Study of the Viscosity and Thermal Characteristics of Polyolefins / Solvent Mixtures: Applications for Plastic Pyrolysis

Plastic pollution is one of the biggest environmental problems that the world is currently facing. Pyrolysis is a frontier technique aimed at converting plastic waste back into virgin-quality resin. However, the transfer of the waste plastic feed into the pyrolysis reactor must be solved before the process can be up-scaled to a continuous process. Even though the effects of various solvents on the viscosity of polyolefin have been studied previously, an appropriate solvent that can prepare waste plastics as feed for pyrolysis has not yet been found. In this study, a new solvent that reduces the viscosity of molten plastic was introduced and characterized. The results revealed that the polymers are soluble in the ratio of up to 75 wt% plastic 25 wt% solvent. The viscosity of pure low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP) in the solvent was measured in different weight percentages (30% - 80% wt%) and at 160, 180, 200, 220, 240 and 260℃. The viscosity decreased with the decreasing polymer-weight percentage and increasing temperature. The viscosity of LDPE + solvent is much lower than for HDPE + solvent, and for PP + solvent. Also, the Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA) were applied to characterize the thermal behavior of LDPE, HDPE, and PP in the solvent in three different weight percentages (25%, 50% and 75wt%). The DSC results indicate that in the mixture of PP + solvent the melting point of PP decreases as the amount of solvent increases. Overall, these results indicate that the selected solvent is an effective agent to prepare waste plastics for pyrolysis.