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INVESTIGATION IN THE MANUFACTURE OF NON-WOVENS INVESTIGATION IN THE MANUFACTURE OF NON-WOVENS FROM POLYLACTIDE BY SPUNBOND METHODFROM POLYLACTIDE BY SPUNBOND METHOD
K. Sulak1, M. Lichocik1, T. Mik1, I. Krucińska2, M. Puchalski2, J. Jarzębowski3
1Institute of Biopolymers and Chemical Fibers,M. Skłodowskiej-Curie 19/27, 90-570 Lodz, Poland, e-mail: [email protected]
2Technical University of Lodz, Faculty of Material Technologies and Textile Design, Department of Fibre Physics and Textile Metrology,Żeromskiego 116, 90-924 Lodz, Poland, e-mail: [email protected]
3Research and Development Centre of Textile Machinery “Polmatex-Cenaro”,Wólczańska 55/59, 90-608 Lodz, Poland
BACKGROUNDBACKGROUND
Poly(lactic acid) or polylactide (PLA) is an aliphatic polyester that can be
produced from renewable materials such as corn, sugar or vegetables1,2. The production of PLA is based on
the polycondensation of lactic acid or the ring-opening polymerisation of lactide obtained from the
depolymerisation of oligomers of lactic acid, which is a product of the fermentation of biomass such as corn.
In comparison with conventional polymers, which are produced from petroleum, PLA is an environmentally
friendly biodegradable polymer, and it has attracted increased attention in recent years. However, due to high
manufacturing costs, the use of PLA has been limited for many years to medical applications3,4,5. A decrease in
the price of PLA expands the range of possible applications. For example, PLA has become a major starting
material in the manufacture of biodegradable textiles6. The preparation, structure and properties of products
made of PLA and its modification are the subjects of intensive scientific7 and technological investigations.
Compared with classical polyesters such as polyethylene terephthalate (PET), PLA products are
characterised by a higher water sorption of 0.4-0.6% and better resistance to UV radiation. The latter feature,
in combination with biodegradability, makes polylactide fibres and non-woven fabrics particularly useful raw
materials for the preparation of disposable medical and hygiene textiles. Other applications include technical
textiles used in filtration or in agriculture and in cloth for garments and underwear. The ability of PLA to
crystallise depends strongly on the stereochemical form of PLA and is different for isotactic poly(L-lactide)
(PLLA) or poly(D-lactide) (PDLA), syndiotactic poly(meso-lactide), atactic poly(meso-lactide) or poly(D,L-
lactide), PLLA/PDLA stereocomplexes and copolymers with random levels of meso-, L-, and D-lactide. As a
consequence, the physical properties of fabrics manufactured from different PLAs can be differ. Moreover
supermolecular structure of PLA fabrics strongly depends on the stereoregularity of the PLA form of the
polymer and the technological conditions applied during the fibre manufacturing process. Therefore, it is
important to elucidate the relationships between the conditions of formation and the properties of the
resulting fabrics.
A B
AIM OF WORKAIM OF WORK
The aim of work was to determine the influence of different forming parameters (especially thermal
conditions of stabilisation at the embossing roll of the calender) on the physical and mechanical properties
and supermolecular structure of PLA spun-bonded nonwoven fabrics.
ACKNOWLEDGEMENTACKNOWLEDGEMENT
The presented research was performed within the framework of the key project titled “Biodegradable
fibrous products” (acronym: Biogratex) supported by the European Regional Development Fund; Agreement
No. POIG.01.03.01-00-007/08-00.
MATERIALS AND MATERIALS AND TEST METHODSTEST METHODS
Raw materialRaw material
Non-woven fabrics were manufactured from commercially available PLA
6251D (Nature Works LLC, USA) specifically designed for the spun-bonded technology. A molar mass of PLA
6251D Mn of 45 800 g mol-1 and a polydispersity Mw/Mn of 1.29 were determined by size-exclusion
chromatography (SEC) with a multi-angle light scattering (MALLS) detector in methylene chloride. The D-
lactide content was 1.4%, as determined based on the specific optical rotation measurements. The glass
transition temperature (Tg) and melting temperature (Tm), determined by differential scanning calorimetry
(DSC), were equal to 61°C and 128°C, respectively.
DryingDrying of of polpolyymermer
To reduce the moisture content below 50 ppm, prior to spinning, the PLA was
dried for at least 4 h at 80°C (dew point -30°C) in a Piovan dryer that is part of the laboratory setup for studying
non-woven fabrics manufacturing with the spun-bonded technique. The moisture content in the polymer was
measured by the Karl Fischer coulometric method using the DL39X apparatus (Mettler Toledo).
