“In situ” compatibilization of poly(L-lactic acid)/epoxidized soybean oil bio-blends by reactive additives

Abstract

Three reactive additives, i.e., dicumyl peroxide (DCP), styrene-glycidyl methacrylate oligomer (Joncry® ADR 4370 S) and 1, 4-phenyl diisocyanate (PDI), were used to compatibilize polyL-lactic acid (PLLA)/epoxidized soybean oil (ESO) bio-based blends via one-step melt blending. The bio-blends were characterized by means of Fourier transform infrared spectroscopy, field emission scanning electron microscopy, dynamic mechanical analysis, dynamic rheological analysis, thermogravimetric analysis, contact angle testing, differential scanning calorimetry and tensile testing. It is confirmed that the reactive additives interact with PLLA and ESO, and “in situ” graft copolymers are formed, which improves the interfacial compatibility. The stiffness of PLLA/ESO/additive bio-blends is greater than that of the PLLA/ESO blend, reflecting the enhanced interfacial adhesion between the PLLA and ESO phases. The melt viscosity and elasticity of the PLLA/ESO/4370 S and PLLA/ESO/PDI bio-blends are significantly improved, showing obvious non-Newtonian behaviors because of branched entanglements generated by chain extensions. However, the addition of DCP reduces the complex viscosity because the chain scissions destroy the macromolecular entanglements. The thermostability of the PLLA/ESO blend is decreased by the reactive additives. The surface hydrophobicity of PLLA/ESO/additive blends is improved due to the formation of branched grafts. The crystallinity of PLLA/ESO/additive bio-blends is increased because the “in situ” grafts serve as nucleating agents. The tensile strengths of the PLLA/ESO/4370 S and PLLA/ESO/PDI bio-blends are significantly increased due to the enhanced interface adhesion. The inferior tensile properties of the PLLA/ESO/DCP blends are ascribed to the degradation of the PLLA matrix. “In situ” reaction mechanisms for the compatibilized blends are proposed.