Wood Modification for Wood Protection

Abstract

Wood-based materials are used in variety of applications. It is a good engineering and structural material because of good mechanical strength, low thermal expansion, and esthetic appeal. However, being biological material, it is susceptible to environmental degradation. It is necessary to treat wood to provide specific properties depending on the intended application. A usual problem associated with wood during its outdoor application is degradation resulting from solar UV radiation. The degradation starts immediately after the wood is exposed to sunlight. All the constituent polymers of wood possess reactive -OH groups, which are hydrophilic in nature that results in its dimensional instability and makes it susceptible to microbial attack termed biodegradation. Wood changes dimension with changing moisture content because the hydroxyl groups present in cell wall polymers attract moisture through hydrogen bonding resulting in cell wall swelling. The process is reversible, and wood shrinks during drying process as it loses moisture. Wood undergoes biodegradation because organisms recognize the polysaccharide wood polymers (cellulose and hemicelluloses) and have very specific enzyme systems which can degrade these polymers resulting in strength loss. Traditional wood preservatives such as chromated copper arsenate (CCA) are under threat because of environmental concerns about leaching of copper, chromium, and particularly arsenic into the environment. Accordingly, there is a need to develop alternative more environmental friendly treatments to prevent such degradation. One of the viable methods is to chemically modify the wood to increase its hydrophobicity, thereby arresting biological attack. Wood modification is one of the effective methods to enhance durability of fast-growing timbers usually having low durability. With increased dimensional stability and resistance to microorganisms, modified wood can be an excellent choice for outdoor applications. This chapter describes the overview of wood modification technologies particularly the processes of thermal and chemical modification. Modified wood can be useful for many specific end uses including fencing, decking, wall paneling, etc. Modification of wood is one of the most effective methods to obtain dimensionally stable wooden product.