Effects of Mixed Microcapsules in Different Proportions on Aging Resistance and Self-Healing Properties of Waterborne Coatings for Tilia europaea L

Abstract

In order to prolong the effective time of the self-healing properties of waterborne coatings containing shellac microcapsules coated with melamine rice husk powder (MRHP), three kinds of MRHPs with better microscopic morphologies, which contain 2.8% (type A), 5.5% (type B), and 8.0% (type C) of a rice husk powder (RHP), in shell materials were mixed according to three different proportions, and added to the waterborne coatings based on Tilia europaea L., under the conditions of the most proper addition amount of 6.0% microcapsules. The results indicated that the waterborne coatings containing mixed microcapsules can still maintain the best state in terms of optical properties and mechanical properties, with a chromatism of 1.10, an adhesion of zero, a hardness of 4H, an impact resistance of 7 kg·cm, and an elongation at break of 35.28%, respectively. According to the aging resistance test, the waterborne coating containing microcapsules “type A + type B + type C” demonstrated a longer effective time. After aging for 200 h in the UV climate resistance test chamber, the light loss rate at an incident angle of 60° was 2.91%. Through scratch testing, it is verified that the mixed microcapsules can prolong the self-healing time, reduce the crack size, and achieve a coating self-healing rate of 41.11%. They can also inhibit the crack growth rate to a certain extent. Roughness tests indicated that the surface roughness of the coating with mixed microcapsules increased by 0.038 μm in comparation with the single microcapsule, but the surface can still remain smooth after being covered by the topcoat without the microcapsules. Studying the ratio of mixed microcapsules provides new ideas for the optimization of a wood-based coating self-healing effect.