Microwave Modification of Wood Properties

High intensity microwaves have been used to generate steam pressure in green timber. This results in the rupturing of un-lignified ray tissue and pit membranes in radiata pine, the generation of micro-voids at the ray/fibre interfaces, and the rupturing of tyloses in hardwoods. The degree of modification varies with the intensity of microwaves applied. At low levels, micro-voids are created that cannot be seen, but nevertheless have a major impact on the drying properties of the wood. In addition, there is relatively little strength loss. At very high microwave intensities, the micro-voids expand to become visible; the wood expands in cross-section and becomes very permeable and the strength properties are reduced substantially. However, the high permeability of the wood is exploited by impregnating the wood with resins and other chemical modification agents. The wood is then pressed back to its original dimensions and cured. The resulting properties include improvements in durability, dimensional stability, strength, hardness and other aesthetic characteristics. The technology appears to be suitable for hardwoods and softwoods alike.