Proceedings e report - Firenze University Press

WOOD SCIENCE FOR CONSERVATION OF CULTURAL HERITAGE
2.2. Evaluation of modulus of elasticity
Modulus of elasticity (MoE) was determined before and after fungal exposure. Specimens were oven
dried prior MoE measurements. Because of difficulties encountered in measuring the axial vibrations,
flexural vibration modes were used to characterize elastic parameters. Considering the hypothesis of
the homogeneity of geometrical and mechanical properties along the sample, basic dynamics theorems
can be applied to obtain the motion equation of first vibrations. Analysis was performed on specimen
with clamped–free end conditions. During the test the lateral displacements of vibrating sample in
damped vibration with known vibration mode was measured. As, an inductive proximity sensor was
used, a small piece of metal foil of neglected mass was glued on the surface of each sample. The
damped frequency was obtained by FFT analysis of the exponentially decayed displacement signals
detected in time domain. For determination of Young modulus of samples we used the frequency
equation deducted from Bernoulli model, which was assumed as acceptable because of the relatively
high length-to-depth sample ratio, (E - Young modulus (N/m2), ν - natural frequency (s-1), C =
3.51563 – constant derived from Bernoulli equation, ρ – density (kg m-3), l – free sample length (m),
h – sample height (m). Measurements were performed on seven replicates.
2.3. Chemical analysis (CNS) of wood
Prior to nitrogen and carbon analysis, wood blocks, that was used for MoE measurements, were milled
into particles (MESH 80) and homogenized. Approximately, 0.15 g of an oven dry sample was
combusted in the oxygen atmosphere at 1350°C in LECO 2000-CNS analyzer to determine carbon and
nitrogen content.
2.4. FTIR and colour measurements
FTIR spectra were recorded with the Perkin Elmer FTIR Spectrum One Spectrometer, using Abrasive
Pad 600 Grit-Coated, PK/100 (Perkin Elmer) paper. DRIFT spectra of wood samples were recorded
between 4000 cm-1 and 450 cm-1. Colour of the specimens was recorded with HP Scanjet 4800
scanner. Scanner was chosen, as specimens were to narrow for measurements with colorimeter. Colour
obtained with scanner and colorimeter gives comparable results. The reported values are average value
of seven replicate measurements. The colour was expressed in CieL*a*b* format.
3. Results and discussion
3.1. Brown rot fungi
Eight weeks of exposure to brown rot fungi resulted in notable mass loss of spruce wood specimens,
indicating that both brown rot fungi were active. The decay of control spruce wood by G. trabeum
caused higher mass loss than did exposure to A. vaillantii, as expected from previous studies [6]. After
eight weeks of exposure to G. trabeum, a mass loss of 28.0% was detected, while the mass loss of
spruce wood exposed to A. vaillantii was only half as much (14.3%). This difference was not
consistent across all exposure times. For example, neither fungus caused detectible decay within the
first week of exposure, but two weeks of decay resulted in almost two times higher mass loss by A.
vaillantii (4.5%) in comparison to specimens decayed by G. trabeum (2.6%). After four weeks of
decay, mass loss caused by G. trabeum (13.0%) surpassed those of A. vaillantii (10.2%) and then
doubled again by week 8 (Tab. 1).
Measurements of modulus of elasticity (MOE) revealed similar trends as those reported for mass loss
data with one significant difference. The first sign of incipient decay was clearly seen even after one
week of exposure of specimens to both fungal strains. This proves that a nondestructive measurement
of MOE loss is a very sensitive tool. After one week of exposure, G. trabeum reduced MOE by 7.4%
and A. vaillantii by 8.3%. Comparable findings are reported in the literature as well [7,8]. As shown
with the mass loss measurements, changes in MOE demonstrated that A. vaillantii was more effective
during the first two weeks of exposure and G. trabeum during the remaining period. The remarkable
decay capacity of G. trabeum can be clearly seen from MOE losses after eight weeks of exposure of
control, un-impregnated, specimens where G. trabeum caused MOE losses of more than 75%. On the
other hand, eight weeks of exposure of the un-impregnated specimens exposed to A. vaillantii resulted
89