: (i)
exposure of the polymer to scCO2 for a period of time; (ii) introduction of the scCO2
containing solutes to the polymer and conducting the subsequent solute transfer from scCO2
to polymer phase; and (iii) the release of the CO2 in a controlled manner, trapping the solutes
in the polymer. Many researchers have demonstrated that small molecule additives can be
impregnated into fiber using scCO2 as a solvent and swelling agent. Knittel et al. 12 showed
that synthetic fibers like PET can be dyed via a dye impregnation in scCO2, avoiding water
pollution and the need for drying, with excellent firmness levels. Tabata et al.13 investigated
the relationship between the solubility of disperse dyes and the equilibrium dye adsorption in
supercritical fluid dyeing. Xun Ma and Tomasko14 reported the impregnation of a non-ionic
surfactant (N,N-dimethyl-dodecylamine N-oxide) into non-woven fibrous samples of
high-density polyethylene (HDPE) using scCO2 as the only solvent. Zhao et al.15 proposed a
pretreatment method whereby palladium (II)-hexafluoroacetylacetoneate (Pd(hfa)2) was
impregnated into KevlarR fiber with scCO2 for producing conductive aramid fibers by
subsequent electroless copper plating. Based on these uses of scCO2 in fiber finishing, a
cross-linking method of using scCO2 is examined in the present study in order to introduce
intermediate active-linker agents into PET and PP fibers for coupling a functional molecule.
Sericin and chitosan are well known as functional biomolecules to modify polymers for
good hydrophilicity and biocompatibility.16, 17 For example, Kamitani et al.18 investigated a
physical method of modifying polyester fabric with sericin, with data on the moisture regain
and washing fastness of the finished fabric. Hudson et al.19 used two different cross-linking
agents – butanetetracarboxylic acid, BTCA) and Arcofix NEC (low formaldehyde content) –
in the presence of chitosan to provide cotton fabrics with a durable press finishing and
antimicrobial properties by chemical linking of chitosan to the cellulose structure. In the
present study, in order to anchor biomolecules (sericin/chitosan) onto the PET and PP fabric
- 55 -
surfaces, cyanuric chloride (CC), an active-linker agent that is not reactive to CO2, was
chosen to impregnate the fabric substrate with the help of scCO2 for attaching sericin or
chitosan. Cyanuric chloride is a heterocyclic molecule, which allows the subsequent
substitution of its three chlorine atoms by nucleophiles as amine, alcohol or thiols. According
to the literature,20 the substitution of chlorine can be controlled by temperature to run in a
stepwise manner. An empirical rule, based on observation, is that mono-substitution of
chlorine occurs below or at 0°C, di-substitution occurs at room temperature and
tri-substitution occurs above 60°C. The application of cyanuric chloride to serve as a linker
agent can easily react with biomolecules, such as enzymes, antibody protein, silk fibroin and
chitosan. 21-23
With the purpose of giving hydrophilicity as well as biocompatibility to a synthetic fabric
(PET/PP) for some useful application, the present research reports a 2-step process as
described in Scheme 1, i.e. (i) impregnation of cyanuric chloride into PET/PP fabric substrate
and (ii) immobilization of sericin or chitosan onto the CC-PET and CC-PP fabrics via reacting
with cyanuric chloride implanted on the surfaces of PET and PP fabrics. The treated fabrics
are characterized in spectrometrical and morphological analyses. The hygroscopic properties
of the treated fabrics are also evaluated.
Supercritical CO2
N
N
N
Cl
ClCl
Cyanuric chloride
NN
NCl
Cl
Cl
N
NN
Cl
Cl
Cl
NN
N
Aqueous solution
Biomacromolecules(Sericin/Chitosan)
NH
Cl
Cl
N
NN
Cl
Macromolecule
Cl
HN Macromolecule
PP/PET fabric CC-impregnated PP/PET fabric
Biomacromolecule-immobilized PP/PET fabric
Scheme 1. Schematic representation of the immobilization of biomacromolecules (sericin or
chitosan) onto PET (or PP) fabric surface by reacting with cross-linking agent of CC
impregnated into PET (or PP) substrate using scCO2.
- 56 -
3.2. Experimental procedures
3.2.1. Materials and Reagents
The poly(ethylene terephthalate) (PET) fabric (90 g/m2) and the polypropylene (PP) fabric
(224 g/m2) used as base polymer for modification was supplied by Toyobo Co. Ltd. and Asahi
Kasei Ind. Co. Ltd., respectively. First, the PET fabric was washed and was stabilized by
immersing in acetone at 35°C for 30 minutes, while the PP fabric was rinsed with
tetrahydrofuran (THF) for 30 minutes at 35°C, followed by a rinse with acetone. Both fabrics
were then dried in a vacuum at 60°C. The cross-linking agent of cyanuric chloride used in the
scCO2 impregnation to PET and PP fabrics was purchased from Tokyo Chemical Industry Co.
Ltd. Two types of biomolecules – sericin (Mw: ca. 17,000) and chitosan (Mw:
50,000~100,000) – were used as hydrophilic, together with antimicrobial material for the
immobilization onto the surface of PP and PET fabrics. The sericin was supplied by Seiren
Co., Ltd. and the chitosan was purchased from Sigma-Aldrich Inc. All solutions of functional
reagents were prepared with distilled water. The carbon dioxide used in all the experiments
was purchased from Uno Sanso Co. Ltd. (99.5% pure). Several organic solvents and inorganic
salts were purchased as guaranteed-grade reagents from Wako Pure Chemical Industries Ltd.
3.2.2. Treatment
3.2.2.1. Impregnation of CC into PP and PET fabrics by means of scCO2
The high pressure equipment (Model SCF-Sro, JASCO Co., Tokyo) used to impregnate
PP and PET fabric with CC consisted of a 50 ml stainless steel autoclave (Pmax = 30 MPa), a
magnetic stirrer, a constant temperature air bath, a thermocouple and a pressure gauge. The
CO2 was stored in a cylinder and pressurized to the above system by a syringe pump. The
PET (10 cm×12 cm, ca. 1.10 g) or PP (5 cm×5 cm, ca. 1.20 g) fabric substrate was suspended
on a stainless steel net inside the vessel and cyanuric chloride was placed on the bottom of the
vessel. When the autoclave reached the desired temperature, CO2 was let in slowly and
isothermally compressed to working pressure; then, the system was agitated for a certain
period of time to impregnate the substrate fabric with CC. After impregnation, CO2 of the
- 57 -
system was released at ca. 0.5 MPa min-1 to ambient pressure. The same experiment was
performed with a help of a 3% modifier (acetone, dichloromethane or ethyl acetate) to CO2.
Later, the sample was shaken off and was flushed with air to remove the cross-linking agent
adhering to the surface. The absorption of the cross-linking agents into the PET and PP
fabrics using scCO2 were determined gravimetrically and are expressed as a percentage of
impregnation according to Equations (1) and (2), respectively:
G (PET) impregnation (%) = [W (PET) 1 – W (PET) 0] / W (PET) 0 × 100 (1)
G (PP) impregnation (%) = [W (PP) 1 – W (PP) 0] / W (PP) 0 × 100 (2)
where W1 and W0 correspond to the weight (g) of CC-impregnated and untreated fabrics.
3.2.2.2. Immobilization of biomacromolecules (sericin or chitosan) onto CC-PET and
CC-PP fabrics
The immobilization of biomacromolecules (sericin or chitosan) onto CC-PET and CC-PP
fabric was performed in aqueous solution. The mechanism of immobilization relies on the
reaction of the CC moieties penetrated on the surface of fabric with the active groups (amino
or hydroxyl) of biomacromolecules by the nucleophilic substitution of the chlorine atom.
For the immobilization of sericin, 3wt% finishing solution was prepared and its pH
adjusted to ca. 10 with K2CO3 to trap the HCl formed during the substitution reaction.21, 22
Subsequently, the CC-PET or CC-PP sample was immersed in the sericin solution and was
shaken for 6 hours at 30°C. Then, the solution temperature was raised to 70°C and the
reaction was continued for another 6 hours. Although an alkaline chitosan solution can be
obtained according to the literature,24 the solution was prepared with acetic acid in order to
prevent the reaction of CC with alcohol used in the aqueous solution. The CC-PET or CC-PP
sample was placed in 0.2wt% chitosan water solution containing acetic acid (5vol%) for
reaction at 30°C. After one day, the solution temperature was raised to 70°C and the solution
was maintained for another day. At the end of the immobilization, the samples were removed
from solution, were squeezed and were air-dried. The finished fabric samples were then rinsed
with water, were dried again at 60°C in a vacuum and were conditioned prior to testing. The
- 58 -
immobilization ratio of functional molecules (sericin or chitosan) onto CC-PET and CC-PP
fabrics are defined by Equations (3) and (4), respectively:
G (PET) immobilization (%) = [W (PET) 2 – W (PET) 1] / W (PET) 1 × 100 (3)
G (PP) immobilization (%) = [W (PP) 2 – W (PP) 1] / W (PP) 1 × 100 (4)
where W2 represents the weight (g) of the functional macromolecules-finished CC-PET and
CC-PP fabrics.
3.2.3. Analysis method
Attenuated total reflection-infrared spectra were collected using a Fourier-Transform
Infrared Spectrometer (FT-IR-4100, JASCO), equipped with an ATR accessory (ZnSe crystal,
45°). 200 scans were accumulated for each spectrum at a nominal resolution of 4 cm-1. The
FT-IR spectrum of the CC was also recorded in the apparatus with the method of detecting the
KBr pellets (ca. 0.5% w/w), where a total of 16 scans were accumulated at a resolution of 4
cm-1.
X-ray photoelectron spectroscopy (XPS) measurements were performed on a
photoelectron spectrometer (JPS-9010MCY) with Mg Kα excitation radiation (1253.6 eV).
The X-ray source was run at a potential of 10 kV, a current of 10 mA and an incident angle of
45○. The pressure within the XPS chamber was maintained at 10-7 Pa during the
measurements. Binding energies were calibrated using the containment of carbon (C1s = 285
eV).
Scanning electron microscopy (SEM) images were obtained from detection of the
secondary electron images on a scanning electron microscope (Hitachi S-2600 HS), operating
at 15 kV. Before the SEM observation, the samples were fixed onto a double-faced carbon
tape adhered to a gold support and sputter-coated in an ion sputter (E-1030 Hitachi).
