Surface characteristics of coated soft- and hardwoods due to UV-B ageing

Wood is a valuable building material, but it is susceptible to degradation if left unprotected especially when using less durable species. Protection is commonly achieved by applying a suitable finish that should exhibit sufficient penetration, good adhesion and resistance to photo-degradation and weathering. The performance of wood coatings is largely influenced by the adhesion between the coating and substrate and any degradation of the substrate will also affect the coating. The aim of this study was to determine the degree to which the substrate degrades despite the coating and adds to the ageing of the coating from the interface. This effect can be expected to differ for soft- and hardwoods. Coated wood samples from pine and meranti wood - a soft- and hardwood - were irradiated with UV-B light to detect surface changes at various length scales and to assess the impact of the underlying wood substrate on the ageing performance of a commercially available acrylic coating. Surface modifications were determined with atomic force microscopy, Fourier transform infrared spectroscopy, colour spectroscopy, static contact angle and a surface roughness profiler.