Proceedings e report - Firenze University Press

WOOD SCIENCE FOR CONSERVATION OF CULTURAL HERITAGE
microcracks and fibres being torn from the wood surface. In the samples consisting of loose fibres,
individual fibres whose length and thickness decrease gradually even within one sample can be observed
(Fig. 1-3).
Fig. 1 – A chip sample of the
defibred wood.
Fig. 4 - Wood cells separation in
the chip sample taken from
defibred roof beam surface.
Fig. 2 and 3 - The fibres occurred on the wood surface
Fig. 5 - Cells separation and cell wall
crack in the chip sample taken from
defibred surface.
283
Fig. 6 - Cell wall damage and
missing margo strand.
Examination of the anatomical structure of the damaged wood by electron microscopy revealed that
both cellulose and lignin are damaged by chemical reactions. In some cases, mechanical damage of the
wood structure due to crystallization pressures is also conceivable. Separation of cells, apparently due
to a damaged middle lamella, was observed (Fig. 4-5). Damaged of margo strand of bordered pits on
the tracheid walls were also apparent (Fig. 6). Both the middle lamella and the margo strand consist
mainly of lignin. Some samples have damaged secondary cell walls, which primarily consist of
cellulose. This damage is represented by various cracks in the cell walls (Fig. 5-6). Fig. 7-9 show the
wood fibers which originated from the beam surface damaged by defibring. Samples consisting of fine
fibres did not exhibit any wood structure and this indicates that the cell walls have been disintegrated
into the fibrous tangle - presumably supermolecular cellulose formations. Additional experiments will
be necessary to gain a deeper insight into this.
The infrared spectra were evaluated in dependence on the degree of wood defibring, i.e. very fine fibres,
coarser fibres and chips (Fig. 1-3). The infrared spectra show that with the increasing level of wood defibring
decreases relative lignin content in wood which is demonstrated mainly by the decrease of the absorption
band with its peak in 1510 cm -1 . This band belongs to the stretching vibrations of the lignin aromatic ring
double bond. The decline of this band, indicating the decrease of lignin, was evaluated by means of
correlation with the chosen reference absorption bands of cellulose with its peaks in 1372 cm -1 (out-of-plane
bending vibrations of CH bonds of cellulose glycoside ring). The intensity rate of the bands I1510/I1372 drops
rapidly in the connection with the level of wood defibring (see Table 1). This relative decrease of lignin was
observed in all the samples of the damaged wood taken from all of the observed buildings.