Study and optimization of PET recycling via glycolysis and the synthesis of recycled polyester

The problem of the growing consumption of polyethylene terephthalate (PET) and the environmental challenges associated with its waste treatment, can find a solution by applying an efficient recycling strategy. This work investigates the chemical recycling of PET reinforced with 30 wt% glass fiber via a glycolysis process using ethylene glycol (EG) as a solvent and reactant, and zinc acetate as a catalyst. A parametric preliminary study was initially performed to analyze the individual effects of temperature (180 - 196 °C), reaction time (3 - 5 h), EG/PET molar ratio (3 - 5), and weight percentage of catalyst over PET (0.5 - 1%) on the hydroxyl index (IOH) and polymer degree of depolymerization (DDp) in the reaction matrix. To identify the optimal operating conditions, a Design of Experiments (DoE) approach was implemented and analyzed via statistical software. The statistical analysis revealed that temperature, time, and their mutual interaction have the most significant influence on the depolymerization process, while the catalyst efficiency plateaus within the investigated range. The optimal glycolysis product was successfully integrated at different weight percentages (5%, 10%, 15%, and 20%) into an erythritol-sebacic acid prepolymer matrix to synthesize a new recycled polyester (RPET) network. Thermo-mechanical and viscoelastic characterizations, conducted via tensile testing, Thermogravimetric Analysis (TGA), and Dynamic Mechanical Analysis (DMA), confirmed that the addition of the recycled product effectively modulates the structural network, shifting the material from highly flexible, homogeneous matrices to tighter, more rigid elastomeric networks, thereby demonstrating a viable pathway for high-quality plastic waste upcycling.