Static water contact angle (SWCA) was determined by the sessile drop method of placing a
5-μL distilled water droplet on the untreated and the modified PET fabrics via a microsyringe.
The drop images were taken after 20 seconds by a monochrome video camera, using
PC-based control acquisition and data processing. All measurements were carried out at room
- 59 -
temperature and the average of at least 5 readings was taken at different positions across the
surface.
The wicking property was estimated by measuring the height of H2O rise through a strip
sample of 5 cm×2 cm fabric which was suspended vertically above the colored distilled water
surface in a glass beaker, such that the horizontal bottom edge just touched the colored water.
The height was recorded after 8 minutes and was repeated twice.
3.3. Results and discussion
3.3.1. Supercritical impregnation with cyanuric chloride
3.3.1.1. Impregnation in pure scCO2
It is well known that impregnation of organic solute into polymer with scCO2 is mainly
dependent on two factors: solubility of the solute and swellability of the polymer. The scCO2
treatment of PET and PP fibers (fabrics) in dye impregnation have been reported in many
studies,13, 25, 26 where the relations between dye uptake and temperature are stated as
120-130°C for PET dyeing and 100-110°C for PP dyeing.
Before the impregnation of CC into PET and PP fabrics, the solubility of CC in scCO2
was investigated by a supercritical apparatus with optical windows. Unfortunately, CC was
found difficult to be dissolved in scCO2 deriving from a turbidity state of the supercritical
fluid viewed with the optical windows. Some researchers have pointed out that the insoluble
dyes in scCO2 can also be incorporated into a polymer matrix because of the high partition
coefficients between polymer and scCO2 phase.27 Thus, the attempt of impregnating PET and
PP fabrics with CC were carried out in pure scCO2 at 120°C for PET and 100°C for PP. The
amount of solute (CC) loaded in the vessel was 0.20 g (ca. 20% of fabric weight), which
guaranteed a saturated bath during the whole impregnation. Figure 1 shows the CC uptake
curves for PET and PP fabrics as a function of time at a variety of pressures in pure scCO2.
It can be noted that the adsorption equilibrium on the PET fabric was obtained within 4
hours at 25 or 30 MPa, and at about 5 hours at 20 MPa, but the equilibrium was not reached
after 6 hours at 15 MPa. The results obtained at 120°C show that pressure influences the
- 60 -
impregnation rate of CC into the PET fabric. The solute uptake by PET increased with a rise
in pressure from 15 to 25 MPa, and then decreased at 30 MPa. This may be due to fluid
density and solute solubility. When the pressure rose to 25 MPa, scCO2 density was increased
and it facilitated the penetration of CC to the matrix region of PET. Once the pressure
exceeded 25 MPa, the solubility of CC in scCO2 phase became stronger than the polymer
phase, resulting in a CC desorption from polymer phase.
The equilibrium time of CC adsorption by the PP fabric at 100°C was relatively short –
about 2 hours at 20 or 25 MPa. Although the impregnation of CC into PP at 30 MPa was
conducted, data are not shown because the treated sample had a severe shape distortion which
is likely due to a change in the molecular chain. CO2 swelled the PP fabric more at higher
pressure when the temperature was far above its Tg, thus the molecular chain might suffer
distortion in the decompression process.
- 61 -
0 60 120 180 240 300 3600.0
0.2
0.4
0.6
0.8
1.0C
ross
-link
ing
agen
t upt
ake
[wt%
]
Impregnation time [minute]
120°C, 15MPa 120°C, 20MPa 120°C, 25MPa 120°C, 30MPa
(a)
0 30 60 90 120 150 1800.0
0.2
0.4
0.6
Cro
ss-li
nkin
g ag
ent u
ptak
e [w
t%]
Impregnation time [minute]
100°C, 15MPa 100°C, 20MPa 100°C, 25MPa
(b)
Figure 1. Impregnation of CC into a) PET and b) PP fabrics with pure scCO2.
- 62 -
3.3.1.2. Impregnation in scCO2 with co-solvents
In order to improve the solubility of CC in scCO2, and in turn to increase the impregnation
amount of CC into PET and PP fabrics, three co-solvents (3mol% of CO2) – acetone,
dichloromethane and ethyl acetate – were added separately into the supercritical vessel used
in the impregnation experiments. It has been reported that polar solvent participating in scCO2
can enhance the affinity of the fluid by selective interaction with the solute or simply by
changing the polarity of the fluid.28 Three co-solvents chosen here can dissolve CC in ambient
state. Moreover, it was found that CC was also soluble in scCO2 with each co-solvent and
these fluids were clear when they were viewed through the optical windows of the
supercritical vessel. The impregnation of CC into the PET by scCO2 with co-solvent was
performed for 4 hours at 120°C and 25 MPa, while the PP was impregnated with CC for 2
hours at 100°C and 25 MPa. The loading amount of CC was maintained as in the pure scCO2
treatment.
Table 1 shows the CC uptake by the PET and PP fabrics in a variety of fluids. Compared
with the value obtained in pure CO2 treatment, the mass uptakes by PET and PP were
increased in the scCO2-CH2Cl2 and the scCO2-AcOEt fluids. The scCO2-CH2Cl2 treatment
seemed to be more effective, resulting in higher solute adsorption of 1.48wt% in PET and
0.86wt% in PP. It is thought that CH2Cl2 possessed good affinity to CC and CO2, so that much
CC can be carried into the polymer matrix; another possibility is that the presence of CH2Cl2
may increase the swelling of the PET or PP substrate. For the impregnation experiment using
CO2-Acetone, the PET sample was distorted, which is considered as the result of CC reacted
with few -OH of the PET side chain because acetone promoted the activity of the side chain in
scCO2. Thus, CH2Cl2 was judged to be a good modifier to join in the supercritical
impregnation in this study.
- 63 -
Table 1. Solute (CC) uptake by PET (120°C, 25 MPa, 4 hr) and PP (100°C, 25 MPa, 2 hr)
fabrics.
Solvent Pure CO2 CO2-Acetone CO2-Dichloromethane CO2-Ethyl acetate
Mass uptake by PET (wt%) at 120°C
0.85 distorted 1.48 1.03
Mass uptake by PP (wt%) at 100°C
0.54 0.61 0.86 0.69
After the co-solvent was confirmed, the optimization of impregnation on the influence of
temperature in scCO2-CH2Cl2 was investigated at three levels of pressure (15, 20 and 25
MPa). It is known that the temperature needs to exceed the Tg of the material29, 30 for fiber
swelling in scCO2. In the present study, the two initial temperatures (80 and 60°C) used for
treating PET and PP fabrics were sufficiently higher than their glass transition temperatures,
respectively.
Figure 2 shows CC uptake by PET and PP fabrics as a function of temperature. The
impregnation amount of CC into PET displays a groove at ca. 120°C in the top graph (a). A
possible explanation is that is favorable to swell the polymer matrix and to increase the chain
mobility at higher temperature, but a decrease of fluid density will be combined with solute
solubility. This circumstance may result in a stripping effect, whereby the solute actually
desorbs from the fiber into the solution. As regards the result of the CC-impregnated PP by
scCO2-CH2Cl2, it was found that the sample can be partially molten at 110°C, although some
studies of PP fabric dyeing were performed at this temperature. The effect on the PP fabric at
110°C may be that the modifier CH2Cl2 lowers the melting point of the PP fabric. However,
the value of CC uptake by PP increased with temperature up to ca. 100°C without distortion.
Therefore, 100°C was confirmed as the maximum temperature to impregnate PP in
scCO2-CH2Cl2. Furthermore, the CC absorption by PET or PP is increased from 15 to 25 MPa
at either constant temperature, which is consistent with the case in pure scCO2. Thus, the
optimal conditions for impregnating fabrics with CC by scCO2-CH2Cl2 are 120°C, 25 MPa, 4
hr for PET, and 100°C, 25 MPa, 2 hr for PP.
- 64 -
80 90 100 110 120 1300.3
0.6
0.9
1.2
1.5C
ross
-link
ing
agen
t upt
ake
[wt%
]
Impregnation temperature [°C]
15MPa, 4 hr 20MPa, 4 hr 25MPa, 4 hr
(a)
60 70 80 90 100
0.2
0.4
0.6
0.8
1.0
Cro
ss-li
nkin
g ag
ent u
ptak
e [w
t%]
Impregnation temperature [°C]
15MPa, 2 hr 20MPa, 2 hr 25MPa, 2 hr
(b)
Figure 2. Impregnation of CC into a) PET and b) PP fabrics by scCO2-CH2Cl2.
- 65 -
3.3.2. Biomacromolecules immobilization
The samples obtained by the impregnation treatment in optimal conditions were used to
immobilize biomacromolecules. In order to investigate the reaction of CC situated on the
surface of samples under different stages, some samples were deliberately washed to weigh
after treatment at 30°C for 6 hours. Table 2 shows the immobilization of biomacromolecules
(sericin and chitosan) onto the surface of CC-PET and CC-PP fabrics after different
treatments.
For the CC-PET sample, the immobilization amount increased after the whole treatment
when it was compared with treatment at 30°C, and the values of sericin immobilization are
always higher than those of chitosan immobilization. However, for the CC-PP sample, there
was a decrease in the immobilization amount after the whole treatment when it was compared
with treatment at 30°C. This decrease of immobilization amount after treatment at 70°C could
be due to some CC penetrated on the PP surface generating a desorb phenomenon due to the
medium's temperature being excessively over the Tg of the PP fabric. In addition, the reaction
at 70°C did not geminate the immobilization amount on CC-PET. This may be due to the H2O
in the finishing solution which participated in the tri-substitution reaction with CC at high
temperature. The reaction of CC with H2O should also be included in the second step of the
process in immobilizing biomacromolecules onto the CC-PP sample. The immobilization of
sericin onto CC-PET or CC-PP is higher than the value of chitosan immobilization onto these
CC-fabircs. This is accounted for by the reaction of CC with chitosan in which amine groups
are fewer than those in sericin. Another explanation may be that an alkaline system is more
suitable than an acidic system during the process of nucleophilic substitution (deacidification
reaction). The biomacromolecules-immobilized CC-PET and CC-PP fabrics after the whole
finishing treatment were then characterized.
