Study On Properties And Preparation Of Reconstituted Lumber Made Of Resin Impregnated Veneer

The reconstituted lumber made of resin reinforced veneers selected low density wood species especially plantation as raw materials, was manufacutured from veneer preparation, dyeing, resin infusing, forming and hot-pressing to a new kind of wood-based reconstituted lumber. Dyeing induced imparting wood with fancy color and clear surface texture, thereby greatly enhancing the decorative effects of wood products in service; resin infusing could improve density, fracture strength, abrasive resistance, water-proof ability, weathering resistance, dimensional stability of the reconstituted lumber. This study will provide a new method for the high value-added utilization of plantation, solve the contradiction between supply and demand of expensive wood species, expanding the plantation timber utilization.In this paper, poplar (Populus×canadensis cv.'Sacrou 79') and birch (Betula platyphylla Suk.) were selected as the raw materials, melamine-formaldehyde resin(MF) was selected as adhesive,Thorough studies on resin impregnation techniques for wood veneers under atmospheric pressure and pressure-rolling process, reconstituted lumber was made by high-frequency hot-pressing process. An appropriate resin impregnation technique for wood veneers was put forward by Visual Basic (VB) and Matlab; Wood veneer-based computer color matching system was developed for color matching techniques and vein emulating; High-frequency hot pressing process was used to analyze the variation of temperature inside the mats for thick wood-based panels. In addition, variance analysis and multicomparison was used to analyze resin infusion, mat forming and pressure worked on properties of the reconstituted lumber.The main research results are summarized as follows:1. The pressure-rolling equipment was explored and prepared in this study. Roll pressure was found to facilitate resin impregnation into wood substance, which is faster and more convenient than the atmospheric pressure. In general, the weight percentage gain (WPG) of wood veneers was not found to increase throughout the impregnation process. For wood veneers 85mm×55mm and 360mm×180mm wide, 0.7mm-1.9mm in thickness, the WPG slowed down after 3 h of impregnation. The WPG of veneers showed an increasing tendency with the decrease of the roller gap. More specifically for the veneers of poplar, the maximum WPG of 89.15% was obtained for the process of atmospheric pressure impregnation, while the maximum WPG of 110.79% was obtained for the process of roll pressure based impregnation. For the veneers of birch, the maximum WPG of 48.89% was obtained for the process of atmospheric pressure impregnation, while the maximum WPG of 55.10% was obtained for the process of roll pressure based impregnation.2. During the process of impregnation, the resin entered wood veneers mainly along the longitudinal direction, and this also occurred along the transverse direction. The resins infused into poplar veneers were mainly distributed within the vessels, and also in the xylon adjacent to the vessels, resin in birch was almost in vessels. WPG of poplar was much more than birch. For wood veneers 360mm×180mm wide and 0.7mm-1.9mm in thickness,the resin could arrived in centric position after 7h of immersion or the roller gap was set to 0.4mm. resin was more even by rolling than immersion so that resin could reach the centric site.3. Generalized neural network (GRNN) was established to predict the content of resin impregnated into veneers measured by weight percentage gain (WPG). GNN models included the relationship in the predictors such as wood species, veneer gain angle, veneer thickness, solid content of resin, impregnation time of resin and roller gap, and the dependent variable WPG. Correlation coefficients was over 93% and mean relative errors was less than 10.2%.4. Base on the computer-aided color matching system for printing and dyeing in textile industry, a corresponding computer-aided color matching system for wood dyeing application was developed. The most economical dyeing solution for wood veneers could be calculated automatically and the quality of color matching could also be guaranteed. Compared with the commonly used man-made color matching, the computed-based color matching system was more efficient, economical and convenient. Based on the established database for poplar and birch, the developed color matching system was used to carry out imitation of precious wood species such as Dalbergia fusca Pierre, Dalbergin bariensis Pierre and Juglans. It was found that the imitated wood colors were comparable to those of natural precious wood with 0~2 times of uniformity, they had litle color distribution and small color differences.5. For the process of high-frequency hot pressing of the reconstituted lumber, power function was appropriated in describing the variation of temperatures inside the mats as a function of time. Besides, fourth order polynomial function also performed well in describing the relationship if only the regression performance of functions was considered. In length-width direction, the temperature may be different in heating process due to the moisture content. However, when the temperature surpass 100℃, temperature will gradually become stable. Along the direction of the thickness, the highest temperature was observed neither at the middle nor the surface layers of mats in high-frequency electric field, it occurred somewhere close to the positive plate, and the lowest temperature occurrrd near the negative plate.6. When thickness of mat was exceeded over 30 mm, high-frequency hot pressing could reduce press time considerably, and greatly improve the production efficiency. When the moisture content of mats was constant, the factor that influenced the temperature elevation most during high-frequency heating was hot-pressing pressure. When the pressure was elevated from 1.0 MPa to 2.5 MPa, the pressing time needed for mats of 47 mm thick reduced from 35 min to 7 min. In addition, thicker mats appeared to result in more hot-pressing time needed when the other conditions were kept constant. It was also found that the content of resin impregnated into wood veneers had no significant effect on hot-pressing time. The order of these factors on the physical and mechanical properties of the lumber was: wood speices>hot-pressing pressure>WPG>method of impregnation. Different immersion method had different influence on physical and mechanical properties.7. The reconstituted lumber achieved in this paper can be designed according to the requirement of different products by structure design, resin control and unit pressure and so on. Different properties of reconsititued lumber was achieved with the density from 0.44g/cm3 to 0.91 g/cm3, MOR was 32.16MPa~80.40 MPa, MOE was 3.64GPa~9.48MPa, TS was 4.97%~1.03%, water absorption rate was 19.33%~7.88%, shear strength was3.39MPa~12.27 MPa, and hardness was 15.84MPa~57.88MPa, respectively. Parameters control could change the properties of reconstituted lumber, it could satisfy requirements of flooring, decoration, gymnasium equipments and other handcrafts.