Alternatives for the valorization of isocyanate derived residual products from the glycolysis of polyurethane

Abstract

Polyurethane is among the most popular six polymers that are employed most frequently. So, at the end of its usage, a huge amount of material was produced as waste. One of the most intriguing options for polyurethane foam chemical recycling was split-phase glycolysis which produced polyol as a top phase. Polyol is incorporated in the synthesis of new polyurethane. The isocyanate derivate part (bottom phase) mainly consisted of carbamates. These carbamates cannot be discharged into the environment due to high toxicity. In addition, the bottom phase should be valorized to establish a system of circular economies and close the recycling cycle. In this thesis, the bottom phase was valorized by converting the carbamates into toluene diamine and glycol by hydrolysis at 200°C using sodium hydroxide solution for 3 hours. Then, the toluene diamine was recovered at high purity by vacuum distillation at 10 mbar after the complete removal of diethylene glycol from the hydrolysis product. The separated toluene diamine was incorporated in the synthesis of polyurea. The resultant polymer had quite similar properties to those having structure similarities. The toluene diamine was further incorporated into the synthesis of polyamide using two different synthetic methodologies. A set of comparisons was done to compare both methodologies using GPC, NMR, FT-IR, TGA, and DSC. In addition, limonene was incorporated as a green biobased solvent in one methodology of polyamide synthesis in order to make the process environmentally friendly. The results showed the ability to valorize the separated toluene diamine in the synthesis of these families of polymers. In addition, the characteristics of the synthesized families of polymer were similar to some examples reported in the literature.