- 66 -
Table 2. Immobilization amount of biomacromolecules (sericin or chitosan) onto CC-PET
and CC-PP fabrics.
Samples
Immobilization amount after the
treatment at 30°C
Immobilization amount after the
whole treatment
Sericin solution Chitosan solution Sericin solution Chitosan solution
CC-PET 0.47 0.38 0.58 0.46
CC-PP 0.38 0.30 0.24 0.19
3.3.3. XPS spectra analysis
Surface chemical characterization of the untreated and modified fabrics (PET and PP) was
investigated by XPS measurement. The wide scan spectra of XPS are shown in Figure 3 for
the PET fabric and in Figure 4 for the PP fabric. After the impregnation of CC into PET and
PP fabrics in scCO2-CH2Cl2 fluid, new peaks appeared at 197.2, 268.2 and 399.2 eV, and
were assigned to Cl2p, Cl2s and N1s. This is confirmed that the CC impregnated can be bared
on the surfaces of the PET and PP fabrics. From the disappearance of Cl2p and Cl2s in the
CC-PP or CC-PET samples finished by sericin or chitosan solution, it is indicated that CC
bared onto the surface of fabric has taken part in some reactions. For the CC-PET samples
finished by macromolecules (sericin or chitosan), the increase in N1s shows that CC
impregnated on the surface of PET engaged in the reaction with sericin and chitosan,
respectively. Correspondingly, an increase of N1s in spectra of sericin-CC-PP is also an
evidence of the reaction of sericin with CC settleed on the surface of the PP sample. The
intensity of N1s in chitosan-CC-PET showed no obvious change, which was due to the result
of CC desorption from the CC-PP sample in the higher temperature aqueous system (as
mentioned in Section 3.3.2), even though some chitosan is linked on the PP surface. The
intensity of O1s in spectra of sericin-CC-PP and chitosan-CC-PP clearly increased, but this
result may be include the instance that H2O participating in the reaction with CC penetrated
on the surface of the PP sample. Aside, the O1s peak in the untreated PP spectrum was
accounted for by the influence of surface contamination.
- 67 -
500 400 300 2000
5000
10000
15000
20000
25000
Cl2p
O1s
Inte
nsity
[a. u
.]
Binding energy [eV]
Sericin-CC-PET Chitosan-CC-PET CC-PET Original PET
N1s
C1s
Cl2s
Figure 3. XPS spectra of untreated and finished PET fabrics.
500 400 300 2000
5000
10000
15000
Inte
nsity
[a. u
.]
Binding energy [eV]
Cl2s
Sericin-CC-PP Chitosan-CC-PP CC-PP Original PP
O1sN1s
C1s
Cl2p
Figure 4. XPS spectra of untreated and finished PP fabrics.
- 68 -
3.3.4. FT-IR spectra analysis
To analyze the impregnation CC into fabrics, the infrared spectrum of the cross-linking
agent was measured and is shown in Figure 5. Three clear groups of absorption peaks,
centered at 1497, 1270 and 850 cm-1, were assigned to the C=N, C-N and C-Cl stretching
vibration modes in heterocyclic rings, respectively. Here, the C=N stretching is shifted to
lower frequency from common region (1500-1600 cm-1) and was explained by a resonance
phenomenon occurring at the bond of C=N and C-N within the ring benzenoid-like
structure.31
2400 2000 1600 1200 8000.0
0.5
1.0
1.5
N
N
N
Cl
ClCl
Abs
orba
nce
Wavenumber [cm-1]
Cyanuric chloride
1497.45
1270.86 850.45
Figure 5. FT-IR spectrum of cyanuric chloride.
ATR-IR spectra of several PET fabrics are shown in Figure 6. After the impregnation of
CC into PET with scCO2, the characteristic peaks of CC at 870 cm-1 and 1500 cm-1 can be
noted; simultaneously, a shoulder appeared at the left side of -C(=O)-O band (1245 cm-1),
which was attributed to the effect of C-N stretching vibration of CC in the surface of PET.
When the immobilization of biomolecules onto CC-PET finished, the broad heave of
chitosan-CC-PET and sericin-CC-PET at 3300-3500 cm-1 was considered as the hydrogen
bonding of hydroxyl and amine groups. Some weak peaks at ca. 1640 cm-1 might be the
amide groups of biomacromolecules. For the spectra of chitosan-CC-PET, a protrudent
shoulder at the right of 1090 cm-1 should be the -C-O-C- peak of chitosan. Furthermore, a
- 69 -
decrease of C-Cl intensity at 850 cm-1 was very clear in the spectra of chitosan-CC-PET and
sericin-CC-PET. These changes suggest that CC was impregnated into PET successfully and
the Cl atoms of CC impregnated onto the PET surface were substituted by biomacromolecules
in aqueous processing.
3500 30000.0
0.1
0.2
0.3
0.4
Abs
orba
nce
Wavenumber [cm-1]
Sericin-CC-PET Chitosan-CC-PET CC-PET Original PET
a)1800 1600 1400 1200 1000 800
0.0
0.1
0.2
0.3
0.4
0.5
Abso
rban
ce
Wavenumber [cm-1]
Sericin-CC-PET Chitosan-CC-PET CC-PET Original PET
b)
Figure 6. Comparison of ATR-IR spectra of various PET fabrics.
Figure 7 shows the spectra of untreated and modified PP fabrics. Compared with the
spectrum of original PP, the CC-PP sample displayed absorption bands at around 1500, 1272
and 850 cm-1, corresponding to the characteristic peaks of CC, whereas these characteristic
peaks decreased greatly in the spectra of chitosan-CC-PP and sericin-CC-PP fabrics. This
decrease of peaks may imply that some CC was disengaged after the process of
biomacromolecules immobilization in the hot aqueous system. Furthermore, there are no
obvious changes observable in the hydroxyl and amine stretching regions around 3300-3500
cm-1 in the spectra of CC-PP fabrics finished by sericin or chitosan. From these effects, one
can conclude that although PP fabric can be impregnated with CC by scCO2, the
immobilization of sericin or chitosan onto CC-PP in an aqueous medium (temperature over
the Tg of PP) is much smaller than is the case with the CC-PET fabric.
- 70 -
1600 1400 1200 1000 8000.00
0.02
0.04
0.06
0.08A
bsor
banc
e
Wavenumber [cm-1]
Sericin-CC-PP Chitosan-CC-PP CC-PP Original PP
a)
3500 3250 3000 27500.00
0.03
0.06
0.09
0.12
Abs
orba
nce
Wavenumber [cm-1]
Sericin-CC-PP Chitosan-CC-PP CC-PP Original PP
b)
Figure 7. Comparison of ATR-IR spectra of various PP fabrics.
- 71 -
3.3.5. Surface morphology
SEM images were examined in order to understand the alteration of the untreated,
CC-impregnated and functional macromolecules-immobilized fabrics of PET and PP. The
results are shown in Figure 8 and Figure 9. As can be seen in Figure 8(a) and Figure 9(a),
the untreated PET and PP fabrics had smooth surfaces, which generally had a poor ability to
attach biomolecules or to capture water. The CC-impregnated PET and PP samples exhibited
micro-roughness on their surfaces. After immobilization treatment, some particles were
distributed on the surface of the PET and PP fabrics, indicating that the rough surface
endowed by sericin or chitosan may provide more capacities for the fabrics to capture water
and also to facilitate the penetration of water into these fabrics. The fact that the
micro-roughness of the biomolecule-CC-PP was smaller than that of the
biomolecule-CC-PET can be attributed to the lower immobilization amount. In addition, no
change in the appearance of the SEM images was observed in PET or PP fabrics before and
after treatment in scCO2-CH2Cl2 without the cross-linking agent of CC (Figure 10).
- 72 -
Figure 8. SEM images of a) untreated PET, b) CC-PET, c) Sericin-CC-PET and d)
Chitosan-CC-PET fabrics.
- 73 -
Figure 9. SEM images of a) untreated PP, b) CC-PP, c) Sericin-CC-PP and d)
Chitosan-CC-PP fabrics
- 74 -
Figure 10. Comparison of SEM images of PET and PP fabrics before and after treatment
in scCO2-CH2Cl2 without the cross-linking agent of CC.
3.3.6. Hydrophilicity characterization
3.3.6.1. Water contact angles
The surface wettability of several PET and PP samples was evaluated by measuring the
static contact angle of water droplet on each fabric's surface. Table 3 gives the contact angles
recorded. Compared with the original fabric, several of the modified fabrics showed an
evident decrease in contact angle, which means that the surface wettability of the PET fabric
has improved to a certain extent. Although CC is insoluble in water at low temperatures, the
CC-impregnated PET and PP samples also displayed a decrease in contact angle, which may
be caused by the increase in surface roughness of those finished fabrics. Sericin-treated
CC-PET and CC-PP fabrics showed smaller contact angles than chitosan-treated samples,
which is due to the immobilization amount of sericin being more than that of chitosan.
- 75 -
Another explanation might be that the hydrophilicity of sericin is inherently stronger than that
of chitosan. Generally, the water contact angles of PET fabrics are smaller than those of PP
fabrics because small hydrophile groups such as hydroxyl existed in PET fabric.
Table 3. Static water contact angles of untreated and modified PET and PP fabrics.
PET samples Static water contact angle, θ (o) PP samples
Untreated PET 102.6 132.2 Untreated PP
CC-PET 94.5 121.4 CC-PP
Sericin-CC-PET 78 112.7 Sericin-CC-PP
Chitosan-CC-PET 82.4 117.8 Chitosan-CC-PP
3.3.6.2. Wicking properties
Testing wicking properties is a conventional method to evaluate the water imbibition
ability of a fabric. The higher the height of the water climbed, the better the wickability of the
fabric. The wicking heights on the PET samples are shown in Table 4. It can be seen that the
wicking heights of untreated and CC-impregnated PET were very low because of their
hydrophobicity, but the value greatly increased after the CC-PET sample was finished by
sericin or chitosan. This behavior is consistent with the results obtained for the static water
contact angles on these PET fabrics (see Section 3.3.6.1). A conclusion that sericin and
chitosan linked on a CC-PET surface has improved the hydrophilicity of the PET fabric can
be obtained.
For the PP samples, the water boundary did not rise, with the slight exception of the
sericin-CC-PP which had a small change (less than 2mm/8min). Thus, the improvement of
hydrophilicity in the PP fabric was not as successful as in the PET fabric.
