Delaminations Induced by Weathering in Wood andWood-Based Composites Panels

On our planet, there are probably more buildings such as residential, commercial industrial or farming constructed with wood and wood-based composites than any other structural materials. The widespread use of wood and wood-based composites in the construction of buildings has both an economic and aesthetic basis. The natural beauty of these products is difficult to match with other materials. The weathering durability of wood, wood products and wood - based composites is an important quality factor, essential for environmental friendly exterior uses in buildings. Weathering produces unfavorable quality changes such as discoloration, roughening and checking of surface or modification of physical and mechanical properties.Weathering of wood depends on many environmental factors and among them the ultraviolet component of sunlight is responsible for cell wall lignin depolymerization. This effect is amplified by reining water which erodes the surfaces exposed to weathering. The erosion process id very slow and was estimated to be of about 5 mm thickness decreasing of a board during 100 years of exposure in Northern Hemisphere. The erosion of the earlywood is always greater than that of latewood. The checks and delaminations at wood surface can be detected visually or automatically. Visual detection refers to the check length, width, depth or number. Modern methods use reflection of laser and fluorescent light to detect cracks at wood surface. The width of cracks has been determined with stylus profilometry. Automatic detection of checks at wood surface was performed using waveform analysis of the reflected digital image. Variation in the brightness profile of a board is also a good indicator of checks presence.