Synthesis and Healing Behavior of Thermo-reversible Self-healing Epoxy Resins

Cracks may appear in epoxy resins once suffered the external impact and pressure. If cracks can be remended by material itself, then the service life of the materials can be extended and severe incident can be avoided. Herein, an epoxy monomer containing diene is synthesized via the reaction between epichlorohydrin and furfuryl alcohol. A self-healing epoxy resin based on thermo-reversible Diels-Alder reaction (EP-DA) is prepared by the reaction between the resultant epoxy monomer and bismaleimide. The chemical structure, thermal property, and thermal reversibility of the prepared EP-DA are characterized by FTIR, DSC, and gel-sol transition. Results show that thermo-reversible DA bonds are introduced into the epoxy resin successfully. Consequently, EP-DA is endowed with excellent thermal reversibility and reprocessing performance. The self-healing behavior is examined by investigating both the crack evolution and the recovery of mechanical property. Based on the study about the effect of heat treatment on the crack repair in depth, the optimal heat treatment parameters are determined as 122 degrees C/45 min and 67 degrees C/36 h. By simulating the impact failure situation in actual state, the self-healing performance of the epoxy resin is investigated by a combination of qualitative observation and quantitative measurement of flexural load restoring. Results reveal that the crack narrows down and flexural strength enhances gradually with extended heat treatment. It is shown that the epoxy resins exhibit excellent self-healing performance, and the healing efficiency can achieve 77.1%. Meanwhile, cracks can be caused and repaired for more than three times. The healing efficiency can still reach 53.9% when the same sample has been impacted and repaired for three cycles. These manifest that the epoxy resins also show outstanding multiple self-healing performance. Additionally, the EP-DA exhibits excellent reprocessing performance, and PU-DA fragments can recombine together as a whole upon heating treatment at 122 degrees C/2 h and 67 degrees C/36 h. The result makes it possible for recycling the waste epoxy resins.