- 76 -
Table 4. Wicking heights of untreated and modified PET fabrics.
Samples Untreated PET CC-PET Sericin-CC-PET Chitosan-CC-PET
Wicking height (mm) 10 13 42 28
3.4. Summary
The active-linker agent of CC can be introduced into PET and PP fabrics by the
impregnation method in scCO2 to couple biomacromolecules (sericin or chitosan).
Dichloromethane is recognized as an effective co-solvent that boosts the solubility of CC in
scCO2 and further increases the impregnation amount of CC into fabrics of PET and PP. The
optimal conditions for impregnation are localized at 120°C, 25 MPa, 4 hr for PET, and 100°C,
25 MPa, 2 hr for PP. During the process of immobilizing sericin or chitosan onto CC-PET and
CC-PP, the tri-substitution reaction at 70°C is not favorable to the CC-PP sample because of
the decrease of immobilization amount.
Chemical analysis reveals that sericin or chitosan can react with CC impregnated on the
surface of PET and PP fabrics more or less. The SEM images of modified samples show an
increase in the micro-roughness of the fabric surface. Water contact angles and wicking
heights conclude that the hydrophilic properties of PET fabrics are improved effectively after
the whole treatment described in this study.
- 77 -
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Chapter 4. Modifying poly(ethylene terephthalate) fabric by supercritical carbon dioxide
4.1. Introduction
In the textile industry, poly(ethylene terephthalate) (PET), has been an important class of
fibers ever since it was first created in 1946.1 Its basic properties satisfy the highest
requirements, such as excellent mechanical properties, weather resistance, and so on;
moreover, its production cost is low. But then, the PET fabric has also some drawbacks
including weak hydrophilicity and poor biocompatibility, due to the lack of active side chain
as well as rare active binding on organic backbone. In order to create cloth in conformity with
the health safety requirements of the living human body, such as somewhat complicated
processes are conventionally adopted to add value to PET in textile finishing, involving
co-spinning,2 physical coating,3, 4 plasma discharge,5, 6 alkaline treatment,7, 8 graft
polymerization,9, 10 etc. Nevertheless, some of these methods have limited practical use, and
frequently lead to the hardening of the PET material, elevated production costs and
complicated work procedures. Accordingly, there is a demand for a finishing technology that
can be applied to PET fabric more easily and efficiently.
Recently, the use of scCO2 fluid in polymer processing has had a marked effect on
dyeing,11-13 expanding foam,14 plating,15 impregnation,16-18 etc. ScCO2 (Tc = 31°C, Pc = 73.8
bar) is one of the most commonly used supercritical fluids. It is naturally abundant,
chemically inert, non-flammable, essentially non-toxic, easy to handle, and the least
expensive solvent after water.19 Moreover, scCO2 is a good solvent for many non-polar (and
some polar) low-molecular-weight compounds,20, 21 and a few polymers are also known to
have good solubility in scCO2;22 however, it is generally a very poor solvent for
high-molecular-weight polymers under readily achievable conditions, because of its very low
dielectric constant, ε, its low polarizability per volume, α/ν, and its reluctance to engage in
van der Waals interactions. Although scCO2 is a poor solvent for most polymers, it does have
the capability to swell polymers up to several mass percentages;23, 24 thus, a
low-molecular-weight agent dissolved in scCO2 can diffuse into the polymer phase, achieving
- 81 -
the modification of that polymer.25 The swelling of a polymer occurs only in its amorphous
phase, and depends on the interaction of the supercritical fluid with the polymer and on the
crystallinity of the polymer. The higher the crystallinity, the more difficult it is to swell the
polymer.26 The degree of swelling of the polymeric matrix can be modulated by adjusting the
pressure and temperature, and the mass transfer of agents within the polymer can also be
controlled in the same way.27 In addition, a co-solvent participating in scCO2-polymer
processing can also increase the solute uptake in polymer, which attributed mainly to the
solubility improvement of solute in scCO2.28
In the field of polymer fabric modification, sericin,4 , 29, 30 collagen,31, 32 and chitosan33, 34
are known as top natural functional agents; they have been applied widely to improve the
hydrophilicity and biocompatibility of polymer fabric. If these agents can be impregnated into
PET fabric, they can impart desirable properties to the PET. However, this is conventionally
impossible due to the higher molecular weight of these functional agents. In order to modify
PET fabric with these natural macromolecules, on the basis of use of scCO2 fluid in polymer
processing, a type of epoxy compound, GPE35, 36 is chosen in our present study as a
cross-linking agent which will be impregnated into PET fabric with the help of scCO2 to
attach functional macromolecules. As far as we know, there are not other conventional
techniques which can achieve the same result in impregnation of cross-linking agents into
pre-existing polymer without changing their inherent properties but the method of solid-state
foaming or swelling with CO2 as a gas blowing agent.37, 14 This project will be a simple, low
cost and environmentally benign process together with a firm penetration of GPE into
amorphous region of PET fabric. This epoxy compound is chosen here, because the epoxy
group existing at the end of the chain is bared on the surface of the PET fabric and acts as a
reactive site for functional nucleophilic reagents, including proteins, polysaccharides, nucleic
acids, and various small molecules.38
Based on the above considerations, we tried to modify the surface of PET fabric with
natural functional agents (sericin, collagen or chitosan). In this study, the impregnation of
GPE into PET fabric was investigated under various supercritical conditions, in pure CO2 as
well as in CO2 with a co-solvent, by measuring the mass uptake. The surface immobilization
- 82 -
sericin, collagen or chitosan on GPE-PET fabric was conducted by the solution method and
by the Pad-Dry-Cure method.
4.2. Experimental procedures
4.2.1. Materials and reagents
The fully oriented yarn poly(ethylene terephthalate) (PET) fabric (warp/weft, 78T/216; 90
g/m2) used as the substrate for modification in this study was supplied by Toyobo Co., Ltd.
First, the PET fabric was washed and stabilized by immersing it in acetone at 30°C for 30
minutes. The epoxy compound used as a cross-linking agent and impregnated to the PET
fabric with the help of scCO2 was glycerol polyglycidyl ether (GPE, Denacol EX-313, Mw:
ca. 250), which was supplied by Nagase Chemtex Co. without further purification; its main
components have the structural formulas shown in Figure 1. Three natural functional regents,
sericin (SERICIN POWDER, Mw: ca. 17,000), collagen (MARINE COLLAGEN CF, Mw:
ca. 1,000) and chitosan (low-molecular-weight) were used as hydrophilic agents together with
antimicrobial material for immobilization onto the surface of the PET fabric; the former two
were supplied by Seiren Co., Ltd. and Chisso Co., Ltd., respectively, and the third was
purchased from Sigma-Aldrich, Inc. Sodium hydroxide (NaOH) and sodium tetraborate
decahydrate (Na2B4O7・10H2O), used for modulating the pH of the functional solutions, were
purchased from Nacalai Tesque, Inc. All the functional reagent solutions were prepared with
distilled water. The carbon dioxide used in all of the experiments was purchased from Uno
Sanso Co., Ltd. (99.5% pure). Several organic solvents (acetone, ethyl acetate, chloroform
and isopropyl alcohol) were guaranteed-grade reagents obtained from Wako Pure Chemical
Industries, Ltd.
- 83 -
OH2CH2C
HC
HC
CH2
OH
H2C
O
OH2C
HC O
H2C
HC CH2
OCl
OH2CH2C
HC
HC
CH2
O
H2C
O
OH2C
H2C
HC CH2
OHC O
H2C
HC CH2
OCl
OH2CH2C
HC
HC
CH2
OH
H2C
O
OH2CH2C
HC
HC
CH2
O
H2C
O
OH2C
HC CH2
O
H2C
HC CH2
O
(ca. 42mol%) (ca. 14mol%)
(ca. 4mol%)(ca. 39mol%)
OH2C
HC CH2
O
Figure 1. Structural formulas of glycerol polyglycidyl ether (GPE, Denacol EX-313).
4.2.2. Methods
The whole process of PET fabric treatment, including the impregnation of the crosslinking
agents and surface immobilization of the functional agents, is shown schematically in Figure
2. The details of each sub-process are described below.
4.2.2.1. Impregnation of GPE into PET by scCO2
The apparatus for the preparation of the GPE-PET composite consisted of a 50-mL
stainless steel vessel (Tmax=200°C, Pmax=30 MPa), a magnetic stirrer, a constant-temperature
air bath (Model SCF-Sro, JASCO Co., Tokyo), a thermocouple and a pressure gauge. It is a
batch system operating in three main steps: charge, impregnation and discharge. CO2 is stored
in a cylinder and pressurized to working pressure by a pump. The PET fabric substrate (10
cm×12 cm, ca. 1.10 g) was suspended on a stainless steel net inside the vessel, and the
cross-linking agent (0.20 g) was placed on the bottom of the vessel. The quantity of
cross-linking agent was in large excess of the amount required to saturate the CO2 during the
entire course of impregnation into the PET fabric. When the autoclave reached the desired
temperature, CO2 was let in slowly (ca. 5 mL/min) and isothermally compressed to working
- 84 -
pressure; then, the system was agitated for a certain period of time to impregnate the GPE into
the PET fabric. After the impregnation, the system was depressurized at 0.5 MPa/min and
allowed to cool to room temperature in air. The same experiment was performed using a batch
program with the addition to CO2 of 4% modifier (acetone, ethyl acetate or chloroform).
Afterward, the sample was flushed with air and washed with distilled water at room
temperature in order to remove the cross-linking agent adhered on the surface. Finally, the
impregnated sample was dried in an oven at 50°C.
Cross-linking Agents (GPE)
Supercritical CO2
O
O
H2C
OH
H2C
OH
HN MacromoleculeH2N Macromolecule
(Sericin, Collagen, Chitosan) HN Macromolecule
Aqueous solution/Pad-Dry-Cure
PET Fabric GPE-impregnated PET Fabric
Functional Agents-immobilized PET Fabricl
Figure 2. Schematic illustration of the entire process of PET fabric modification.
4.2.2.2. Immobilization of functional agents onto PET fabrics
The immobilization of natural functional agents onto GPE-PET fabric was performed in
two ways: processing in an aqueous solution, and processing by the Pad-Dry-Cure method.
