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March 9, 2007
Abstract
A new technique for measuring the monolayer water content of fiber is presented. Tritiated water is added to a pulp/water suspension, whereupon the tritium partitions between the bulk water and the pulp. In the pulp phase the tritium can exchange with free water, bound water, and with hydroxyl and other protons present in the pulp matrix. The free water in the pulp is then removed by displacement with acetone. The tritium remaining in the pulp is mostly associated with tightly bound water, with a small fraction being tied up with the exchangeable hydrogen in pulp. The procedure provides a value of 10% for the tightly bound water content of hardwood or softwood fiber, either bleached or unbleached. If this water is assumed to cover the fiber surface as a monolayer, then an estimate of the wet surface area of the fiber can be obtained. This estimate compares well with independent measurements of surface area.
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March 9, 2007
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The surface area of pulp increases upon refining, which also increases the quantity of bound water. The subfraction of water attached to the surface as a monolayer can be determined by adding tritiated water to a pulp/water suspension and measuring the distribution of tritium between the pulp and bulk water. For bleached kraft pulp the tightly bound water slowly increases with progressive refining, increases sharply at 360 ml Canadian Standard Freeness (CSF), and then falls below CSF 220 ml. The fiber saturation point displays a similar profile, although the changes are much less pronounced. It is proposed that refining occurs in three discrete stages. First, refining down to CSF 360 ml removes the primary cell wall and S1 layer, while the S2 layer begins to swell. Next, internal delamination occurs within the S2 layer between CSF 360 and 220 ml, as confirmed by scanning electron microscopy. The onset of delamination is sudden: dramatic changes in fiber structure occur at CSF 360 ml, at which point the tightly bound water content rapidly increases. Finally, fiber destruction occurs below CSF 220 ml.
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March 9, 2007
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The length data from 12 samples of wood fibers and particles were described using lognormal and Weibull distributions. While both distributions fitted the middle range of the data well, the lognormal distribution provided a closer fit for short fibers and particles and the Weibull distribution was more appropriate for long ones. A mixture of the lognormal and Weibull distributions was developed using a variable weight to allow the new distribution to take the lognormal form for short fibers and gradually change to the Weibull form for long fibers. In the segmented distribution approach, a left segment of the lognormal distribution was joined to a right segment from the Weibull form. The Anderson-Darling goodness-of-fit test at the 5% level failed to reject the hypothesis that the mixture distribution and the segmented distribution fitted the data. Q-Q plots showed that both the mixture and segmented distributions provided an excellent fit to the fiber and particle length data, combining the best features of the lognormal and the Weibull distributions. These two new distributions are therefore better alternatives than the single lognormal and Weibull distributions for this data set.
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March 9, 2007
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Samples of two historical papers from the late 17th and early 18th centuries were irradiated with a 350-nm λ max light source. Atomic force microscopy examination of untreated samples of these laid paper sheets revealed notable surface inhomogeneity. Diffuse brightness values show that irradiation resulted in an initial decrease followed by a rapid increase in brightness with increasing irradiation time from 0.5 to 28 h. The bleaching effect then slowed, following a logarithmic path that did not plateau within 197 h of irradiation time. Irradiated sheets stored for 3 months exhibited brightness reversion of 7%. Fluorescence also decreased with irradiation time if excitation wavelengths of 320, 350, and 400 nm were applied for samples exposed to narrow-band irradiation at 350 nm. The fold endurance decreased by 34–72% after 197 h of irradiation. Changes in tear and tensile values were less dramatic. The Z -direction ultrasonic velocity decreased after 197 h of irradiation; however, the ultrasonic conductivity partially recovered during 9 months of storage.
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March 9, 2007
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A number of softwoods and hardwoods (beech, rubberwood, Corsican pine, Korean pine) were reacted with acetic anhydride to a variety of weight percentage gain (WPG) values and the volume change due to reaction was determined both by measurement of the external dimensions and by helium pycnometry. The volume change due to modification determined by helium pycnometry was found to be equal to that calculated, except for Corsican pine. The volume change as determined by the external dimensions was not a reliable method for determining cell-wall volume changes. The molar volume of the acetyl group in the cell wall was calculated over a range of WPG values, with volumes ranging from approximately 32 to 42 cm 3 mol -1 , depending on the wood species studied. The differences in acetyl molar volume observed between most wood species were significant.
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March 9, 2007
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A novel method for the acetylation of wood was investigated and compared with the classical method based on acetic anhydride. The transesterification reaction between vinyl acetate (VA) and hydroxyl groups of maritime pine sapwood ( Pinus pinaster Soland) was performed in the presence of potassium carbonate as a catalyst and led to acetylated wood in high yield. The transesterification reaction was confirmed by FTIR and 13 C CP-MAS NMR spectroscopy. The efficiency of the VA transesterification increased with increasing temperature, reaction time, and catalyst amount, but a significant weight percentage gain (WPG) was obtained after only 3 h at 90°C.
