Effects of Compatibilizers on the Mechanical Properties and Interfacial Tension of Polypropylene and Poly(lactic acid) Blends

The effects of compatibilizers and hydrolysis on the tensile and impact strength, interfacial tension and morphology of the PP/PLA (80/20) blends were investigated. For the PP/PLA (80/20) blends before hydrolysis, the tensile strength of the blends reached a maximum when the polypropylene-g-maleic anhydride (PP-g-MAH) copolymer was added at 3 phr. For the PP/PLA (80/20) blends after hydrolysis, the tensile strength did not change appreciably with the PP-g-MAH content. For the blends with the styrene-ethylene-butylene-styrene-g-maleic anhydride (SEBS-g-MAH) before or after hydrolysis, the tensile strength of the blends decreased with increasing SEBS-g-MAH content. The interfacial tension of the PP/PLA (80/20) blend was determined from the relaxation time using the Palierne and Choi-Schowalter models, and showed a minimum value at a PP-g-MAH content of 3 phr in each model. For the PP/PLA (80/20) blends with the SEBS-g-MAH before and after hydrolysis, the increase in impact strength was more significant for the blends after hydrolysis. This suggests that PLA becomes less brittle after hydrolysis. The impact strength suggests that the SEBS-g-MAH is an effective impact modifier to improve the impact strength of the PP/PLA (80/20) blends.