Chemical recycling of technical textiles

This study investigates the chemical recycling of technical textile waste with the goal of producing recycled polyols for the synthesis of new polyisocyanurate (PIR) and polyurethane (PUR) rigid foams. The materials used originate from post-industrial ski boot padding waste, comprising flexible polyurethane foam coupled to a polyester fabric. Glycolysis was selected as chemical recycling method, employing either dipropylene glycol (DPG) or a 50/50 wt/wt.% mixture of DPG and polyethylene glycol 400 (PEG 400). This differentiation was necessary to meet the specific hydroxyl value requirements associated with the production of different foam types. During the glycolysis process, 2,4 and 2,6 toluene diamine (TDA) are generated as by-products and their concentration in the final polyol needs to remains below 1000 ppm to avoid mandatory regulatory labeling, due to their carcinogenic nature. In the initial phase, the depolymerization behavior of the textile materials was examined by varying key parameters, including the type of glycol and the catalytic system—potassium acetate and titanium (IV) butoxide—while maintaining constant reaction temperature, catalyst concentration, and reaction time. The preliminary results indicated an unexpected consumption of aromatic amine over reaction time, so a significant part of this work was spent on understanding this TDA side reaction. It was proved that during glycolysis toluene diamine interacted with the polyester fraction, through aminolysis, yielding amide species and hydroxyl terminated compounds. The extend of this reaction, using different catalyst and different waste type, was investigated in order to produce polyols with optimal characteristic in terms of viscosity, hydroxyl number and TDA content. The system that yielded the lowest TDA concentration in the glycolyzate was selected for further post-treatment via a deamination step aimed at reducing TDA levels below the legal threshold. Two glycidyl ethers—2-ethylhexyl glycidyl ether (2-EHGE) and 1,6-hexanediol diglycidyl ether (D.E.R.® 734)—were evaluated for this purpose. The latter proved to be more effective due to its bifunctional nature, which promoted faster reaction kinetics. In the final phase, the recycled polyols were utilized to produce new PIR and PUR rigid foams. These foams were subsequently characterized to evaluate their mechanical properties and thermal conductivity. The results demonstrated that the recycled foams exhibited optimal compressive strength and successfully met the thermal insulation performance targets w.r.t the virgin foam.