Fragmentation effect of solvent in recovery of unsaturated polyester resin and its composites

As the most productive thermosetting polymer, unsaturated polyester resin (UPR) and its composies were difficult to be chemcycled due to the mass transfer barrier in dense network structure. High temperature/pressure and mechanical crushing were usually applied to improve the mass transfer during chemcycling processes, but at the sacrifice of reaction selectivity and fiber integrity. Here, a unique fragmentation effect of aprotic solvents was observed in UPR, which is a non-reactive solvation that has the potential to replace mechanical fragmentation and improve the recyclability of UPR and its composite materials. The solvation was found to be based on the hydrogen bond between the solvent and ester group of UPR through Hansen solubility parameters and molecular dynamics simulation. It was the intermolecular force between the polyester clusters of UPR that was destroyed, leading to the fragmentation of UPR into micron-sized powder. The fragmentation effect is also applicable to other ester-containing polymers and provides a simple, facile, and energy-efficient method for the chemcycling of thermosetting resins, as well as direct exfoliation of reinforced fillers.