| Summary: | 碩士 === 國立宜蘭大學 === 森林暨自然資源學系碩士班 === 101 === Heat treatment is an environmentally sound physical process performed
between the temperatures of 160-230°C to modify the properties of wood through
mild pyrolysis. These changes include improvement of dimensional stability, a
darkening uniform color of the material, improvement of resistance to biological
attack, and enhance anti-shrinkage efficiency of wood. However, a reduction in
mass and some mechanical strength of heat-treated wood would occur. In this
study, sixteen imported wood species were heat-treated with nitrogen (N 2 ) and
steam atmosphere in a sealed reactor. Heat treatments were carried out at
temperatures of 150, 170, 190, 210, and 230°C for time duration of 2 hours.
Physical properties of heat-treated wood including mass loss, bending
strength, anti-shrinkage efficiency, and color changes were examined. The
chemical properties of heat-treated wood were determined by compositions
analysis, FT-IR, and thermal gravimetric analysis. The chemical compositions of
wood vinegar collected from this process were measured by GC-MS analysis.
Values of reduction in bending strength, mass loss, anti-shrinkage efficiency,
and color difference between treated and control samples were increased with an
increase in temperature. The maximum value of mass loss was 13.67% on average
of wood treated at 230°C. The anti-shrinkage efficiency of specimens treated at
230°C were 45-50% higher than those treated at 150°C. The surface color changes
of 150°C and 230°C heat-treated specimens were respectively 13.6 and 38.8 on
average.
The loss in hemicellulose content of sixteen wood species treated at 230°C
was 12% on average, the mean value of cellulose content remain around 55% and
the percentage difference of lignin was 7%. The primary thermal degradation
temperature of heat-treated species was 380°C according to thermal gravimetric
analysis. The relative intensity absorption of the carbonyl group (C=O)
(A 1745 /A 2900 ) and OH group (A 3425 /A 2900 ) of heat-treated specimens determined
from FT-IR analysis were slightly lower than those of untreated wood, and an
increase in 0.3 of lignin. This result verify heat-treatment process leading to a
decrease in OH content, and an increase in lignin content. The crystalline index
of heat-treated hardwood was on average 10% higher in comparison to untreated
specimens, and the changes in softwood specimens were limited.
The organic components of wood vinegar could be separated into three
fractions, included acid (55-80%), neutral (5-25%), and phenolic (5%) fractions.
The main chemical compounds of acid, neutral, and phenolic fractions were acetic
acid, furfural, and vanillin, respectively. The higher heat treatment temperature
induced, the more kinds of organic compounds obtained.
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