Acrylonitrile-Methyl Methacrylate Copolymer Films Containing Microencapsulated n-Octadecane

1

Acrylonitrile-Methyl Methacrylate Copolymer Films

Containing Microencapsulated n-Octadecane

Li Jun1, Han Na2, Zhang Xing-xiang3 (Tianjin Municipal Key Lab of Fiber Modification and Functional Fibers, Tianjin Polytechnic

University, Tianjin 300160)

Abstract: Acrylonitrile-Methyl methacrylate copolymer was synthesized in aqueous solution by

Redox. The copolymer was mixed with 10-40wt% of microencapsulated n-octadecane

(MicroPCMs) in water. Copolymer films containing MicroPCMs were cast at room temperature.

The copolymer of acrylonitrile-methyl methacrylate and the copolymer films containing

MicroPCMs were characterized by using Fourier Transform Infrared Spectroscopy (FTIR),

Differential Scanning Calorimetry (DSC), Thermogravimetric Analyzer (TG), X-ray Diffraction

(XRD) and Scanning Electron Microscopy (SEM), etc. The microcapsules in the films are evenly

distributed in the copolymer matrix. The heat-absorbing temperatures and heat-evolving

temperatures of the films are almost the same as that of the MicroPCMs, respectively. The

heat-absorbing temperatures increase slightly with the contents of MicroPCMs increasing. In

addition, the enthalpy efficiency of MicroPCMs rises with the contents of MicroPCMs increasing.

The crystallinity of the film increases with the contents of MicroPCMs increasing.

Keywords: Acrylonitrile-methyl methacrylate copolymer, MicroPCMs, film, heat storage

Sponsoring fund：name of the fund or sponsoring institution (project no.), or delete the line

* Corresponding author：Zhang Xing-xiang, Doctor, Tianjin Municipal Key Lab of Fiber

Modification and Functional Fibers, Tianjin Polytechnic University, email:

[email protected]

转载

http://www.paper.edu.cn

2

1. Introduction Microcapsules are small particles that contain an active agent or core material

surrounded by a coating or shell [1]. When the core material is phase change material

(PCM), the microcapsules have the thermal performance. The PCM stores and

releases thermal energy as the solid-liquid transitions take place [2]. The technology

of using phase change material (PCM) in clothing was developed and patented in

1987 for the purpose of improving the thermal insulation of textile materials during

changes in environmental temperature conditions [3, 4]. MicroPCMs have also been

used in the manufacture of foams and coatings [5-9]. Phase change materials are

applied to improve the insulation effect of the membrane material [10].

In this paper, the fabrication of acrylonitrile-methyl methacrylate copolymer

films containing 10-40wt% of MicroPCMs was studied; and the films were

characterized by using various test methods.

2. Experiments 2.1 Raw materials

Acrylonitrile (AN), analytical reagent, was purchased from Tianjin Kermel

Chemical Reagent Development Center and treated by atmospheric distillation before

used. Methyl acrylonitrile (MMA), analytical reagent, was purchased from Tianjin

Wen Da Xi Gui Reagent Chemical Plant and washed by the solution of sodium

hydroxide (5wt%) then treated by atmospheric distillation prior to use to remove

inhibitor purified. Chain transfer agent, dodecyl mercaptan (RSH) was a product of

Shanghai Qingpu synthetic reagent plant. Potassium persulphate (KSP), analytical

reagent, was purchased from Tianjin Standard Technology Ltd. Sodium bisulphate

(SBS), analytical reagent, was purchased from Beijing purchasing and supply station,

China Medicament Company. N, N-Dimethylformamide (DMF), analytical reagent,

was purchased from Tianjin Chemical Reagent Institute. MicroPCMs were prepared

in our laboratory. The diameters of the microcapsules are in the range of 0.3∼4μm.

2.2 Fabrication of Acrylonitrile-Methyl methacrylate Copolymers

The reactor was charged with predetermined mass of distilled water and purged

with dry nitrogen for 30 min while heating to the reaction temperature (40 ). The ℃

mixture of AN, MMA and mercaptan were added followed by the sodium bisulphite

中国科技论文在线 http://www.paper.edu.cn

3

(SBS) in distilled water. After 5 min, the potassium persulphate (KSP) dissolved in

distilled water was added and the reaction was allowed to proceed for 3h at 40 . The ℃

product was then directly filtered and washed with distilled water and dried [11].

