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The objective of this study is to determine optimum parameters for double dowels in medium density fiberboard components, and the maximum value of the strength of joints loaded in tension and compression bending. This study analyzes dowel diameter, clearance or interference fit value, and dowel spacing by using the orthogonal experiment method. Optimum parameters for double dowels in medium density fiberboard component structures were obtained by orthogonal experiment and verified by simulation using ANSYS finite element analysis software. Experimental and simulation-based results revealed that the optimal parameters for double dowel joints with maximum tensile strength were a dowel diameter of 10mm, an interference fit of 0,20mm, and a spacing of 64mm.The optimal parameters for double dowel joints with maximum bending strength were a dowel diameter of 10mm, an interference fit of 0,10mm and a spacing of 48mm.

In this study, different molar of methylolureas (MMU) were used to improve the properties and drying speed of the raw lacquer (RL). The drying time, gloss, pencil hardness and impact resistance of the lacquer film were tested. The thermal behaviors and chemical structures of the lacquer membrane were also discussed by thermal gravimetric analysis (TGA), fourier infrared spectrometer (FT-IR) and nuclear magnetic resonance (NMR) analysis, respectively. The results demonstrated that lower molar ratio MMU can significantly improve the properties of lacquer. The TGA analysis showed that the modified lacquer had high thermal stability than that of the control. The FT-IR and 13C NMR analysis revealed that the structures of the modified lacquer were significantly improved by cross-linking with the hydroxymethyl groups and methylene methyl ethers of MMU. In addition, through scanning electron microscopy (SEM) characterization, it was found that the introduction of MMU can effectively improve the surface smoothness of the lacquer film.

Using CiteSpace software, a comparative analysis method and a quantitative analysis method were used to visually analyze 912 articles in the field of wood defect knots in the CNKI total library from 1980 to 2019. And built a knowledge map in the field. Including research hotspots, annual publication volume, core author groups and major research institutions. Research indicates: From 1980 to 2014, the annual publication volume tended to rise, reaching the highest peak in 2014, but after 2014, the annual publication volume showed a significant downward trend. The research topics of 1980-2019 knots mainly focus on “wood defects”, “non-destructive testing”, “neural networks”, etc. Wang L H, Hao J C and Ye N, etc. are the main authors. Northeast Forestry University, Institute of Wood Industry and Chinese Academy of Forestry, etc. are the main publishing institutions. Forestry machinery and woodworking equipment and journal of Northeast Forestry University, etc. are the main journals of knots, and the National Natural Science Foundation of China is the fund project that invests the most in researching knots. Through the visual analysis of CiteSpace, we can know that in the future, we should use advanced technology to conduct in-depth research on the chemical properties of knots. Develop a variety of detection methods to organically combine to improve the non-destructive detection results of knots, enhance the cooperation of authors, institutions and funds to communicate, and build a database for this research.

The quantitative comparison of essential oils extracted from various parts of Cupressus funebris and Juniperus chinensis was studied. With increased height, the content of essential oils from branches decreased, while the content of essential oils from leaves increased for both species. A maximum amount of essential oils were found in the west and a minimum in the east of branches and leaves for the two species. Moreover, the content of essential oils in trees with a knot was higher than in those without a knot. The order of essential oil content was as follows: leaf > fine root > coarse root > bark > bough > branch > trunk in C. funebris, and leaf > fine root > bark > coarse root > bough > trunk > branch in J. chinensis. The essential oils extracted from various parts of C. funebris and J. chinensis were analyzed by gas chromatography-mass spectrometry. A total of 67, 33, 69, 65, and 69 components were identified from the roots, trunks, barks, branches, and leaves of C. funebris, respectively. A total of 72, 46, 79, 55, and 82 components were identified from the roots, trunk, bark, branches, and leaves of J. chinensis, respectively.

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The effects of wood knots of Chinese weeping cypress (Cupressus funebris Endl.) wood on selected physical and color properties were investigated. Thirty samples of live knots, dead knots, and clear wood groups were selected for experiments to determine the physical properties of wood density, wood shrinkage, wood swelling, and wood color. The experimental analysis results showed that the wood density values are in the order: dead knots > live knots > clear wood, with a significant difference in wood density between different groups (p < 0.01). In addition, the values of the air-dry volumetric wood shrinkage, air-dry volumetric wood swelling, oven-dry volumetric wood shrinkage, and oven-dry volumetric wood swelling ratios are in the order: dead knots > live knots > clear wood, being consistent with a variation in wood density. Three groups of wood colors were provided: the color of clear wood is light, the color of live knots is reddish, and the color of live knots is blackish, in relative terms. The chromatic aberration between the three groups can be identified, and the wood color difference resulted from the discrepancy in the lightness index.