The mechanism of immobilization relies on the GPE epoxy compound impregnated on the
surface of fabric, which can graft the functional agents by the ring-opening reaction of the
epoxy groups. In addition, the original PET fabric was also treated with the two methods to
- 85 -
anchor functional agents.
4.2.2.2.1. Processing in an aqueous solution
For the immobilization of sericin or collagen, 3wt% finishing solutions were prepared and
the pH of the solutions was adjusted to 10~11 with Na2B4O7・10H2O so that the amines
became unprotonated.35, 38 Then, the sample was immersed in sericin or collagen solution and
shaken for 1 week at room temperature. It has been reported that dermal sheep collagen can
be cross-linked by epoxy compound at mild condition for a long time.39 In the case of
chitosan, it was first added to a 30wt% NaOH aqueous solution, stirred for 2 h and placed in a
refrigerator; the lyophilized mixture was then thawed and filtered with isopropyl alcohol to
prepare the chitosan solution.40 Then, the fabric was immersed in the solution under stirring
for 16 h at 50°C. At the end of the immobilization, the fabrics were taken out, squeezed and
air-dried. The finished fabric samples were then rinsed with water and finally dried again at
50°C in vacuum and conditioned prior to testing.
4.2.2.2.2. The pad-dry-cure treatment
Padding is a well-known technique for treating textile materials. The textile is padded into
a chemical solution, followed by a squeezing using two pad rolls to remove the excess liquid
trapped in the textile. The finishing solutions were prepared as mentioned above in Section of
processing in an aqueous solution. The amount of functional agent (sericin, collagen or
chitosan) in the solution was in large excess of the cross-linking agent on the surface of the
PET fabric. The fabric samples were padded by the two-dip-two-nip process to about 90%
wet pickup with freshly prepared aqueous solutions of each of these functional agents. After
treatment, the padded fabrics were dried at 85°C for 3 min, cured at 150°C for 3 min, washed
thoroughly, and finally dried.
4.2.3. Characterizations
The absorption of the cross-linking agent into the PET fabric using supercritical CO2 was
determined gravimetrically and is expressed as a percentage of impregnation, according to
- 86 -
equation (1):
G impregnation (%) = (P1 – P0) / P0 × 100 (1)
where P0 and P1 are the weight (g) of untreated PET fabric and impregnated PET fabric,
respectively. The immobilization ratio of functional agents onto GPE-PET fabric is defined
by equation (2):
G immobilization (%) = (P2 – P1) / P1 × 100 (2)
where P2 represents the weight of the GPE-PET fabric finished with the functional agent.
Analysis was performed using a photoelectron spectrometer (JPS-9010MCY) with Mg Kα
excitation radiation (1,253.6 eV). The X-ray source was run at a potential of 10 kV, a current
of 10 mA and an incident angle of 45°. The pressure within the XPS chamber was maintained
at 10-7 Pa during the measurement. The binding energy of carbon 1s was fixed to 285 eV and
was used as the internal reference for the binding energy scale. The depth profiling of the
samples was performed with argon ion sputtering (1kV, 8 mA) at an incident angle of 90° for
15 second. Deconvolution analysis of the peaks was carried out using the
Gaussian-Lorentzian component profile in the Peakfit○R software.
The FT-IR spectrum of the cross-linking agents (GPE) was obtained using a
Fourier-Transform Infrared Spectroscope (FT/IR-4100, JASCO), by the usual method of
making pellets (ca. 0.5% w/w) with potassium bromide (KBr), where a total of 32 scans were
accumulated at a resolution of 4 cm-1. All spectra of the fabrics were collected at a resolution
of 4 cm-1 and 200 scans using the same instrument with a 45° ZnSe prism (n = 5) as the
internal reflection element wafer set in a single ATR accessory.
Elemental analysis of the functional agents (sericin, collagen or chitosan) and several
types of PET fabrics was carried out to precisely determine the amount of nitrogen, the
analysis was carried out on an elemental analyzer (EA 1110-W) using the classical technique
of combustion analysis. In this technique, the sample is burned in an excess of oxygen, and
various traps collect the combustion products — carbon dioxide, water and nitric oxide. The
weights of these combustion products can be used to calculate the composition of the sample.
Before measurement, each sample was ground to crumb and dried at 100°C for 24 h, after
which it was analyzed to measure the organic content.
- 87 -
Dynamic water contact angle used to evaluate surface wettability of the PET fabric was
measured in a room condition (20°C) by the sessile droplet method using a Contact Angle
Measuring Instrument EasyDrop (RÜSS DSA20). A distilled water droplet of 3-μL was
placed on the sample surface and a picture of the droplet was taken within 5 s. A new water
droplet of 3-μL was added to the sample surface every 15 s and the procedure was repeated 5
times (total 18μL) for each advancing step. Then 3-μL water was retracted every 15 s for each
receding step. The receding procedure was stopped until the surface water droplet disappeared
in camera image.
The moisturization of the PET fabric was measured in a humidity chamber (IH400,
Yamato) in which a weight meter was installed. For the measurement of the isothermal
hygroscopicity, the samples were weighed after the given environmental condition was
maintained for 2 hours. In the experiment for the hygroscopicity/dehygroscopicity, the sample
was weighed for a random period of time under two environmental conditions (25°C, 65%
RH; 30°C, 95% RH). Moisture regain is defined by equation (3), in which Wm is the weight
(g) of the moisturized sample, and Wd is the weight (g) of the sample dried in an oven (100°C,
2 h):
Moisture regain (%) = (Wm – Wd) / Wd ×100 (3)
The antimicrobial assessment of the PET fabric was made through the quantitative method
of microbe absorption proposed by the Japan Spinners Inspection Foundation. The microbe
used here was Staphylococcus aureus (S. aureus), a Gram-positive bacterium, which usually
exists in human nose or skin and often causes an infection on the skin as lesions, pimples or
boils, even brings pneumonia if the infection got worse. All of the samples were incubated for
18 h at 37°C before the bacterial colonies were counted. The antimicrobial effects of the
specimens are evaluated, as a rule, based on the bacteriostatic and bactericidal activities. The
bacteriostatic and bactericidal activities were calculated as follows:
Bactericidal activity = log A – log C
Bacteriostatic activity = log B – log C
where A, B, and C are the number of bacteria in the initial inoculation, the number of colonies
on an incubated piece of control calico, and the number of survivors on the untreated and the
- 88 -
modified PET fabrics after incubation, respectively.
4.3. Results and discussion
4.3.1. Supercritical treatment of PET fabric
ScCO2 can swell PET fiber, and the temperature usually has to reach 80°C in order to
exceed the Tg of PET.23 ScCO2 can also dissolve a wide range of compounds, including epoxy
compounds.41 Here, the solubility of the cross-linking agent GPE in scCO2 was evaluated by
using a stainless steel vessel with transparent windows. In the experimental conditions of the
present study, the fluid had optical uniformity in pure scCO2, but it became clearer in the
presence of a co-solvent such as acetone, ethyl acetate or chloroform. This indicates that these
co-solvents can enhance the solubility of GPE in scCO2. The reason why small amounts
(typically < 5%) of a polar co-solvent as a modifier added to scCO2 increases the solvating
power of CO2 is that the affinity between the solute and fluid is improved.41, 42
To optimize the process of impregnation in the case of pure scCO2, a study on the
absorption of the cross-linking agent by the PET fabric at different temperatures (80, 100 and
120°C) and pressures (10~30 MPa) was carried out. It has been reported that the conventional
dyeing time for PET fiber in scCO2 is 30-120 min.11, 12 With regard to the swelling of PET
fiber in CO2, K. Hirogaki et al. have described that the swelling behavior reached a maximum
after 2 h.24 Therewith, a time period of 2 h was adopted here to impregnate the PET fabric
with cross-linking agents in scCO2. Figure 3 shows the influence of pressure on the uptake of
the cross-linking agent by the fabric at the three temperatures.
- 89 -
10 15 20 25 300.0
0.5
1.0
1.5
2.0
Cro
ss-li
nkin
g ag
ents
Upt
ake
[wt%
]
Pressure [MPa]
120 ° C 100 ° C 80 ° C
Figure 3. Impregnation of GPE into PET fabric for 2 h in pure scCO2.
The results show that the uptake of the cross-linking agent by the PET fabric increased
initially as the pressure increased up to 25 MPa, but fell at pressures higher than 25 MPa,
particularly at higher temperatures. Similar results were obtained when using scCO2 modified
with chloroform. The main reason may be for this explanation that partitioning of GPE in the
fluid phase is enhanced. First, CO2 readily swells PET at higher pressures; however, it is also
a much better solvent for cross-linking agents, and this tendency was reinforced at higher
temperatures considered as the cause of the decreased fluid density.
In addition, we found that the equilibrium concentration in the fabric is much more
sensitive to temperature than to pressure, and that is more profitable to implement the process
at a higher temperature. The temperature influences the uptake of the cross-linking agent
because it affects the polymer matrix. Above the temperature of the glass transition, the free
volume of the polymeric matrix and the chain mobility is increased, and this results in a
higher PET infiltration concentration. Nevertheless, at higher temperatures, certain addition
reactions, including the self-polymerization of the epoxy groups,43 the formation of vinylene
carbonate44 and the carboxylic-acid end-group modification of PET with the epoxy groups
- 90 -
may occur.26 Thus, the maximum temperature for controlled scCO2 treatment was set at
120°C in this study.
To increase the content of the cross-linking agent absorbed by the PET fabric in scCO2,
three co-solvents (4% mol/mol), acetone, ethyl acetate and chloroform, were added to CO2 for
impregnation, respectively, at 120°C and 25 MPa for 2 h. Although alcohols are good
modifiers which can enhance the swelling of PET fiber in scCO2,24 they cannot be used
because epoxy compounds react with alcohols. The results for the uptake of the cross-linking
agent in supercritical CO2 with a co-solvent are shown in Table 1.
Table 1. Mass uptake of the cross-linking agent by the PET fabric in supercritical fluid
at 120°C, 25 MPa for 2h.