2.3 Fabrication of Acrylonitrile-Methyl Methacrylate Copolymer Films

Containing Microencapsulated n-Octadecane

The moisture content of the copolymer and the MicroPCMs wet cakes were

determined before they were dried; and then the copolymer and the MicroPCMs were

mixed in water in predetermined ratios. The mixtures containing 0, 10, 20, 30 and

40wt% of MicroPCMs were obtained, and then were dried, mixed with predetermined

volume of N, N-Dimethylformamide (DMF). Copolymer films containing

MicroPCMs was cast with the mixtures of copolymers containing MicroPCMs at

room temperature. The films containing 0, 10, 20, 30 and 40wt% of MicroPCMs

were nominated as F0, F10, F20, F30 and F40.

2.3 Characterization of the copolymer and film

2.3.1 Fourier Transform Infrared Spectroscopy (FTIR) of the copolymer

The FTIR Spectra of the acrylonitrile-methyl methacrylate copolymer and films

containing microencapsulated n-octadecane were obtained using a spectrophotometer

(FTIR; Pekin Elmer system 2000), wave numbers 400- 4000cm-1.

2.3.2 Scanning Electron Microscopy (SEM)

The micrographs of the films containing MicroPCMs were obtained by using a

scanning electronic microscope (SEM; Leica Stereoscan 440).

2.3.3 Differential Scanning Calorimetry (DSC)

The phase change properties of MicroPCMs and the films containing

MicroPCMs were obtained by using a Differential Scanning Calorimeter (DSC;

Perkin Elmer DSC-7) at a heating rate 10℃/min in a nitrogen atmosphere from -20℃

to 100℃, waiting for 3min the cooled to -20℃ at the same rate.

2.3.4 X-ray Diffraction (XRD)

X-ray diffraction patterns of the films and the MicroPCMs were obtained by

using X-ray diffraction (XRD; Bruker Aux D8 Advance, 40kv, 40mA, Cu Kα1) at

room temperature in a scanning range of 5-25° (2 theta).

2.3.5 Thermogravimetric Analyzer (TG)


4

The thermal stabilities of the films and the copolymer in the film were

obtained using thermogravimetry (TG; NETZSCH STA 409 PC/PG TG-DTA) at a

heating rate of 10℃/min from room temperature to 1000℃ in a nitrogen atmosphere.

3. Results and Discussion 3.1 FTIR spectra of the copolymer

4000 3500 3000 2500 2000 1500 1000 500

Tran

smitt

ance

[%]

Wavenumber cm-1

1

2

2243 1728

Figure 1 FTIR spectra of the copolymer

（1-AN/MMA copolymer, 2-AN/MMA copolymer treated by acetone）

The FTIR spectra of the copolymer and the copolymer treated with acetone are

shown in Fig. 1. The polymethylmethacrylate (PMMA) can be dissolved in acetone,

while the polyacrylonitrile (PAN) and the AN/MMA copolymer cannot. The peaks in

spectrum 1 and 2 are associated with: 2243 cm-1 (CN stretching); 1728 cm-1 (C=O

stretching in methyl methacrylate). From the spectrum 2, the peak 1728 cm-1 still

exists after the treatment of acetone, which indicates that the sample contains the

component of MMA; and the copolymerization between acrylonitrile and methyl

methacrylate monomers has occurred.


5

4000 3500 3000 2500 2000 1500 1000 500

ATR

Uni

ts

Wavenumber(cm-1)

F40

F30

F20

F10

F0

2243 1722

2931

2860

1674 14581381

1234

1149

Figure 2 FTIR spectra of the copolymer films containing MicroPCMs

FTIR spectra of the copolymer films containing various contents of MicroPCMs

are shown in Fig. 2. The peak at 2243 cm-1 is attributed to the CN stretching in

acrylonitrile in the spectrum F0; and the peak 1727 cm-1 is from the C=O stretching in

methyl methacrylate; and 1668 cm-1 is derived from C=O stretching in residual DMF.

However, the other spectra also have these three peaks. Peaks from 2952 to 2852 cm-1

(C-H stretching in CH2 and CH3 groups), 1454 cm-1 and 1388 cm-1 (C-H blending in

CH2 and CH3 groups) are shown in spectrum F0. From F0 to F40, peaks from 2952 to

2852 cm-1 are enhanced relative to the other peaks on the respective spectrum while

the reverses appear on the 2243 cm-1 and 1727 cm-1 because of the contents of the

microcapsule increasing.

3.2 The morphology of the copolymer films containing MicroPCMs

F10 F20


6

F30 F40

Figure 3 SEM micrographs of the copolymer films containing various contents of

MicroPCMs

The morphologies of the copolymer films containing various contents of

MicroPCMs are shown in Fig. 3. The microcapsule is a sphere particle with a

diameter of 0.3-4μm. The MicroPCMs are evenly distributed in the copolymer film.

