Recycled Post-Consumer HDPE As a Matrix for Hemp Hurd Bio-Composites for Commercial Scale-Up Operations

Two types of high-density polyethylene (HDPE) were studied, post-consumer HDPE (P.C. HDPE) and virgin HDPE (vHDPE), to observe how properties may change after a polymer has undergone additional thermal, environmental, and service histories. The difference between the virgin and P.C. HDPE was analyzed via rotational rheology as well as thermal and mechanical evaluations. Hemp hurd powder (HP) was then melt compounded with the P.C. and vHDPE polymers at 30 and 50 wt% to fabricate hemp plastic composites (HPCs). Finally, 3 wt% maleated HDPE was introduced as a compatibilizer to better ease stress transfer and particle distribution. All melt mixing operations were prepared using a melt kinetic mixer followed by injection molding. The P.C. HDPE had undergone severe cross-linking reactions, shown by a substantial increase in melt viscosity, which correlated to changes with weight average molecular weight and molecular weight distribution, obtained via rotation rheometry. The crosslinking-mediated increase in viscosity also led to an increase in tensile strength and notched izod impact strength. After compatibilizing, there were notable increases in all tensile and impact strengths while also displaying a decrease in apparent thermal conductivity due to a reduction in crystallinity. Finally, when scaling up a selected composite it was found that a twin screw extruder bestows enhanced properties, due to higher shear forces and better mixing when compared to a lab scale processes.