Improvement of the mechanical behavior of bioplastic poly(lactic acid)/polyamide blends by reactive compatibilization

Polymer blends are of significant interest for reinforcing bioplastics via addition of a second polymer and a blend compatibilizer or in situ reaction. However, increased costs associated with additional materials and extra processing steps can limit the viability of this solution. Here, a simple, continuous reactive extrusion processing method was examined for producing tougher bioplastic blends. p-Toluenesulfonic acid (TsOH) catalyst was added to two immiscible biobased polymers, poly(lactic acid) (PLA) and polyamide11 (PA11), to induce ester-amide exchange reaction. The mechanical properties of PLA were improved through mixing with PA11 by introducing copolymers at the interface thereby reducing interfacial tension. The morphology, chemical structure analysis, and tensile testing supported that copolymerization reaction occurred resulting in improved bonding between PLA and PA11 with 0.5 wt % TsOH catalyst in the batch mixing, but depolymerization dominated at higher shear stress (2000 rpm) and catalyst loading (over 2 wt %). The PLA/PA11 blend with 0.5 wt % TsOH catalyst displayed around 50% improvement in elongation at break in twin-screw extruder blending (around 5 min mixing time) at 250 rpm screw speed, which was similar to the improvement using batch mixing (20 min mixing time). (C) 2016 Wiley Periodicals, Inc.