Effect of microwave treatment on the wood structure of Norway spruce and Radiata pine

Low permeability of many wood species causes problems during timber manufacturing, including long drying times, 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, use of low permeability wood results in shallow chemical penetration, and it requires the use of small-sized chips, high chemical usage, and high-energy consumption. Microwave (MW) wood modification technology can provide solutions to many of these problems. The wood structural changes in Norway spruce and radiata pine after MW modification with 0.922 and 2.45 GHz of were investigated. High intensity MW application (specific MW power 22 to 25 W/cm3, applied energy 79 to 102 kWh/m3) to moist wood caused the following wood structural changes: pit opening and pit membrane rupture; middle lamella weakening and rupture; and ray cell wall destruction and check (voids) formation mainly in the radial-longitudinal plane caused by the destruction of rays and weak middle lamella regions. Microwave destruction of different wood structure elements provided a significant increase in wood permeability for liquids and gases. Knowledge of the effects of MW treatment to the wood structure elements allows assessment of opportunities for the use of microwave irradiation in wood technology