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Basic information about a final thesis
|Type of thesis:|
|Microwave modification of wood|
Written by (author):
prof. Ing. Jozef Kúdela, CSc.
|Opponent 2:||Dr. Robert Nemeth|
|Opponent 3:||doc. Andreja Kutnar, PhD.|
Final thesis progress:
Final thesis was successfully defended.
Additional informationAdditional information about the final thesis follows. Click on the language link to display the information in the desired language.
Language of final thesis:
|Title of the thesis:||Microwave modification of wood|
|The microwaves as a rapid and highly effective heating was well-established in society and was recognised as potentially useful method for many industrial applications. On the contrary, wood modification using microwave (MW) energy is not very common. Therefore, the main motivation of this thesis was to enhance the knowledge about the utilization of MW treatment in wood technology. The aims of this thesis can be divided into two main tasks. In first task the author has been intended to develop, analyse and optimise various MW modification techniques. The second task investigates the relationship between MW modification techniques and selected physical and mechanical properties of treated wood. The basic information and theoretical background as well as the application of MW heating were given in the introduction and literature review. The experimental part consisted of several investigations dealing with MW wood modification. These investigations were focused on the improving of the permeability and impregnability, pre-drying, plasticization, and acceleration of chemical reactions. Differences between particular modification treatments can be found in the power levels and duration of treatment. Within the work, the different wood species i.e. European beech (Fagus sylvatica L.), hybrid poplar (Populus hybrids) and Norway spruce (Picea abies L.) have been studied. The effect of MW radiation on the fluid permeability and compression strength parallel to the grain was investigated in the first experiment on the beech false heartwood. The treatment was performed in discontinues MW device in different modification modes. The coefficient of specific permeability was calculated using Darcys law and results showed the increase of specific permeability by 159%. On the contrary, the compression strength parallel to the grain decreased by up to 15%. Following experiment evaluated the influence of MW modification on impregnability of wood. The evaluation of impregnability was calculated by weight percentage gain (WPG). The samples exposed for shorter time intervals showed the improvement of impregnability (WPG 33.84%). On the contrary, samples treated for longer time results lower substance uptake. Investigation dealing with wood pre-drying was performed using a continual laboratory MW device, which was developed for the wood modification purposes. The effect of MW radiation on moisture loss, surface temperature, and mechanical properties of Norway spruce (Picea abies) has been studied. The results indicated that by using low power mode and fast conveyor speed the mechanical properties of the material will be maintained. On the contrary high power mode and slow conveyor speed will have a negative impact on the changes in the wood structure and the mechanical properties when high initial moisture content (MC) of wood is used. Investigation of MW plasticization was focused on wood densification and following application of material for flooring system purposes. The plasticization treatment was performed in different power modes. The results showed the influence of the chosen power mode on moisture decrease and rapid temperature increase, which had significant effect on plasticization and following densification process. This investigation was followed by experiment which evaluated the efficacy of MW plasticization by microstructural analysis using a scanning electron microscope (SEM) and by density profiles measurement. Results showed uniformity of density profiles through samples thickness which confirmed even plasticization in sample volume. Microscopic structure observation revealed that the MW plasticization was not accompanied with any fractures and that deformations present in the densified wood were due to viscoelastic buckling of cell walls without cracks propagation. The investigation dealing with MW acceleration of chemical reaction has been carried out in the process of wood acetylation. Beech (Fagus sylvatica L.) and poplar (Populus hybrids) wood were impregnated using acetic anhydride, and chemical reactions were initiated by MW and conventional heating. The results showed that no significant differences were found between conventional (60 min) and MW heating (15 min). From this point of view, the MW heating can reduce the reaction time and make the process more effective. This investigation should provide a better insight into details of the MW wood modification and could became a basis for future research.|
bending strength, SEM , impregnability, drying, permeability, modification, densification, acetylation, dimensional stability, temperature, plasticization, density, compression strength, microwave, high-frequency energy
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