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June 1, 2005
Abstract
Relative proportions of cellulose in the I α and I β molecular packing forms were estimated through a relationship between molecular packing and the center of gravity of a 13 C NMR signal assigned to C-4 of cellulose. An alternative method, based on generation of linear combinations of spectra of 2 samples of wood, was too time-consuming for routine use but provided data for calibration purposes. NMR spectra of algal, tunicate, bacterial and commercial fibrous-powder cellulose were also used for calibration purposes. Mass fractions of the I α form were estimated as 0.51 for Pinus radiata wood and 0.25 for Castanea sativa wood. The difference is too small to have an important effect on moduli of elasticity.
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June 1, 2005
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The woods of Alder and Eucalypt were examined by light microscopy before and after a chemical treatment by the Indurite process to increase the hardness of the wood. The pattern of wood cell impregnation for Alder differed significantly from Eucalypt in some respects. In Alder wood all cell types eg. vessels, fibres and rays, were impregnated in similar proportions. In comparison, in Eucalypt wood the impregnation material was largely confined to ray cells and the lumina of vessels; other cell types were either not impregnated or impregnated in very small numbers. Transmission electron microscopy of Alder and Eucalypt woods suggests that ultrastructural differences in the texture and porosity of pit membranes may be the main reason for the observed differences between these wood species with regard to their impregnability by the impregnation material used.
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June 1, 2005
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The influence of the geometrical distribution of cell-wall tissues on the transverse anisotropic dimensional changes of softwood has been studied using two isotropic models. A finite element model has been used to calculate the thermal expansion of two aluminium plates without and with holes in the two perpendicular directions. Moisture expansion measurements in the two perpendicular directions were conducted using a polyamide (PA6) plate containing several holes. No differences were found in either the thermal expansion of the aluminium plates or the moisture expansion of the PA6 plate between the two perpendicular directions. Thus, the investigation suggests that the geometrical distribution of cell-wall tissues has no effect on the transverse anisotropic shrinkage of softwood.
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June 1, 2005
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This research dealt with the longitudinal air permeability of 40 important Chinese woods. The air permeabilities measured at about 10% moisture content for softwoods ranged between 0.00759 and 1.87130 darcy, while for hardwoods ranged between 0.00182 and 13.49867 darcy. The sapwood permeability of both softwoods and hardwoods was generally much higher than that of heartwood with 3 to 144 and 1 to 1302 times, respectively. The permeability values of wood were not affected by density between and within species. In all species studied, the permeability of heartwood of all softwoods, about 70% ring-porous and about 30% diffuse-porous or semi-diffuse porous hardwoods were below 0.1 darcy. The number of low permeability softwoods was higher than that of hardwoods. The number of low permeability ring-porous hardwoods was higher than that of diffuse-porous or semi-diffuse porous hardwoods. Finally, all the studied species were classified into five categories by their longitudinal permeabilities.
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June 1, 2005
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The development of cracks and changes in appearance have been investigated on radial and tangential surfaces of pine ( Pinus silvestris L.) and spruce ( Picea abies Karst.) which have been exposed outdoors for 33 months. The degradation of the surfaces has also been studied at the micro-level. Untreated samples, samples impregnated with a CCA-agent and samples surface treated with linseed oil have been tested. The annual ring orientation is the most important factor for crack development on weathering. The type of wood, impregnation treatment and surface treatment with linseed oil have only a marginal effect on the crack development. No relation has been found between the density of the samples and the crack development. After 33 months of outdoor exposure, tangential surfaces of pine have 13 times more total crack length per unit area than the corresponding radial surfaces. In spruce, the total crack length on the tangential surfaces is 6 times greater than on the radial surfaces. Tangential surfaces of both pine and spruce have a greater number of cracks per unit area and wider cracks than the corresponding radial surfaces. Tangential and radial surfaces show the same colour change in the surface as a result of weathering. On the micro-level, tangential surfaces have more and deeper cracks than radial surfaces. The cracks on the tangential surfaces occur frequently in both earlywood and latewood. On radial surfaces, cracks occur primarily at the annual ring borders, but to a certain extent also in the earlywood. The radial cell wall of the earlywood has a large number of pits which are degraded at an early stage. Decomposition of the cell wall takes place on both radial and tangential surfaces. Cracks arise which follow the S2 fibril orientation in the cell-wall. Delamination in the middle lamella is especially noticeable in the latewood on tangential surfaces. No differences have been observed regarding linseed oil treatment, impregnation or type of wood.
