Simulated thermo-mechanical recycling of high-density polyethylene for the fabrication of hemp hurd plastic composites

High density polyethylene (HDPE) was reprocessed up to six times to simulate recycling. The effect of recycling on HDPE was analyzed via molecular weight and rheology analysis as well as thermal and mechanical evaluations. Fine powder of hemp hurd (HP) was then melt compounded with the recycled HDPE at 5 to 50 wt.% to fabricate hemp plastic composites (HPCs). Finally, maleated HDPE was introduced (3 and 5 wt.%) as a compatibilizer to better facilitate stress transfer. All formulations and reactions were prepared via a melt batch mixer followed by injection and compression molding. The simulated recycling led to crosslinking reactions, shown by an increase in melt viscosity, with minimal changes to the weight average molecular weight. All composites were analyzed for water absorption kinetics, thermal and mechanical properties, morphology, as well as other physiochemical properties. Before maleation, increase in the hemp content led to an increase in tensile modulus, all the while, maintaining their tensile strength. Additionally, substantial increase in water absorption kinetics was noted as hemp content increased. After compatibilizing, there was notable increases in all tensile and impact properties while also displaying a dramatic decrease in the water absorption kinetics.