The microstructure of birch (Betula pendula) false heartwood, FHW, was studied in comparison with clear birch samples using FTIR spectroscopy and SEM analysis with the aim of determining whether this defect is as a result of fungal infection or a colour difference due to its secretions. Ground and veneer strips of FHW and clear birch were used for the FTIR study. Microtome device was used to cut thin slices of the birchwood samples in radial-longitudinal, tangential-longitudinal and transverse sections containing both the FHW and clear part was used for the SEM study.
In the FTIR study, similar fingerprints resulted for both the FHW and clear samples for both the veneer and ground samples. However, the FHW samples had stronger intensities and absorbance of the IR spectra, especially in the veneer samples, at the different associated bands of cellulose, hemicellulose and lignin at 898 cm-1, 1032 cm-1, 1233 cm-1, 1323 cm-1, 1368 cm-1, 1420 cm-1, 1460 cm-1, 1596 cm-1 and 1733 cm-1. This is as a result of the higher extractive content in the FHW. Also, the ground samples had missing peaks at 1160cm-1, 1460 cm-1 and 1651 cm-1 which were present in the veneer samples and a missing peak at 2186 cm-1 for the veneer sample which was present in the ground sample.
The variations observed in the SEM study include wider lumen in FHW samples, thicker cell walls in clear sample fibres, simple pitting in clear sample fibres, more uniseriate wood rays in clear samples in clear sample. As a result, there will be larger space for extractives to be secreted in the cell lumens of the FHW, clear samples will be stronger than the FHW samples because of its thicker cell walls, more extractive locked in the cell lumens of the FHW because of lack of pitting and more multi-seriate wood rays in the FHW samples may have a negative effect on the strength. The FHW is therefore more as result of chemical activities in the wood structure, because fungal attacks in the wood cell wall were not detected with SEM analysis.
Keywords: Birch (Betula pendula), false heartwood (FHW), discoloured wood, FTIR, SEM
Authors
Bankole O.S.
Department of Polymer Materials, Tallinn University of Technology, Tallinn, Estonia
Rohumaa A.
Department of Forest Product Technology, Aalto University
Kers J.
Department of Polymer Materials, Tallinn University of Technology, Tallinn, Estonia
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