Synergistic Effects of Chain Extender and Nanoclay on the Crystallization Behaviour of Polylactide

Abstract

The crystallization behavior of polylactide (PLA) with various branching degrees and nanoclay contents were investigated using a differential scanning calorimeter (DSC). The dispersion quality of nanoclay within PLA and reactivity of chain extender with PLA molecules were analyzed using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy test (FT-IR), respectively. The results showed that chain branching in PLA produced higher crystallinity and fastened its slow crystallization kinetics. Also, the effects of processing (i.e., the same compounding process through a twin-screw extruder as for the PLA nanocomposites) on the crystallinity of "as received" PLAs were investigated to better compare them with the PLA nanocomposites. The results showed that the addition of nanoclay in different loadings did not have a significant effect on the melt crystallization of linear PLA. However, as the clay loading increased in half-branched and fully branched PLA's the reduced molecular mobility started to hinder the crystallization started to be hindered due to the reduced molecular mobility. This threshold occurred at lower clay loadings in fully branched PLA as the mobility started to be limited earlier. On the other hand, clay could improve even the linear PLA's crystallinity during isothermal treatments. On the other hand, branched PLA's processing significantly improved crystallinity due to the completion of chain-branching reactions during the processing. The effects of chain branching and nanoclay on PLA's isothermal melting crystallization kinetics at different temperatures were also studied using Avrami analysis.