High-intensity microwave wood modification for increasing permeability

Low permeability of many wood species causes problems during timber manufacturing including very long drying times, large material losses after drying, and expensive drying processes. Impregnating low permeability timber with preservatives and resins is extremely difficult. In the pulp and paper industry, a low permeability wood results in shallow chemical penetration, requires the use of small-sized chips, a high chemical usage, and high energy consumption. New microwave (MW) technology provides solutions to many of these problems. Experimental studies into M W wood modification at 0.922 and 2.45 GHz revealed a dramatic increase in wood permeability when MW power is applied in the range of 250 to 1200 MJ/m(3). Physical and mechanical characteristics of modified wood also change. MW process parameters were developed to provide reproducible levels of timber modification taking into consideration variations in species, size, and moisture content which provided a sound foundation for the new technology. Research results demonstrated that this technology could be applied to any wood species. The following commercial applications were identified: the treatment of refractory wood species with preservatives, rapid drying of hardwoods, growth and drying stress relief in timber, and manufacturing of the new wood materials Torgvin and Vintorg. Additionally improvements in wood pulping properties could be obtained through MW modification of sawn timber, logs, and chips. The cost of AU$28 to $69/m(3) for MW conditioning is acceptable to the industry and provides good commercial opportunities.