Synergistic catalysis of binary alkalis for the recycling of unsaturated polyester under mild conditions

Abstract

With high dimensional stability, chemical resistance, and thermal stability, unsaturated polyester (UP) resins are indispensable for many applications, causing the ever-increasing generation of waste UP. However, the conventional chemical recycling of UP is usually carried out under harsh conditions to produce monomers or oligomers along with a complex separation process. Developing a facile and easy approach is highly desired to explore the inherent value of UP and transform it into high-value products. In this study, an efficient strategy was developed for the chemical recycling of UP with the synergistic catalysis of the binary alkali of diethylenetriamine and sodium hydroxide under mild conditions. Diethylenetriamine functions as both a reactive solvent and a catalyst. The presence of diethylenetriamine facilitates the degradation, while only hydrolysis is observed without amination. The compositions of the degraded products can be controllably adjusted by varying the amount of binary alkali. Moreover, the main products can be easily separated from the reaction system by simple filtration. The ester bonds in the UP are selectively cleaved, producing large amounts of active groups such as hydroxyl, sodium carboxylate, ammonium carboxylate and amino groups. A novel gel material can be obtained and it demonstrates a fast adsorption performance and large adsorption capacity for cationic dyes and heavy metal ions.