Synergistic effect of chain extender and glass fiber in recycling of post‐consumer poly(ethylene terephthalate) through promotion of long‐chain branching

Abstract Poly(ethylene terephthalate) (PET) products are major contributors to plastic waste, and recycling helps mitigate the problem. This study explored how one‐step melt compounding of flakes of post‐consumer PET bottles with an epoxy‐type chain extender (CE) and glass fiber (GF) would impact the properties of the resulting composite (rPET/GF/CE). Remarkably, the elongation at break and impact strength of rPET/GF/CE nearly matched those of PET/GF, and its yield stress exceeded that of PET/GF by approximately 15%. GF and CE synergically improved the complex viscosity of rPET (400‐fold increase for rPET/GF/CE vs. 2‐ and 3‐fold increases for PET/CE and rPET/GF, respectively.) The highly pronounced shear thinning of rPET/GF/CE was the primary marker of extensive long‐chain branching (LCB). LCB also altered the thermal properties of rPET/GF/CE and was the main factor responsible for the enhancements in mechanical and rheological properties. The promotion of LCB in rPET/GF/CE is likely due to the diffusion of amine groups from the surface of sized glass fibers into the matrix, where they act as catalysts for the chain extension reaction, giving rise to extensive LCB. This study demonstrates that post‐consumer PET waste can be recycled and used in high‐performance applications, for example, the automotive industry. Highlights Mechanical performance of rPET/GF/CE is comparable to that of PET/GF. The greatest increase in complex viscosity is seen for rPET/GF/CE. Amino groups of silane‐sized glass fibers boost the chain extension reaction.