Green composites based on blends of polypropylene with "liquid wood" reinforced with hemp fibers: thermomechanical properties and the effect of recycling cycles

Green composites from polypropylene and lignin-based natural material were manufactured using a melt extrusion process. The lignin-based material used was the so called "liquid wood". The PP/"Liquid Wood" blends were extruded with "liquid wood" content varying from 20wt% to 80wt%. The blends were thoroughly characterized by flexural, impact and dynamic mechanical testing. The addition of the "liquid wood" resulted in high improvement of both flexural modulus and strength but, on the other hand, the reduction of the impact strength was observed. For one blend composition, composites reinforced with hemp fibers were also studied. The addition of hemp allowed to further improve the mechanical properties. The composite with 20wt% of hemp, subjected up to three recycling cycles, showed good mechanical property retention and thermal stability after recycling.