Combined Densification, Drying And Thermal Modification Processing Of Pinus Sylvestris By Hot-Pressing:An Integrated Approach

In order to improve the physical and mechanical properties of Pinus sylvestris timber, the paper used the plate hot-pressing method to finish the modification of wood of drying, densifying and heat-treating. We also investigated the effects of compression ratio, drying temperature, heat-treated temperature and heat-treated time on the mechanical properties of treated wood by using the orthogonal experiment method. According to the analysis results of treated wood density, equilibrium moisture content, water absorption, shrinking and swelling ratio, hardness, MOR and MOE, we determined the best technology.Then, we not only studied the mechanical properties, but also discussed the changes of the stress relaxation and FTIR and XRD under the different experimental conditions. The main conclusion of the study was followed:1. We choiced the sawn lumber for the test material, compressing the plate in three-stage process with the position control technology. The drying process had been carried with a perforated plate, and when it was the moisture content of 10%,we began to heat treating. The experiment used the PressMAN to test the internal temperature changes in wood by on-line monitoring in order to control the heating time.2. When the compression ratio was 50%, the drying temperature was 160℃,the heat-treated temperature was 200℃ and the heat-treated time was 3h, the process was the best.3. Compared with the control, the mechanical properties of treated wood were increased significantly; with the compression ratio and the drying temperature increasing, the mechanical properties of the test material were improved to some extent; with the increase of heat-treated temperature, the mechanical properties were increased first and then decreased.4. By analysising the sylvestris tensile stress relaxation of the different factors, the results stated the internal bond strength had been increased, the residual stress had been decreased slowly which was not prone to relaxation exercise, the relaxation rate was small, and the mechanical properties were significantly improved.5. By the FTIR analysis of heat-treated wood, we found with the heat-treated prolonging the chemical reactions occur strongly, increasing the degree of hydroxyl group and carbonyl group of reduction in the absorption intensity obviously. The heat-treated time was prolonged so that the chemical reactions inside the timber were more complete.6. Under different heated treated temperature conditions, the crystallinity showed a decreasing trend after the first increase, and the heat-treated time had the same effect on the change of crystallinity of cellulose. Compared with control, the crystallinity of cellulose of different heat-treated temperature and time were increased greatly.