MECHANICAL PROPERTIES OF BIO-BASED SELF-HEALING COATING WITH EMBEDDED MICROCAPSULES

Abstract

Self-healing coating is one of the smart coatings that can restore physical appearance and performance after exposure to damage such as scratches and weathering. Self-healing coatings have several benefits, including extending material life and lowering operating costs by reducing the need for planned maintenance, especially in situations involving remote locations. Microcapsule is one of the techniques that are widely used in the preparation of self-healing coating. This approach used an active healing agent to be stored in the microcapsule. In the previous work, pure jatropha oil (JO) and its derivatives known as jatropha oil-based polyurethane acrylate (JPUA) were encapsulated into a polyurea formaldehyde (PUF) microcapsule. In this study, JO and JPUA-IPDI-based microcapsules were loaded into the JPUA-TDI-based coating. 5 wt% and 10 wt% loading of microcapsules were dispersed using a mechanical stirrer in the coating formulation until a homogenous mixture was obtained. The self-healing coating formulation was coated on a steel plate (100 mm x 100 mm x 1.5 mm) using a bar applicator with a thickness of 50 μm,100 μm, 150 μm and 200 μm. Then, the wet film was irradiated under UV light until fully cured. Mechanical tests such as Pendulum Hardness Test (ASTM D4366), Cross-cut Adhesion Test (ASTM D3359-09), Transmittance Test (ASTM E1348), and Haze Test (ASTM D1003) were performed on the cured self-healing coating. The mechanical properties of the self-healing coating were compared with the coating without microcapsule loading as a control. It was found that the hardness value was reduced as the microcapsules were incorporated into the coating formulation in 5% JPUA and 10% JPUA. This trend continuously declined as the coating was thickened from 50 μm to 100 μm, 150 μm and 200 μm in the self-healing coating containing microcapsules. For the adhesion test, Control samples at all of the testing thicknesses showed a 4B adhesion score where less than 5% of the area was removed. A similar grade was displayed by 5% JPUA at 50 μm. The remaining samples indicated deteriorated adhesion properties as the film thickness increased and microcapsule loading increased. The 10% JPUA at a thickness of 200 μm showed the worst adhesion property with 15% to 35% of the removed area. As a conclusion, self-healing coating with 5 wt% loading of JO and JPUA-IPDI-based microcapsule with thickness of 50 μm has maintained the hardness, adhesion, haze, and transmittance properties when compared with the control sample.