Microwave Wood Modification Technology and Its Applications

The use of microwave (MW) technology is growing in all industries. This increased use has resulted from the high efficiency of converting electricity into MW energy; energy savings associated with rapid, in-depth heating of materials; specific interactions that can be achieved between MW energy and materials; radical acceleration of technological processes; reductions in MW equipment costs; and improvements in the reliability of industrial MW equipment. The new technology of MW wood modification is based on the supply of high-intensity MW power, up to 135,000 kW/m3 at frequencies of 0.922 and 2.45 GHz. Such power induces significant changes to the microstructure of wood and a dramatic increase in wood permeability. A number of commercial applications have been developed based on the fundamental changes in wood structure. These include the treatment of refractory wood species with preservatives, rapid drying of hardwoods, relief of growth and drying stresses in timber, manufacture of the new wood materials Torgvin and Vintorg, and modification of logs, sawn timber, and woodchips for pulping. MW equipment and processing parameters have been developed for three applications that are ready for commercial use. The technology provides significant material and energy savings and will give a new impetus to product development in a very traditional industry. The costs of microwave timber processing range from AU$22 to AU$69 per m3. These costs are acceptable to industry and potentially provide wide appeal for use in the timber, biocomposite, and pulp and paper industries.