Significance of the thermal design and the sorption isotherm shape in hygroscopic wood moisture dynamics and service life
Moisture dynamics are considered important for predicting the service performance of wood in exterior applications. Above a critical moisture content, water acts a softener on the structural polymer matrix of the wood cell wall, enabling the necessary diffusion of molecular species involved in the fungal degradation mechanism of wood. Water may enter solid wood in either liquid form or in vapor form, whereas it can only leave in vapor form. In exterior applications with prolonged exposure to rainwater, wood moisture may quickly accumulate to the critical moisture content for fungal degradation. On the other hand, moisture loss during dry weather conditions proceeds by relatively slow vapor transfer, leaving wood vulnerable to fungal decay for extended periods of time. This conference contribution addresses the latest scientific work, showing the role of heat transfer - associated with moisture changes in wood - as a major physical cause for the slow moisture content change rates in a humid ambient. The results from this work may guide the wood technologist to improve the service performance of wood through thermal detailing in the application design and/or by wood modification of the moisture sorption isotherm.
Keywords: moisture dynamics, coupled heat-mass transfer, unsteady-state diffusion, moisture sorption isotherm, service life