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1.
Summary The relative migration of the major endogenous ions (K+, Ca2+ Mg2+, Na+, Cl– in green sapwood ofPinus sylvestris L. was measured in a modified Hittorf transference cell. The transference numbers obtained gave the fractions of the current carried by these ions when an electric field was applied across the wood samples under the conditions used.Potassium and calcium ions were always found to be the main endogenous current carriers, followed by magnesium, sodium and chloride ions. No significant differences in transference number were found between wood stored under refrigeration or in a deep freeze, nor was there any effect on prior -irradiation. Fungal contamination in a few non-irradiated specimens led to lower transference numbers. Changes in moisture content from 86 to 141% produced no significant change but the results did depend on the tree from which the samples had been taken. A decrease in the length of the wood sample from 100 to 50 mm had little effect on the transference numbers of calcium ions but caused a decrease in those of potassium when larger quantities of electricity were passed. Transversely- and longitudinally-oriented wood samples, however, gave very similar results. Visual observation of the anode compartment indicated that the ions followed the path of least resistance between cathode and anode and that the current passed along the grain of the wood.Symbols ci molar concentration of ion i - F Faraday's constant (96 494 C/mol) - I current - t time - ti transference number of ion i (also shown as t(i) in tables) - V volume of electrode compartment - Zi charge number of ion i The authors thank SERC and Rentokil PLC for the award of a CASE Research Studentship to P.J.S. and the Leverhulme Trust for the award of an Emeritus Fellowship to M.S.  相似文献   

2.
Summary A model that predicts heat and moisture transfer through wood in the hygroscopic range and which is based on the principles of irreversible thermodynamics, was evaluated with unsteady-state nonisothermal moisture desorption experimental data. The model predicted the phenomenon of thermal diffusion during the initial stages of desorption and results in a very good simulation of the desorption curve and the center's temperature change with time.Symbols Cp specific heat of air (= 0.24 cal/g K @ 70 °C) - CT specific heat of wood, cal/g K - D transverse diffusion coefficient, cm2/s - Eb activation energy, cal/mol - Eo heat of vaporization, cal/mol - EL differential heat of sorption, cal/mol - G specific gravity of wood - H relative humidity, % - hT convective heat transfer coefficient, cal/cm2 s K - hc convective mass transfer coefficient based on the concentration of moisture in wood, cm/s - hv convective mass transfer coefficient based on the concentration of moisture in the air in equilibrium with the wood surface, cm/s - KM coefficient for diffusion due to moisture gradient, g/cm s % - KT transverse thermal conductivity coefficient, cal/cm K s - M moisture content, % - Po saturated vapor pressure, atm - R universal gas constant, cal/mol K (= 82.056 cm3 atm/mol K) - t time, s - T temperature, K - x distance, cm Greek Letters evaporation or condensation criterion - wood density, g/cm3 - W water density (=1), g/cm3 - a air density, g/cm3 Department of Wood Science and Forest Products Virginia Polytechnic Institute and State University Blackburg, Virginia 24061-0503  相似文献   

3.
Summary The diffusion equation for water in wood is expanded in terms of temperature and moisture gradient on the assumption that the driving force for the diffusion of water in wood is the partial pressure of water vapour. An analytic expression is then developed for the activation energy of diffusion in terms of enthalpy and entropy changes associated with the sorption process. The expression is compared with another published curve and some similarity was observed.Symbols C water concentration, kg/m3 - D diffusion coefficient for water vapour in wood with vapour pressure as the driving potential, kg/ms Pa - Dc diffusion coefficient for water vapour in wood with water concentration as the driving potential, m2/s - Dc a constant value of Dc, m2/s - E activation energy of diffusion, J/kg - F flow density, kg/m2 s - f h/l - h specific enthalpy, J/kg - L l/R T - l latent heat of vapourization of free water, J/kg - ls latent heat of vapourization of sorbed water, J/kg - p partial pressure of water vapour, Pa - ps pressure of water vapour at saturation, Pa - R specifc gas constant for water, J/kg K - r relative humidity - s specific entropy, J/kg K - w dry basis moisture content - x length coordinate, m - a constant temperature equal to 6,800 K - -/ln r - w density of wood (dry mass/moisture volume) at a given moisture content, kg/m3 - s/R - L style as 2 lines above - free water relative to sorbed water The author is grateful to the Editorial Board in relation to the use of (4)  相似文献   

