Study On The Procedure Of Densification Of Laminated Veneer Lumber Of Fast-growing Trees

In recent years ,with the depletion of worldwide natural resources ,the implementation of Natural Forest Protection Project and the people'growing demand for wood and wood products,the utilization of wood species out of plantation forest has become the main solution to deal with the contradiction between the growing demand of wood and the lack of forest resource. Fast-growing lumber are increasingly becoming the main raw material of wood industry,playing a significant role in providing wood supplies. Therefore, in the current and over the long term, the development and utilization of fast-growing lumber in wood industry in China will be a further development.The fast-growing lumber pinus and fir wood were used as the research object to manufacture low molecular weightimpregnated melamine modified phenolic resin in this paper . The pressure impregnation treatment and orthogonal experiment were used to carry out the hot pressing of laminated veneer lumber . This paper studied the main physical and mechanical performance of densification of laminated veneer lumber produced by different impregnation methods and hot pressing , investigated the various factors significant effect on the properties of densification of laminated veneer lumber. We got the results as the follows:(1)The optimum molar ratio of low molecular weightimpregnated melamine modified phenolic resin was that the molar ratio of formaldehyde, phenol and sodium hydroxide was 2:1:0.08, The content of melamine was 20% of the phenol content.The viscosity of low molecular weight phenolic resin produced by this synthetic process was low, color of resin was lighter, free formaldehyde and free phenol content were less, water combination was well ,the low molecular weight phenolic resin was very suitable for impregnating veneer.(2)The weight gain rate changed with impregnation conditions changed in 30% concentration phenolic resin.As the impregnating time prolonging weight gain rate increased at the conditions of normal or pressure. In the same impregnation process using different concentrations, the wet weight gain rate first ascended and then descended with the change of concentration , but the dry weight gain rate increased with the concentration increased. The density of strengthened laminated veneer lumber increased with the weight gain rate increased under different impregnation process;The TS and 24 hour water absorption of laminated veneer lumber decreased gradually. Weight gain rate significantly affected the static bending strength and modulus of elasticity of strengthened laminated veneer lumber. MOE and MOR separately were 15659.4MPa, 127.43MPa when the wet weight gain rate was 164.8% , which reached and exceeded Japans structural LVL standard 14OE(14GPa)and180E(67.5MPa) respectively.(3)There were many factors effect on the properties of densification of pinus laminated veneer lumber during the production process.The study of the factors showed that: compression ratio, veneer moisture content and hot pressing time significantly affected the properties of densification of pinus laminated veneer lumber ,but drying temperature and pressing temperature had no significant effect on the properties of densification of pinus laminated veneer lumber. The study of various factors in multi-level showed that: when manufactured pine laminated veneer lumber by impregnating resin manner, suggested that the hot-pressing procedure parameters were : dry temperature 60℃,compression ratio30%, pressing temperature140℃, pressing time 24 min ,moisture content of veneer16%. And it could be chose according to the requirements of the product last utilization and the final properties .(4)The parameters of the hot pressing to manufacture densification of fir laminated veneer lumber were :dry temperature 60℃, compression ratio 35%, hot pressing temperature 145℃, hot pressing time 24min.The parameters of the hot pressing to manufacture densification of pinus and fir wood composite laminated veneer lumber were: dry temperature 60℃, compression ratio 40%, hot pressing temperature 145℃, hot pressing time 24min.