Proceedings e report - Firenze University Press

CHANGES OF MECHANICAL AND CHEMICAL PROPERTIES OF WOOD AFTER BROWN-ROT DECAY AND BLUE STAINING
wood as a constituent of fungal hyphae. Similar as nitrogen content, carbon content decreased as well
from initial 47.63%. to final 46.27 at S. pithyophila and to 45.97% at A. pullulans.
Unexpectedly. modulus of elasticity (MoE) of blue stained specimens did not decrease but even
slightly increase (Tab. 5). The first increase of MoE was observed immediately after sterilization, even
at specimens that was not exposed to wood decay fungi at all. Similar phenomenon is reported for heat
treated wood. where MoE firstly increases with temperature of treatment, but when temperatures reach
over 150°C, MoE starts decreasing [11]. This increase of MoE is assigned to fact that after water
evaporation, cellulose hydroxyl groups form hydrogen bonds between neighbouring micro-fibrils,
which results in improved MoE of steam-sterilised wood. Another possible explanation for increased
MoE values of blue-stained wood is the presumption that melanin could interact with wood functional
groups and additionally crosslink wood components. However. this is only presumption which is very
difficult to prove.
74.2
72
70
68
66
64
62
60
%R
58
56
54
52
50
48
46
45.1
4000.0 3600 3200 2800 2400 2000 1800
cm-1
1600 1400 1200 1000 800 600 450.0
Fig. 1: FTIR spectra of control (lower line) Pinus sylvestris wood and wood exposed to Sclerophoma
pithyophila for eight weeks (upper line)
Infra red spectra confirms. previously observed results. There were no differences in IR peaks between
control unexposed pine wood and blue-stained wood even after eight weeks of exposure (Fig. 1). This
confirms that blue stain fungi did not change lignin. cellulose and hemicelluloses structure.
Additionally. it seems that the amount of melanin in wood is to low to be observed from FTIR spectra.
Secondly. as functional groups of melanin are relatively similar to lignin functional groups, melanin
can not be resolved from FTIR spectra [12].
These data are important from application point of view. Blue stained wood can be therefore used for
various construction applications. And secondly, if albino blue stain fungi are utilised for biocontrol
applications [13], it could be presumed that these fungi will not significantly influence mechanical
properties of colonised wood.
4. Conclusions
Comparison of results obtained with different experimental techniques gives very interesting details on
brown rot decay of Norway spruce wood. Decay caused by the A. vaillantii is faster during the initial
stages, but then decreases compared to decay by G. trabeum. FTIR analysis of decayed specimens
resolved that A. vaillantii decays predominately hemicelluloses and cellulose and that lignin remains
almost unaffected. On the other hand. G. trabeum decays hemicelluloses and cellulose, as well as
lignin, which results in significantly higher mass losses compared to decay caused by A. vaillantii.
Aureobasidium pullulans and Sclerophoma pithyophila significantly blue-stained pine wood
specimens. However, the results of the experiments showed that this change is only aesthetic and does
not influence neither weight or mechanical properties of blue-stained wood.
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