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March 9, 2007
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Wood polymer nanocomposites were prepared from solid aspen wood, water-soluble melamine-urea-formaldehyde (MUF) resin, and silicate nanoclays. The nanofillers were ground with a ball-mill before being mixed with the MUF resin and impregnated into the wood. The water-soluble prepolymer was mixed with the nanoclays at a mixing speed of 3050 rpm for 20 min to form impregnation solutions. Wood was impregnated with resin, which polymerized in situ under certain conditions. The physical and mechanical properties of the composite and the effect of ball-milling treatment of nanofillers on these properties were investigated. Significant improvements in physical and mechanical properties, such as density, surface hardness, and modulus of elasticity, were obtained for specimens impregnated with MUF resin and nanoclay-MUF resin mixtures. Ball-mill treatment favors dispersion of the nanofillers into the wood, but also appears to interfere with particle-resin adhesion.
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March 9, 2007
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The ellagitannins and ellagic acid from extracts of Portuguese oak wood chips ( Quercus pyrenaica ) used in cooperage from different origins (Gerês and Guarda forests) were analysed by HPLC. The results were compared with the ellagitannin content of wood chips obtained from American ( Q. alba ) and French ( Q. petraea ) oak. The influence of heat treatment and the coarseness of the grain on ellagitannins and ellagic acid were also studied. Five ellagitannins (vescalagin, castalagin, roburin D, roburin E and grandinin) and ellagic acid were quantified. Vescalagin and castalagin were the most abundant individual ellagitannins in all of the oak wood chips studied. Portuguese oak wood had the highest content of ellagitannins and ellagic acid, followed by the French and American oaks. The geographical origin of Portuguese oak and the coarseness of the grain of French oak affected the content of ellagitannins and ellagic acid. In general, the ellagitannin content decreased with the toasting process, while the ellagic acid content increased. The toasting process had the highest impact on ellagitannin composition in comparison to the other variables studied.
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March 9, 2007
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Three epimeric phenylpropanoid glycosides have been isolated from the aqueous acetone extract of Paulownia coreana inner bark. One compound is new and its structure has been established by spectroscopic methods as R,S- 7″′-(3″′,4″′-dihydroxyphenyl)-ethyl- O -α-L-rhamnopyranosyl(1″→3′)-β-D-(6′- O -caffeoyl)-glucopyranoside.
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March 9, 2007
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The lipid and lignin compositions of woods from the eucalypt species Eucalyptus globulus , E. nitens , E. maidenii , E. grandis , and E. dunnii have been characterized. The lipid composition was analyzed by GC and GC/MS using short- and medium-length high-temperature capillary columns, which allowed the detection of intact high-molecular-weight compounds. Similar lipid compositions were observed in all eucalypt woods, which were dominated by sitosterol, sitosterol esters and sitosteryl 3β-D-glucopyranoside. These substance classes are mainly responsible for pitch deposition during kraft pulping of eucalypt wood. However, some quantitative differences were found in the abundance of different lipid classes, with wood from E. globulus containing the lowest amounts of these pitch-forming compounds. The lignins of all eucalypt woods were analyzed in situ (without previous isolation) by pyrolysis-GC/MS. A predominance of syringyl (S) over guaiacyl (G) lignin units was observed and the S/G ratio was in the range from 2.7 to 4.1. E. globulus wood had the highest S/G ratio, a finding that, together with its low lignin content, explains its easy delignification under kraft cooking conditions.
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March 9, 2007
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The equilibrium moisture content in wood depends not only on the current relative humidity in ambient air, but also on the history of relative humidity variations. This hysteresis dependence of sorption in wood implies that in the worst case the moisture content for a given relative humidity may deviate by 30–35%. While researchers seem to have reached a general agreement on the hypothesis for the sorption hysteresis phenomenon, only a few models describing the phenomenon are available. Current models such as the independent domain model have numerical deficiencies and drawbacks. This paper presents a new hysteresis model, which mathematically resolves in closed-form expressions, with the current relative humidity and moisture content as the only input parameters. Furthermore, the model has the advantage of being applicable to different sorption isotherms, i.e., different species and different temperatures. These features make the model relatively easy to implement into a numerical method such as the finite element method.
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March 9, 2007
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Simple equations are proposed for calculation of critical stress intensity factors by tests using double cantilever beam (DCB) and three-point end-notched flexure (3ENF). The calculation modes are named here as modes I and II and are based on the beam theory and 95 previously published data on the elasticity properties of woods. The validity of the data was examined on specimens of western hemlock wood with various crack lengths. The influence of the elastic properties is more significant on the stress intensity factor calculated in mode I than that calculated in mode II. Further work is needed, particularly for measuring the mode I stress intensity factor. However, it is obvious from the experiments with western hemlock that the critical stress intensity factors can be determined by the equations proposed here.
