Dynamic Viscoelastic Properties For Wood Treated By Different Drying Methods

In order to investigate the effect of drying methods on physical and mechanical properties of wood, and provide theoretical basis and scientific instructions for drying techniques, techniques processing and highly additional value materials of plantation wood, the dynamic viscoelastic properties of wood treated by high temperature drying (HTD, 115℃), low temperature drying (LTD, 65℃) and freeze vacuum drying (FVD) methods were studied respectively in this study.Dynamic viscoelastic properties of wood treated by three drying methods were examined under completely dried state, and dynamic viscoelastic properties of drying treated wood and untreated wood were also examined respectively under various equilibrium moisture contents. The effect of water on dynamic viscoelastic properties of both drying treated and untreated wood were discussed, and the apparent activation energy of two mechanical relaxation process were calculated. The dynamic viscoelastic properties in longitudinal, radial and tangential directions were also investigated, the reasons for differences among three directions were analysed. The sameness and difference of dynamic viscoelastic properties of both drying treated and untreated wood were finally investigated under single cantilever bending mode and tension mode. The main research results are summarized as follows:(1) The storage modulus of drying treated wood and untreated wood were decreased with temperature increasing, and this trend was almost not affected by moisture content, testing frequency, structural direction and strain mode of wood. The decreased extent of storage modulus of HTD specimens were lower than that of the other two drying treated wood and untreated wood with temperature increasing, and the decreased extent of FVD specimens were maximal. The results indicated that the rigidity of wood were increased after HTD, the reason was that the possibility of crosslink reaction or crystallization in wood cell wall during drying process. To some extent, the reason why rigidity decreased was possibly that the cell wall destroyed during FVD process. With moisture content increasing, the decreased extent of...