Silane crosslinkable polyethylene waste as bitumen modifier: A new fortunate destiny by in time recycling of thermoplastic waste before conversion to thermoset end-of-life unrecyclable polymer

Abstract

Polymer modification of bitumen is a popular method to enhance its performance. Over the years, researchers have suggested and developed various polymeric bitumen modifiers, and this trend in research is in progress to introduce new polymers with higher modification efficacies. Silane crosslinkable polyethylene is a widely used polymer as cable insulation, and its waste was used as bitumen modifier in this study. After shaping this polymer around the metal conductors and providing the crosslinking condition, silane-crosslinked polyethylene (Si-XLPE) insulation is obtained. When compared to ordinary polyethylene, Si-XLPE exhibits superlative performance, such as enhanced thermal, mechanical, elasticity, and stress cracking properties. Herein, the cable production wastes of this polymer were utilized for bitumen modification before crosslinking. Comprehensive analyses were carried out for characterizing the fabricated samples, including conventional physical (softening point, penetration, and storage stability), morphological (optical and fluorescence microscopies), chemical (FTIR), thermal (DSC), and performance grade (PG) assessments. For PG determination, rolling thin film oven (RTFO) and pressure aging vessel (PAV) tests, along with rotational viscometer (RV), dynamic shear rheometer (DSR), and bending-beam rheometer (BBR) tools were employed. Findings indicated the formation of a polymeric phase network in the bitumen matrix with altering shapes depending on the polymer content. This was identified to be the origin of appeared structural enhancements in the Si-XLPE modified bitumen samples. Moreover, it was revealed that Si-XLPE contents in 2% and more led to phase separations in the unaged or aged states due to high swelling ratio of Si-XLPE. Strikingly, it was seen that only 1% of Si-XLPE could change the PG 58-22 of base bitumen to PG 70-22, which confirmed promising efficiency of recycled Si-XLPE in low contents for significant improvements in the bitumen's high temperature performance without adverse effects on its low temperature performance. Eventually, recycled silane crosslinkable polyethylene can be an advantageous potential bitumen-modifier that is favorable from technical, environmental, and economical perspectives.