Effect of intermittent heat treatment on crystallinity in wood cellulose

The effect of intermittent heat treatment on cellulose crystallites in wood was studied to evaluate quantitatively the changes of crystallinity induced by intermittent and continuous heating. The changes in crystallinity were found to be strongly affected by the intermittent heat treatment. The increased crystallinity, the width of the crystals, and the piezoelectric properties were the same for the first intermittent heating as for continuous heating. Further intermittent heating for the same time duration and temperature had no effect on the above properties, probably due to the stopping of the thermal reaction during the interval. Our results suggested that intermittent heat treatment has certain critical cooling temperatures that stop the thermal reaction and are closely related to the duration of the interval. Samples once exposed to a certain duration of heat treatment and then cooled need more time, about twice that of the first duration of intermittent heating compared with continuous heating, to reach maximum crystallinity in wood cellulose.     

Study of crystalline behavior of heat-treated wood cellulose during treatments in water

The crystalline behavior of heat-treated wood cellulose treated at 85% relative humidity (RH), in water, or boiled in water after heat treatment was investigated. The normal increased crystallinity was significantly depressed for samples that were oven-dried and then treated in 85% RH or in water. In the case of boiling-water treatment, a more pronounced increased in crystallinity was initially observed, which then decreased gradually. The crystallinity decreased more than untreated wood for samples that were heat treated for long periods and was slightly higher than the decreased crystallinity from the beginning of the above two treatments. On the other hand, no significant change in crystallinity was observed for samples of increased crystallinity or decreased crystallinity that were treated under high-moisture conditions, for all three treatments. The results show that the crystalline state of wood cellulose heat treated under oven dry or high-moisture conditions behave differently if treated in water after heat treatment. Results suggested that the mechanism of crystallization might be different for samples that are subjected to heat treatment under oven-dry and high-moisture conditions.     

THE EFFECT OF HEAT TREATMENT ON DIFFERENT SPECIES WOOD COLOUR

Woodisnaturalmaterial,naturegivewoodsurfacecolor,g]oss,grain,qualitysenseetc-,whichconsititutedwoodaesthet-icfeeling.Forthisreson,peoplealwaysusedwide]ywoodtomakefurnitureanddecorating,andstlldiedonthequntitativetestingofwoodsurfacevisualphysicalmagnitude.tl-8jTreeswereprocessedoperationbyaseriesofworkingprocesstoformthewoodsurfacewhichwesawandtouchedonfur-nitureanddecorating.Inthesekindsofworkingprocess,whetherthevisualphysi-calmagnitudeofwoodsurfacehadvaria-tionsorthisvariationschangedwoodna…     

Effects of heat treatment on brittleness of <Emphasis Type="Italic">Styrax tonkinensis</Emphasis> wood

A new approach is proposed for the evaluation of the brittleness of heat-treated Styrax tonkinensis wood. Heat treatment made wood more brittle when wood was heated at a higher temperature or for a longer time. The brittleness increased to four times that of the control when wood was heated at 200°C for 12 h. For treatment at 160°C, the increase in brittleness without any change in weight is thought to be possibly caused by the relocation of lignin molecules. At higher temperatures, loss of amorphous polysaccharides due to degradation is thought to become the main factor affecting brittleness. The crystallites that were newly formed after 2 h of treatment showed brittleness that was different from that of the inherent crystallites remaining after 12 h of heat treatment. This inherent crystalline cellulose possibly plays a role in brittleness. There is also the possibility of using color to predict the brittleness of heat-treated wood.     

AN ANALYSIS OF HEAT AND MASS TRANSFERPHENOMENON IN WOOD DURING DRYING

INTRODUCTIONTheconventionaltwingmethodisgener-all3usedduringwoocldryinginChinaandothercountriesatpresent.Fluidvelocity,tem-peratUreandrelativehumidityofdryingmediaarecontrolledmainlybymoisbecontentofwood'dunngwtingprocess.Soitisveryim-portanttounderstandthephenomenonofheatandmasstransferinwoodduringdIyingproc-essformakingreasonablythewtingtechnoI-ogy-controlwtingprocess,heightenwtingquality'.decreasewtingenergyconsumptionanddiminishwtingtime.Thephenomenonofheatandmasstrans-ferinwooddurin…     

Effect of relative humidity on thermal degradation of Norway spruce (<Emphasis Type="Italic">Picea abies</Emphasis>) wood

The rate of thermal degradation of wood as a function of the extent of heat-bath treatment was investigated. At both 150°C and 170°C, the rate of degradation increased along with increasing relative humidity in the heating atmosphere. However, up to intermediate relative humidity (in the vicinity of 50%), the higher the temperature, the less was the effect of increasing relative humidity on the degradation rate. Furthermore, the greater the relative humidity, the less was the effect of increasing temperature on the degradation rate. On the other hand, between intermediate relative humidity and water-saturated conditions, the effect of increasing relative humidity on the degradation rate was the same regardless of the temperature, and the effect of increasing temperature on the degradation rate was the same regardless of the relative humidity. In moist conditions, significant thermal degradation occurred at temperatures as low as 150°C.     

