Three-Layered Particleboards with Steram Pre-Treated Face Strands-Effects of Panel Density on the Basic Properties
Noboru SEKINO, Masafumi INOUE and Hidefumi YAMAUCHI
Abstract:Mechanical properties of particleboards such as surface hardness, modulus of elasticity (MOE), bending strength (MOR) can be improved by high densification of its face layers. One of the effective ways for this purpose is introducing a steam pre-treatment technique into preparations of wood furnish for face layers, because steaming wood at high temperature increases wood compressibility. Also steam treated and then compressed particles show much less irreversible swelling than ordinary particles. This excellent dimensional stability would contribute to reductions of panel thickness swellings. Three-layered particleboards with a density ranging 0.5-0.8 g/cm3, a face to core ratio of 2/3, and a thickness of 12 mm were manufactured from Sugi (Cryptomeria japonica D.Don) face strands (75mm~9.0mm~0.67mm) and core particles (14.9mm~2.9mm~0.97mm). The face strands were steam pre-treated in an autoclave by introducing high pressure steam at 210Ž for 10 minutes. Phenol-formaldehyde resin was used as a binder. The manufactured panels showed the following characteristics, when compared to control panels with non-treated face strands: 1) the maximum density through the thickness increased by 10-15 percent, 2) surface hardness increased by 30 percent, 3) thickness swellings were greatly improved, this being pronounced at higher density panels, 4) however, the reduction of linear expansion was not obvious because this layer structure showed excellent resistance against for in-plane swelling, 5) in spite of face layerfs high densification, MOE and proportional limit stress in bending were almost the same as the controls, 6) MOR and withdrawal resistance of wood screw decreased at most by 30 percent due to the reduction of wood cohesion itself caused by steaming. Key Words:Steam pre-treatment, Three-layered particleboard, Mechanical property, Dimensional stability