Improving the processibility and mechanical properties of poly(lactic acid)/linear low-density polyethylene/paraffin wax blends by subcritical gas-assisted processing

Previous studies have shown that paraffin wax (PW) is capable of improving the ductility and fluidity of poly(lactic acid) (PLA) matrices. However, PLA and PW are immiscible, thus the low melting temperature of PW (at around 55°C) will pose some processing difficulties and/or practical application limitations on PLA/PW blends. Since linear low-density polyethylene (LLDPE) and PW exhibited miscibility at a 90%/10% weight ratio and a melting temperature of 123°C, LLDPE was added to the PLA/PW blends in order to increase their thermal stability, processability, and elongation-at-break. The blends were prepared by a twin-screw extruder using two different melt compounding processes: conventional melt compounding extrusion and subcritical gas-assisted processing. Then, neat PLA, LLDPE, and the blends were injection molded into tensile bars for evaluation. To observe the effects of the two melt compounding processes, the thermal properties, mechanical properties, and phase morphologies of the various blends were characterized. The physical foaming agent (nitrogen, N₂) used in the subcritical gas-assisted processing process also plasticized the melt, thereby reducing the likelihood of thermal degradation and improving the mixing performance. POLYM. ENG. SCI., 58:2320–2331, 2018.