Solvent Pure CO2 CO2-Acetone CO2-Ethyl acetate CO2-Chloroform
Mass uptake (wt%) 1.62 2.14 2.47 3.26
In contrast with the sorption of the cross-linking agent into PET fabric treated with pure
scCO2, the sorption increased when the co-solvent entered the supercritical fluid. Chloroform
was more effective than the other two co-solvents examined, owing to its lower dielectric
constant. The uptake of the cross-linking agent by PET as a function of pressure was also
compared in scCO2 with and without CHCl3 at 120°C. The data are shown in Figure 4; the
results were similar, but the uptake tended to decline more strongly in the presence of
chloroform than in pure CO2 over 25 MPa. This is considered that chloroform enhanced the
solubility of GPE in fluid phase more significantly with pressure at the higher pressure.
Another reason may be based on H-bonding interactions between the cross-linking agents and
the polymer matrix.45 While more cross-linking agents penetrated into PET with
scCO2-CHCl3 at higher pressure, H-bonding may form by the OH-functional group of GPE
with the carbonyl group in PET matrix, this bond will introduce more hindrance in polymer
matrix, and thus slow down any further diffusion of GPE into PET fabric. Although the
- 91 -
uptake of GPE into PET decreased at higher pressure, the incorporation of GPE into the PET
fabric was almost twice the value in pure scCO2 for the solubility improvement of GPE or the
enhancement on swelling ability of PET in scCO2-CHCl3.
10 15 20 25 300.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Cro
ss-li
nkin
g ag
ents
Upt
ake
[wt%
]
Pressure [MPa]
scCO2 - CHCl3
Pure scCO2
Figure 4. Comparison of the uptake of the cross-linking agents by the PET fabric in pure
scCO2 and scCO2-CHCl3 (4% mol/mol) at 120°C for 2 h.
Information concerning the manner in which the cross-linking agent was impregnated into
the PET with the scCO2-CHCl3 treatment can be obtained from the XPS signals shown in
Figure 5. It can be seen that the XPS spectrum of original PET mainly contains carbon (C) 1s
and oxygen (O) 1s peaks. After the scCO2-CHCl3 treatment of PET fabric with GPE, new
peaks appeared at 199.8 eV and 269 eV, which were attributed to chlorine (Cl) (2p and 2s)
electrons, regardless of the implementation of argon (Ar) ion etching. These results suggest
that the cross-linking agent (at least the chlorine-containing compounds) was impregnated
into the PET fabric by scCO2. After Ar ion etching of GPE-impregnated PET, the content of
C1s increased markedly and the peak of O1s decreased in height, indicating that the depth
profiling of PET removed its surface contaminants (hydrocarbon) and oxides at the same time.
It was also noted that the surface N1s peak disappeared completely.
- 92 -
500 400 300 2000
10000
20000
30000 GPE-PET with Ar ion etching
GPE-PET without Ar ion etching
Original PET without Ar ion etching
Inte
nsity
(a. u
.)
Binding energy (eV)
O1s
N1s
C1s
Cl 2pCl 2s
Figure 5. Changes in the surface elements on the PET substrate and the GPE-PET fabric
obtained in scCO2-CHCl3 with/without argon ion sputtering.
In order to analyze the surface of original PET and GPE-PET fabric, deconvolution
analysis of the C1s peak in the XPS spectra was carried out, as shown in Figure 6. The C1s
signal of original PET contained three separate peaks at 284.9 eV, 286.6 eV and 288.7 eV,
which were assigned to the functional groups of C-C, C-O and O-C=O, respectively. In the
XPS signal of GPE-PET (Figure 6b), a fourth peak appeared around 286.3 eV, attributable to
the epoxy carbon atoms. Moreover, an increase of the C-O band peaking at 286.6 eV was
observed relative to the spectra for the original PET fabric. These data further confirm that the
cross-linking agent was impregnated into the PET fabric by means of scCO2.
- 93 -
290 288 286 284 282
n* OCH2CH2OC
OCO
*
-C(=O)−C-
-C−O-
-C−C-
Binding energy [eV]
a)
Original PET
290 288 286 284 282
GPE-PET
-C(=O)−C-
-C−O-
-C−C-
Binding energy [eV]
-C−C-O
b)
Figure 6. Deconvolution of the C1s peak in the XPS spectra of PET recorded for a) original
PET fabric and b) GPE-PET fabric obtained in scCO2-CHCl3.
- 94 -
FT-IR spectra were subsequently used to characterize the chemical structure of the
cross-linking agent. Figure 7 shows the spectrum for GPE: 3416 cm-1 (O-H stretching and
O-H…O-H hydrogen bonding); 3050 and 2990 cm-1 (CH2 of the epoxy ring); 2920-2880 cm-1
(CH3, CH2); 1465 cm-1 (CH2 bending); 1342 cm-1 (O-H bending); 1256 cm-1 (symmetrical
stretching of the epoxy ring); 1080-1125 cm-1 (C-O stretching); 950-810 cm-1 (asymmetrical
stretching of the epoxy ring); 754 cm-1 (C-Cl stretching).
3500 3000 2500 2000 1500 10000.0
0.5
1.0
1.5
2.0
2.5
3.0
Abs
orba
nce
Wavenumber [cm-1]
GPE (Cross-linking agents)
Figure 7. FT-IR spectrum of the cross-linking agents (GPE).
The FTIR-ATR spectra of original PET fabric and GPE-PET fabric are shown in Figure 8.
Compared with the original PET spectrum, in the GPE-PET spectrum, a prominent epoxy ring
signal occurred at 847 cm-1, and the absorbance of 2900 cm-1 was attributed to the C-H
stretching which increased with the amount of GPE; furthermore, a new band at a higher
frequency (~3400 cm-1) was discernable, which suggests that a weaker hydrogen-bonding
interaction occurred in O-H…O-H due to the increase in the number of hydroxyl groups in
GPE. Also, the area ratio of C=O band to C-C-O band in GPE-PET spectrum was observed
- 95 -
decreasing versus the ratio of same bands in original PET. This change is due to the influence
of C-O band of GPE impregnated in the fabric.
It was found that the FTIR-ATR spectra of the PET fabric GPE-impregnated with pure
scCO2 was analogous with the spectrum of PET fabric GPE-impregnated with scCO2-CHCl3,
except that the absorbance of some bands decreased markedly. This implies that few GPE
molecules penetrated on the surface of the PET fabric, leading to the small impregnated
amount.
3500 3000 2500 2000 1500 10000.0
0.2
0.4
0.6 OH STR (Alcohol and H-bonding, broad)
C-H STR(Aliphatic groupand epoxy ring)
C-H DEF(Epoxy ring)
Abs
orba
nce
Wavenumber [ cm-1]
PET treated with GPE in scCO2-CHCl3 PET treated with GPE in pure scCO2 Original PET
Figure 8. FTIR/ATR spectra of PET substrate and GPE-PET fabric.
4.3.2. Immobilization of functional agents (sericin, collagen, or chitosan) onto GPE-PET
and original PET fabrics
Samples of GPE-impregnated PET fabric in pure scCO2 and in scCO2-CHCl3 were treated
for the immobilization of functional agents. The results of the immobilization of the three
functional agents onto GPE-PET fabric obtained in scCO2-CHCl3 are shown in Table 2. From
- 96 -
the data, it was concluded that the Pad-Dry-Cure method gives a higher yield than treatment
in an aqueous solution. This indicates that at high temperatures, nucleophilic reagents can
induce the ring-opening of the epoxy groups. Moreover, the low amount of immobilization in
the aqueous solutions might be due to the unstable contact of the functional agents with the
GPE-PET fabric. Collagen was immobilized onto GPE-PET fabric to a higher degree than the
cases of sericin and chitosan, which can be explained for the high-molecular-weight reactant
such as chitosan or sericin, the low-molecular-weight collagen had predominance to access
the epoxy ring bared on the surface of the PET fabric. Regardless of the immobilization
method, i.e., aqueous solution versus pad-dry-cure, there was a small increase of weight, less
than 0.30%, in the GPE-PET fabric obtained in pure scCO2. About the immobilization of
functional agents to the original PET fabric, it was unsuccessful in either immobilization
method, owing to the changeless weight of fabric once the treated sample was washed by
water. Thus, the GPE-PET fabric obtained in scCO2-CHCl3 fluids was elected as the optimal
object for immobilizing functional agents, the pad-dry-cure treatment was also considered as
a better immobilization method to finish GPE-PET fabric with functional agents.
Table 2. Amounts of functional agent immobilized onto GPE-PET fabric and nitrogen
contents of GPE-PET fabric finished with functional agents.
Functional agent Fishing processes Immobilization amount (wt%) Nitrogen content (%)
Sericin
N(%) : 21.1997
Aqueous solution 0.18 0.0365
Pad-Dry-Cure 0.83 0.1739
Collagen
N(%) : 22.7477
Aqueous solution 0.22 0.0474
Pad-Dry-Cure 1.24 0.2791
Chitosan
N(%) : 10.7254
Aqueous solution 0.15 0
Pad-Dry-Cure 0.78 0.0818
- 97 -
GPE-PET fabrics modified with the three functional agents by the Pad-Dry-Cure method
were further investigated by XPS analysis, and wide scan spectra for the identification of the
elements on the PET surface are presented in Figure 9. In contrast with the spectra of
GPE-PET and original PET, there is an obvious N1s peak at 399.5 eV in the spectrum of
GPE-PET fabric modified with each functional agent. This is a convincing qualitative
argument that the functional agents were immobilized on the surface of the GPE-PET fabric.
The order of intensity of the N1s signal was as follows: collagen-GPE-PET >
sericin-GPE-PET > chitosan-GPE-PET; however, the element content obtained from the peak
ratio did not mean the essential value of nitrogen in the fabric because the measurement
belongs to surface analysis. In order to precisely calculate the value, the nitrogen contents of
all the materials were measured by combustion analysis instead of XPS analysis. The values
of N (%) are shown in Table 2; the quantitative order of nitrogen in the PET fabrics modified
with the three functional agents by the combustion method accorded with the intensity order
of N1s in the XPS spectra. The three measured values were almost consistent with the values
calculated from the immobilization amounts and nitrogen contents of the functional agents
(sericin, collagen and chitosan), except when chitosan solution was used for finishing the
GPE-PET fabric. In Figure 9, corresponding to the spectra of GPE-impregnated PET, we also
found that the peak area of Cl2p and Cl2s decreased in the spectra of the three functional PET
fabrics. This was probably due to the fact that the chloride on the GPE-PET surface
participated in the reaction with the functional agents.
