High Resolution Measurement of the Surface Layer Moisture Content during Drying of Wood Using a Novel Magnetic Resonance Imaging Technique

Abstract

Summary The moisture content profile in the surface layer of Scots pine (Pinus sylvestris) sapwood has been measured using the MRI (Magnetic Resonance Imaging) technique.Anovel high-gradient permanent magnet was used for the measurement of the moisture profile in the wood during the drying process, giving a depth resolution of better than 20 μm. This paper demonstrates for the first time the possibility of measuring the moisture content depth profile in the surface layer from raw state down to 4% moisture content without removing the wood sample from the apparatus. The main advantage of this technique and apparatus is a high resolution over a large field of view. It is possible to measure the moisture content in the wood surface layer during drying up to a depth of 300 μm. A single moisture content profile may be obtained in less than 5 min. Hence, more accurate dynamic drying information, on a single sample, maybe achieved than with current techniques. In this preliminary studywe observed that the wood cells at the surface had a moisture content higher than the equilibrium moisture content for wood in the surrounding bulk air. We conclude that for a wood moisture content of above approximately 50% the resulting profiles were almost flat from a depth of 90 μm and further into the wood and in between the surface and 90 μm deep there was a steep gradient. Below 50% there was a gradient in moisture content to at least 300 μm depth.