| This study investigated the veneer of fast growing poplar. The variable surface free energy(SFE) of veneer under different compression rate was calculated and analyzed by critical surface tension method(SCTM), geometric mean method(GMM) and harmonic mean method(HMM). And the mechanical properties of poplar plywood and LVL reinforced by veneer compression and PF resin impregnation were also studied. The processing characters of poplar plywood and LVL with extreme low formaldehyde emission manufactured by using new soybean protein adhesive were also studied. The conclusions were listed as following:1) The advanced contact angles of water and glycerol on the surface of poplar veneer were 60.7°and 116.8°respectively. With the increasing compression rate, the contact angles of water enlarged slowly. The SFE of poplar veneer calculated by SCTM and HMM were 63.23mJ/m2 and 53.33mJ/m2 respectively and increased slowly with the aggrandized compression rate. The SFE got maximum at veneer compression rate of 35%. A striking correlation was found between SFE of poplar calculated by HMM and the compression rate of veneer. The dispersion componentγSd was 10.8 mJ/m2 and the polar componentγSp was 42.5mJ/m2.2) The compression treatment of veneer can improve the resin impregnation. In compression limit rage, the bigger the increasing compression rate, the higher weight percent gain(WPG), and the better resin impregnation. The mechanical properties of poplar plywood could be remarkably improved by using poplar veneer compression and PF resign impregnation. When the compression rate of poplar veneer was 35%, PF resin concentration was 40%, impregnation time was 2h and hot-pressing temperature was 150℃, the MOE, MOR and bond strength were 127%,212%,77% higher than relevant indexs specified in national standard of plywood respectively.3) The mechanical properties of non-structural poplar LVL could be remarkably improved by veneer compression and PF resign impregnation. But it doesn't mean the more layer numbers of compressed and resign impregnated veneer, the more enhanced effective, but not absolutely. When the veneer compression rate was 35%, PF resin concentration was 40%, impregnation time was 2h, mat pressure was 1.2MPa, pressing time was 70 s/mm, pressing temperature was 150℃and the surface and the back of mats all had two layers of compressed and resign impregnated veneer, MOE of the non-structural poplar LVL was 14.7 GPa, MOR was 145MPa, and horizon shear strength (HSS) was 8.7MPa, which were 75%,101% and 16% higher than normal poplar LVL. The mechanical properties of structural poplar LVL could be remarkably improved with the increasing layers of compressed and resign impregnated veneer, the mean MOE could reach 14.0 GPa, mean MOR was 100MPa, mean HSS were 7.6 MPa (Vertical Loading) and 18.5 MPa (Horizon Loading)4) The results of experient showed that manufacturing plywood II by using new soybean protein adhesive was feasible. The optimum process parameter on manufacturing this kind of plywood were:pressing temperature 160℃, mat pressure 1.6MPa, pressing time 80s/mm and glue spread amount(two faces) 450-500g/m2. The glue bond strength of poplar plywood manufactured by new soybean protein adhesive could reach the requirements of national standard II.The formaldehyde emission was 0.02 mg/L, extreme lower than the eco-friendly grade EO which was under 0.5 mg/L.5) Influence of prepressing temperature on MOE, MOR and HSS of poplar LVL using new soybean protein adhesive was significant. And influence of pressing time on imersion-peel performance was significant too. When the pressing temperature was 160℃, glue spread amount(two faces) was 450-500g/m2, mat pressure was 1.6MPa, prepressing temperature was 70℃, pressing time 100s/mm, structural poplar LVL had best combination properties. The mean MOE could reach 14.4GPa, mean MOR was 78MPa, mean HSS with vertical loading was 6.8MPa, mean HSS with parallel loading was 8.9MPa, imersion-peel rate was only 0.4%. |
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