Reprocessing of Poly(ε-Caprolactone) Into Tough Hydrogels via Deep Eutectic Solvent Photografting and Thermal Crosslinking

Poly(ε-caprolactone) (PCL) is a sustainable polyester with excellent mechanical properties and processability. Conventionally, PCL can be chemically recycled into monomers for repolymerization. Moreover, reprocessing PCL into value-added products can reintegrate it into extensive use, yet it remains relatively unexplored. To enhance the value of PCL in applications, this study develops a hydrogel system that enables PCL reprocessing. A deep eutectic solvent-assisted photografting strategy was employed to introduce itaconic acid (ITA) onto PCL, followed by hydrogel formation through subsequent crosslinking. Comprehensive characterization confirmed that the combination of a deep eutectic solvent (DES) and a photoinitiator system achieves the highest degree of ITA grafting at a PCL:ITA ratio of 1:25, producing hydrogels with a tensile strength of 0.82 MPa, an elongation at break of 431%, and a toughness of 2.32 MJ m⁻³. The hydrogels also exhibit low hysteresis even after 40 stretch–release fatigue cycles and are recyclable. Furthermore, enzymatic hydrolysis with lipase depolymerizes the hydrogels, confirming the system's degradability. Collectively, this study presents a PCL reprocessing strategy that fabricates hydrogels with enhanced toughness, recyclability, and hydrolytic ability.