Proceedings e report - Firenze University Press

WOOD SCIENCE FOR CONSERVATION OF CULTURAL HERITAGE
speed and length of the frame. In these cases you have expect much higher differences of
temperatures.
Fig. 3. IR- image of test DA 4 I (left), DA 4 II (middle) and DA 4 III (right) after microwave treatment
of up to 50 ± 5°C. The heat distribution is inhomogeneous and unpredictable, despite comparable
experimental set-ups.
It was also observed that the wood loses increasing humidity with longer periods of treatment. The
determination of the moisture content of the samples sometimes showed massive losses of moisture.
The diagram 1 below shows the wood moisture before and after interval treatment. You can see that
the wood moisture decreases with rising temperature and duration. Already after 20 minutes of heating
at 30°C the moisture fell to half. Extreme moisture loss was caused with 30 mins at 40°C. After
treatment the samples in these series possessed only a moisture content of 2%, which is almost kilndried.
Comparable drying tendencies showed the tests with permanent and pulsed microwave treatment. In
these test series the wood moisture clearly fell with increasing time duration, even when the surface
temperature rise was marginal. Noticeable was, that the duration of the pulse (5, 10 or 15 seconds) had
no influence on the moisture change.
moisture content (%)
20
15
10
5
0
up to 25 ± 5°C, hold temperatures till 10 min
up to 25 ± 5°C, hold temperatures till 30 min
up to 25 ± 5°C, hold temperatures till 20 min
up to 40 ± 5°C, hold temperatures till 30 min
up to 40 ± 5°C, hold temperatures till 20 min
up to 30 ± 5°C, hold temperatures till 10 min
up to 30 ± 5°C, hold temperatures till 10 min
up to 30 ± 5°C, hold temperatures till 30 min
up to 30 ± 5°C, hold temperatures till 20 min
temperatures and duration of treatment
151
w ooden humidity
before treatment
w ooden humidity
after treatment
Fig. 4. Change of wood moisture of dry samples with mycelia in a passive state
before and after interval treatment