Effect of targeted acetylation on wood–water interactions at high moisture states

Abstract

AbstractAcetylation is a wood modification used to increase the durability. Although it is known that the wood moisture content is lowered, the exact mechanisms behind the increased durability are not known. However, since fungi need water in different locations for different purposes the location and state of water is most probably of importance in addition to the total moisture content. In a previous study, we used targeted acetylation to alter the wood–water interactions in different parts of the wood structure in water saturated and hygroscopic moisture states. The main range for fungal degradation is, however, between these moisture ranges. This study investigated the effect of targeted acetylation on location, state and amount of water at non-saturated, high moisture states using the pressure plate technique. Specimens were modified using acetic anhydride by two approaches: (1) uniform modification (2) interface modification acting on the cell wall-lumen interface. They were then conditioned to eight moisture states between 99.64 and 99.98% relative humidity in both absorption and desorption and the location and state of water was studied using Low Field Nuclear Magnetic Resonance, X-ray computed tomography and Differential Scanning Calorimetry. Capillary water was present at all the included moisture states for all specimen types, but the amounts of capillary water in absorption were small. Increasing degree of interface modification increased the amount of capillary water compared to untreated wood. In addition, the uniformly modified wood often had higher amounts of capillary water than the untreated wood. The amount of cell wall water was decreased by uniform modification, but slightly or not reduced by the interface modification. The combination of targeted modification and conditioning to high well-defined moisture states thus gave very different amounts of capillary water and cell wall water depending on the conditioning history (absorption or desorption) and choice of modification. This opens new possibilities for designing materials and moisture states for fungal degradation experiments of wood.