Production and properties of high performance wood-based panels.

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Sodium hydroxide was used with a molar ratio of phenol to formaldehyde in the range of 1 : 2. After the reaction, two kinds of low molecular-eight (number average molecular-weight, Mn=300) Phenol-formaldehyde (PF) resin were prepared : alkaline PF resin (pH : 10.3) and neutral PF resin (pH : 6.0). In the latter, organic acid was added to reduce the pH to 6.7. The neutral resin is more stable under ambient storage condition than the alkaline resin and color of the neutral resin treated wood was yellow. On the other hand, color of the alkaline resin treated wood was blackish-brown. Dimensional stabilization and biological resistance of the PF resin-treated wood were not significantly different between neutral and alkaline resin.The penetration of PF resin into cell walls on sub-and ultramicro levels was investigated by means of light microscopy, electron probe X-ray microanalysis (EPMA), and X-ray photo-electron spectroscopy (XPS). Three kinds of m-bromophenol-formaldehyde resin having Mn of 290,470, and 820 were synthesized to detect the presence of resin as a signal of bromine (Br). In the specimens impregnated with small molecular-weight resins at concentrations of 1 and 15%, light microscopic observation revealed that the PF resins were hardly located in tracheid lumina at lower concentrations. Even at a concentration of 15%, the number of tracheids filling the resin in their lumina was very small. Judging from both light microscopy and EPMA,the PF resin with small and middle molecular-weights proved to penetrate mostly into cell walls, contributing to the enhancement of dimensional stability in resin-treated wood. Also, for PF resin with larger molecular-weight, the resin components with smaller molecular-weight was suggested to be present in the walls.