Exploring and Understanding the Recycling of a Bio-Based Epoxy Thermoset via Saponification

Abstract

The chemical recycling of a fully bio-based thermoset has been investigated by developing an innovative in situ monitoring methodology. Within this study, two distinct recycling pathways utilizing KOH/EtOH or NaOH/water were successfully developed for the solvolysis process of SuccELO, an epoxy/acid cross-linked polymer, by targeting its fragile ester bonds. The solvolysis was monitored by calorimetry, FT-IR, mass loss measurements, and optical microscopy. The kinetic parameters evaluated by calorimetry have been interpreted in terms of solvolysis mechanisms and used to discriminate four stages of the recycling process, beginning with a diffusion-controlled stage. The second step combines both diffusion and solvolysis, the later process corresponding to the formation of carboxylate ions. A third stage was identified and is associated with an autocatalytic step driven by the formation of sodium salts acting as a solubilizer for triglycerides. Finally, the diffusion of small chains is identified as the rate-limiting step at the end of the process. Validation of these findings is reinforced by comprehensive surface analysis using microscopy and FT-IR techniques. Besides the novelty of monitoring solvolysis by calorimetry, a simulation tool was developed based upon this method. These simulations were compared with mass loss measurements, highlighting drawbacks in the procedure used for these mass loss tests. Lastly, it is shown how prediction of the solvolysis at various temperatures not experimentally accessible can be achieved using kinetic modeling, facilitating process design and optimization strategies.