Relaxation mechanism of residual stress inside logs by heat treatment: choosing the heating time and temperature

 Some methods to reduce residual stress inside logs have been reported, although the conditions for stress relaxation are not yet clarified. Our study using precise experiments revealed that residual stress relaxation occurs only when both heat and moisture exist inside the logs. We then determined the heating time and temperature required to relax the residual stress inside the logs. Short air-drying treatments did not relax residual stress even though free water in the logs was greatly reduced. The residual stress of the 33-h 80°C-heated bolts was relaxed, whereas that of the 48-h 70°C-heated bolts was not. As for the influence of treatment time, bolts heated at 100°C were relaxed after 18 h of treatment. The 13-h heated bolts did not show any relaxation. Therefore, residual stress relaxation occurred rapidly owing to the thermomechanical change of the individual wood components comprising the cell wall. The moisture content inside all the bolts was much higher than the fiber saturation point. This is because relaxation occurs only when the heating temperature is maintained above 80°C for a particular duration of treatment. Received: December 12, 2001 / Accepted: February 18, 2002 Present address: Institute for Structural and Engineering Materials, National Institute of Advanced Industrial Sciences and Technology, Independent Administrative Institution, Nagoya 463-8560, Japan Tel. +81-52-736-7320; Fax +81-52-736-7419 e-mail: m.nogi@aist.go.jp Part of this report was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, April 2000 Correspondence to:M. Nogi     

Change in mechanical interaction between cellulose microfibril and matrix substance in wood cell wall induced by hygrothermal treatment

To investigate in detail the mechanical interactions and associations between cellulose microfibrils (CMFs) and the matrix substance, we measured the dimensional changes in cellulose crystals in wood cell walls after different treatments. The transverse expansion of CMFs observed after hygrothermal treatment and subsequent drying suggests that the matrix substance compresses the CMFs transversely under green conditions. However, as heat treatment breaks or weakens the association of the CMFs and the matrix substance, under hygrothermal treatment and drying at high temperature the matrix substance cannot compress the CMFs in the direction of the chain.     

Growth of cone-shaped carbon material inside the cell lumen by heat treatment of wood charcoal

Conclusions With treatment at 2500°C, wood cell walls partially transform into a turbostratic carbon structure, which has an X-ray diffraction peak corresponding to a layer plane spacing of 0.343 nm. Despite this change, there was no apparent change within the cell wall seen by SEM.Cone-shaped carbon material was formed inside the cell lumen after treatment at 2500°C. This is not a feature originating from any wood cell organism and seems to result from vaporized carbon or pyrolysis gases that originate within the cell wall.Part of this work was presented at the 52nd Annual Meeting of the Japan Wood Research Society, Gifu, April 2002     

桉材热处理及其渗透性能的改善

本文以高温软化和瞬时降压之方法对三种桉材（Ｅｕｃａｌｙｐｔｕｓ）进行了汽蒸热处理试验。结果表明：除赤桉（Ｅ·Ｃａｍａｌｄｕｌｅｎｓｉｓ）外，热处理后的桉材导管壁上纹孔膜出现了不同程度的破裂，甚至脱落为空洞。其渗透性能得到了较明显的改善。其中以１４０℃、５ｈ的热处理效果为佳。     

Relationship between production of hydroxyl radicals and degradation of wood, crystalline cellulose, and a lignin-related compound or accumulation of oxalic acid in cultures of brown-rot fungi

The degradation of wood, filter paper cellulose, and a lignin-substructure model, was measured in cultures of seven fungi usually regarded as brown-rot fungi. Hydroxyl radical production and the accumulation of oxalic acid in the cultures were also measured. Four of the fungi, Gloeophyllum trabeum, Tyromyces palustris, Laetiporus sulphureus, and Postia placenta, were typical brown-rot fungi, in that they preferentially degraded and eliminated the polysaccharides in wood and produced large amounts of hydroxyl radical. The rates of hydroxyl radical generation in cultures of the four fungi were directly proportional to the degradation rates of wood, cellulose, and the lignin-related compound, and inversely proportional to the amount of oxalic acid in the cultures. Two of the fungi, Daedalea dickinsii and Lentinus lepideus, did not degrade any of the substrates significantly and produced very little hydroxyl radical. Coniophora puteana had the highest rate of cellulose degradation, but did not degrade wood or the lignin model significantly and produced only negligible amounts of hydroxyl radical. These results indicate that brown-rot fungi produce large amounts of hydroxyl radical for the degradation of wood and crystalline cellulose.     

