Improving Crystallization Behavior and Melt Strength of Poly(lactic acid) via Adding Talc and PLA-g-MAH†

doi:10.7503/cjcu20180006

Abstract

Abstract:

Talc and PLA-g-maleic anhydride(PLA-g-MAH) were added to polylactide(PLA) to simultaneously improve its melt strength, crystallinity(X_c) and mechanical properties. Using a single-screw extruder with a chaotic mixing screw developed in our group, the PLA-g-MAH was prepared via reactive extrusion. Its grafting rate is measured to be 1%. Then, a series of PLA/talc(5%, 10% and 20%, mass fraction) and PLA/talc(20%, mass fraction)/PLA-g-MAH(5% and 10%, mass fraction) composites were prepared using the same extruder. The chaotic mixing in the extruder effectively improves the dispersion of the talc in the PLA matrix, and the talc of up to 20% almost does not agglomerate. Adding the PLA-g-MAH into the composites reduces the voids and the gaps around the talc on the cyrofractured surfaces and improves the interfacial adhesion between the PLA and talc. For the PLA/talc(20%) composite samples with 10% PLA-g-MAH, the α crystal content of the PLA is increased obviously and its X_c is increased to 31.6%. At 175 ℃, the melt strength for the PLA sample is relatively low(3.6 mN), and it is obviously enhanced(11.6 mN) for the composite sample with 20% talc. The explanation for this is as follows. The well dispersed talc has a reinforcing effect on the PLA melt and increases the crystallization behavior of PLA; moreover, the draw-down force can improve both effects of the orientation-induced PLA crystallization and the increased PLA crystallization behavior by the added talc. Compared with the PLA sample, the PLA/talc(20%)/PLA-g-MAH(5%) sample exhibits increments of 51.7% and 16.9% for the Young’s modulus and impact strength, respectively.

Key words: Poly(lactic acid), Talc, Maleic anhydride, Composite, Crystallization behavior, Melt strength

TrendMD:

HAN Jiahui,HUANG Hanxiong,HUANG Yuxiao. Improving Crystallization Behavior and Melt Strength of Poly(lactic acid) via Adding Talc and PLA-g-MAH^†[J]. Chem. J. Chinese Universities, 2018, 39(9): 2089.

Figures/Tables 14

Table 1 Mass fraction of samples

Sample	w(PLA)(%)	w(Talc)(%)	w(PLA-g-MAH)(%)
PLA	100	0	0
PLA/T5	95	5	0
PLA/T10	90	10	0
PLA/T20	80	20	0
PLA/T20/M5	75	20	5
PLA/T20/M10	70	20	10

Fig.1 FTIR spectra of PLA(a) and PLA-g-MAH(b) samples

Fig.2 SEM images of cyrofractured surfaces for PLA/T5(A), PLA/T10(B) and PLA/T20(C) composite samples

Fig.3 SEM images of cyrofractured surfaces for PLA/T20/M5(A) and PLA/T20/M10(B) composite samples

Scheme 1 Schematics of mechanism for compatibilizing PLA and talc by PLA-g-MAH

Fig.4 DSC curves of PLA and PLA/talc composite samples (A) Second heating scans; (B) cooling scans. a. PLA; b. PLA/T5; c. PLA/T10; d. PLA/T20; e. PLA/T20/M5; f. PLA/T20/M10.

Table 2 Thermal analysis data for PLA and PLA/talc composite samples

Sample	T_g/℃	T_cc/℃	X_cc(%)	T_m1/℃	T_m2/℃	X_c(%)
PLA	59.6	109.8	27.9	152.9	159.7	—
PLA/T5	60.0	101.7	15.0	151.5	158.7	15.2
PLA/T10	59.8	99.1	7.6	152.2	158.7	19.8
PLA/T20	59.8	96.6	4.5	151.7	158.7	25.1
PLA/T20/M5	59.6	96.5	2.8	152.9	160.3	27.2
PLA/T20/M10	59.8	—	—	154.4	162.1	31.6

Fig.5 Relative crystallinity versus crystallization time curves for PLA/talc composite samples a. PLA/T5; b. PLA/T10; c. PLA/T20; d. PLA/T20/M5; e. PLA/T20/M10.

Table 3 Crystallization half-time(t1/2) and Jeziorny-modified-Avrami crystallization kinetic parameters for PLA/talc composite samples

Sample	t_1/2/min	n	K/mi $n - n$	K_c/mi $n - n$
PLA/T5	1.38	2.60	0.3217	0.8928
PLA/T10	1.13	2.64	0.5284	0.9382
PLA/T20	1.09	2.76	0.5672	0.9449
PLA/T20/M5	0.92	2.37	0.8831	0.9876
PLA/T20/M10	0.76	2.67	1.4421	1.0373

Table 3 Crystallization half-time(t1/2) and Jeziorny-modified-Avrami crystallization kinetic parameters for PLA/talc composite samples

Sample	t_1/2/min	n	K/mi $n - n$	K_c/mi $n - n$
PLA/T5	1.38	2.60	0.3217	0.8928
PLA/T10	1.13	2.64	0.5284	0.9382
PLA/T20	1.09	2.76	0.5672	0.9449
PLA/T20/M5	0.92	2.37	0.8831	0.9876
PLA/T20/M10	0.76	2.67	1.4421	1.0373

Fig.6 XRD patterns for PLA and PLA/talc composite samples a. PLA; b. PLA/T5; c. PLA/T10; d. PLA/T20; e. PLA/T20/M5; f. PLA/T20/M10.

Fig.7 Draw-down force versus draw ratio(A) and extensional viscosity versus extensional strain rate curves(B) for PLA and PLA/talc composite samples a. PLA; b. PLA/T20; c. PLA/T20/M5; d. PLA/T20/M10.

Fig.8 Storage modulus(A) and tanδ versus temperature curves(B) for PLA and PLA/talc composite samples a. PLA; b. PLA/T20; c. PLA/T20/M5; d. PLA/T20/M10.

Fig.9 Young’s moduli(A) and tensile strengths(B) of PLA and PLA/talc composite samples a. PLA; b. PLA/T5; c. PLA/T10; d. PLA/T20; e. PLA/T20/M5; f. PLA/T20/M10.

Fig.10 Notched Izod impact strengths of PLA and PLA/talc composite samples a. PLA; b. PLA/T5; c. PLA/T10; d. PLA/T20; e. PLA/T20/M5; f. PLA/T20/M10.

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