Chemical recycling of fabrics based on polyethylene terephthalate and polyurethane by glycolysis process

The constant increase in textile waste determines a significant environmen- tal challenge that needs to be solved with new recycling strategies. This the- sis explores the chemical recycling of blended fabrics based on polyethylene terephthalate (PET) and polyurethane (PU) through a glycolysis process. In the first part of the study, preliminary tests were performed to analyze the glycol- ysis of a textile made only of polyethylene terephthalate and a fabric made of polyurethane only. Furthermore, it was investigated on the original textile made of 30% of PU and 70% of PET, which was the maximum amount of waste to be subjected to the glycolysis process. This resulted to be equal to 60% in mass with respect to the glycol (DPG). The study used the Design of Experiments (DOE) to find the best glycolysis operating conditions applicable to a wide range of polyurethane/polyethylene terephthalate textile compositions. Three variables were considered: the per- centage of material-to-reactant (glycol), the polyurethane content in the textile, and the reaction temperature. The type and concentration of catalyst were kept constant. The resulting polyols from the glycolysis processes were then characterized in terms of viscosity, gel permeation chromatography (GPC) to determine the molecular weight distribution, infrared spectroscopy (FT-IR) to analyze the chem- ical structure of products, and hydroxyl value to define the final use of the prod- uct. Furthermore, the free amine content in the polyol was evaluated using high-performance liquid chromatography (HPLC). The optimal polyols obtained were those with the smallest amount of polyurethane inside the fabrics and the smallest waste-to-glycol ratio used in the glycolysis process. These require a successive deamination step in order to reduce the free aromatic amine content below the safety limit of 1000 ppm. The latter was performed us- ing a bio deaminating agent. Finally, the deaminated polyols were transformed into new rigid polyurethane foams. This was made using a mixture with a virgin polyol and different per- centages of recycled polyols: 25%, 50 % and 75%. They were subsequently characterized by mechanical and thermal tests and morphological analysis. The results show the possibility of obtaining high-value applications.