Changes in impact bending strength, weight and alkali solubility following fungal attack on birch wood

Specimens of birch sapwood were decayed according to the soil jar method. Twelve different fungi commonly found in birch wood were used as test organisms. Every week after the inoculation, the moisture content, the weight loss and the impact bending strength were investigated. Samples with the same incubation time were ground up, and their solubility in 1 % NaOH was calculated. During the course of decay, the moisture content increased more rapidly in samples decayed by brown rot fungi than in samples decayed by white rot fungi. After an incubation time of seven days when, in many cases, the weight loss was negligible, there was already a substantial loss in strength. For high weight losses, the samples decayed by brown rot fungi had lost more of their strength than those decayed by white rot fungi. For low weight losses, however, there seemed to be little difference in the reduction in strength between samples decayed by white rot fungi and samples decayed by brown rot fungi. The alkali solubility of the samples decayed by brown rot fungi increased steeply during the course of decay, unlike that of the samples decayed by white rot fungi, the solubility of which increased only slightly. The possible cause of the reduction in impact bending strength resulting from fungal attack on wood is discussed. The hypothesis is presented that the dissolution of the chemical and physical linkages between lignin and carbohydrates is the cause of at least the early reduction in impact bending strength