Effects of wet-heat treatment on the performance of waterborne paint film of Fraxinus mandshurica

Objective When Fraxinus mandshurica wood is used in the fields of furniture, interior decoration and architecture, it is often protected by surface coating. However, the adhesion of waterborne paint coating is limited. In order to improve the adhesion of waterborne paint coating on the surface of F. mandshurica, we conducted a wet-heat pretreatment on F. mandshurica and tested the effect of this pretreatment on other coating properties of waterborne paint coating.

Method Using F. mandshurica wood as the substrate, it was subjected to a wet-heat pretreatment, and the surface roughness, glossiness, and chromaticity were tested. Then, it was painted with waterborne paint. After the paint film was fully cured, the adhesion improvement effect of waterborne paint was quantified through a 180° peeling test. The influence of wet-heat treatment on the thermal and cold resistance of paint film was also studied. In addition, infrared spectroscopy and electron microscope were used to explore the mechanism of the treatment in improving the adhesion of waterborne paint on the substrate surface.

Result The thickness of the paint film was 110.8 μm after the wet-heat treatment. Compared with the untreated sample, this pretreatment can effectively improve the surface roughness of the substrate, and the peel strength of the paint film after coating increased by 120.0% and the thickness increased by 14.6%. The water resistance grades of the untreated and treated samples were the same, which showed that the quality of the paint film was not reduced by wet-heat treatment. Further analysis showed that the peak strength at 1 734 and 1 604 cm⁻¹ decreased, which indicated that the degradation of lignin was caused by wet-heat treatment, and that the peak strength at 1 728 and 1 050 cm⁻¹ decreased, which indicated that the degradation of hemicellulose was also caused by wet-heat treatment. These changes led to the increase of surface roughness and porosity of the substrate, thus improving the adhesion of waterborne paint.

Conclusion Wet-heat treatment is an efficient and environmentally friendly pretreatment to improve the adhesion of waterborne paint on the surface of wood substrate, which can improve the protective ability of waterborne paint on the surface of the substrate while maintaining other properties of the paint film.