Research On The Technology And Performances Of Structural Plywood Made Of Pinus Massoniana Veneer With Different Thickness

As specific and resource-rich native tree species in subtropical regions in China, Masson pine (Pinus massoniana Lamb.) is the most extensively distributed, it is the largest in number, and its use is extensive. It is the important commercial species in China. The development of the structural plywood can meet the changes in the situation of wood raw materials, the plantation resources can be used well, and the timber utilization can be improved. It has great meaning to develop structural plywood with high strength, high flexibility, resistance to climate, and resistance to outdoor conditions with fast-growing tree species. In this study, the performances of structural plywood made of Masson pine veneer with different thickness are researched. The effect of the veneer thickness on the performances of the plywood is discussed.In this study the physical and mechanical properties, thickness swelling after soaked in water, and the wettability of veneer are studied at first. Then the mechanical properties, dimensional stability, and bond performance of structural plywood made of Masson pine veneer with different thickness are researched.The conclusions are as follows:(1) With the increase of the thickness of veneer, veneer density increase, the MOE and MOR parallel to grain also increase.(2) With the increase of the veneer thickness, the wettability becomes good. When the veneer thickness is same, the wettability of loose side is better than that of the tight side, the wettability parallel to grain is better than that perpendicular to grain, the wettability of early wood is better than that of late wood.(3) With the increase of the veneer thickness, the heating rate of middle layer increases.(4) The bond strength increases with the increase of the glue spread. When the glue spread reached some value, the bond strength gets stable or decreases slightly. When the glue spread is same, the bond strength decreases with the increase of the veneer thickness. The thicker the veneer is, the more the glue spread is. (5) The water absorption thickness swelling decreases with the increase of the hot-press time, temperature or plywood density. The thickness swelling after soaked in water increases with the increase of veneer thickness.(6) With the increase of the hot-press time, temperature or plywood density, the bond strength, modulus of elasticity (MOE) and modulus of rupture (MOR) increase gradually, then get stable or decrease slightly.(7) The best technology is as follows: the glue spread of A-type veneer (1.7mm) is 350g/m2, B-type (3.2mm) is 400g/m2, C-type (5mm) and D-type (7mm) are 500g/m2; hot pressing time is 1.0-1.2min/mm, hot-pressing temperature is about 140℃, the plywood density is about 0.75g/cm3.(8) The percentage of core layer thickness has great effect on the MOE and MOR. The smaller the percentage of core layer thickness is, the larger the MOE and MOR parallel to grain are, the lower the MOE and MOR perpendicular to grain are.(9) The Digital Speckle Correlation Method (DSCM) is used to study the tiny strain of the Masson pine structural plywood. In the bonding strength test, In the middle region where the deformation is larger, the largest deformation is not coherent. That is affected by lathe-check. When the bonding strength tests are carried out, the region where the deformation is largest is at the lathe-check. In the bending test, from the correlation coefficient diagram of the displacement field, we can notice that the correlation coefficient is above 0.95, the correlation is good. Therefore, the place where the timber is damaged can be analyzed and deduced from the tiny strain process by using DSCM.(10) The data of he bending test of big panel similarly obey Weibull distribution.(11) The performances of Masson pine structural plywood that are tested according to different testing methods are different.(12) The prediction model of MOE of Masson pine structural plywood is built. The predicted value is correlated with the results of ASTM D3043 method D.(13) With the increase of veneer thickness the glue spread in unit area decreases gradually. The MOE and MOR parallel to grain of the structural plywood made of thick veneer is high. That can be used in the situation where the demand of MOE and MOR parallel to grain is high. With the increase of veneer thickness the assembly is various to meet different demand. The advantage of structural plywood made of thick veneer is obvious. The structural plywood made of thick veneer has great foreground.