| This thesis studies transverse compressive deformation recovery rate and recovery mechanism of five representative species in China and Japan (Ussuri Poplar, Larch, Common Chinese Fir, Japanese Cedar, Whiteleap Japanese Mangnolia) by four physical treatment methods. It stresses on the influence of each treatment method on compressive deformation fixation as well as their impact mechanisms. ASE, WL, density, change of colors, mechanical strength property of processed samples is tested. On the basis of above, it analyzes the influence of factors which affect the result of compressive deformation's fixation on physical & mechanical properties and puts forward the reasonable process parameters for compressive solid wood, which is a theoretical guidance on manufacturing of compressive wood. Moreover, it gives the research prospects of compressed wood in future. Therefore this research has great significance.Four physical treatment methods employed in the experiment are usual-pressure-cooling treatment, heat treatment, water steam treatment before compression and water steam treatment after compression. In compressive experiment, the sample size is 10×30×30mm. The compression set is about 50%. In strength property experiment, the sample size is 150×15×5mm. The span is 100mm. Samples destructive strength, deformation are measured. MOR and MOE are calculated after that. In ASE and WL experiment, the sample size is 5 × 30 × 30mm. Samples size and weight are measured after treatment. ASE and WL are calculated later. By analyzing experiment data, we find that compressive deformation would be fixed after more than ten minutes' high temperature, high-pressure treatment or a few hours' heat treatment, while the effect of usual-pressure-cooling is not remarkable. During the process of heat treatment and water steam treatment, the mechanical strength property will go down with time and change of colors. ASE and WL will go up with time. On the condition of heat treatment, MOR will first go up then go down with time. On the condition of water steam treatment before and after compression, MOR will go down with time. During the usual-pressure-cooling treatment, the recovery rate of Common Chinese Fir is 29%, which is the lowest, while that of Whiteleap Japanese Mangnolia is 65%, which is the highest. During the heat treatment, the recovery rate of Japanese cedar is 2.1%, the lowest one, while that of Whiteleap Japanese Mangnolia is 11.6%, the highest one. During the water steam treatment before compression, therecovery rate of Ussuri Poplar is -3%, the lowest one, while that of Common Chinese Fir is 6.7%, the highest one. During the water steam treatment after compression, the recovery rate of Ussuri Poplar is -3%, the lowest one, while that of Larch is 11.6%, the highest one. Through thermodynamic experiment study, loss angle tangent, dump modulus and loss modulus of Ussuri Poplar and Larch samples after heat treatment and water steam treatment are analyzed.According to the theory of stress-strain relationship of transverse compressive deformation and wood rheological character, it studies the factors about deformation permanent fixation caused by different methods, and analyzes the component change of wood cell wall caused by four physical treatment methods in this experiment. According to the newest research achievements, it is thought that the absolute release of deformation stress and the effective formation of cohesion inside wood are the main reasons of compressive deformation's permanent fixation. Through analyzing the contents of lignin, semi-cellulose, their softening and degradation degree of each treatment, we discover that the degradation of semi-cellulose is both the main reason of inside stress release and a main aspect of decreasing the compressive deformation's recovery rate. Lignin's softening, flowing and the formation of cohesion is another main aspect that decreases compressive deformation's recovery rate. Excessive degradation would cause the decrease of wood mechanical strength property.
|
PDF Full Text Request