Synthesis and characterization of TPO–PLA copolymer and its behavior as compatibilizer for PLA/TPO blends

Abstract

A thermoplastic polyolefin elastomer-graft-polylactide (TPO–PLA) was prepared by grafting polylactide onto maleic anhydride-functionalized TPO (TPO–MAH) in the presence of 4-dimethylaminopyridine (DMAP). The characterization of the TPO–PLA copolymers was conducted by FT-IR and 1H NMR. The effects of reaction temperature and concentration of DMAP on the reactivity of graft polymerization were investigated by FT-IR, which revealed that a high reaction temperature and a high DMAP concentration are associated with dramatic depolymerization of PLA and reduction of steric hindrance effect in the graft reaction. A Molau test, SEM observations of cyro-fractured surface morphology and particle size analysis of PLA/TPO blend system demonstrate that this new copolymer, acting as a premade compatibilizer, significantly improved the compatibility of the PLA/TPO blends. As the concentration of TPO–PLA copolymer increased, elongation at break and tensile toughness increased with compatibilizer concentration up to 2.5wt%, beyond which it declined, but TPO–PLA copolymer did not affect the tensile strength or modulus. The effect of the chemical composition of the TPO–PLA copolymer on the compatibilization efficiency and mechanical properties of the PLA/TPO blends was examined by altering the number of grafting sites and concentration of DMAP, suggesting that DMAP concentration dominated the properties of the ternary blend system. Two compatibilizers, TPO–MAH and TPO–PLA, were used to compatibilize the PLA/TPO blend; the results suggested that TPO–PLA was more efficient in reducing the interfacial tension between the two immiscible polymers and in improving the mechanical properties of PLA/TPO blending specimens.