Compatibility and phase structure of binary blends of poly(lactic acid) and glycidyl methacrylate grafted poly(ethylene octane)

This work study is the compatibility, phase structure, and component interaction of poly(lactic acid) (PLA) and glycidyl methacrylate grafted poly(ethylene octane) (GMA-g-POE denoted as mPOE) blend by Fourier transform infrared (FTIR) spectra, dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), and wide-angle X-ray diffraction (WAXD), respectively. All the binary blend compositions exhibit two distinct glass transition temperatures corresponding to the mPOE-rich and PLA-rich phases, respectively. Moreover, these two peaks approach each other with increasing mPOE content, indicating partial compatibility between the PLA and mPOE. Chemical reactions between the end carboxyl groups of the PLA and epoxy groups of the mPOE are considered as the driving force of the enhanced compatibility. They lead to an increase in viscosity of the blends and a decrease in the structural symmetry of PLA. This result brings about a decrease in the spherulite growth rate and the degree of crystallinity. Glass transition temperature (T_g) depression of mPOE is attributed to the negative pressure imposed on the dispersed rubber phase, resulting from differential contraction due to the thermal shrinkage mismatch upon cooling from the melt state. The negative pressure in the dispersed particles, in turn, would cause a dilational effect for the matrix ligament between the particles, and therefore increases the ductility and toughness of PLA.