The copolymer has pore structure. With the contents of microcapsule increasing, more

and more microcapsules are inserted into the copolymer matrix.

3.3 The thermal property of the copolymer films containing MicroPCMs

The phase change properties and the efficiency of enthalpy of the copolymer

films containing MicroPCMs are listed in Table 1.

Table 1 Phase change properties of the copolymer films containing MicroPCMs

Sample No Tm

(℃)

ΔHm

(J/g)

Efficiency of

enthalpy*(%)

Tc

（℃）

ΔHc

(J/g)

Efficiency of

enthalpy*(%)

F10 37.7 8.2 57.7 23.3 8.9 63.9

F20 37.7 13.1 46.1 23.4 15.3 55.0

F30 38.1 30.0 70.3 22.7 33.7 80.7

F40 38.8 39.8 70.0 22.1 47.1 85.0

MicroPCMs 38.0 142.2 100 24.4 139.2 100

* Efficiency of enthalpy is defined as the ratio of the theoretical enthalpy and the

measured value.

It is shown that the heat-absorbing temperatures (Tm) and the heat-evolving

temperatures (Tc) of the films containing various contents of MicroPCMs are almost

the same as that of MicroPCMs respectively; and fluctuate in a slight range. The

melting enthalpy (ΔHm) and the crystallizing enthalpy (ΔHc) increase with the


7

contents of MicroPCMs increasing, which is similar to that in literature [12]. The

efficiency of enthalpy of the films increases with the content of MicroPCMs

increasing, while the F20 is exceptional. The reason leading to the abnormal

phenomenon may be that the distribution of the MicroPCMs is not even; and the

thermal conduct between the copolymer chain and MicroPCMs, shell and core of the

microcapsule is poor [12]. The crystallization enthalpy (ΔHc) is higher than the

melting enthalpy (ΔHm) from F10 to F40, which may be attributed to the imperfect

crystallization of the MicroPCMs in the films. The films containing 30 and 40wt% of

MicroPCMs, which have enthalpy of more than 30J/g, are potential for used as

insulating membranes in non-woven [10].

3.4 The thermal stabilities of the copolymer films containing MicroPCMs

0 200 400 600 800 1000

Mas

s(%

)

Temperature/ 0C

F0F10F20F30F40

Figure 4 TG curves of the films containing MicroPCMs


8

0 200 400 600 800 1000

DTG

(%/m

in)

Temperatue( 0C)

F0F10F20F30F40

M

Figure 5 DTG curves of the films containing MicroPCMs

The thermal stabilities of films containing MicroPCMs are shown in Fig. 4. The

weight loss before 200℃ is caused by the evaporation of residual DMF and the

breakage of MicroPCMs. The boiling point of DMF is 152.8℃; and the weight loss of

the MicroPCMs at 183.3℃, which is regarded as the decomposition temperature, is

above 5% [13].

Table 2. The thermal stability of the films containing MicroPCMs

Sample No F0 F10 F20 F30 F40

Thermal stable temperature (℃) 180.9 193.7 229.5 216.1 189.7

Peak temperatures (℃) 359.3 343.4 334.2 314.8 317.3

The thermal stable temperature (5wt% weight loss) is listed in Table 2. With

the contents of MicroPCMs increasing, the thermal stable temperature increases and

then decreases. The F20 has the highest thermal stable temperature, 229.5℃.

DTG curves of the films containing MicroPCMs is shown in Figure 5. It is

shown that the small peaks exist before the 200℃. When comparing the curve of the

films and that of the MicroPCMs, we conclude that all of the obvious peaks are above

300℃, which are resulted from the decomposition of the copolymers. The peak


9

temperatures are listed in Table 2. The peak temperatures decrease with the contents

of MicroPCMs increasing. It is explained that the decomposition temperature of

copolymers containing various contents of MicroPCMs decreases with the contents of

MicroPCMs increasing.

3.5 The crystallization of the copolymer films containing MicroPCMs

10 15 20 25 30 35 40 45

Inte

nsity

2-Theta( 0 )

F0

F10F20F30

F40

M

Figure 6 XRD patterns of the copolymer films containing various contents of

MicroPCMs and the MicroPCMs

The XRD patterns of the copolymer films containing various contents of

MicroPCMs and the MicroPCMs are shown in Fig. 6. The peaks at 21.5° and 23.7°

are attributed to n-octadecane in the MicroPCMs; and the peak at 16.8° is attributed to

the PAN crystal. With the contents of MicroPCMs increasing, the intensity of PAN

crystallization peak (16.8°) reduces; and the intensity of MicroPCMs crystallization

peak (21.5° and 23.7°) increases. The crystallinity increases with the contents of

MicroPCMs increasing. Such a phenomenon can be explained as the interaction

between the reduction of crystallizable copolymer and the increase of MicroPCMs

contents.


