Reprocessed, shape-memory and self-healing robust epoxy resin by hindered urea bond

Abstract

Given the fossil fuel energy crisis and serious environmental pollution in recent years, one way to alleviate the problem is to introduce dynamic covalent chemistry into thermosetting resins to give the material processable and recyclable properties, creating a new type of eco-friendly material. Hindered urea bonds can undergo reversible exchange reactions at high temperatures to decompose into amine and isocyanate. This reversible addition reaction is currently a prominent research focus in the development of reprocessable thermosets. In this work, we synthesize a novel curing agent with hindered urea bonds without any catalysts. Then characterize the resulting epoxy vitrimers based on hindered urea bond (HUG-EP) using FT-IR and 1H NMR, confirming the successful introduction of hindered urea bonds into the epoxy resin. A variety of tests are carried out, such as those to assess thermal stability, swelling, shape-memory, re-processability and tensile strength. The results demonstrate that HUG-EP can rapidly self-healed within 20 min at 160 °C, with the tensile strength was maintained at 87.15 % of the original during the welding experiments. Furthermore, it can also be reprocessed by hot-pressing several times at 160 °C. Thus, the introduction of hindered urea bonds into the crosslinked network proves to be an effective and practicable approach for producing thermosetting resins with reprocessing, self-healing, and shape memory capabilities.