4.
To investigate the possibility of decontaminating 137Cs-contaminated Cryptomeria japonica wood, kraft pulping was conducted and the Cs behavior in the reaction process was examined. 133Cs-treated or 137Cs-contaminated bark, sapwood, and heartwood chips of Cryptomeria japonica were digested using an aqueous solution of NaOH and Na2S. The pulp was washed with ultrapure water and filtered, after which the filtrate (black liquor) was collected. The black liquor was acidified to separate the supernatant and precipitation. The Cs (133Cs and 137Cs) concentrations in the chip and reaction products were measured. As for wood samples, the majority of Cs was present in black liquor, while only a minor amount of Cs was retained in the pulp (<1%). In the case of bark, although the majority of Cs was present in the black liquor, the proportion of Cs in the pulp was much higher than that in the wood pulp. In addition, the Cs in the precipitation of the bark was higher than that in the wood, possibly because the Cs in the bark was combined with some components, which is insoluble in alkaline solution. Our results suggest that 137Cs-contaminated Cryptomeria japonica wood can be used in the pulp and paper industries.  相似文献   

5.
Summary Various chemicals are used for protecting wood samples against fungi, and some of them are released in water, leading to pollution of the water. The kinetics of release of pentachlorophenol in water has here been studied, by considering the diffusion through the wood along the three principal axes of diffusion. The experiments and the modelling of the process is successfully coupled. The numerical model takes the three principal diffusivities, the partition factor, the volumes of wood and water into account. The effect of the length of the wood sample taken along the longitudinal axis of diffusion is especially studied, as the longitudinal diffusivity is much higher than the other two principal diffusivities. The effect of the relative volumes of wood and water is also of considerable interest not only for the concentration of the chemical in water but also for the rate of release.Symbols C concentration of liquid (g/cm3) - Cs, Ceq,t concentration of liquid on the surface, at equilibrium with the surrounding, respectively - Ci,j,k concentration of liquid in the wood at position (i, j, k) - D diffusivity (cm2/s) - h coefficient of mass transfer on the surface (cm/s) - i, j, k integers characterizing the position in the wood - K partition factor - L, R, T dimensions of the parallelepipedic wood sample - Mini amount of chemical contained in the wood at the beginning of the desorption - ML, MR, MT dimensionless numbers - Mt, M amount of chemical released up to time t, up to infinite time, respectively - N half-number of slices taken in the wood parallelepiped along each dimension - Vwater volume of the surrounding water - x, y, z coordinates - L, R, T thickness of the slices taken in the wood for calculation - t increment of time  相似文献   

6.
Summary It is demonstrated that there can be only one driving potential for the movement of water through wood and this will be a function of wood state. On the assumption that the driving potential is the partial pressure of water vapour, a theoretical expression is derived for the diffusion coefficient. Such expression is fitted to diffusion coefficients for Scots pine and a remarkably good fit is obtained.Symbols a reciprocal mean radius of curvature of a capillary meniscus; also taken to be the radius of the corresponding exposed liquid surface, m - b spacing between flow paths in the cell wall, m - D diffusion coefficient for water in wood with vapour pressure as the driving potential, kg/ms Pa - Da diffusion coefficient for water vapour through air, kg/ms Pa - D diffusion coefficient for water in wood with the driving potential - D diffusion coefficient for water in wood with the driving potential - D0 diffusion coefficient for water in wood with vapour pressure as the driving potential, which is associated with leakage paths through the wood, kg/ms Pa - Df diffusion coefficient for water in wood with vapour pressure as the driving potential, corresponding to fibre saturation and with no leakage paths, kg/ms Pa - Dc diffusion coefficient for water in wood with vapour pressure as the driving potential, which is associated with the constriction of the vapour flow as it approaches the cell wall, kg/ms Pa - D diffusion coefficient for water in wood with moisture content as the driving potential, kg/ms - diffusivity for water vapour in air, m2/s - F flux of water, kg/m2 s - p partial pressure of water vapour, Pa - R specific gas constant for water, J/kg K - r fractional relative humidity - T temperature, K - x length coordinate in direction of flow, m - the dimensionless ratio Df/Dc evaluated at r=1/e - arbitrary driving potential for movement of water in wood - cell spacing in the direction of water flux, m - density of liquid water, kg/m3 - coefficient of surface tension, N/m - arbitrary driving potential for movement of water in wood - fractional moisture content  相似文献   