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June 1, 2005
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The ability of coniferous leaves to remove Cr(VI) from dilute aqueous solutions by physico-chemical adsorption and chemical reduction was investigated. Of 30 coniferous tree species tested, relatively high removal ability was found in Ginkgo , Larix , Pinus , Cryptomeria , Metasequoia , Taxodium , Thuja and Thujopsis spp. To search for optimum operation condition for treatment of wastewater containing Cr(VI), factors affecting Cr(VI) removal were studied using P. densiflora leaves. The extent of the removal was dependent upon the initial solution pH, contact time, temperature and initial concentration of Cr(VI) in solution. The Cr(VI) removal was mainly governed by the physico-chemical adsorption onto the substrate. The adsorption data were well fitted to the Freundlich isotherm.
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June 1, 2005
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The use of wood preservatives based on copper, chromium and arsenic (CCA) has become restricted in several countries due to environmental concerns. As a consequence, several chromium and arsenic free preservatives based on fungicides, regarded as more environmentally acceptable, have been developed. Most of these preservatives have only been tested in the laboratory against pure cultures of basidiomycetes and their long term effectiveness in practice is in many cases unknown. The effectiveness of six different preservatives, representing different types and combinations of fungicides, against mixed natural populations of micro-organisms, was evaluated during one year in terrestrial microcosms with soils known to provide high activity of different types of wood destroying micro-organisms. Of the fungicides tested, copper compounds provided the best protection against wood destroying micro-organisms. Copper free preservatives provided good protection against pure cultures of brown- and white rot fungi, but were ineffective when treated stakes were exposed in unsterile soils.
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June 1, 2005
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A screening of wood-rotting basidiomycete fungi was conducted for glucose 1-oxidase (GOD) and laccase (LAC) production as well as for ligninolytic activity measured by a Rhemazol reaction. The results showed that genera rich in GOD are lignin degraders as well as effective producers of extracellular LAC. The fungi poor in GOD neither showed LAC, nor ligninolytic activity. The Björkman lignin and 3 phenolic compounds, hydroquinone and syringic and vanillic acids, were tested on the sequential activity of LAC and GOD. In the presence of LAC, quinoid intermediates formed from Björkman lignin and phenolic compounds were observed. The addition of GOD caused a diminution of the quinone level. During incubation of Björkman lignin with LAC and GOD depolymerization occurred, and in the experiments omitting GOD the quantities of low molecular products were markedly lower. Consequently, the consecutive ping-pong activity of LAC and GOD reduced the polymerization and improved the efficiency of depolymerization processes.
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June 1, 2005
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The degradation characteristics of waterlogged archaeological compression wood excavated in South Korea were examined by transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). Degradation of Pinus compression wood occurred mainly in the inner part of the S 2 layer. In contrast, the outer part of the S 2 layer remained relatively intact. CLSM and TEM showed the erosion type of bacterial attack to be dominant in the secondary cell walls of both severe and mild compression wood. However, in some cases the middle lamella was also degraded, which suggests that other forms of microbial attacks, such as bacterial tunnelling, were also present. Bacterial erosion in the severe compression wood was mainly confined to the inner part of the S 2 layer whereas in the mild compression wood it also extended into the outer part of the S 2 and the S 1 layer. The extent of erosion correlated to the differences in the amount and distribution of lignin, particularly in the outer S 2 layer between the severe and mild compression wood cells. These features are compared with the degradation of normal Pinus wood.
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June 1, 2005
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Mechanical bending stress due to wind exposure has been suggested to be of major importance for induction of resin pockets in gymnosperm trees. In this study, this idea was tested experimentally by applying bending stress to 1-year-old internodes of five-year-old Pinus sylvestris L. seedlings during dormancy and/or growth. The stems were bent manually to 30° from their original upright position at regular intervals. About 30% of the stems that were bent during growth were wounded in the xylem, whereas no wounding was observed in control stems or stems bent during dormancy. Similarity of these wounds to naturally-occurring resin pockets leads us to conclude that exposure of seedlings to mechanical bending stress due to wind during growth can be a source of formation of resin pockets.