Spun-bonded technology detailsSpun-bonded technology details
The non-woven fabrics were formed by a spun-bond technique on a
laboratory line designed and constructed by the Research and Development Centre of Textile Machinery
Polmatex-Cenaro, Poland. The process parameters were as follows: a temperature in the range from 205°C to
216°C and a polymer throughput in the range of 0.10-0.43 g/min/hole can be used. A spinneret with 467 holes
was used. The calender temperature was varied from 60°C to 130°C.
Thermal propertiesThermal properties
For characterisation of the thermal properties of fabrics formed under the
various manufacturing conditions, DSC measurements were carried out using a Q2000 (TA Instruments, UK).
Specimens were first heated from 0C to 250C and then cooled to -30C and immediately reheated to 250C at a
rate of 10C/min.
Mechanical propertiesMechanical properties
The tensile strength and elongation analysis of the studied spun-bonded
fabrics was conducted using the mechanical testing machine Instron 5511 according to EU standard EN
29073-3:1992 “Methods of test for nonwovens. Determination of tensile strength and elongation”.
Shrinkage analysisShrinkage analysis
The changes in the dimensions of the non-woven fabrics in hot air (both the
length and width) were determined in accordance with standard ISO 3759:2011 “Textiles - Preparation,
marking and measuring of fabric specimens and garments in tests for determination of dimensional change”.
RESULTSRESULTS
Structural properties of PLA spun-bonded non-woven fabricsStructural properties of PLA spun-bonded non-woven fabrics
Mechanical properties of PLA spun-bonded non-woven fabricsMechanical properties of PLA spun-bonded non-woven fabrics
Table 1. DSC calorimetric data obtained for the investigated variants of spun-bonded, non-woven fabrics.
Temperature of calender
(°C)
Degree of crystallinity
(wt. %)
Glass transition
temperature Tg,(°C)
Cold crystallisation temperature
Tc,(°C)
Melting temperature
Tm ,(°C)
Enthalpyof cold
crystallisationHc, (J/g)
Changein heat
capacity ΔCp, J/g°C)
Enthalpyof meltingHm (J/g)
70 21 66 76 166 28.3 2.52 47.9
75 20 66 75 167 29.9 2.12 48.8
80 40 66 80 166 10.9 0.69 47.9
85 54 66 - 165 - 0.34 49.6
90 54 65 - 165 - 0.19 50.3
95 55 65 - 165 - 0.29 51.1
100 54 65 - 164 - 0.34 50.1
105 54 64 - 164 - 0.17 50.7
110 56 65 - 164 - 0.22 52.3
120 56 64 - 164 - 0.17 51.1
130 55 64 - 164 - 0.15 50.0
Fig. 1. DSC thermograms recorded during the first heating
Fig. 2. Relationships between the calculated degree of crystallinity and the change in heat capacity (ΔCp) for each sample stabilised at different thermal conditions.
The data in Table 1 and Figure 2 clearly indicate that
the elevation of the stabilisation temperature to 85°C
markedly increased the crystallinity level of the fibres,
which limited or even eliminated the possibility of cold
crystallisation during heating.
Fig. 3. Changes of the mechanical properties of non–woven fabrics stabilised at different thermal conditions in the machine (MD) and transverse (TD) directions: a) tenacity of non-woven fabrics and b) elongation at break of non-
woven fabrics.
Fig. 4 Changes in the length of the investigated samples in the machine direction as a function of the stabilisation
temperature.
When the stabilisation temperature rises above 85°C,
the degree of crystallinity increases to a maximum value
of approximately 55%, the overall molecular orientation
increases and the ordered α crystals are developed. The
development of such a supermolecular structure results
in stability of the fabric dimensions in hot air.
CONCLUSIONCONCLUSION
Results showed the rebuilding of the supermolecular structure of the investigated samples of PLA
fabrics under the influence of different stabilisation temperatures adjusted at the embossing roll in the range
of 70-130°C. The crystallinity degree increased to 54% when the temperature of the calender was changed to
85°C. Further increases of the stabilisation temperature did not have any significant influence on the
crystallinity degree of the tested samples.
The increased crystallinity level was reflected in the reduction of thermal shrinkage and in the
increase of the stress at the breaking point of the investigated samples. The maximum value of the stress at
the breaking point was observed for PLA non-woven fabrics stabilised at a temperature of 90°C.
The stabilisation of non-woven fabrics in the optimum temperature range of 85-100°C made it possible
to reach high values for the stress at the breaking point and small values of thermal shrinkage. An
insignificant increase of the strain at the breaking point was observed for the ordered crystalline phase of
PLA.
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