Quantifying mechanical recycling of Phillips catalyst HDPE with rheological measurements

The challenge of recycling and waste management has become increasingly critical in the current era due to the escalating volume of plastic waste and its environmental impact. This study investigates the mechanical recycling of a Phillips catalyst high density polyethylene (P-HDPE) by using a twin-screw extruder with altering different parameters such as temperature (170 °C & 210 °C), recycling time (30 min, 60 min, 120 min & 240 min) and screw rotation speed (60 rpm, 120 rpm & 180 rpm). Recycled P-HDPE exhibits altered rheological properties compared to virgin materials due to chain scission, crosslinking and branching during recycling, leading to variations in molecular weight (MW), molecular weight distribution and in melt viscosity. Recycled P-HDPE at 170 °C shows a higher melt flow index (MFI) value than virgin P-HDPE due to chain scission. The MFI value increases with increasing recycling time and screw speed. In the case of recycled P-HDPE at 210 ⁰C, crosslinking or branching occurs at low screw speed and recycling time. At high speed and higher recycling time, it shows again chain scission. Time-temperature superposition graphs of recycled P-HDPE clearly distinguish the chain scission occurring at 170 °C and crosslinking or branching occurring at 210 °C. The overall study gives an idea of how screw speed and recycling time influence the recycling of P-HDPE at different temperatures.