- 98 -
600 500 400 300 2000
5000
10000
15000
20000
25000 Original PET GPE-PET Chitosan-GPE-PET Sericin-GPE-PET Collagen-GPE-PET
Inte
nsity
[a. u
.]
Binding energy [eV]
Cl2p
Cl2s
C1s
N1s
O1s
Figure 9. Comparison of the surface chemical elements based on the XPS spectra of the
PET.
The same kinds of samples were also evaluated by FTIR/ATR spectral analysis to
investigate the reaction circumstances of the epoxy groups; unfortunately, the three spectra for
sericin-GPE-PET, collagen-GPE-PET and chitosan-GPE-PET were indiscernible in this
respect, despite these functional agents (sericin, collagen and chitosan) have different
structures and discernible bands of IR spectra. This is due to the case that those discernible
bands are weak usually, and that some discernable bands of the functional agent overlapped
with the band of the PET substrate because of the small immobilization amounts. Figure 10
shows, for comparison, the FT-IR/ATR spectra of GPE-PET and sericin-immobilized
GPE-PET treated by the pad-dry-cure method. A shoulder band occurred at 3300 cm-1 in the
sericin-GPE-PET spectrum, which is characteristic of the amide unit, despite the fact that the
deformation of amide did not appear clearly at 1654 and 1544 cm-1. At the same time, a
remarkable decrease of the bands at 845 cm-1 was observed, indicating that the epoxy groups
bared on the surface of the PET fabric were ring-opened mostly by sericin.
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3500 3000 2500 2000 1500 10000.0
0.1
0.2
0.3
0.4
0.5
0.6A
bsor
banc
e
Wavenumber [cm-1]
Sericin-GPE-PETGPE-PET
Amine absorption
Figure 10. Comparison of the FTIR/ATR spectra of GPE-PET and sericin-immobilized
GPE-PET fabric.
4.3.3. Surface wettability and moisture regain of the original and the modified PET
fabrics
The surface wettability of diversified PET fabrics was evaluated by the contact angle of
water on the fabric surface. For a sample of non-ideal surface such as a tissue or fabric, static
water contact angle always change with the contact time, which is accounted for surface
roughness, surface heterogeneity, penetration of liquid into the surface region etc. Dynamic
contact angle describe the processes at the liquid/solid boundary during the increase in
volume (advancing angle) or decrease in volume (receding angle) of the drop, i.e. during the
wetting and dewetting processes. Thus, dynamic water contact angle was tested as a replace
of static measurement for the advancing contact angle can average negative effect of static
contact angle on the surface heterogeneity and the receding angle can make statements about
the penetration of water or the roughness of solid sample.
The mean values of water contact angles and the retracted volume of water obtained for
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several modified PET fabrics and original PET fabric are presented in Table 3. The samples
of functional agent immobilized GPE-PET fabrics for measurement here were the GPE-PET
fabrics processed with the pad-dry-cure method. It can be seen that, compared with the
original PET fabric, both of the θA and θR of the modified PET fabrics were decreased, and
the decrease of θR was greater than that of θA. Therefore, modification degree impacted θA
slightly, and impacted θR greatly. The decrease in both of θA and θR of the modified PET
fabrics disclosed the improvement in hydrophilicity of these fabrics, which is mainly deduced
that polar functional groups (O-C-O and OH) of cross-linking agents and functional agents
interact with water and the interaction contributes to the decrease of the interfacial free energy
of the fabric surface. The value of receding contact angle basically reflected surface
characterization of polymer reconstruction in water. While the droplet was retracted in the
receding step, surface restructuring minimize the interfacial free energy in water,46 polar
groups of modifiers can be isolated on the surface and θR is decreased greatly resulting in a
greater improvement of surface wettability. Moreover, the decrease of θR here is also affected
by the water imbibition mostly. The water imbibition effect is educed by the retracted volume
of water as the value (18μL-Retracted volume). It can be noted that the GPE-PET fabric held
the strongest water imbibition abilities owing to the least volume of retractile water. The
desirable effects were not achieved because GPE-PET fabric on which functional agents were
immobilized showed some hydrophobicity, unlike simple GPE-PET fabric. This might be due
to hardening caused by the reaction between the epoxy groups of GPE and the amine groups
of the functional agents. The wettability of the PET fabrics increased in the following order:
Original PET < collagen-GPE-PET < sericin-GPE-PET < chitosan-GPE-PET < GPE-PET
Chitosan-GPE-PET showed better wettability than sericin-GPE-PET and
collagen-GPE-PET may be the reason fewer amine groups participated in the reaction with
the epoxide in chitosan, as compared with sericin or collagen. The fact that sericin-GPE-PET
gave better wettability than collagen-GPE-PET was attributed to the higher molecular weight
of sericin than that of collagen, which lessened the reaction opportunity of the amine with
epoxide. Another possible explanation of these results may be functional agents immobilized
into the PET mesh restrained the penetration of water. The more immobilization quantity, the
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more difficult is the water penetration.
Table 3. Water dynamic contact angle and retracted volume of water obtained for original and
several modified PET fabrics.
Samples Advancing angle (o) θA Receding angle(o) θR Retracted volume (μL)
Original PET 92.9±1 62.8±0.5 16.2
GPE-PET 73.7±2 31.7±1 13.2
Chitosan-GPE-PET 76.9±3 37.0±1 13.8
Sericin-GPE-PET 80.5±3 41.5±1 14.2
Collagen-GPE-PET 84.3±4 47.2±2 15.0
The isothermal moisture regain of all the PET fabrics was investigated at 30°C, and the
results are plotted in Figure 11. All of the curves show a reversed S shape, and the moisture
regain increased markedly in the region of high humidity. Clearly, the GPE-PET fabrics on
which functional agents were immobilized were capable of higher water sorption than the
original PET, but could not absorb as much as simple GPE-impregnated PET fabric.
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0 20 40 60 80 1000.0
0.1
0.2
0.3
0.4
0.5
0.6M
oist
ure
rega
in [w
t%]
Relative humidity [%]
Original PET Collagen-GPE-PET Sericin-GPE-PET Chitosan-GPE-PET GPE-PET
Figure 11. Isothermal sorption diagrams for PET fabrics at 30°C.
The moisture-retaining property is another important issue in the study of hydrophilicity of
a fabric. A hygroscopicity/dehygroscopicity experiment was performed to evaluate the
moisture-retaining property of the same kinds of PET samples measured on wettability.
Figure 12 shows the changes in moisture regain of the PET fabrics from the hygroscopicity to
dehygroscopicity phase. During the entire course of the experiment, hygroscopic equilibrium
was reached after 40 min without reference to any phase at (25°C, 65%RH) or (30°C,
95%RH), but, the dehygroscopic behavior went on for close to 2 h. By contrast with the
original PET fabric, the modified PET fabric became hygroscopic quickly and dehygroscopic
slowly. Furthermore, the moisture regains of these PET samples maintained the same order as
the water contact angles in wettability measurement with sessile droplet method.
The samples of functional agents immobilized onto GPE-PET fabrics in aqueous solution
were also measured on water contact angle and moisture-retaining properties. Although the
samples exhibited goodish hydrophilicities in two aspects, the effect is not appreciated
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because these data were almost similar with that of GPE-PET. As viewed from lesser
immobilization quantities by this method, this came down to the cause that GPE bared on the
surface of PET fabric only a little participated in reaction with functional agents in solution.
0 100 200 300 400
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.825°C, 65%RH30°C, 95%RH25°C, 65%RHDry
Moi
stur
e re
gain
[wt%
]
Treating time [min]
Original PET Collagen-GPE-PET Sericin-GPE-PET Chitosan-GPE-PET GPE-PET
Figure 12. Changes in hygroscopicity and dehygroscopicity with the change in the
environmental conditions.
4.3.4. Antibacterial efficiency of the untreated and the modified PET fabrics
In the experiment for microbial absorption, a log (B/A) value of ≧ 1.5 was considered
necessary to claim antibacterial activity due to the intrinsic variability of the antibacterial test
results. In order for a sample to be considered to have antibacterial activity, the value of the
bacteriostatic activity should be over 2.0, and the value of the bactericidal activity should over
0.0. Here, the number of Staphylococcus aureus bacteria at the initial inoculation was A = 2.1
× 104, and the number of colonies of S. aureus on an inoculated piece of control calico was B
= 8.3 × 106. Table 4 lists the data for the antibacterial effect of the PET fabrics against S.
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aureus. The results show that the original PET fabric had no effect against S. aureus, which is
in agreement with the current literature. The GPE-impregnated PET fabric showed some
inhibition of the growth of S. aureus, although it could not kill the bacterial cells. The number
of viable cells decreased after they were inoculated on GPE-PET fabrics on which sericin,
collagen or chitosan had been immobilized, which indicates that these functional modified
PET fabrics killed bacterial cells at a high rate and had a high antibacterial activity.
According to the immobilization amounts of sericin, collagen or chitosan on GPE-PET
fabric listed in Table 2, collagen-GPE-PET containing higher immobilization amounts of
collagen did not show higher antibacterial values than the other two fabrics. This implies that
the antibacterial efficiency of collagen is naturally lower than that of sericin or chitosan.
The antibacterial test was also performed with GPE-PET fabrics on which functional
agents were immobilized in an aqueous solution, but no antibacterial effects against S. aureus
were found. It was considered that the immobilization amounts of functional agents onto
GPE-PET fabric were too little to kill the bacterial cell. This demonstrates that the
pad-dry-cure method is more effective than the solution method for the immobilization of the
functional agent (sericin, collagen or chitosan) onto the surface of GPE-impregnated PET
fabric again.
Table 4. Antibacterial activities of the original and the modified PET fabrics against
Staphylococcus aureus.
Samples Cell number [C] log C Bactericidal activity Bacteriostatic activity
Original PET 7.9×106 6.9 -2.6 0
GPE-PET 4.8×104 4.7 -0.4 2.2
Sericin-GPE-PET 1.0×103 3 1.3 3.9
Collagen-GPE-PET 1.6×103 3.2 1.1 3.7
Chitosan-GPE-PET 2.5×103 3.4 0.9 3.5
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4.4. Summary
The results obtained show that the method of impregnating a cross-linking agent by means
of scCO2 can be used to prepare intermediate PET fabric on which various functional agents
can be immobilized. The scCO2 technique is a powerful method of modifying fibers. The
scCO2 process can not only swell the polymer but also impregnate finishing agents or
cross-linking agents into the polymer under controlled temperature and pressure conditions
and in the presence of co-solvents. In the process of impregnation of an epoxy cross-linking
agent into PET fabric, a good co-solvent proved to be chloroform, which greatly boosted the
uptake of GPE into the PET fabric in scCO2.
