Preparation and Degradation of Waste Polycarbonate-Derived Epoxy Thermosets and Composites

We report a robust, 100% atom-efficiency strategy for preparing waste polycarbonate (WPC)-derived epoxy resin. To demonstrate the preparation process, we perform a pyridine-catalyzed model reaction between diphenyl carbonate (DPC) and diglycidyl ether of bisphenol A (DGEBA) in a molar ratio of 1:2. After epoxy-equivalent titration and two-dimensional nuclear magnetic resonance (2D-NMR) analysis, we confirm that the product is bis(1-(4-(2-(4-(oxiran-2-ylmethoxy)phenyl)propan-2-yl)phenoxy)-3-phenoxypropan-2-yl) carbonate (DPC-EP2). Based on the model reaction, three WPC-based epoxy resins (WPC-EPX, X = 2, 3, and 4) were prepared by the reaction of WPC with DGEBA in a molar ratio of 1:2, 1:3, and 1:4 in the presence of pyridine. The WPC-EPX epoxy resins were cured with WPC, phenol novolac (PN), diamino diphenylmethane (DDM), and dicyandiamide (DICY). The mechanical and thermal properties of the thermosets were discussed. We also prepared epoxy/carbon fiber composites and investigated the degradation of epoxy thermosets and the recycling of the carbon fiber. When the WPC-EP2 epoxy resin was cured with WPC, it can be successfully degraded to a phenoxy resin and 1,3-dihyexylurea through a catalyst-free aminolysis process. Undamaged carbon fibers have been recycled, according to the scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS) and tensile stress-strain data. The transformation of WPC to WPC-EPX, the aminolysis of WPC-EP2/WPC to a phenoxy resin and 1,3-dihexylurea, and the recycling of carbon fiber in the composite have been successfully demonstrated. Therefore, we believe that this work contributes greatly to the field of sustainable approaches in waste utilization.

Automated summary

A 100% atom-efficient strategy for preparing waste polycarbonate-derived epoxy resin was reported, demonstrating the preparation process with a model reaction and the production of three different WPC-based epoxy resins. The study also included the curing process, mechanical and thermal properties discussion, as well as the successful degradation of the epoxy resin and recycling of carbon fibers in the composite, contributing greatly to sustainable waste utilization techniques.