The effect of hot-pressing parameters on resin penetration and flakeboard layer properties

The area of penetration of phenol-formaldehyde resin into aspen (Populus tremuloides) and Douglas-fir (Pseudotsuga menziesii) flakes, and the layer properties of yellow poplar (Liriodendron tulipifera) flakeboard were investigated to determine how they were influenced by various pressing parameters. The evenness of penetration was found to be a function of the natural variability of the wood and was not influenced by the pressing parameters of temperature, moisture content, pressure, or time. These four parameters were found to influence the area of penetration by controlling the viscosity and flow of the resin.

The temperature, gas pressure, and platen pressure history at any particular plane through a flakeboard panel thickness were found to be directly and interactively determined by the pressing parameters of platen temperature, initial mat moisture content, and press closing time. The specific gravity profile was observed to be a function of the press closing time while platen temperature and the mat moisture content influenced the amount of springback which the panel exhibited. Layer-shear and the corresponding specific gravity at a particular plane were found to be similarly dependent on environmental history. The layer-shear strength increased consistently toward the surface of the panel and exhibited a lower coefficient of variation nearer the surface.