Two methods of immobilizing functional agents onto GPE-impregnated PET fabrics were
compared, the pad-dry-cure method and the solution method; the former was found to be
more effective in terms of the immobilized amounts of functional agent and the antibacterial
efficacy. The surface hydrophilicity of the PET fabric can be improved to a certain extent by
immobilizing of a functional agent such as sericin, collagen or chitosan.
Conventional methods of modification of polymer fiber using scCO2 rely on changes in
the fiber structure which lead to the improvement of the physical and mechanical properties of
the fiber. However, cross-linked intermediate fibers can also participate in the reaction with
functional agents for further, surface modification. Generally, this scCO2 pretreatment is
expected to represent a new approach as simplifying the process, lowering the cost of surface
modification of polymer fabrics; also, the subsequent chemical immobilization of functional
agents onto the fiber surface is stronger and more stable when scCO2 pretreatment is carried
out.
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Chapter 5. General conclusion
Generally, synthetic fabrics (PET and PP), onto which the surface immobilization of
natural macromolecules can not be achieved by immersing them directly to the
macromolecules solution even followed by the cure process. Besides, the impregnation of
natural macromolecules into PET or PP fabrics is also impossible due to the higher molecule
weight of these macromolecules, even though supercritical impregnation technology can dye
the synthetic fiber successfully with or without any co-solvents. In order to immobilize
functional macromolecules effectively, it is necessary to introduce some functional molecules
or active cross-linking agents to the inert surface of PET and PP fabrics. Considering the
points of no-pollution, low-cost and easy-operation in current industry manufacture, the
introduction of cross-linking agents to synthetic fabrics by using the supercritical carbon
dioxide was designed. A research on surface immobilization of natural macromolecules onto
PET and PP fabrics functionalized by the impregnation of cross-linking agents with the scCO2
was investigated here.
The surface modification design come down to these explanations. Synthetic fibers can be
penetrated by scCO2 resulting in plasticization and dramatically swelling. Meanwhile, the
cross-linking agents as solute of scCO2 will be diffused to fibrous region with the distribution
of scCO2. After depressurization, CO2 desorbed from fiber quickly, and the cross-linking
agents remain in the inner or surface of fibers. Because the cross-linking agents were active
functional molecules, the reaction of natural macromolecules and the cross-linking agents
remained on the fiber surface will lead to the immobilization of natural macromolecules.
In this research, three types of active organic agents, cyanuric chloride (CC), epoxy
compounds and Tolylene 2,4-Diisocyanate (TDI), as intermediate cross-linking agents, were
selected and used in impregnation into PET or PP fabrics with the aid of scCO2. By viewing
the states of cross-linking agents in pure supercritical dioxide, cyanuric chloride is found to be
difficult to dissolve, Tolylene 2,4-Diisocyanate has good solubility, and epoxy derivative can
dissolve by and large. After several co-solvents were added to scCO2, the CC fluid presented
good optical uniformity, and epoxy derivatives fluid became also clearer than that in pure
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scCO2.
About the impregnation of CC into synthetic fabrics in scCO2, CH2Cl2 was judged to be a
better modifier for increasing the uptake of CC than others greatly, although the uptake in PP
is always less than it in PET. The impregnation of TDI into PET or PP with scCO2 need not
add any co-solvents because TDI can dissolve in scCO2 well. The impregnation of epoxy
compound into PET attained an optimization with the presentation of chloroform. Relatively,
the impregnation effects of these cross-linking agents into synthetic fabric behaved in this
order: TDI > Epoxy derivatives > CC. In addition, the impregnation of these cross-linking
agents into PET is easier than the operation to PP fabrics. Generally, the impregnation
conditions were optimized at 120°C, 25MPa for PET, and 100°C, 25MPa for PP.
The impregnated synthetic fabrics were investigated by the ATR-IR and XPS
measurement. The spectra showed that these cross-linking agents can be introduced into PET
or PP fabrics more or less. For example, a peak of typical epoxy ring was found at 847 cm-1
after epoxy compounds was impregnated into PET fabric. Another example, in the XPS
spectra of the CC-impregnated PET and PP fabrics, new peaks appeared at 197.2 eV, 268.2 eV
and 399.2 eV were assigned to Cl2p, Cl2s, N1s respectively.
After natural macromolecules immobilization finished, chemical analysis revealed that
these macromolecules can react with cross-linking agents in the immobilization process. The
increase of element content on the modified fabrics also indicated that macromolecules were
attached on the surface of cross-linking agents-impregnated fabrics. The SEM images of
modified samples showed changes on the micro-roughness of these fabric surfaces. Surface
wettability and moisturization efficiency of the modified fabrics got improved at different
levels. The modified PET fabric which was cross-linked by epoxy compounds displayed
outstanding antibacterial characteristics against S. aureus. The protein-immobilized fabrics
can also be stained by methylene blue readily. These measurements and analyses
demonstrated that functional macromolecules had been immobilized onto the surface of
synthetic fabrics.
The surface modification of synthetic fabrics were achieved first by the cross-linking
agent impregnation in scCO2, followed by a substitute reaction of impregnated cross-linking
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agents with natural functional molecules for the immobilization of natural macromolecules on
the surface of synthetic fabrics. Generally, this study represented a new approach as
simplifying the process; lowering the cost of surface modification of polymer fabrics. We
expect that the method here help to expand the field of application for modifying polymeric
materials.
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Publication list (1) Wen-Xiao Ma, Chuan Zhao, Satoko Okubayashi, Isao Tabata, Kenji Hisada, Teruo Hori.
『A novel method of modifying poly(ethylene terephthalate) fabric using supercritical
carbon dioxide』
Journal of Applied Polymer Science, 117 (4), p1897 (2010)
(2) Wen-Xiao Ma, Satoko Okubayashi, Kazumasa Hirogaki, Isao Tabata, Kenji Hisada, and
Teruo Hori
『Impregnation of Cyanuric Chloride into Synthetic Fabrics (PET and PP) by
Supercritical Carbon Dioxide and its Application in Immobilizing Natural
Biomacromolecules』
Journal of the Society of Fiber Science and Technology, 66(10), p243 (2010)
(3) Chuan Zhao, Wen-Xiao Ma, Satoko Okubayashi, Isao Tabata, Kenji Hisada, and Teruo
Hori.
『Impregnation of fluorescence dyes into polymer optical fiber with carbon dioxide
fluid』
Coloration Technology (submitted)
(4) 奥林里子, 麻文效, 星野芳哲,岡田睦馬,趙川,堀照夫
『趙臨界流体を用いる革新的加工方法の開発』
福井大学ベンチャービジネスラボラトリー年報,2,p28 (2006)
- 114 -
Presentations
(1) Wenxiao Ma, Satoko Okubayashi, Isao Tabata, Teruo Hori. Modification of polyester
fabric using supercritical carbon dioxide, The 16th Fiber Union Research Symposium, Ueda
of Japan (2005), p207.
(2) Wenxiao Ma, Satoko Okubayashi, Isao Tabata, Teruo Hori. Chemical modification of
polyester fabric using supercritical carbon dioxide, Fifth International Fiber Symposium in
Fukui, January 17-18, 2006.
(3) Wenxiao Ma, Satoko Okubayashi, Isao Tabata, Teruo Hori. Impregnation of the
crosslinking agent using supercritical carbon dioxide into polyester fabric and fixation of
some medicine in polyester cloth, Annual Meeting of The Society of Fiber Science and
Technology, Tokyo (2006), p260.
(4) Wenxiao Ma, Satoko Okubayashi, Isao Tabata, Kenji Hisada, Teruo Hori. Modification of
polyester fabric by impregnation of diisocyanate using supercritical carbon dioxide, Autumn
Meeting of The Society of Fiber Science and Technology, Kanazawa (2006), p79.
(5) Wenxiao Ma, Satoko Okubayashi, Isao Tabata, Kenji Hisada, Teruo Hori. Chemical
modification of polyester fabric by the impregnation of epoxy compound using supercritical
carbon dioxide, Proceedings of International Symposium on Dyeing and Finishing of Textiles,
Kyoto, Japan, December 17-19, 2006, p189.
(6) Wenxiao Ma, Satoko Okubayashi, Isao Tabata, Kenji Hisada, Teruo Hori. Fixation of
functional medicaments and impregnation of epoxy compounds using supercritical carbon
dioxide on polyester fabric, Annual Meeting of The Society of Fiber Science and Technology,
Tokyo (2007), p218.
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- 116 -
Acknowledgements
This research is possible based on the support and encouragement of many people. In this occasion,
the author wish to express his gratitude for those contributions and concern during the period of his
doctoral course.
The works presented in this thesis where carried out at Fiber Amenity Course, Graduate School of
Engineering, University of Fukui. Grateful acknowledgement is given to Professor Teruo Hori for his
kind help, encouragement and guidance.
The author would like to express his sincere thanks to Associate Professor Kenji Hisada and
Technician Isao Tabata, for their instruction and assistance and support during these years. The
thankfulness will also be given to Assistant Professor Kazumasa Hirogaki for his generous help.
The author would like to express sincere thanks to Associate Professor Satoko Okubayashi, from
Division of Advanced Fibro Science, Graduate School of Science and Technology, Kyoto Institute of
Technology, for her guidance and advices on the experiment of this research.
The author is extremely thankful to Associate Professor Yuji Tokunaga, from Dept. of Materials
Science & Engineering, University of Fukui, for his guidance and training in the field of organic
synthesis, which were indispensable for this research.
The author do not have enough words to express his gratitude to all members of Hori’s Laboratory,
with a special thanks to Nora Martinez engaged in the supercritical group for her assistance with the
XPS measurements.
Finally, the author would like to express his full gratitude, to his mother and his father for their
love and understanding, to his sister and her family for the support in economy and the encouragement
in mentality.
Wen-Xiao Ma
Intelligent Fiber Engineering
Fiber Amenity Engineering Course
Graduate School of Engineering
University of Fukui