Research On Dielectric Properties Of Wood And Plywood

The quality of wood is mostly decided by the defects of timbers. Those defects make wood become lower level. In order to improve the quality of wood and economic benefits, it is important to choose a reasonable detection methods of wood defect.On the basis of expounding the research progresses of dielectric properties in testing wood properties in abroad and home, the dielectric properties of wood and plywood had been investigated to detect the quality of wood and plywood in the paper. Then, it was found main factors which effect the qualities were moisture content, grain direction, heart sapwood, frequencies, defects of wood and hot-pressing process parameters(such as glue content, pressing pressure, pressing temperature) of plywood.The results were summarized as follows:1. The investigations of dielectric constants of wood and influencing factors: Dielectric constants is influenced by moisture content, wood grain, density and frequencies of electric field. The study shows that: Firstly, Moisture content in wood is the most important factor, and the dielectric properties increase with rising moisture content within the ranges studied. Secondly, the dielectric parameters parallel to grain are higher than those of the transverse direction, while the radial dielectric properties are similar to tangential ones. Thirdly, within a certain ranges of frequencies, the dielectric constant reduce as frequencies increase. Fourthly, wood with bigger density normally have higher dielectric constant. When the wood densities reach 1.53g/m3 of wood substance density, the dielectric parameters are maximum. Fifthly, The dielectric constants of heartwood is a little higher than those of sapwood, and dielectric constants reach the maximum at pith.2. The investigations of influences of wood defects on electric constants: The holes reduce the dielectric properties of wood. There is a linear negative relationship about the area of holes and dielectric parameter, just the opposite, it has a linear positive correlation about the diameter of knot and dielectric parameter.3. The investigations of influences of Hot-pressing technology parameters on dielectric constants for plywood: The dielectric constants of plywood increase with the increasing of glue content and hot-processing pressure. And the influences of hot-pressing temperature on dielectric parameters is not very significant. In addition, the layers of adhesive play an important role in the increasing of dielectric parameters.4. The investigations of influences of defections in the wood and plywood: According to the study about dielectric properties of lumber and plywood, non-destructive testing are conducted, finally analysis out the wood defects(holes, knob) and the quality of the plywood. The research results of this paper will has higher theoretical significance and application values to test the defects of wood and plywood.