杉木热处理材结晶度及力学性能的研究

热处理对木材力学性能的影响是多样的,这与热处理条件下木材的物理化学变化密切相关。本次研究将杉木板材在160℃、180℃和220℃常压蒸汽条件下进行热处理,考察处理材的结晶度、抗弯弹性模量、抗弯强度及相互可能的关联。结果表明,热处理使试材结晶度增加,有助于提高木材的刚性,使热处理材的抗弯弹性模量高于常规对照材;结晶度的提高对抗弯强度没有改善作用,热处理后试材的抗弯强度明显下降。     

Crystallinity of wood and the size of cellulose crystallites in Norway spruce (<Emphasis Type="Italic">Picea abies</Emphasis>)

X-ray diffraction was used to study variations in the crystallinity of wood and the average thickness and length of the crystallites of cellulose as a function of the number of the year ring in Norway spruce [Picea abies (L.) Karst.]. The crystallinity increased from ring 4 to ring 10 from the pith and was constant after ring 10. The crystallinity of mature wood was about 30% ± 5%. The average thickness and average length of the crystallites were 3.2 ± 0.1nm and 28 ± 2nm, respectively; and no systematic variation of these values with the number of the year ring was observed. The mean microfibril angle decreased near the pith but was constant in the mature wood.     

Dynamics and potentials of carbon sequestration in managed stands and wood products in Finland under changing climatic conditions

Carbon (C) sequestration was studied in managed boreal forest stands and in wood products under current and changing climate in Finland. The C flows were simulated with a gap-type forest model interfaced with a wood product model. Sites in the simulations represented medium fertile southern and northern Finland sites, and stands were pure Scots pine and Norway spruce stands or mixtures of silver and pubescent birch.

Changing climate increased C sequestration clearly in northern Finland, but in southern Finland sequestration even decreased. Temperature is currently the major factor limiting tree growth in northern Finland. In southern Finland, the total average C balance over the 150 year period increased slightly in Scots pine stands and wood products, from 0.78 Mg C ha⁻¹ per year to 0.84 Mg C ha⁻¹ per year, while in birch stands and wood products the increase was larger, from 0.64 Mg C ha⁻¹ per year to 0.92 Mg C ha⁻¹ per year. In Norway spruce stands and wood products, the total average balance decreased substantially, from 0.96 Mg C ha⁻¹ per year to 0.32 Mg C ha⁻¹ per year. In northern Finland, the total average C balance of the 150 year period increased under changing climate, regardless of tree species: in Scots pine stands and wood products from 1.10 Mg C ha⁻¹ per year to 1.42 Mg C ha⁻¹ per year, in Norway spruce stands and wood products from 0.69 Mg C ha⁻¹ per year to 0.99 Mg C ha⁻¹ per year, and in birch stands and wood products from 0.43 Mg C ha⁻¹ per year to 0.60 Mg C ha⁻¹ per year.

C sequestration in unmanaged stands was larger than in managed systems, regardless of climate. However, wood products should be included in C sequestration assessments since 12–55% of the total 45–214 Mg C ha⁻¹ after 150 years' simulation was in products, depending on tree species, climate and location. The largest C flow from managed system back into the atmosphere was from litter, 36–47% of the total flow, from vegetation 22–32%, from soil organic matter 25–30%. Emissions from the production process and burning of discarded products were 1–6% of the total flow, and emissions from landfills less than 1%.     

Mechanical interaction between cellulose microfibril and matrix substance in wood cell wall determined by X-ray diffraction

We investigated mechanical interactions between the cellulose microfibril and the matrix substance in wood cell walls. X-ray diffraction measurements showed that the peak positions of (200) and (004) from cellulose crystals in wood cell walls tended to shift lower and higher toward 2θ, respectively, during water desorption in wood. From our simulations, it is shown that the peak shift of (200) during water desorption is not due to changes in the scattering pattern of the amorphous substance or to lateral expansion of the cellulose crystals due to the Poisson effect in the cellulose microfibril, which is compressed in the molecular chain direction as the amorphous substance shrinks. This suggests that the cellulose microfibril expands transversely during water desorption in the wood cell wall, and that there is a mechanical interaction between the cellulose microfibril and the matrix substance.     

