Styrene and BPO poly (urea-melamine-formaldehyde) microcapsules prepared via in situ polymerization to promote the self-healing properties of epoxy composites

Styrene has the characteristics of low viscosity, low shrinkage, and excellent adhesion to a variety of polymer materials and is a good candidate for healing agents. In this work, styrene and benzoyl peroxide (BPO) are coated, respectively, by in situ polymerization using poly(urea-melamine-formaldehyde) as shell materials to prepare two microcapsules for self-healing materials. IR, SEM, TGA, and DTA characterize the morphology, structure, composition, and thermal properties of the microcapsules. The optimized reaction parameters of the BPO microcapsule are as follows: the combination ratio of emulsifier DBS and GA is 2:1 (0.2% + 0.1%). The pH value of in situ polymerization is 3, the stirring speed is 700 r/min, and the core-shell ratio is 1:1. The content of the two microcapsule cores can reach more than 80%. In addition, the fracture toughness and healing efficiency of the double-microcapsules epoxy self-healing composites containing 2.5, 5, 7.5, 10, and 12.5 wt% of styrene and BPO microcapsules are measured using a tapered double cantilever beam (TDCB) specimen. The weight ratio of the two microcapsules in all self-healing epoxy composites was 1:1. The results show that the healing efficiency reached 37.3% when the content of the two microcapsules was 12.5 wt% at room temperature after 24 h healing. DTA results also indicate that this system has good potential for spontaneous self-healing performance at room temperature.