Reusing Chemically Recycled Cross-Linked Matrix from Succinic Acid–Epoxidized Linseed Oil

Abstract

To address the challenges of thermoset resin circularity, the solvolyzed products from biobased succinic acid/epoxidized linseed oil (ELO) cross-linked resin were valorized into new starting materials for the preparation of recycled cross-linked systems. First, the recycled product was characterized by using spectroscopy and chromatography techniques (FT-IR and LC-MS), providing insights into their molecular composition. The recovered compounds were employed to synthesize new thermosetting resins, as polyacid hardeners for epoxy systems. The mechanical and thermal properties of the cross-linked samples were obtained by means of Dynamic Mechanical Analysis (DMA), tensile tests, and thermogravimetric analysis (TGA). The recycled formulation (named “Rec-ELO”) showed comparable or enhanced performance relative to similar fresh biobased resins. Notably, Rec-ELO displayed a higher glass-transition temperature and a broader relaxation profile, indicative of increased network heterogeneity. Advanced kinetics studies further highlighted differences in the apparent curing behavior between formulations from virgin and recycled compounds, as evidenced by Differential Scanning Calorimetry (DSC). These differences were attributed to lower reactive group concentration effects, reduced mobility, and the heterogeneous nature of the recycled polyacid fraction. These findings demonstrate that solvolysis effectively allows the recovery of valuable materials from biobased thermoset recycling, offering a sustainable approach to reducing waste and reliance on virgin resources.