Synergistic effects in the co-pyrolysis of thermoset epoxy resin and biomass on kinetics and product distribution

Abstract

With the rapid growth of wind power, batteries, and aerospace industries, sustainable disposal of thermoset plastics has become a long-term concern. However, pyrolysis, a highly promising solution for this issue, has seen limited studied on thermoset plastics. Drawing inspiration from the synergistic interactions observed between thermoplastics and biomass, this study explored the co-pyrolysis of a thermoset epoxy resin, diglycidyl ether of bisphenol A, cured with 4,4′-Diaminodiphenylmethane, with ash-free biomass pseudo-components (cellulose, lignin, and xylan) using thermogravimetry and Py-GC/MS. The results revealed distinctive synergistic effects in Epoxy-Cellulose and Epoxy-Lignin mixtures, delaying the onset and hastening the conclusion of weight loss. This was accompanied by increased activation energies, assessed through the Friedman and Kissinger-Akahira-Sunose methods, as well as higher char yields. Conversely, in Epoxy-Xylan, synergistic effects led to reduced activation energy across most α values, resulting in a lower onset temperature and a heightened maximum rate of mixture degradation. Regarding product distribution, all three pseudo-components, particularly lignin, enhanced the selectivity of bisphenol A. Additionally, cellulose and xylan altered the kinetics of N–C and C(N)–C(OH) bond cleavage, reducing the amount and altering the distribution of 2-B-N compounds (compounds featuring two benzene rings and nitrogen). Conversely, the presence of resin reduced the volatiles from cellulose and xylan, promoting phenol-type products and –H and alkylene side chains while diminishing guaiacol-type products and alkyl side chains. Three mechanisms were proposed to elucidate these observed synergistic effects: catalytic effects of –OH groups from biomass pseudo-components, hydrogen exchange or hydrogen bonding between resin-derived nitrogen and biomass-derived oxygen-containing functional groups, and radical reactions. These insights into the co-pyrolysis of biomass and cured epoxy resin can inform the selection of suitable feedstocks for various applications.