Cold crystallization behavior of poly(lactic acid) induced by poly(ethylene glycol)-grafted graphene oxide: Crystallization kinetics and polymorphism

Cold crystallization between the glass transition and melt temperature is of particular significance for crystalline regulation due to the slow crystallization rate of poly(lactic acid) (PLA). Incorporation of nucleation agents can promote PLA crystallization by reducing the nucleation activation energy and offering nucleation sites. Herein, we investigated the cold crystallization behavior of PLA induced by poly(ethylene glycol)-grafted graphene oxide (PEGgGO) which was synthesized and identified as a powerful nucleation agent for melt crystallization. The obtained results showed that PEGgGO not only accelerated the cold crystallization kinetics of PLA, but also promoted the polymorphic transition kinetics during the heating process. The half crystallization time of PLA induced by PEGgGO was shortened by 51 % and the final crystallinity increased by 57 % compared to that induced by GO alone at the same loading of 0.5 wt%. In addition, relative to GO, PEGgGO enabled the alpha '-to-alpha phase transition kinetics of PLA by a reduced transition temperature range of 26 % due to its excellent nucleation ability even at cold crystallization. The flexible PEG chains on GO facilitated crystalline regulation of PLA owing to the improved chain mobility. This work provides a broader framework for fashioning semicrystalline PLA products with enhanced crystallinity and refined crystal structure towards prospective applications.