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

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 2.5 wt%, 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.