Enhancing toughness of poly(lactic acid) by regulating the hydroxyl value and viscosity of hydroxyl terminated polybutadiene

Brittleness of poly(lactic acid) (PLA), a biocompatible and biodegradable polymer obtained from renewable and natural sources, hinders its widespread applications. This study provides a convenient and economical way to enhance the toughness of PLA by using hydroxyl terminated polybutadiene (HTPB) liquid rubber to modify PLA. Four types of HTPB with varied hydroxyl values and viscosities were used to prepare PLA/HTPB blends. The effects of HTPB content on the mechanical characteristics, phase structure, thermal and crystalline properties of the toughened blends were systematically investigated. For PLA/HTPB2-5%, the elongation at break and impact strength was 87% and 58 kJ/m2, respectively, which was 12.8 and 3.5 times that of neat PLA. Due to the relatively lower hydroxyl value and suitable viscosity of HTPB2, PLA/HTPB2-5% exhibited the best impact toughness and had the highest impact strength. When the content of HTPB exceeded 5%, the mechanical properties of PLA/HTPBs gradually decreased. This could be due to the gradual increase of particle size of the dispersed phase with increasing HTPB content, resulting in serious phase separation between the dispersed phase and continuous phase. The resultant PLA/HTPB2 composites with improved toughness could have potential applications in engineering materials thus enlarging the spectrum of applications for PLA.