7.
Summary Selected tropical hardwoods from Cameroon were impregnated with methyl methacrylate and polymerized in situ using a catalyst-heat technique. The fractional volumetric retentions of monomer and polymer were determined and expressed in terms of the fraction of voids filled by the impregnant. Of the three species tested, Movingui and Bilinga were easily treatable and therefore considered suitable for wood-polymer composites; on the other hand Sapelli was difficult to treat.Notations M Movingui - B Bilinga - S Sapelli - MMA Methyl Methacrylate - PMMA Polymethyl Methacrylate - Fvl average values of the fraction of voids filled by monomer - Fvp average values of the fraction of void filled by polyme - Vm volume fraction of impregnant - Vv void volume fraction of the unimpregnated material - mc mass of the impregnated material - mw oven-dry mass of the wood prior to impregnation - w density of the wood based on oven-dry mass and volume - m density of the impregnant - ws density of cell wall material assumed to be 1.54 g/cm3  相似文献   

8.
Summary The diffusion equation (sometimes referred to as Fick's second law) is derived in terms of water movement under the action of capillary forces. The mass diffusivity is thereby expressed in terms of the capillary diffusion coefficient. A numerical calculation is given for yellow poplar.Notations C diffusion coefficient for water in wood with capillary pressure as the driving force, kg/msPa - D diffusion coefficient for water in wood with moisture content as the driving force, kg/ms - F mass flux, kg/m2s - pc capillary pressure, Pa - pcf capillary pressure extrapolated linearly to fibre saturation, Pa - T absolute temperature, K - t time, s - x distance ordinale in the direction of flow, m - mass diffusivity, m2/s - density of liquid water, kg/m3 - g basic density (dry mass/green volume), kg/m3 - w density of wood substance, kg/m3 - moisture content of wood - cls moisture content at continuous liquid saturation - cs moisture content at complete saturation - f moisture content at fibre saturation  相似文献   

9.
Summary The purpose of this study was to examine the influence of the moisture level on the cell-wall material in wood using pulsed proton nuclear magnetic resonance. The wood species used were western hemlock (Tsuga heterophylla (Raf.) Sarg.) and sitka spruce (Picea sitchensis (Bong.) Carr.), distinguishing between heartwood and sapwood regions. The moisture contents of the specimens were below the fibre saturation point and they were conditioned to equilibrium moisture contents based on initial desorption, adsorption and secondary desorption processes. From the FID experiments, the NMR-based moisture contents and the solid-wood lineshape second moments were determined. Average relative proton-spin densities, which were needed to calculate the NMR-based moisture contents, were determined from known moisture contents and they were: hemlock sapwood: 0.616; hemlock heartwood: 0.537; spruce sapwood: 0.679; and, spruce heartwood: 0.446. The average RSD value, considering both heartwood and sapwood, for western hemlock species was 0.577 and for sitka spruce was 0.563; these are close to published RSD values for other species. The condition as to how the equilibrium moisture content was attained did not influence the second moment for hemlock; however, for spruce sapwood, the second moments were sorption dependent. The hemlock M2 decreased from about 5.1 × 109 s-2 at low MNMR to 4.5 × 109 s-2 (heartwood) and 4.3 × 109 s-2 (sapwood) at higher mnmr. The adsorption and secondary desorption M2 for the spruce sapwood region decreased from about 5.0 × 109 s-2 at low mnmr to about 4.1 × 109 s-2 near the MF, whereas M2 for the spruce heartwood decreased from about 4.3 × 109 s-2 at low MNMR to about 3.5 × 109 s-2 near MF. Extractives may have a key role in obtaining the RSD and second moments.This project was financially supported by the Science Council of British Columbia, MacMillan Bloedel Research. The Natural Sciences and Engineering Research Council of Canada is acknowledged for their support of the NMR spectrometer measurements  相似文献   

