Painting properties and lightfastness of microwave puffed wood-based metal composites

Objective Puffed wood-based metal composite (PWMC) is decorative metallic wood material with a high thermal conductivity and moderate density. To provide technical reference for its future high value-added applications in the fields of interior decoration and household wooden products, the research on painting properties and lightfastness of PWMC had been carried out in this paper.

Method Waterborne polyurethane paints were coated on PWMC surface. We studied the effect of painting number on the colorimetric parameters and gloss. The relationship between sandpaper grit and film adhesion was investigated by comprehensively analyzing the surface roughness parameters. Meanwhile, the surface color changes and gloss loss rate were characterized after 720 h artificially accelerated UV ageing treatment. The photodegradation mechanism was also analyzed by comparing the surface chemical structures.

Result Clear varnish finishes play a dual role of protection and decoration for PWMC. After the three-primers and two-topcoats painting treatment, the total color difference values of PWMC, wood area, and metal area were 10.26, 9.07 and 3.22, respectively. It indicated that the color variation of the wood area was larger than that of the metal area. The gloss value difference between wood and metal areas decreased from 17.7 to 2.3 after painting, representing that the painting treatment resulted in a more uniform surface gloss. The roughness parameters of PWMC wood and metal areas were similar when sandpaper grit was 240. It maintained a flat and homogeneous surface, thus PWMC had a best paint film adhesion (level 0). Under artificially accelerated UV ageing of 720 h, PWMC wood area changed to greenish-yellow, and the lightness of wood and metal areas increased. The colorimetric parameter changes and light loss rate of wood and metal areas were reduced after painting. It confirmed that the enhancement of waterborne polyurethane paints on the lightfastness of PWMC. Infrared spectroscopy and X-ray photoelectron spectroscopy showed an increase in the oxidation state of carbon atoms, indicating oxidative degradation happened in PWMC wood area and coating paints under light irradiation.

Conclusion The painting properties and lightfastness are investigated, providing a theoretical and technical basis for the value-added utilization of PWMC.