Bound water states in small wood samples were investigated by means of time-domain nuclear magnetic resonance. A bench-top low-field NMR instrument (Bruker minispec mq20) with a proton resonance frequency of 20 MHz was employed. The mobility of the water molecules depends on the environment they exist in. This is reflected in the observed relaxation times of the water’s protons during nuclear magnetic resonance experiments. The measurement of this relaxation behaviour can therefore not only help to non-invasively determine the total moisture content of the sample but also makes different water states discernible in terms of their relative proton amount and mobility. The Carr-Purcell-Meiboom-Gill pulse sequence was employed to observe transverse relaxation times (T2). All measurements were done at the NMR magnet’s operating temperature of 40 °C. Results were analysed using the CONTIN algorithm. The samples were conditioned from the oven-dry state to different moisture contents below fibre saturation by single-step absorption. Two different water populations were observed below fibre saturation.
Keywords: Transverse relaxation, moisture content, TD-NMR, CPMG, relative humidity
Authors
Lübke L.
Department of Wood Science and Technology, Eberswalde University for Sustainable Development, Eberswalde
Hill C. A. S.
Norwegian Forest and Landscape Institute, Ås
Pfriem A.
Department of Wood Science and Technology, Eberswalde University for Sustainable Development, Eberswalde
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