Wood-based materials weathering

The weathering process described thus far has been for solid wood. The introduction of another variable, the adhesive, in the weathering of wood-based materials such as plywood and particle board creates additional complications. Wood substance is still ex-... 

Aydin, I. Colakoglu, G. The Effect of Steaming and Veneer Drying Temperature on the Weathering Reactions, Wood-based materials, wood composites and chemistry, International Symposium. 2002, pp 1-9. 

Hazarika and Maji 2013a, b, 2014a, b, c, d). Dimensional stability, UV protection, and weather resistance are very significant properties for wood-based materials used in exterior applications. Bio-based wood polymer nanocomposites will have superior properties and can be regarded as high-performance material for the future generation. 

Polymer based materials (wood, plastics) used in the exterior of buildings and in construction have a service life determined by their exposure to UV radiation from sunlight and consequently their farther deterioration through weathering process. Both climate changes which determine a substantial temperature increment, as well as increasing of the UV radiation levels, mainly UV-B radiation component, cause a significant diminution of service life for such materials in outdoor applications. 

Problems and facts that in the author s personal experience arise in the industrial application of tannin-based adhesives for timber sometimes indicate lack of correspondence with laboratory practice and results. These are often problems related to unusual characteristics of the adhesive itself, or of its application technique, which could not be noticed during research under laboratory conditions, but the existence of which could easily jeopardize successful implementation of laboratory technology into industrial practice. Correcting the credibility gap between research focus and industrial usage is seen as a critical step toward market expansion for these new products. Important considerations are consistency of tannins, extracts and adhesives properties due to the natural raw material variability formulation in cold-setting adhesives and application conditions (such as wood moisture and adhesive-content or pressing time) in particleboard adhesives. These problems have been overcome in use of wattle tannin-based adhesives as shown by a visual comparison of tannin-, phenolic-, and melamine-bonded particleboards exposed to the weather for 15 years and the growing use of tannin-based adhesives in other countries. 

The treatment of wood to reduce or eliminate the effects of weathering could potentially open up new market opportunities for wood as a material and research has therefore targeted chemical pretreatments that might provide such benefits. Chromium-based pretreatments are particularly effective in this regard but, presumably for environmental reasons, such systems have generally not been adopted by industry and the search continues for effective, low-toxicity photostabilizing agents for wood. 

UV absorbers generally decrease the oxidative degradation of plastics and plastic-based composites. However, they do not always significantly change the fading of WPC materials. For example, wood flour (50% w/w, 40 mesh)-fllled HDPE (MFI 0.72) after an accelerating weathering in a box for 3000 h increased its L value by 115% after... 

Rubber composites made from NR are used in adhesives. This investigation is concerned with the preparation of rubber blends based on NR and PMMA because incorporation of PMMA into the NR phase may lead to materials with improved strength, clarity and weather resistance and could be used in automotive and other applications. Rubber composites from NR and PSf containing cofibre could be expected to find use in artificial wood applications, cups and picture frames, as shown in Figure 13.53. 

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