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June 1, 2005
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A fossil Picea abies from Zeifen (Germany), 100,000 years old and still presenting good physical and anatomical properties, is analysed with respect to its lipophilic content. Comparisons are made with a recent Picea abies , with a subfossil larch and with Taxodioxylon gypsaceum fossils ranging from 1.7 to 20 million years ago. Due to the relatively small age and the low degree of degradation, terpenes having structures intermediate between the original compounds and the final terpanes are looked for. Lipophilic components obtained from the fossil Picea abies by extraction with dichloromethane include linear alkanes, fatty acids, high MWs alcohols and terpenoids such as sesquiterpanes, diterpanes and diterpenoids. Some of extractive components result unchanged after the process of ageing while others correspond to substances derived by a process of hydrolysis of original extractives occurring in recent Picea abies . Diterpanes (norabietatriene, norpimarane, retene and α-phyllocladane) correspond to those present in most fossils of conifers, even if a trend to the formation of demethylated compounds is observed. Diterpenoids, on the contrary, are present exclusively as the dehydroabietic acid structure, the form preceding or responsible of those of most diterpanes, while different structures are not found. Since intermediate compounds with structures different from the abietic one are absent they might be looked for in younger fossils. The presence of a large amount of terpanes places this fossil rather closer to Taxodioxylon gypsaceum samples than to the subfossil larch.
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June 1, 2005
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The cork from the outer bark of Douglas-fir ( Pseudotsuga menziesii ) was exhaustively extracted and submitted to a mild CaO-catalyzed methanolic depolymerization. The solubilized material (2.5 % yield) was derivatized and analysed with GC-MS. Glycerol was the main component (41.2%), followed by aliphatic acid monomers (30.6%) and glyceryl and feruloyl dimers (14.5%). Monoacylglyceryl esters of α,ω-diacids were dominant (68% of glyceryl dimers), followed by monoacylglyceryl esters of alkanoic acids and of ω-hydroxyacids (respectively 20% and 9%). For all cases 1- and 2-monoacyl-glyceryl esters were present. Dimers of ω-hydroxyacids esterified to ferulic acid through their primary hydroxyl were also found. The feruloyl ester of docosanol could also be identified. The relative abundance of the dimers followed the proportion of acid monomers. The direct evidence found here for P. menziesii , and previously for Q. suber , that glycerol is esterified to all suberinic acids and that ω-hydroxyacids are esterified to ferulic acid supported the discussion of a suberin structure developing on glyceryl-diacyl-glyceryl and glyceryl-hydroxyacyl-feruloyl backbones.
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June 1, 2005
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Lignin composition and lignin removal were investigated in loblolly pines ( Pinus taeda L.) deficient in the monolignol biosynthesis enzyme, cinnamyl alcohol dehydrogenase (CAD). The CAD-deficient pines were homozygous for the cad - n1 allele, a mutant form of the gene encoding CAD. We show that lignin from CAD-deficient seedlings is more easily removed by mild alkali at room temperature. The nature of the phenolics recovered from this treatment link the increased lignin solubility to a build up of aromatic aldehyde lignin subunits. We carried out a retrospective genetic analysis to identify a 12 year-old CAD-deficient tree from which we isolated Milled Wood Lignin (MWL) and obtained wood chips for pulping studies. The UV absorption spectra of MWL and the effect of sodium borohydride reduction of MWL showed that the CAD-deficient tree had substantially higher incorporation of aldehyde subunits. The CAD-deficient wood was delignified more extensively than the wild type in soda pulping but not in kraft conditions. More extensive lignin removal, both in mild alkali treatment and in soda pulping, indicate that suppression of CAD in softwood trees may hold promise to produce woods well suited for “milder” pulping conditions that consume less chemicals and generate less waste.
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June 1, 2005
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Polyhydric alcohol pulping was developed to separate components of low-quality softwoods that are produced by thinning and improvement cutting as well as to establish a self-supporting pulping system. Propylene glycol (PG) was superior to ethylene glycol (EG) as solvent for polyhydric alcohol pulping at atmospheric pressure. PG pulping of fir, larch and cedar, with sulfuric acid as a catalyst, gave satisfactory pulps with few rejects and a very low level of residual lignin as compared with EG pulping. The PG pulps were readily bleached to approximately Kappa number 1 and 80% brightness by one treatment with sodium chlorite. The yield of bleached pulp from fir was 44.7% based on chips. The bleached pulps had very high α-cellulose content and crystallinity, and their mechanical properties were similar to those of kraft pulp. Therefore, polyhydric alcohol pulping appears to be promising for pulping of softwoods by an organosolv method.
