Significant enhancement of crystallization kinetics of polylactide in its immiscible blends through an interfacial effect from comb-like grafted side chains

A significant enhancement in isothermal crystallization kinetics of biodegradable polylactide （PLA） in its immiscible blends can be accomplished through blending it with a comb-like copolymer. PLA was blended with poly（ethylene glycol） methyl ether acrylate （PEGA） and poly[poly（ethylene glycol） methyl ether acrylate] （PPEGA, a comb-like copolymer）, respectively. The results measured from phase contrast optical microscopy （PCOM） and differential scanning calorimetry （DSC） indicate that PLA and PEGA components are miscible, whereas PLA and PPEGA components are immiscible. The study of crystalliza- tion kinetics for PLA/PEGA and PLA/PPEGA blends by means of polarized optical microscopy （POM） and DSC indicates that both PEGA and PPEGA significantly increase the PLA spherulitic growth rates, G, although PLA/PPEGA blends are immisci- ble and the glass transition temperatures of PLA only have slight decreases. PPEGA component enhances nucleation for PLA crystallization as compared with PEGA component owing to the heterogeneous nucleation effect of PPEGA at the low compo- sition of 20 wt%, while PLA crystallization-induced phase separation for PLA/PEGA blend might cause further nucleation at the high composition of 50 wt%. DSC measurement further demonstrates that isothermal crystallization kinetics can be rela- tively more enhanced for PLA/PPEGA blends than for PLA/PEGA blends. The ＂abnormal＂ enhancement in G for PLA in its immiscible blends can be explained by local interfacial interactions through the densely grafted PEGA side chains in the comb-like PPEGA, even though the whole blend system （PLA/PPEGA blends） represents an immiscible one.