School of Agriculture, Food and Ecosystem Sciences - Theses

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    Factors affecting microwave modified wood permeability and strength
    Aitken, Leigh ( 2013)
    Microwave treatment can be used to increase wood permeability, speeding subsequent drying or impregnation processes with potential savings in time, energy and cost. However microwave treatment can reduce the strength of the treated timber. Treatment pressure can be used to alter the boiling point of water, which could have a significant effect on the resultant strength and permeability. Three methodologies were used to investigate the relationship between microwave treatment conditions, in particular pneumatic pressure, and the resultant strength and permeability of the timber. A device was designed and constructed with the aim of enabling the simultaneous measurement of the permeability of small cylindrical samples during microwave treatment. Testing of the individual components proved successful, however moisture vapour generated during microwave heating of the timber samples presented problems during combined testing. Permeability measurements were performed separately in the second and third methodologies and utilised larger samples. Controlled temperature and controlled power density treatments were trialled with the controlled power density treatment providing more consistent results. Bending testing and an impregnation cycle were found to be the most reliable methods of assessing strength and permeability respectively. High power microwave treatment increased the permeability and reduced the strength of the treated timber. Treating the samples under elevated pressure, followed by an immediate pressure delta minimised this strength loss. A ranking system was proposed to assess the combined strength and permeability resulting from treatment. Using this ranking system, an optimum balance between high permeability and maximum strength was obtained using a high power, Elevated Pressure Microwave treatment followed by an Immediate Pressure Delta (EPMIPD). This treatment performed better than atmospheric pressure microwave treatments conducted as part of this research.