Effects of Lignocellulosic Fillers from Waste Thyme on Melt Flow Behavior and Processability of Wood Plastic Composites (WPC) with Biobased Poly(ethylene) by Injection Molding

Wood-like plastic composites were manufactured with a thermoplastic matrix polymer from renewable resources, i.e. high-density poly(ethylene) from bioethanol and a lignocellulosic filler obtained as a byproduct of the industrial distillation of thyme. The potential manufacturing of these composites by injection molding was studied. For this purpose, an in depth study of the effects of the lignocellulosic loading (comprised between 10 and 50 wt%) on the rheological properties of these composites was carried out by using capillary rheometry and model fitting with the Cross-WLF rheological model. In addition, a side by side comparison of the experimental results and those obtained by simulations with MoldFlow® was provided. In addition, the values of the pressure in the cavity and in the sprue were measured and collected by two selectively mounted pressure sensors and the results were compared with those predicted by MoldFlow® with the inputs provided by the Cross-WLF fitting model. The results showed a remarkable increase in viscosity with increasing lignocellulosic filler content, which has a negative effect on overall processability. This phenomenon specifically intense at low shear rates. However, this phenomenon could be potentially minimized using high shear rates because of the shear thinning effect of pseudoplastic fluids. Both the experimental and simulated results suggest the need of higher pressures to fill the cavity with these WPC, specifically for those with high filler content of up to 50 wt%. The results of the study indicate that melt viscosity is highly linked to the cavity pressure which is the dominant factor determining the quality of the final product in plastic injection molding.