10.
Summary Various chemicals are used for protecting wood samples against fungi, and some of them are released in water, leading to pollution of the water. The kinetics of pentachlorophenol release in water has here been studied by considering the diffusion through the wood along the three principal axes of diffusion. The experiments and the modelling of the process is successfully coupled. The numerical model takes into account the three principal diffusivities, the partition factor, the volumes of wood and water. The effect of wood sample length along the longitudinal axis of diffusion is studied especially, as longitudinal diffusivity is much higher than the other two principal diffusivities. The effects of the relative volumes of wood and water are also of considerable interest not only for the concentration of the chemical in water but also for the rate of release.Symbols C concentration of liquid (g/cm3)_ - C c ,C eq concentration of liquid on the surface, at equilibrium with the surrounding, respectively - C i,j,k concentration of liquid in the wood at positioni, j, k - D diffusivity (cm2/s) - h coefficient of mass transfer on the surface (cm/s) - K partition factor - i, j, k integers characterizing the position in the wood - M L ,M R ,M T dimensionless numbers - M t ,M amount of chemical released after time t, after infinite time, respectively - t increment of time - L, R, T thickness of the slices taken in the wood for calculation - N L ,N R ,N T number of slices taken in the wood - x, y, z coordinates - V water volume of the surrounding water  相似文献   

11.
u| li]? Genotypic variation in wood total and partial shrinkage, basic density and growth traits was estimated in 51÷2 year old Acacia auriculiformis trees in a clonal test. li]? In the tangential, radial and longitudinal directions, the mean values were 2.64%, 1.64% and 0.77% for partial shrinkage, and 5.92%, 3.23%, and 0.96% for total shrinkage, respectively. Total and partial transverse shrinkage were significantly greater in sapwood than in heartwood. li]? Clonal repeatability (H C 2 ) estimates for partial shrinkage were lower than those for total shrinkage, and heartwood shrinkages had lower H C 2 than those for sapwood. Estimates of H C 2 were from 0.32 to 0.38 for total transverse shrinkage, comparable to H C 2 for both total and partial volumetric shrinkages (0.40 and 0.32, respectively). However, H C 2 for longitudinal shrinkages, total and partial coefficients of anisotropy were only from 0.09 to 0.18. li]? The genotypic coefficients of variation of all shrinkage traits varied from 5.45% to 8.02%. Total shrinkage was strongly positively correlated with partial shrinkage in each dimension. Genotypic correlations were not significant between shrinkage and growth traits or density. Strong and significant correlations between transverse shrinkage in heartwood and sapwood (0.87) indicated that juvenile shrinkage is a good genetic indicator of this trait in older trees. Utilisation du retrait du bois dans l’amélioration de l’Acacia auriculiformis A. Cunn. ex Benth à croissance rapide au Vietnam.  相似文献   

