Developing Easy Processable, Recyclable, and Self-Healable Biobased Epoxy Resin through Dynamic Covalent Imine Bonds

Abstract

Growing sustainability concerns have promoted the rapid development of reusable and environmentally friendly thermosetting materials. Herein, a recyclable biobased curing agent (vanillin-based imine curing agent) was produced from vanillin in a single-stage process. However, this curing agent was fully solid and difficult to process, requiring large amounts of solvent during processing. Since the viscosity of 4-methyl-1,3-cyclohexendiamine (HTDA) is low, it can be used as a cocuring agent at various amounts to make a viscous liquid curing agent for diglycidyl ether of bisphenol F. The curing behaviors and thermomechanical and mechanical properties of the cured thermosets were evaluated along with their self-healing ability. The results reveal that the viscosity and activation energy of curing are reduced as the weight ratio of HTDA increases, whereas the flexural strength (106–122 MPa), moduli (2365–2587 MPa), and Tg values (95–110 °C) increase gradually. Additionally, the heat-resistant temperature (Ts) values (166–162 °C) and char residue at 700 °C (26–10%) of the cured samples continuously decreased. Overall, 40% HDTA containing VH03 showed a suitable viscous form for processing and mechanical and thermal properties. Subsequently, the flexural strength retention and Tg were still 80% and 115 °C, respectively, and it also demonstrated absolute solvent resistance at room temperature. The excellent integrated properties clarified that VH03 is favorable for easy processability, recyclability, and sustainable improvement.