Proceedings e report - Firenze University Press

DISINFECTION AND CONSOLIDATION BY IRRADIATION OF WOODEN SAMPLES FROM THREE ROMANIAN CHURCHES
about 20-30 kGy. Radiation polymerization has a great advantage over conventional polymerization
by chemical catalysts as the heat rise can be perfectly controlled by varying the radiation dose rate.
The other advantage of radiation polymerization is that the excess resin from an impregnation can be
reused, due to the absence of chemical catalysts in the resin storage. The disadvantage of this
consolidation treatment in comparison to other consolidation methods of cultural heritage objects is
that the process is not reversible. However, it can save from destruction artifacts which present a very
high degree of deterioration (4).
2. Materials and methods
Samples
The studied wooden samples came from three Romanian churches:
A. piece from wooden ceiling of an evangelical church in Sibiu county,
B. piece of sycamore maple from resistance structure of an orthodox wooden church,
C. piece of fir from resistance structure of an orthodox wooden church in Dretea, Cluj county, which
was build in 1690, painted in 1770 and now is rebuild at “Astra” Traditional Civilization Museum
in Sibiu.
Treatment
The consolidation of the studied samples was carried out using a standard resin of styrene-unsaturated
polyester type tetrahydrophtalic. The samples were treated at the irradiation facility of Regional
Conservation Workshop Nucléart (ARC-Nucléart), using a gamma source of Co-60. The irradiation
was done at room temperature in open air. The delivered mean irradiation dose was about 24 kGy,
enough to disinfect the samples from insects and moulds, and consolidate them through
polymerization of the resin. The irradiation dose rate was set up as to not exceed a polymerization
temperature of 50-60°C. After treatment, different properties of the impregnated samples were
assessed in order to prove that the gamma irradiation process brings a real improvement in wood
condition, in terms of disinfection and structure consolidation.
Characterization and testing
First were assessed the biodeterioration factors (insects and moulds) and their effects. Using a photo
camera and a stereomicroscope, were taken pictures before and after treatment and assessed the
biodeterioration factors (insects and moulds) and their effects on wooden samples. Samples were also
weighed before and after consolidation treatment.
A HunterLab Miniscan XE Plus portable spectrophotometer has been used for colour measurements.
The geometry of measurement is d/8° with a view area of 6 mm in diameter, specular component is
included, combination illuminant - standard observer is D65/10°. All values are reported in CIELAB
and CIELCh colour spaces. Every value is obtained averaging 30 measurements.
Mechanical testing has been carried out using Zwick / Roell equipments. For dynamical test (impact
test) has been used a Zwick / Roell Pendulum model 5113. The test parameters were: pendulum of 25
J, Charpy impact test, distance between sample holders 35 mm, impact speed 3.85 m/s and angle of
pendulum launching 160°. Through Charpy impact test has been measured the impact energy E (J).
For statically tests (penetration and bending) it has been used a Zwick / Roell Universal Testing
Device model Z005. The penetration test has measured the force F (N) necessary to push 1 mm in the
sample a metallic ball of 6 mm diameter. The bending test has measured the bending tensile strength σ
(MPa) necessary to bend 2 mm a sample. The distance between sample holders was 60 mm.
For electron spin resonance (ESR) testing was used a Magnettech Miniscan MS200 X band
spectrometer. The measurement parameters were: Microwave radiation – 9,3-9,6 GHz, Power – 0.8
mW, Centre field – 335 mT, Sweep width – 15 mT, Modulation amplitude – 0.5 mT, Sweep time – 60
s, Steps – 4096, Pass number – 5, Temperature – room temperature. Gain varied according to the
signal intensity of the measured sample. A single signal (gsymm=2,004) is observed in the ESR spectra
of all samples containing cellulose, including unirradiated samples. In the case of irradiated samples,
the intensity of this signal is usually much greater. The intensity of signal is proportional with the
quantity of cellulose free radicals present in the sample.
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