133. Studies on crystallization kinetics of bimodal long chain branched polylactides
writer：Bai J, Fang HG, Zhang YQ and Wang ZG*
keywords：結晶動力學，聚乳酸，長鏈支化
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 (Kg) and fold surface free energy (se) 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.