Image analysis study of mould susceptibility of spruce and larch wood dried or heat-treated at different temperatures

Abstract

In this study, mould growth on wood was investigated by image analysis. The studied parameters were drying and heat-treatment temperatures (20–210°C), original and resawn surface and different wood species (spruce and larch). Small specimens—some of which were inoculated with a spore suspension—were stored under humid conditions and photographed once a week. Mould growth was assessed by image analysis. In general, results found in earlier studies regarding the influence of several parameters could be confirmed. Image analysis was found to be a useful method to quantify mould growth in an objective and reproducible way.     

Rapid prediction of wood crystallinity in <Emphasis Type="Italic">Pinus elliotii</Emphasis> plantation wood by near-infrared spectroscopy

Crystallinity is an important property of woody materials; it responds to tree growth traits, structure, and chemical composition, and has a significant effect on Young’s modulus, dimensional stability, density, and hardness, etc. The ability of near-infrared (NIR) spectroscopy coupled with multivariate analysis to rapidly predict the crystallinity of slash pine (Pinus elliotii) plantation wood was investigated. The results showed that the NIR data could be correlated with the X-ray diffraction (XRD)-determined crystallinity of slash pine wood by use of partial least squares (PLS) regression, producing excellent coefficients of determination, r ², and root mean square error of calibration, RMSEC. The use of either reduced spectral ranges or the selection of certain wavelengths consistent with known chemical absorptions did not have any detrimental effect on the quality of PLS models allowing the use of inexpensive, small, and portable spectrometers. These studies show that NIR spectroscopy can be used to rapidly predict the crystallinity of slash pine wood.     

Evaluation of wood cutting forces in dry and wet conditions by small-scale chipping tests applying different analysis methods

ABSTRACT

The aim of this paper is to study the effect of high moisture content in comparison to dry timber on the resulting cutting forces based on experimental small-scale chipping tests. Therefore, a wood chipper for single cuts is designed and different species of Austrian locally growing trees are utilized. The test specimens are investigated in almost dry and soaked wet conditions. The resistance of wood is measured utilizing a force sensor and the signal during the cutting process is subsequently analysed by two different methods. The results reveal that the mean value of the acting force during cutting is 38–81% minor compared to the maximum force. Even though the peak of the dynamically acting load is measured for just a comparably small time range, it reveals an impact on the fatigue behaviour of the tool as well as the tool supporting material. Hence, an approach of evaluated load spectra is applied to include the load distribution of the chipping process. The effect of dry and wet wood on the cutting resistance is examined, whereby wood exhibiting a high moisture content of 30–40% changes the acting load up to 98%, depending on the method of analysis.     

Testing and evaluation of natural durability of wood in above ground conditions in Europe – an overview

Natural durability of wood is determined by the European standard EN 252 for specimens in ground contact and EN 113 for basidiomycetes in the laboratory, but no test exists for above ground conditions. For above ground conditions, the European prestandard ENV 12037 and EN 330 are used to determine the durability of treated wood. The most important factors for fungal establishment on the surface and within wood are the moisture content, the surrounding temperature, and the relative humidity. Strength tests are the most sensitive for decay detection, but neither strength tests nor identification of fungi responsible for the decay are included in the standards of above ground durability in field tests. To detect decay, visual examination, pick or splinter tests, and mass loss determination are used. Identifying fungi with traditional methods, e.g., growth on solid medium, is time consuming and complicated. Molecular methods like polymerase chain reaction and sequencing do not require mycological skill for identification to species level, and furthermore the methods do not depend on the subjective judgement like most traditional methods, but are based on the objective information of the target organism (e.g., nucleotide sequences). The next generation of standard field tests will probably consider the drawbacks of standard tests today and be rapid and include both quality tests like molecular identification and nondestructive quantitative tests, e.g., acoustic tests. Laboratory tests can be improved by using fungi identified from field trials and by combining different fungi in the same test and thus simulate degradation in practice.     

Effects of wood carbonization on soil and initial development of seedlings in miombo woodland, Zambia

An assessment of the effects of wood carbonization by the traditional earth kiln method in Brachystegia-Julber-nardia (miombo) woodland on soil nutrients in the field and seedling growth under laboratory conditions was made from August 1992 to March 1993. Wood carbonization increased soil pH and exchangeable P and K. Generally seed germination was better in charcoal soil than in undisturbed soil among the seven indigenous woody plants studied. Seedling growth in charcoal soil was good, except for Isoberlinia angolensis which had lower growth rate than in undisturbed soil.