A manyfold of biological agents decompose wood, among them fungi and bacteria. They may attack different components, e.g. the brown-rot fungi mainly the polysaccharides, white-rot fungi all cell walls, and this at changing rates depending upon the active species . Such decay by progressive fungal degradation is connected with a loss of strength. Even at slight weight losses of less than 10 % significant reductions of important wood characteristics can occur so that a rapid means to determine the “incipient decay” is of interest beside the usual weight loss evaluation . TA could be such an approach but only few papers are published on microbial deterioration of wood. White- and brown-rotting of birchwood was followed over 12 weeks by means of TG but significant results could only be obtained after a weight loss of more than 50 % . Effects earlier than the readily-obtainable weight losses could be detected from DSC on white- and brown-rotten aspenwood during a seven-week period by evaluating the endothermic peak areas . Both papers assumed that there is a strong correlation between the thermal instabilities and the changes induced by microbial degradation on the degree of polymerization of cellulose
Baldwin and Streisel investigated poplar sapwood samples (Populus maximowiczii × trichocarpa) taken from the same growth ring. After surface sterilization, small specimens were incubated in petri dishes with the brown-rot fungus Lenzites trabea for 3 to 15 days. Every third day samples were analyzed by DSC under nitrogen between 227 and 427°C and by chemical means. Above a weight loss of 4.7 %, DSC was a useful tool to ascertain the extent of decay in agreement with the earlier observations . The highly crystalline alpha-cellulose was the most stable wood component and did not change much during this initial degradation state, while extractive-free wood showed a clear relationship between the size of the endothermic peak and the weight loss .