Magnetic resonance imaging of moisture distribution in Pinus sylvestris L. exposed to daily indoor relative humidity fluctuations

In contact with indoor air, wood materials have a high potential passively to reduce the indoor humidity fluctuations resulting from internal moisture loads and outdoor humidity fluctuations. This ability, characterized by the moisture buffering capacity of building materials, has attracted increasing attention within building physics, but a suitable method to appraise and quantify this phenomenon is still sought. In this study, a non-invasive spectroscopic method of accessing information about the interaction between indoor air and Scots pine was investigated. A comprehensive account is given of spatially resolved moisture absorption (desorption) into (from) Scots pine by proton magnetic resonance imaging ([H-1] MRI) based on an effective single-point imaging (SPI) sequence. SPI images of bound-water distribution in Scots pine with a spatial resolution on a sub-millimetre scale were acquired when one of the orthotropic directions of the wood material was exposed to typical indoor day-to-day moisture fluctuations. The nuclear magnetic resonance imaging measurements presented in this study clearly show the potential of the method to provide accurate spatial information about the wood-water interaction below the fibre saturation point and hence to characterize the moisture buffering capacity of wood materials.