12.
Summary Kraft delignification kinetics has been modelled on the basis of a first order decay process with a time-dependent rate constant. A generalized severity parameter derived from this kinetic model, Roh, has been applied to describe the lignin solubilization during alkaline (soda and Kraft) and bisulphite pulping of different wood species. The model has been succesfuly applied to data sets available from the literature. Our approach has combined the main process variables (temperature, time and chemical load) into a single parameter, Roh, which is then used as a reaction ordinate to map the changes in chemical composition and physical properties. An extension of the initial formulation of the Roh parameter has been made to cover the situations where the catalytic system is composed by two active chemical species, as in the Kraft process.Symbols C Lignin concentration - C0 Lignin concentration at t = 0. - a Average activation energy (kJ/mol) - fi Conversion of the reacting substrate (lignin) - F[ ] A function of the conversion - g(E) Distribution of activation energies function - k(t) Time-dependent rate constant - K Severity model constant - Roh The generalized severity parameter, or reaction ordinate - S i 0 Initial concentration of the reactive substrate (lignin) - t Reaction time (min) - T(t) Reaction temperature (°C),which may vary as a function of time in non isothermal conditions - Tref Reference temperature (°C), normally choosen in the middle of the experimental conditions used - X(t) Chemical load (g chemical/g o.d. wood), for the first active specie - Xref Reference chemical load (g chemical/g o.d. wood). - Y(t) Chemical load (g chemical/g o.d. wood), for the second active specie - Yref Reference chemical load (g chemical/g o.d. wood) Greek Letters Constant in k(t) (min-) - Parameter defining the shape of the Kohlrausch function which describes the distribution of activation energies - () Euler's gamma function - Parameter expressing the strength of the first active chemical in the specific reaction considered - Parameter expressing the strength of the second active chemical in the specific reaction considered - 0 Effective lifetime (min). - /- Average lifetime (min). - Parameter expressing the importance of temperature in the specific reaction considered. For instance a value of 14.75 will indicate that the rate of reaction has doubled ten degrees above the reference temperature, all the other variables remaining constant. Authors are indebted to CICYT (Science and Technology Inter Ministerial Commission, Spanish Government) and Generalitat de Catalunya (Catalan Regional Government) for financial support, project number QFN92-4317 and grant number AIRE 92/I-22. Contributions of the National Science and Engineering Research Council of Canada (NSERC) and Fonds des Chercheurs et Actions de Recherche (FCAR) are gratefully acknowledged.  相似文献   

13.
Diurnal gas exchange characteristics were measured simultaneously in two mangrove species, Avicennia marina and Bruguiera gymnorrhiza, over 7 d in summer (February–March), to compare their productivity. The study was undertaken in the Beachwood Mangroves Nature Reserve, Durban, South Africa, using fully expanded leaves of young and mature trees at the top of the canopy. Gas exchange was strongly influenced by photosynthetic photon flux density (PPFD), leaf temperature and the accompanying leaf to air vapour pressure deficit ( w). Carbon dioxide exchange was saturated at a PPFD of about 600 mol m-2s-1 in B. gymnorrhiza compared to 800 mol m-2s-1 in A. marina. Maximal CO2 exchange occurred between 12h00 and 14h00 and was consistently greater in A. marina (8.8 mol m-2s-1) than in B. gymnorrhiza (5.3 mu;mol m-2s-1). Mean internal CO2 concentrations ( ci) were 260 l l-1 in A. marina and 252 l l-1 in B. gymnorrhiza. Photorespiratory activity was 32% in A. marina and 30% in B. gymnorrhiza. Mean water use efficiency (WUE) was 8.0 mol mmol-1 in A. marina and 10.6 mol mmol-1 in B. gymnorrhiza. Diurnal leaf water potentials ranged from –0.8 to –3.5 MPa and were generally lower in A. marina.  相似文献   

14.
Summary We present experimental data on hydrolysis of wood in high temperature short residence time (HTST) and low acid concentration conditions. Effects of temperature, acid concentration, particle size and liquid/solid ratio are discussed. A kinetic model is proposed which accounts for effects of temperature and acid concentration. This kinetic model is used to predict performance of a twin-screw extruder as a hydrolyser which consists of ideal mixed flow or plug flow reactor units in series.Symbols A Acid concentration in liquid phase - A Acid concentration in solid phase - A0 Initial mass of sulphuric acid, g - C Cellulose content of solid phase, % - d Diameter of wood particles, m - E1 Activation energy of cellulose hydrolysis, cal. mol-1 - E2 Activation energy of glucose degradation, cal. mol-1 - F Objective function, refers to Eq. (5) - G Glucose yield - Ge Glucose yield at equilibrium - Gi, exp Experimental glucose yield (Eq. (5)) - Gi, th Calculated glucose yield (Eq. (5)) - Gmax Maximum glucose yield - k* Parameter defined by Eq. (9) - k1 Rate constant of cellulose hydrolysis, s-1 - k2 Rate constant of glucose degradation, s-1 - k 1 * Apparent rate constant of cellulose hydrolysis, s-1 - k 2 * Apparent rate constant of glucose degradation, s-1 - k10 Pre-exponential factor of constant k1, s-1 - k20 Pre-exponential factor of constant k2, s-1 - K Parameter defined in Table 3 - m Constant - mg Mass of glucose produced, g - M0 Initial mass of wood, g - M Mass of saturated steam delivered, g - M Mass of saturated steam delivered after 120 s of reaction time, g - m0 Initial mass of water, g - n Constant - N Number of reactor units - qi Volume flow rate in reactor units, m3 · s-1 - rg Conversion rate of glucose, s-1 - R Ideal gas constant, 1.987 cal · mol-1 K-1 - t Reaction time, s - T Temperature, K - Vi Volume of reactor units, m3 - W Water content of wood sample, % - X, X Parameters defined in Table 3 - Y, Z Parameters defined in Table 3 - Constant defined in Eq. (4), s-1 - v Number of experimental points (Eq. (5)) - i Residence time in plug flow unit, s - i Residence time in mixed flow unit, s  相似文献   

