Formation and Structure Analysis of Interfacial Cylindrites Induced by Silkworm Silk Fiber in Poly(lactic acid) Based Composites†

doi:10.7503/cjcu20170194

Abstract

Abstract:

Thin films of poly(lactic acid)(PLA) were prepared using solution method. At different temperatures and fiber-pulling speeds, the morphology of cylindrites induced by a single silkworm silk fiber(SF) in PLA films was investigated by polarized optical microscopy(POM) and Fourier transform infrared spectroscopy(FTIR). The results show that there is a critical fiber-pulling speed, above which the continuous cylindrites structure could be generated on the fiber surface, whereas discontinuous cylindrites would form at a speed lower than that value. Besides, there also exists another special speed defined as saturation fiber-pulling speed, and once the pulling rate exceeds that value, the degree of crystallization and orientation will reach a plateau. Moreover, at the same temperature, the induction period of cylindrites nuclei reduces and its nuclei density and the orientation increase with raising the fiber-pulling speed; under a given fiber-pulling speed, compared to 130 ℃, the induction period of cylindrites is shorter, and its nuclei density, growth rate as well as final crystallinity are much higher at 120 ℃.

Key words: Poly(lactic acid), Silkworm silk fiber, Cylindrite, Fiber-pulling speed

CLC Number:

O631

TrendMD:

LI Guili, HUANG Jingjing, ZHANG Huanhuan, YUAN Chaosheng, SHAO Chunguang, YING Jin, WANG Yaming, CAO Wei, LIU Chuntai, SHEN Changyu. Formation and Structure Analysis of Interfacial Cylindrites Induced by Silkworm Silk Fiber in Poly(lactic acid) Based Composites^†[J]. Chem. J. Chinese Universities, 2017, 38(9): 1663.

Figures/Tables 8

Fig.1 Schematic representations of the experimental installation(A) and applied thermo-mechanical history(B)

Fig.2 Crystalline morphologies of PLA under different crystallization temperatures Crystallization temperature/℃: (A) 100;(B) 110;(C) 120;(D) 130.

Fig.3 POM observation images of crystalline evolution induced by fiber-pullingCrystallization temperature/℃: (A) 120; (B) 130.

Table 1 Effect of different temperature on critical fiber-pulling speed

Temperature/℃	Critical fiber-pulling speed/(μm·s^-1)
Temperature/℃	String shape spherulite	Cylindrite	Saturation	Broken
120	5	40		150
130	10	50	100	250

Fig.4 Nuclei density on the surface of SF vs. crystallization time(A and B) and induction time(C) and the nuclei density of the cylindrites crystallized for 380 s(D) vs. fiber-pulling speedCrystallization temperature/℃: (A) 120; (B) 130.

Fig.5 Radius of the cylindrites vs. crystallization time at 120(A) and 130 ℃(B), and the growth rate of crystals(C) vs. fiber-pulling speed

Fig.6 IR spectra of PLA cylindrites crystallized at 130 ℃(A) and change of Xc(B) vs. fiber-pulling speedInset is the FTIR detection area(dashed area).

Fig.7 Polarized IR spectra of PLA cylindrites crystallized at 130 ℃(A) and changes of the dichroic ratio(B) as a function of fiber-pulling speedFiber-pulling speed/(μm·s-1): a. 40; b. 60; c. 80; d. 100; e. 200. Inset is the FTIR detetion area(dashed area).

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