Wood is a hydrophilic material and very sensitive to the water and other liquids. The changes in H-bonding system caused by cell wall liquids uptake usually leads to the changes in the physical and mechanical properties of wood.
In this study the swelling of pine (Pinus Sylvestris) sapwood in binary mixtures was investigated. Pine was selected as typical representative of softwood and organic solvents ethanol (EtOH), isopropanol (i-PrOH), acetone (Act), dimethylformamide (DMF) used in this study were selected as representatives of different chemical classes. The aqueous solutions of organic solvents were prepared in different concentrations. The tangential, radial and longitudinal swelling was measured and volumetric swelling of oven-dried samples was determined.
Anomalous properties of binary systems have cardinal influence to the swelling of wood [1,2]. Confirmation of the synergistic effect of swelling in binary mixtures has been obtained. Wood swelled in aqueous solutions of alcohol and acetone (MFalcohol 0.4 – 0.6 and MFacetone 0.4 – 0.5) more than in pure liquids. Totally different behaviour was detected for swelling of pine in DMF[3].
Noticeable damping in swelling values occurred during re-swelling. Most significant damping appeared in ethanol and acetone aqueous solutions (MF 0.5). In spite of that, the synergistic effect emerged also in case of second swelling [4].
Microscopy studies of swelled samples showed that after swelling in water the cells were densely packed and the compound middle lamellae (CML) was arranged in a form of continuous ribbon around the cells. The swelling of wood in ethanol-water mixtures had a dramatic effect on the wood structure through dissolving a part of lignin from CML and released individual cells at sectioning. Acetone and acetone-water mixtures had a very mild effect on the cell wall structure and its bonding to the CML. The swelling in DMF opened up the location of the primary wall layer and S layer. There was no substantial difference in the influence on the cell structure between pure DMF and its mixture with water.
Keywords: Synergistic effect on swelling, Damping in swelling, Cell wall structure changes
Authors
P. Meier
Department of Polymer Materials, Tallinn University of Technology, Tallinn, Estonia
U. Kallavus
Centre for Materials Research, Tallinn University of Technology, Tallinn, Estonia
T. Kaps
Department of Polymer Materials, Tallinn University of Technology, Tallinn, Estonia
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