Sugi, (Japanese cedar, Cryptomeria japonica D. Don) sapwood blocks were chemically modified by the reaction with phthalic anhydride and their biological durability was investigated in comparison with acetylated wood. Fungal decay test using the brown-rot fungus Fomitopsis palustris and the white-rot fungus Trametes versicolor revealed that phthaloylated wood has higher durability at lower extent of hydroxyl substitution than acetylated wood, which was remarkable especially against the brown-rot decay. To evaluate the molecular structural characteristics necessary to provide such high resistance, wood samples chemically modified with several acid hydrides having similar structures to phthalic anhydride were prepared and subjected to decay test. The results showed that trimellitic anhydride provided the durability comparable to phthalic anhydride, but neither benzoic nor cis-1, 2-cyclohexanedicarboxilic anhydrides did, indicating that such high durability as found for phthaloylated wood is specific to the chemically modified wood with substiuents carrying aromatic carboxylic acids. Termite feeding test of phthaloylated wood also resulted in the higher resistance than acetylated wood.

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