writer：Defeng Wu, Liang Wu, Weidong Zhou, Ming Zhang, Tao Yang
keywords：polylactide; carbon nanotubes; nanocomposites; crystallization; kinetics; degradation.
source：期刊
specific source：Polymer Engineering & Science
Issue time：2010年

Polymer Engineering & Science, 2010, 50, 1721-1733.

ABSTRACT:

The crystallization behaviour of polylactide/carbon nanotube composites (PLANs) was studied using differential scanning calorimeter (DSC) and polarized optical microscope (POM). The nucleation mechanisms and the crystallization kinetics were then analyzed by both the isothermal and the nonisothermal methods. The results show that nanotubes have nucleating effect on both the melt crystallization and the cold crystallization of the matrix PLA. However, the nanotubes also play the role of physical barrier, impeding the crystal growth dynamically. In the experimental range of temperatures (90-102 ^oC), the nucleation rate is very high and the average separation of nuclei approaches the width of molecular stems. In this case, the crystallization from molten state is controlled by the nucleation, while the crystallization in solid state is governed by the growth. As a result, the presence of nanotubes accelerates the melt crystallization, while retards the overall kinetics of the cold crystallization. The biodegradability of those samples with various crystallization histories were then examined, aiming at relating the aggregation structure of the PLANs to their degradation behaviours. The results show that the presence of nanotubes reduces the biodegradation rate of PLA to some extent, and the amorphous sample always presents highest degradation levels. Moreover, a lower degradation level is observed both on the surface and inside the sample with melt crystallization history in contrast to the one with cold crystallization history. This indicates that the crystals with defective structure could be broken down prior to those with perfect structure in the degradation process.

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http://onlinelibrary.wiley.com/doi/10.1002/pen.21695/abstract