Alternative feedstock for thermoplastic polyurethane chain extenders through chemical recycling of the polyurea fraction in a rigid PVC foam

Thermoplastic polyurethanes (TPUs) are synthetized by using the products from the chemical recycling of polyurea. In particular, the polyurea fraction included in PVC foams typically used in sandwich structures is depolymerized under glycolysis conditions with 1,4-butanediol (BD). After separation of the solid PVC fraction, the liquid part is used as it is, instead of pure BD, as chain extender. Two different depolymerization products obtained with 3/1 or 2/1 BD to foam ratio are tested in combination with methylene diphenyl diisocyanate (MDI) and poly(tetrahydrofuran). Reference samples are also synthetized with pure BD. The hard phase content is kept constant at 39 % of total TPU weight, while the weight ratio of chain extender to MDI is varied in the range from 13 to 25 %. The obtained polymers are characterized by GPC, FT-IR and NMR spectroscopy analyses in order to investigate the effect of the chain extender substitution and of the chain extender to MDI ratio on the macromolecular features. Furthermore, the obtained polymers are characterized by thermal (DSC, TGA) and mechanical analyses (Shore A, stress-strain). The results reveal that the depolymerization products can be used in substitution of pure BD as chain extender, giving TPU with mechanical properties comparable to the one of the reference samples, once the reaction conditions are properly scaled. Only a minor difference occurs in the shore A values, which decrease with the content of polyurea depolymerization fraction (FDP) in the mixture. Despite this, the mechanical properties of the newly synthesized FDP-based TPUs are suitable for several applications, e.g. in the footwear, cable & wire, hose and tube, film and sheet industries.