10

Table 3 Crystallinity of the copolymers in films

Sample No F0 F10 F20 F30 F40 M

Crystallinity (%) 29.9 44.1 47.8 48.2 52.3 26.9

The formula of crystallinity:

ac

cc ss

sX+

= (2)

where, Xc-crystallinity; sc-area of the crystallization zone; sa - area of amorphous

zone .

4. Conclusions Acrylonitrile-Methyl methacrylate copolymers were synthesized in aqueous

solution by Redox. The copolymerization between acrylonitrile and methyl

methacrylate monomers was testified by FTIR. The copolymer films containing

10-40wt% of MicroPCMs were cast at room temperature using the mixture of

microcapsule and the copolymer. The microcapsules in the films are evenly

distributed in the copolymer matrix. The heat-absorbing temperatures (Tm) and the

heat-evolving temperatures (Tc) of the films containing various contents of

MicroPCMs are almost the same as that of MicroPCMs respectively; and fluctuate in

a slight range. The enthalpy (ΔHm and ΔHc) and the efficiency of enthalpy of the

MicroPCMs in the films increase with the content of MicroPCMs increasing. The

thermal stable temperatures increase and then decrease with the contents of

MicroPCMs increasing. The film containing 20wt% of MicroPCMs has the highest

thermal stable temperature (229.5℃). The thermal stable temperatures of the films

decrease with the contents MicroPCMs increasing. The crystallinity of the film

increase with the incresed content of the MicroPCM.

Bibliography:

[1]Benita S, Microencapsulation: methods and industrial applications[M], New York: Dekker,

1996, 1–2

[2]H. Shim, E. A. Mccullough, B. W. Jones, Using phase change material in clothing[J], Textile


11

Res. 2001, 71(6): 495-502

[3]Bryant, Y.G., and Colvin, D. P., Fibers with Enhanced Reversible Thermal Storage Properties[J],

Textil. Sympos.,1992, 1-8

[4]Bryant, Y. G., and Colvin, D. P., US patent 4756985, 1988.

[5]Bryant, Y. G., Melt spun Fibers Containing Microencapsulated Phase Change Material[J], Am.

Soc. Mec.h Eng. Bioeng. Div. BED, 1999,14–19

[6]Kim, J., and Cho, G., Thermal Storage/release, Durability, and Temperature Sensing Properties

of Thermostatic Fabrics Treated with Octadecane-containing Microcapsules[J], Textile Res. J.

2002,72(12), 1093–1098

[7]Nuckols, M. L., Analytical Modeling of a Diver Dry Suit Enhanced with Microencapsulated

Phase Change Materials[J], Ocean Engineering , 1999,26, 547–564

[8]Shim, H., McCullough, E. A., and Jones, B. W., Using Phase Change Materials in Clothing[J],

Textile Res. J., 2001,71(6): 495–502

[9]Zhang, X. X., Wang, X. C., Zhang, H., Niu, J. J., and Yin, R. B., Effect of Phase Change

Material Content on Properties of Heat-Storage and Thermo-Regulated Fibers Nonwoven[J],

Indian J. Fiber Text. Res., 2006, 28(3): 265–269

[10]Barbara Pause, Development of heat and cold insulating membrane structures with phase

change material[J], Journal of coated fabrics,1995,25(7): 59-68

[11]Bhanu V. A., Rangarajan P., Wiles K., Bortner M., Sankarpandian M. etal, Synthesis and

characterization of acrylonitrile methyl statistical copolymers as melt processable carbon fiber

precursor[J], polymer, 2002, 43: 4841-4850

[12]Xing-Xiang Zhang, Xue-Chen Wang, Xiao-Ming Tao and Kit-Lun Yick, Structures and

properties of wet spun thermal-regulated polyacrylonitrile- vinylidene chloride fiber[J], Textile

research journal, 2006, 76(5): 351-359

[13]Zhang X X, Fan Y F, Tao X M and Yick K L, Fabrication and properties of microcapsules and

nanocapsules containing n-octadecane[J], Materials Chemistry and Physics, 2004, 88(2-3): 300


Documents

Acrylonitrile-Methyl Methacrylate Copolymer Films Containing Microencapsulated n-Octadecane