Three-component polypropylene/lignin/flax composites with high natural additive content for structural applications

Abstract

Hybrid composites were prepared from a polypropylene reactor blend (rPP), lignin and flax fibers. Interfacial adhesion was improved using a functionalized PP (maleated PP, MAPP) coupling agent. Composition changed in a wide range; flax content varied between 0 and 30, while lignin content between 0 and 50 vol% in 10 vol% steps. The components were homogenized in a twin-screw compounder, and injection molded specimens were prepared from the compounds for further testing. The processability of the composites was characterized by the measurement of melt flow rate, while mechanical properties by tensile and impact testing. The combination of lignin and flax fibers yields materials with an advantageous property profile, considerably decreased carbon footprint and acceptable price. The application of flax compensates for the deteriorating effect of lignin on deformability and especially on impact resistance. Significant improvement was achieved in stiffness and strength. In order to obtain this property combination, the application of a coupling agent is necessary because of the poor interaction between PP and natural reinforcements. The compounds developed may successfully compete with materials offered on the market.