The water vapour adsorption-desorption behaviour of naturally aged Tilia cordata Mill. wood

The effect caused by the natural ageing of wood on the sorption properties during two consecutive sorption cycles of historical Tilia cordata Mill. wood has been investigated and compared with a reference sample. Differences were found in the sorption isotherm between the first and second sorption cycles for most of the samples and also between the reference and historical wood.All samples exhibited sorption hysteresis, but with important differences in behaviour observed with the historic wood samples. It was interesting to note that the oldest historic wood sample did not display any discernible difference between the first and second sorption cycle throughout much of the hygroscopic range and also exhibited absolute hysteresis values essentially identical with the reference sample. These results indicate that the sorption behaviour of wood is dependent upon the previous exposure of the wood to atmospheric relative humidity. The sorption kinetics was also analysed in terms of the parallel exponential kinetics (PEK) model, and excellent fits to the data were obtained. The PEK model describes the dynamic sorption behaviour in terms of a fast and slow kinetic process and important differences in behaviour for these two processes were found. It is thought that the fast process is associated with a physical diffusion phenomenon, while the slow kinetics process is considered to be associated with cell wall matrix polymer relaxation processes.