Vitrimerization of Crosslinked Unsaturated Polyester Resins: A Mechanochemical Approach to Recycle and Reprocess Thermosets

Abstract

Unsaturated polyester resins (UPRs) are expansively used in different applications and recycling the significant amounts of UPR waste is still a universal problem. Vitrimerization is a feasible, environmental‐friendly, cost effective, and operative method, which can be used for recycling the crosslinked UPRs. In this method, the thermoset permanent network is changed into a dynamic network similar to the vitrimer‐type polymers. The results show that the existence of a transesterification catalyst in the system significantly enhances the efficiency of vitrimerization. The vitrimerized UPR thermosets can be reprocessed three times with mechanical properties comparable to the initial UPR. The results show that the excess of external hydroxyl groups in the system can prevent the formation of zinc ligand complexes in the network and consequently reduce the crosslinked density and mechanical properties of vitrimerized samples. The vitrimerized thermoset powder can be reprocessed through injection molding, extrusion, and compression molding which are conventional thermoplastic processing techniques. The unrecyclable UPR thermoset wastes can be recycled and reused through vitrimerization with the least loss in mechanical properties.

High‐Performance Vitrimeric Benzoxazines for Sustainable Advanced Materials: Design, Synthesis, and Applications

“…[ 28 ] Many epoxy vitrimers have since been reported, featuring excellent properties. [ 29–77 ] Other reported vitrimers are based on polybutadienes, [ 78–82 ] polyurethanes, [ 83–99 ] polyhydroxyurethanes, [ 100,101 ] polyurethane urea, [ 102,103 ] polyesters, [ 104–115 ] polycarbonates, [ 116 ] and polyimides. [ 117,118 ] These materials have low‐to‐medium‐to‐high glass transition temperatures, with polyimide vitrimer achieving T g of 274 °C and a 5% weight loss temperature of 429 °C.…”

Upcycling of thermosetting polymers into high-value materials

“…Based on the transesterification reaction, this method was also used for the vitrimerization of unsaturated polyesters. 80…”

Sustainable polyester vitrimer capable of fast self-healing and multiple shape-programming via efficient synthesis and configuration processing

“…Bandegi et al synthesized an unsaturated polyester via a three-step method, as follows: (1) the resin was crosslinked at room temperature for 24 h, and then at 80 °C for 3 h; (2) the crosslinked polyester was ball-milled into an ultrafine powder with an external catalyst for 1 h; and (3) the powder was compression molded at 200 °C for 1 h to finally obtain the vitrimerized samples. 25 Qiu et al synthesized a PET-based vitrimer through a post-curing method, which required 10 h. 23 However, the long-time reaction at high temperatures will consume large amounts of energy, and the addition of an external catalyst is harmful to both end-users and the environment. 26 Besides, due to the fact that the covalent adaptable networks of vitrimers are hard to flow, they are usually restricted to non-continuous processing, which is inefficient.…”