Investigation of Thermo-mechanical Degradation of Polypropylene-Low Density Polyethylene Blends Exposed to Simulated Recycling

Abstract

Polypropylene (PP) and low-density polyethylene (LDPE) are among the most extensively used resins used mainly in the packaging and automotive sectors and are the largest contributor to municipal waste. Plastic waste accumulation in water bodies and landfill is a major environmental concern due to their resistance to microbial attack and slow environmental degradation process. Thus, recycling and reusing of these plastic wastes is a more viable solution than discarding it in the environment. The physiochemical properties and structure change irreversibly during repeated recycling operations. Hence, it is critical to understand the deterioration of properties during multiple processing and reprocessing steps. In this study, PP blended with 0–10 wt. % of LDPE was subjected to consecutive twin-screw extrusion cycles (0-5 times) to mimic thermo-mechanical recycling. The effect of reprocessing on the rheological, thermal, and mechanical properties of PP/LDPE blends was investigated. An increase in melt flow rate (MFR) and decrease in viscosity was observed for PP and the blends. Differential scanning calorimetry (DSC) results showed that the crystal structure of PP was seriously affected, generating more disorder with reprocessing. Although tensile properties were not substantially affected, all properties had a decreasing trend. While successive thermo-mechanical processing caused chain scission of the PP phase of the blend, the overall property of the studied blend composition maintained mostly acceptable properties. Thus, recycling of PP blends with low-density polyethylene (LDPE) content is a feasible option not only to reduce plastic waste but also to generate value from an otherwise waste product.