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March 9, 2007
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Western red cedar ( Thuja plicata Donn) heartwood samples were extracted in methanol. Reverse-phase HPLC with UV detection was used for extractive separation and analysis. Six major extractives were quantified by comparing analyte response with the response factor of an internal standard using single-point calibration. The limit of detection of the method was estimated as (μg ml -1 ): (–)-plicatic acid, 0.6; γ-thujaplicin, 3.0; β-thujaplicin, 3.0; β-thujaplicinol, 3.0; thujic acid, 0.6; and methyl thujate, 1.2. Yields were 36% higher for powdered than for sliced samples. A temperature of 4°C during ultrasonication yielded 16% more (–)-plicatic acid than in non-cooled extractions, but did not significantly increase yields for the remaining five compounds. The recovery and repeatability of the extraction method were assessed by adding the aromatic compounds methoxyhydroquinone and 2-acetonaphthone to heartwood samples before extraction. The recovery yield was ∼90% with ∼5% variability.
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March 9, 2007
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Western red cedar ( Thuja plicata Donn) is a naturally durable softwood species native to British Columbia in Canada, and Washington, Oregon and California in the USA. Untreated T. plicata products are usually durable because of the presence of extractives with anti-microbial activity. However, there are extractive tolerant fungi that can attack T. plicata . To screen for extractive-tolerant species we developed a T. plicata feeder strip assay. When the feeder strips were placed on malt extract agar, extractives from the wood accumulated in the media and strongly inhibited growth of non-tolerant fungal strains. Extractives remaining in feeder strips following incubation on media were characterized. Of the many compounds leached out, γ- and β-thujaplicin, β-thujaplicinol, plicatic acid and thujic acid were quantified. The growth of selected fungal strains was not affected by plicatic acid; however, it was inhibited to different degrees by β- and γ-thujaplicin. Pachnocybe ferruginea was extractive-tolerant and may play an important role in the initial stages of degradation of T. plicata products.
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March 1, 2007
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This study set out to determine whether wood surface hardness plays a role in determining the resistance to Limnoria attack. The feeding rates of the wood-boring crustacean Limnoria quadripunctata on matchstick-sized samples of a range of timbers were assessed by measuring the production of faecal pellets under forced feeding conditions. Pellet production rates varied significantly between wood species, with production on Lophira alata (ekki) 25-fold lower than that on non-durable Scots pine ( Pinus sylvestris ) sapwood. The surface hardness of the timbers was measured for air-dry and seawater-soaked samples using a microindentation technique. The force required for a universal testing machine to drive a 150-μm-diameter pin 1.2 mm into the samples was measured. For all wood species, the hardness of seawater-soaked wood was lower than that of air-dry wood. Hardness was found to correlate positively with density. Pellet production rates showed a significant negative correlation with hardness across the range of species used, but if the denser species alone were considered, wood species significantly affected the rate, but hardness did not. In view of these observations, tests on resistance to attack by Limnoria should include a denser, non-durable wood species for comparison, as its hardness would likely be more similar to that of the durable species.
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March 1, 2007
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The resistance of Pinus radiata sapwood blocks treated with a boron-based preservative to biodeterioration by five Australian wood destroying fungi [ Fomitopsis lilacino-gilva , Coniophora olivacea , Gloeophyllum abietinum (boron resistant), Serpula lacrymans and Perenniporia tephropora ] was investigated. A phenyl pyrazole termiticide (fipronil) was also incorporated into the formulation to determine whether its presence affects biological efficacy. A linseed oil, liquid wax, terebene and trimethyl borate formulation inhibited decay by the trial fungi. Incorporation of fipronil did not affect the fungicidal properties. Fipronil alone exhibited no fungicidal activity. The termiticidal activity of fipronil was assessed (termite field test) in a formulation incorporating a fungicide, water repellent and drying agent in an alternative solvent carrier to that previously reported. The biological activity of the test compound was not diminished in this system. The 1-year progress performance of an ongoing in ground graveyard trial of similarly treated stakes, exposed to numerous termite species and decay fungi in tropical field conditions, is also presented. The predominant biological agent at the field site is the Australian subterranean termite Coptotermes acinaciformis (Froggatt). Treated stake samples of the Australian softwood Pinus radiata were exposed.
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March 1, 2007
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An accelerated method to evaluate wood preservatives for soil contact was explored using thin (4 mm) pine sticks in small decay cups containing non-sterile soil and wood compost-amended soil. The extent of wood decay was measured by monitoring changes in the bending elasticity (MOE) of the test samples, which was found to be a sensitive measure of the decay extent for both chromated copper arsenate (CCA)- and copper naphthenate (CuNap)-treated wood, and untreated wood. The decay rate was rapid, with significant decay detected in untreated wood after only 2 months of exposure. Decay in both treated and untreated wood samples was observed sooner when the soil was amended with wood compost. The compost-amended soil also gave significantly higher copper depletion for CCA- but not CuNap-treated wood. Although the results from this test should not be extrapolated to predict field test performance, it does appear to be applicable for rapid comparison of the performance of new and established preservative systems.
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