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June 1, 2005
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The chemistry of oxygen delignification of high-yield kraft pulp was studied by analysis of residual lignin extracted from kraft and kraft-oxygen pulps using the acid hydrolysis/dioxane extraction method. For reference pulps cooked to kappa numbers between 20 and 25, the content of free phenolic groups decreased to about 50% the original value upon oxygen delignification, while the content of carboxylic acid groups increased by 50–100%. For lignins isolated from high-yield kraft pulp and oxygen delignified high-yield kraft pulp, it was shown that high-yield kraft pulping with polysulfide (PS) and anthraquinone (AQ) gives a residual lignin which is chemically different from that of kraft pulps cooked to lower kappa numbers. Lignin extracted from oxygen delignified high-yield PS/AQ kraft pulp was more similar to lignins extracted from kraft pulps cooked to lower kappa numbers.
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June 1, 2005
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A new mechanism including a homolytic cleavage of a trioxide intermediate forming superoxide is suggested to be the main course of radical formation in reactions of ozone and lignin like structures. The suggested mechanism is supported by quantum chemical and thermochemical methods.
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June 1, 2005
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In this study, the mechanical pulps were prepared under different preheating time and sulfonation conditions. The pulping conditions chosen yield a gradient of pulps ranging from thermomechanical pulp (TMP) through chemithermomechnical pulp (CTMP) with a low degree of sulfonation to CTMP with a high degree of sulfonation. The increase of the sodium sulfite charge resulted in a gradient of sulfur content which was shown to be related to the introduction of strong acidic groups as well as to the decrease of the carbohydrate content at the surface revealed by Electron Spectroscopy for Chemical Analysis (ESCA). These results together with Scanning Electron Microscopy (SEM) investigations confirm that the plane of rupture in the fiber has been transferred to a more lignin-rich area of the middle lamella. Despite the lower carbohydrate content at the surface, the water wettability of fibers was increased as revealed by dynamic contact angle. This is explained by the polar contribution of sulfonated lignin to the surface energy of the fibers. Inverse Gas Chromatography (IGC) analysis confirmed the differences in the surface properties of the pulps.
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June 1, 2005
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The mechanisms which cause an improvement in the dimensional stability of particleboards made from steam pretreated particles were investigated from the aspects of potential thickness recoveries of densified wood particles and the breakage of the adhesive bond network in particleboards. Since the latter would depend on the balance between bond strengths and stresses imposed on the adhesive bond, the effects of steaming temperature (160 to 220°C) on bond quality, recovery stress of compressed wood and in-plane swelling stress were investigated. Steam pretreatment was found: 1) to reduce thickness recoveries of densified wood particles, steaming temperatures above 190°C are especially effective, 2) not to cause a significant reduction in bond strength when steaming below 210°C or if relatively high press pressures of 1.5MPa are employed, 3) to reduce recovery stress of compressed wood, which is mainly caused by the increase in wood compressibility, 4) to reduce in-plane swelling stress of particles, which was found to correlate with reductions in both hygroscopicity and elasticity.
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June 1, 2005
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The effects of the oriented strand board (OSB) furnish drying temperature and moisture content on VOC emissions were evaluated and compared to those of the OSB pressing time and temperature and resin content. Results clearly showed the important role played by the drying temperature on the strand emissions. A decrease of emissions is observed when the furnish at a given original moisture content had been exposed to increasingly high temperatures. Also, the combined effect of moisture content and heating temperatures showed an increase of the detected TVOC as moisture content and the temperature increased. At a very high temperature however, the furnish at low moisture content started to degrade, and an increase in the emission level could be observed. The results showed that emissions from oriented strand board (OSB) panels were more sensitive to resin content and pressing time. The Box-Behnken statistical linear model used to treat the data revealed that a linear fitting better correlates our results. The correlation between the internal bond (IB) and the panel's emissions indicated a decrease in emissions as the quality of the board (IB) increases in agreement with better resin curing. The acquisition of more data will certainly be helpful to support this preliminary study.
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