DIGITALNA ARHIVA ŠUMARSKOG LISTA
prilagođeno pretraživanje po punom tekstu



ŠUMARSKI LIST 3-4/2009 str. 77     <-- 77 -->        PDF

S. Govorčin, T. Sinković, R. Hrčka: USPOREDBATEHNIČKIH SVOJSTAVATERMIČKI MODIFICIRANOG ...Šumarski list br. 3–4, CXXXIII (2009), 185-191
SUMMARY: The aim of this paper is to study differences in some physical and
mechanical properties of heat treated and recent wood. Wood used in this research
was ash (Fraxinus excelsiorL.) from the area of Otok, region of Slavonia in Croatia.
The felled tree was 85 years old with the diameter at breast height of 53 centimetres.
A heart board was made from the tree trunk in the north-south direction, 4 metre
long and 6 centimetres thick. The heart board was dried naturally with an average
water content of 12 %. The heart board was sawn in four equal parts so that four
heart boards were obtained – each 1 metre long. Looking from stump to top of the
tree, the first and third heart boards were not heat treated and they were used for
establishing the properties of recent ash. From the above four heart boards, samples
were made for determining macroscopic, physical and mechanical properties of recent
and heat treated ash. Treatment of ash (Fraxinus excelsiorL.) at the temperature
of 200 oC caused significant changes of technical properties relatively physical
and mechanical properties of the treated wood. Maximum possible number of samples
was made for each physical and mechanical property in radial direction, i.e.
from heart to bark. Maximum shrinkage was determined in radial and tangential direction,
as well as maximum volume shrinkage, density in absolutely dry condition,
nominal density and water content after a fortnight of soaking in water of physical
properties. Determination was also made of compression strength parallel to the
grain, static bending strength, hardness in longitudinal, radial and tangential direction.
The investigation of some physical and mechanical properties of recent ash
(Fraxinus excelsiorL.) and heat treated ash at 200 oC show diametrically different
values of investigated properties.


The investigation of mechanical properties of recent ash was carried out on samples
with water content of 12 %, while the water content of the heat treated ash samples
was 4 %. In order to be able to compare the results of mechanical properties,
their values were converted to the water content of 4 % for recent ash and 12 % for
heat treated ash. For increasing or decreasing mechanical properties of wood, correction
factor was used in accordance with Forest Product Laboratory, Madison.
The comparison of mean values of physical and mechanical properties of recent and
heat treated ash was carried out in accordance with Mann-Whitney test with the
help of statistical software Statistica. Density distribution in absolutely dry condition
in radial direction of heat treated ash deviates from the distribution common for
recent ash. The loss of mass with a relatively constant sample volume is evident in
radial direction, and especially in the heart section. Mean value of density in absolutely
dry condition of recent ash is higher by 8.4 % than density of heat treated ash.
Shrinkage in radial and tangential direction and volume shrinkage of recent ash are
higher that shrinkage in heat treated ash. Shrinkage in radial direction is higher by
70 %, in tangential direction by 62.2 % and volume shrinkage by 63.7 %. All above
said physical properties of recent ash are significantly different from physical properties
of heat treated ash. The investigated mechanical properties of recent ash are
also significantly higher than mechanical properties of heat treated ash. Compression
strength in longitudinal direction of recent ash is higher by 36.8 %, static bending
strength is higher by 48 %, hardness in longitudinal direction (cross-cut) is
higher by 31.3 %, hardness in radial direction (tangential cut) is higher by 22.8 %
and hardness in tangential direction (radial cut) is higher by 25.9 % than the stated
mechanical properties of heat treated ash at 200 oC. All investigated mechanical
properties of recent ash differ significantly from these properties of heat treated ash.
Dimensional stability of ash under such regime of heat treatment resulted in increased
dimensional stability, and however the investigated mechanical properties are
significantly lower. The above said percentages of higher values of mechanical properties
of recent ash than of heat treated ash with water content of 12 % and 4 % indicate
that they are similar at 12 % and 4 %. The similarity of these percentages
indicates that the correction coefficients for calculating mechanical properties at
different water contents is also satisfactory for heat treated ash.