| Poplar(Populus spp.) was one important kind of fast-growing plantation woods which got developments greatly in China recently. As the qualities of poplar wood material had many defaults, the Laminated Veneer Lumber (LVL) manufactured by poplar veneer could not meet the requirements of some special applications, such as structural or supporting elements etc... This paper used poplar veneer as material raw which was phenol-formaldehyde (PF) resin impregnated and then pre-compressed; Tensile Strength (TS) parallel to the grain of the veneers were tested before and after compression; the influences of different lay-up types on the LVL products were studied, and the reinforced results of poplar LVL enhanced by glass fiber and bamboo curtain were investigated, then the temperature behaviors in the center ply of the poplar mat during the hot-pressing were measured.1. Poplar veneer could get well conventional of impregnation when the processing time was 30 minutes and the solid content of PF resin was 30% under the normal conditions. The raw impregnated should be dried at low temperature, the appropriate temperature was 40℃, and the time was 30minutes.2. As the pressure during hot-pressing was under 3MPa, the TS of the veneer increased with the pressure, and when the pressure was more than 4MPa, the TS of the raw decreased because the veneer was destroyed. The veneer could get well performance when the pressure was 3MPa, the temperature was 150℃and the time was 5 minutes during the hot-pressing.3. The sanding could enlarge the total surface energy of the veneer pre-compressed, compared with the veneer untreated, the veneer processed by sanding had the dispersion forces decreased and the non- dispersion forces which was the indicating of the polar surface free energy increased.4. The density of LVL products was positively correlated with the density of the veneer, and the maximum value of the density distributed in the vertical density profile (VDP) constantly came at the surface of the test specimen, and the value was increased with the density of the raw increased. The products manufactured by high-density veneer had well mechanical properties, and the samples showed the cracking destruction during the bending test. The properties of the Poplar LVL was improved largely when the veneer pre-compressed was set up as the top layer, and the products got less well-performances when the volume element of the material-reinforced grew, as the interface between two different materials increased.5. The LVL products reinforced by unidirectional glass fiber had better performance when contrasted with the sample reinforced by fiber glass mesh, and because of low density of the unidirectional glass fiber, the products which had the same properties got lower density. The bending properties of the LVL enhanced by thinner bamboo curtain were better than that enhanced by thicker bamboo curtain, but poorer horizonal shear strength.6. The veneer had higher coefficient of heat conductivity for the reason that the material had pre-compressing processed and the air inner changed less, consequently, the time when the center of mat reached 100℃became shorted. The core of the mat only got 120℃when the glass fiber which had lower coefficient of heat conductivity was added between the two top layers at the end of hot-pressing, and the bamboo had less influenced on heat transmitting. |
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