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.

Abstract

Thermoset unsaturated polyester resin waste can be recycled through a mechanochemical approach based on ball milling the ground waste with an appropriate transesterification catalyst followed by compression molding, extrusion, or injection molding. This vitrimerization approach converts the permanent network into a vitrimer‐dynamic network, which can be recycled multiple times without significant loss in mechanical properties.