Biological resistance of PF (phenol formaldehyde resin) - treated wood has been tested in relation to the resin properties, wood species and biological factors. When tested using water-soluble PF (mol. wt. 170), ca. 10% RI (resin impregnation) was enough to suppress the decay of Japanese cedar (Cryptomeria japonica) and western hemlock (Tsuga heterophylla) blocks exposed to Tyromyces palustris (brown-rot type) and Coriolus versicolor (white-rot type). For a decay suppression of Japanese beech (Fagus crenata) by treating with the same PF, ca. 20% RI was required for both cases of exposure. When using ethanol-soluble PF (mol. wt. 300), the lesser effect on decay suppression was revealed for most of wood-fungus combinations, suggesting a possible better penetration of lower molecular resin into the wood cell walls. PF treatment of wood also affected the termite Coptotermes formosanus, causing the severe depletion of feeding activity and the higher mortality at 5-15 (%) RI. Of the three species of symbiotic protozoa, the most cellulolytic Pseudotrichonympha grassii diminished first shortly after feeding.

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