15.
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16.
In sapwood challenge experiments in Acer rubrum, columns of discolouration initiated by wounding and inoculation with pioneer fungi (Cephalosporium sp., Phialophora sp.) were similar in size to untreated wounds. Inoculation with decay fungi (Pleurotus ostreatus, Trametes versicolor) produced larger columns of wound-initiated discolouration. The removal of bark around a bore wound caused a significantly larger column to form compared to the sum of the columns inititiated by separate wounds. Stage-I discoloured wood, not associated with obviously rotted wood, had concentrations of mobile cations and soluble phenols similar to sapwood. Stage-II discoloured wood, spatially associated with rotted wood, was frequently bounded by a chemically distinct boundary layer and the discoloured wood contained significantly greater concentrations of mobile cations and soluble phenols than stage-I discoloured wood.  相似文献   

17.
This paper analyses industrial round wood flows into, within, and out of Northwest regions of Russia. We examine sawlogs, pulpwood, and fuelwood used for industrial purposes obtained from logging, and chips obtained from the wood-processing industry. We attempt to clarify different recent trends in wood harvesting, industrial round wood export, and forest industries development that have an influence on unreported wood in Russia. Our method, which uses wood balance diagrams, provides an interpretation of data from different Russian sources in order to offer better transparency regarding wood flows from forests to mills. It also helps to explain the apparent imbalance between round wood supply and demand and it helps one to assess the possible share of unreported industrial round wood production in Northwest Russia. Based on annual forest-related statistical data available from the Ministry of Natural Resources, the State Committee of Statistics, and the Russian Federation’s Customs Department, unreported round wood flows can be estimated to be 23% of the total industrial round wood production, or approximately 9 million m3 u.b. per year. Unreported round wood flows are more common in export oriented regions that have poorly developed forest industries.
Yuri GerasimovEmail: Phone: +358-102-113253Fax: +358-102-113251
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18.
Summary Plastic stress arising in wood during drying is calculated according to the theoretical model developed earlier. The mechanism of stress reversal and the type of resudual stress corresponding to different values of material constants are shown. The results are in qualitative agreement with experimental evidence.List of symbols A coefficient of swelling below the fibre saturation point - C concentration of moisture in wood; weight of moisture per weight of dry wood - C 0 uniform concentration of moisture in wood at the beginning of drying - C 1 equilibrium concentration of moisture at the boundary during drying - C =C-C 1 - non-dimensional concentration - D diffusivity - D 0 first term in the expansion of diffusivity as function of concentration: D=D 0(1+D 1 C+...) - D 1 secondterm in the expansion (see D 0) - E Young's modulus - e ij deviator of tensor of strain: - e ij P deviator of plastic strain: - e ij E deviator of elastic strain - F fibre saturation point (concentration at which the function (c) changes slope) - F =F-C 1 - g(x,t) function which assumes the value 1 in the elastic zone and 0 in the plastic zone - k von Mises' yield stress - L half width of the sample - M total moisture content - P plastic power - S ij deviator of stress - S kk =S 11+S 22+S 33 - S ij E =2 e ij - T ij tensor of stress - T kk =T 11+T 22+T 33 - T non-zero component of stress in a beam or plate - non-dimensional stress - actual stress rate in an elastic zone, fictitious stress rate in a plastic zone - t time - t increment of time - x y z spatial coordinates - X increment of spatial coordinate - Y - Y 0, Y 1 terms in the expansion of Y(C): Y(C)=Y 0(1+Y 1 C+...) - non-dimensional Y - , (c) coefficient of osmotic expansion (dependent on concentration) - ij tensor of strain - kk =11+22+33 - =yy=zz non-zero component of strain in the case of a plate or beam - modified strain - elastic constants of an isotropic body - non-dimensional spatial coordinate - Poisson's ratio - non-dimensional time  相似文献   

