Effects of glycine-based ionic liquid on spherulite morphology of poly(l -lactide)

Crystalline morphology, lamellar assembly, spherulitic growth rate, and physical properties of poly(l-lactide acid) (PLLA) modified by a room-temperature ionic liquid (IL), N-alkyl-substituted-glycine ester [N,N-dimethyl-N-propyl glycine ethyl ester (DMPGlyET)⁺] bis(fluoromethanesufonyl)imide [TFSI^-], are investigated by using polarized optical microscopy, optical microscopy, differential scanning calorimetric, and atomic-force microscopy. Thermal analyses and in situ microscopy characterization reveal the PLLA/IL mixture with upper-critical-solution-temperature behavior. Crystalline morphology of PLLA is significantly changed by the addition of IL to display massive diversification of spherulites morphology which has never been reported before in neat PLLA or PLLA blends with polymers. The morphological change and diversifications in PLLA/IL mixture are associated with strong interactions between PLLA and IL, which impede the melt crystallization of PLLA and tend to form PLLA nuclei of various geometry shapes. In addition, neat PLLA is generally brittle with extensive crack formation during postcrystallization cooling process; however, with the addition of IL, cracks are reduced or diminished entirely, potentially to enhance the performance and properties of PLLA.