writer：Bai J, Fang HG, Zhang YQ and Wang ZG*
keywords：结晶动力学，聚乳酸，长链支化
source：期刊
specific source：CrystEngComm, 2014, 16, 2452-2461.
Issue time：2014年
ABSTRACT: To investigate the effects of long chain branching (LCB) on crystallization kinetics of polylactides (PLA), a series of long chain branched PLA samples have been prepared, which have been proved to be bimodal of linear PLA and long chain branched PLA with different branching degrees. The crystallization kinetics of these LCB PLA samples have been investigated by using polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The POM results show that the spherulitic growth rates of LCB PLA samples are lower than that of linear PLA precursor and the PLA spherulitic growth rate decreases with increasing branching degree at each isothermal crystallization temperature. On contrast, the nucleation density increases with increasing branching degree. The crystallization kinetics from POM observation are analyzed by using the Hoffman-Lauritzen theory. In the studied temperature range, both linear PLA and LCB PLA samples crystallize according to the Regime II mechanism. Nucleation constant (K_g) and fold surface free energy (s_e) decrease with increasing branching degree, suggesting that LCB PLA samples have lower free energy barriers for nucleation than linear PLA precursor. Analysis of DSC data by the Avrami equation indicates that crystallization of both linear PLA and LCB PLA samples follows a three-dimensional crystal growth. The half crystallization time reduces with increasing branching degree and the overall crystallization rates for LCB PLA samples are higher than that of linear PLA.