19.
Previous papers have quantitatively indicated that the total movement of cement bonded particleboard (CBPB) is equal to the sum of the movement of its components. This paper examined the efficacy of the law of mixtures when applied to the movement of a wood-cement composite under internal swelling or shrinkage stresses. Abundant data generated in companion papers were first manipulated to develop the universal formulae for predicting the movement of components. In conjunction with previous numerical results from image analysis of the structure of CBPB, and the orientated elasticity and stress algorithms, the models for theoretically predicting mass and dimensional changes of CBPB were derived. Validation studies were conducted and these demonstrated an excellent agreement of the theoretical predictions with experimental data for both mass and dimensional changes of CBPB due to internal swelling or shrinkage stresses during adsorption and desorption. The success also implied that CBPB can be treated as a composite and its properties can be well derived by the law of mixtures even though CBPB is an unusual type of composite having a very high volume fraction of wood chips, but a very high mass fraction of cement paste.Notation ERT Mean transverse modulus of elasticity of wood - EL Longitudinal modulus of elasticity of wood - Ep Modulus of elasticity of cement paste - Ewa Modulus of elasticity of embedded wood chips at angle - E Modulus of elasticity of wood chips at direction - E Modulus of elasticity of wood chips at direction - GLRT Mean transverse shear modulus of wood - L(T)cp Length/width (thickness) change of CBPB at angle - L(T)p Length (thickness) change of cement paste - mpf Mass fraction of cement paste in unit mass of CBPB - mwf Mass fraction of wood chips in unit mass of CBPB - Mcpj Mass change of CBPB at the various conditions tested - Mpj Mass change of cement paste at corresponding conditions - Mwj Mass change of wood chips at corresponding conditions - M(L; T)w/P Mass, length or thickness changes of wood chips or cement paste at various conditions - t Duration of exposure - LRT Mean transverse Poissons ratio of wood - Vpf Volume fraction of cement paste in unit mass of CBPB - Vwf Volume fraction of wood chip in unit mass of CBPB - cp Density of CBPB - k Density of wood chip or cement paste - cp Overall stresses of CBPB at angle - L Stress in the longitudinal direction of wood - RT Mean stress in the transverse direction of wood - p Stress of cement paste - w Stress of the wood chips at angle - Stress of the wood chips at direction - Stress of the chip at direction - cp Strain in CBPB - p Strain of cement paste - WL Strain in the length of wood chips - WT Strain in the thickness of wood chips - w Strain in wood chips - Angle between the longitudinal direction of wood chips and surfaces or edges of CBPB - Angle between wood chips and edges (length direction) of CBPB - Angle between wood chip and vertical coordinate - A, B, C Coefficients related to the feature of materials and exposure conditions The senior author wishes to thank Professor W.B. Banks of University of Wales, Bangor for his constructive discussions and assistance and the British Council for partly financial support.  相似文献   

20.
Wetting of wood     
Summary Thermodynamic work of adhesion, contact angle, wettability and acid-base contributions of the wetting of four North American wood species were determined using the Wilhelmy technique. The wetting angles with water varied from 60° for Sitka spruce to 74° for Douglas-fir. The wood surfaces had a strong acidic character since the greatest interactions for all the wood species occurred with formamide (basic probe) while lesser interactions were obtained with ethylene glycol (acidic probe). In addition, dispersive and polar surface free energies of wood, d s and p s respectively, were determined using Wu's simultaneous equations. In general, 75 to 80% of the total surface free energy of wood was due to dispersion forces. Specific wettabilities of wood and advancing contact angles in thirty various organic liquids were also evaluated.  相似文献   

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