Optimization of a chemical recycling process for epoxy-amine thermosets and their carbon fiber reinforced composites using a design of experiments approach

Abstract

Over the past decade, the use of carbon fiber reinforced polymers (CFRPs) in highly demanding applications has steadily grown in several industrial fields, leading to a significant increase in waste production in the coming years. Unfortunately, the recycling process of these materials presents significant challenges, due to their heterogeneity and the irreversible nature of the three-dimensional crosslinked network constituting the polymeric matrix, making their end-of-life management particularly critical. As a result, there is an urgent need for economically feasible, safe, and scalable strategies to efficiently recycle these materials and recover valuable components. To address this issue, this work presents an optimization protocol for a Lewis acid-catalyzed solvolysis process at atmospheric pressure, applied to recalcitrant aromatic amine–epoxy thermosets and their corresponding CFRPs. A central composite design of experiments (CCD) was implemented, taking concentration of AlCl₃, resin concentration, process temperature, and process time as factors, while the extent of dissolution of the epoxy matrix was selected as target system response. Process optimization was performed, based on the resulting model, to identify the most favorable operating conditions for the solvolysis, then validated on the corresponding CFRPs. As a result of this validation step, a functional oligomeric organic fraction could be recovered, together with intact and clean recycled CFs able to preserve >95 % of their pristine mechanical properties. This work paves the path for the definition of important guidelines for the implementation of effective chemical recycling processes for amine-cured epoxy-based CFRPs, promoting a more favorable end-of-life management of these materials.