Changes in the acid structure of wood due to ageing and fossilisation processes

Some fossil woods, differing in botanical species, age, degree of degradation and chemical composition, were analysed with respect to their acid structure. A comparison was carried out with corresponding modern species which, in the case of softwoods, contain carboxylic groups as well as ester groups in almost equal amounts. Moreover the former are subdivided into protonated (approximately 20%) and salified forms (approximately 80%). The determination of the acid structures in woods was made by means of cation exchange measurements. In all examined fossils the initially protonated form is changed into the salified one because of the leaching carried out by water containing soluble salts. Despite the loss of polyoses, an increase in the content of carboxylic groups was achieved due to hydrolysis of the ester groups. In more degraded samples the amount of carboxylic groups was larger than in the other fossils even if the former possessed only traces of polyoses due to an attack on lignin assessed by acidity of the trifluoroacetic (TFA) derivatives. Proof of these changes and further information on fossils were obtained by I.R. spectroscopy.