Thiourea Modification of Polyamine to Speed Up the Self-Healing by the Microencapsulated Epoxy-Amine Chemistry

Abstract The relatively slow polymerization between epoxy and polyetheramine limits the practical development of the self-healing epoxy based on microencapsulated epoxy-amine chemistry. How to achieve fast healing by this self-healing system without sacrificing the maximum healing efficiency is of great significance for its practical development. Based on the strategy via chemical modification of polyamines by thiourea to speed up the curing of epoxy, this investigation studied the feasibility of thiourea modifying JEFFAMINE T403 (T403), the microencapsulability of the thiourea-modified T403 (TU-T403), and the application of TU-T403 in the self-healing epoxy. The results demonstrated that T403 can be moderately modified by thiourea to improve the healing speed of the epoxy-amine chemistry. Using the electrospraying and interfacial polymerization (ES-IP) microencapsulation technique, high-quality microcapsules containing TU-T403 can be successfully achieved by reasonably selecting the auxiliary shell-forming monomer and properly adjusting the microencapsulation process. The self-healing epoxy based on dual microcapsules respectively containing epoxy and TU-T403 shows not only the full recovery (104 ± 8%) of the mode I fracture toughness after being healed at room temperature (RT, ∼25 °C) for 48 h but also a faster recovery at RT or 15 °C. The healing efficiency increases rapidly in the first 24 h and reaches 67 ± 7% and 94 ± 7% respectively at 12 and 24 h, which is about 65% and 90% of the maximum healing efficiency, indicating the fast establishment of the effective self-healing function. The self-healing system exhibits good healing performance at 15 °C. Under optimal conditions, healing at 15 °C for 48 h can achieve a healing efficiency close to 90%. The results of this study will greatly promote the practical development of the self-healing epoxy system based on microencapsulated epoxy-amine chemistry.