A biobased modifier, epoxidized cardanol, was used as
a multifunctional
coagent to develop long-chain branched polylactic acid (LCB-PLA) together
with peroxide by a one-step reaction. The molecular structure of LCB-PLA
was evaluated from weight-average molecular weight, intrinsic viscosity,
and shear rheology. The results showed that the branching degree of
LCB-PLA was enhanced with the increased addition amount of epoxidized
cardanol due to the unique structure consisting of an epoxy group
and a long carbon chain with multiple unsaturated bonds. The generated
LCB-PLA exhibited improved crystallization performance and significant
heat resistance. Differential scanning calorimetry (DSC) and polarized
optical microscopy (POM) analyses showed that the long-chain branched
structure could play the role of a nucleation site, resulting in the
improved crystallization performance of PLA. Especially, for 0.3 wt
% peroxide-modified PLA with 0.8 wt % epoxidized cardanol (PLA/0.3T/0.8E),
the crystallinity of LCB-PLA reached approximately 44%, increasing
the Vicat softening temperature (VST) and heat deflection temperature
(HDT) to 156.2 and 82.5 °C, respectively, after a simple annealing
treatment. Moreover, the annealed LCB-PLA exhibited better hydrolysis
resistance than linear PLA in the early degradation stage, while it
degraded rapidly in the later stage. In short, this work provided
a green route to obtain LCB-PLA, which exhibited excellent crystallization
properties and heat resistance.