It has been known that woods are usually acidic materials. This acidity relates closely with some fundamental problems of the wood-based materials, for example corrosion of metals, and discoloration, adhesive property coating property with paints and rot property of wood. Also this acidity has the important significance in the chemical treatment of wood.
In this paper, the measuremental methods of the pH value of wood were reported.
The wood flour (20-40 mesh) from heartwood of 3 species of softwood (HINOKI : Chamaecyparis obtusa SIEB. et ZUCC., SUGI : Cryptomeria japonica D. DON and AKAMATSU : Pinus densiflora SIEB. et ZUCC.) and 4 species of hardwood (KABA : Betula Maximowicziana REGEL, KATSURA : Cercidiphyllum japonica SIEB. et ZUCC., OHNARA : Quercus crispula BLUME and KUSU : Cinnamomum Camphora SIEB.) in Japan and 4 species of tropical wood (RED LAUAN : Shorea negrosensis FOXW., WHITE LAUAN : Pentacme contorta M. et R., RED GUM : Eucalyptus calophylla R. BR. and WHITE GUM : Eucalyptus gomphocephala DC.) were used as the samples for the pH measurement and the potentiometric titration.
The pH measurement was made on the filtrate and the suspension in water. In the potentiometric titration, the filtrate was titrated with 0.01N-NaOH. The total free acid content was calculated as acetic acid per 1 g. of dry wood flour.
In addition to these experiments, the buffering action of wood was estimated. The sample was wood(about 4 grs.) of cross section of 0.3mm. thickness from heartwood of 3 species of softwood (HINOKI, SUGI and AKAMATSU) and 2 species of hardwood (KUSU and KONARA : Quercus serrata THUNB.) in Japan and 5 species of tropical wood (RED LAUAN, WHITE LAUAN, RED GUM, WHITE GUM and TEAK : Tectona grandis LINN.).The reversed S-shape curve indicates the buffering action of wood.
The experimental results are as follows :
(1) There was linear relation between the pH value of wood and its total free acid content calculated as acetic acid. (Fig. 1)
(2) The pH value of the filtrate gave generally higher value than that of the suspension in water. (Table 2)
(3) The buffering action of wood was higher with increasing time. (Fig. 5) Also, the buffering action of wood tended to be higher as its pH value was lower. (Table 1)