Study of the release in water of a chemical used for preservation of wood. Effect of the dimensions of the wood

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) - C_s, C_eq,t concentration of liquid on the surface, at equilibrium with the surrounding, respectively - C_i,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 - M_L, M_R, M_T dimensionless numbers - M_t, 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 - V_water 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     

Process of absorption and desorption of water in a wood board,with 3-dimensional transport beyond the FSP

Summary The process of absorption of water in a piece of solid wood, as well as the following stage of desorption is studied, when the water content is beyond the fiber saturation point. A model based on a numerical method with finite differences is built and successfully tested. This model takes into account a 3-dimensional transport of water controlled by diffusion, with three principal axes of diffusion and three various principal diffusivities. The model is able to predict the kinetics of absorption or desorption when the three principal diffusivities are known, as well as the operational conditions.Symbols C (i, j, k) Concentration at the position of the coordinates i, j, k and at the time t - CN (i, j, k) Concentration at the same position, at the time t + t - C_s Moisture content at the surface - D_L Longitudinal diffusivity - D_T Tangential diffusivity - D_R Radial diffusivity - L Increment of space along the longitudinal axis - T Increment of space along the tangential axis - R Increment of space along the radial axis - t Increment of time - EMC or C_eq Moisture concentration at equilibrium - K Factor of evaporation (cm/s) - L, T, R Dimensions of the board along the longitudinal, tangential, radial directions, respectively - M_L Dimensionless number for the longitudinal axis - M_T Dimensionless number for the tangential axis - M_R Dimensionless number for the radial axis - Th Thickness of a sheet (in Eq. 15)     

On the activation energy of diffusion of water in wood

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 - D_c diffusion coefficient for water vapour in wood with water concentration as the driving potential, m²/s - D_c a constant value of D_c, 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 - l_s latent heat of vapourization of sorbed water, J/kg - p partial pressure of water vapour, Pa - p_s 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)     

The thermodynamics of sorption with reference to klinki pine

Summary An investigation into the bonding energy relationships for water in wood indicates that as the temperature increases at constant total moisture content, water moves from within the chemical structure to the adsorption surface. The analysis is evaluated for the wood Araucaria klinkii Lauterb and it is indicated that at 25 °C, less water is held in the chemical structure during adsorption than during desorption.Symbols A amplitude of liquid surface profile - A₀ amplitude of solid surface profile - a mean radius of curvature of liquid surface (bubble radius), Å - a₀ mean radius of curvature of solid surface, Å - a_c a constant value of a, Å - F a function of temperature - f capisorption energy fraction - G a function of - g specific Gibbs free energy of saturated water vapour relative to unsaturated water vapour at the same temperature, J/kg - g_c specific Gibbs free energy associated with capisorption, J/kg - g_p specific Gibbs free energy associated with physisorption, J/kg - h change in specific enthalpy of liquid water as it is desorbed, J/kg - l latent heat of vaporisation of free water, J/kg - m wave number/m - p_s pressure of water vapour at saturation, Pa - R specific gas constant for water vapour, J/kg K - r relative humidity - s change in specific entropy of liquid water as it is desorbed, J/kg K - T temperature, K - w dry basis moisture content - x ln p_s/p_s25 - y In r - z length coordinate, m - , , constant coefficients - change in mean height of liquid surface, Å - ₀ a constant length, Å - constant - distance from solid to liquid vapour interface measured normal to solid surface, Å - ₀ a constant value of , Å     

The distinction between average enthalpy and the isosteric heat of water sorbed on wood; and the spatial distribution of the specific enthalpy of the sorbed water

Summary It is commonly assumed that specific enthalpy is uniform throughout water sorbed on wood. It is suggested here that this is not the case and that as a result the isosteric heat and the differential heat of wetting are two distinct functions. An analysis is developed which enables the distribution of specific enthalpy within the adsorbed water to be approximated. The results are presented with reference to klinki pine.Symbols a parameter, Eq. (14) - h specific enthalpy of sorbed water, J/kg - h average specific enthalpy of sorbed water, J/kg - h isosteric heat, J/kg - h₁ integral heat of wetting, J/kg - k a constant - l latent heat of vaporization of free water, J/kg - P_s pressure of water vapour at saturation, Pa - q differential heat of wetting, J/kg - R specific gas constant for water, J/kg K - r relative humidity - T temperature, K - enthalpy function defined in Eq. (10), J/kg - moisture content - _p prevailing moisture content The author is grateful to Dr. A. N. Stokes for a substantial simplification of the original derivation of Eq. (13)     

Dimensional instability of cement bonded particleboard: Modelling CBPB as a composite of two materials

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 E_RT Mean transverse modulus of elasticity of wood - E_L Longitudinal modulus of elasticity of wood - E_p Modulus of elasticity of cement paste - E_wa 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 - G_LRT 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 - m_pf Mass fraction of cement paste in unit mass of CBPB - m_wf Mass fraction of wood chips in unit mass of CBPB - M_cpj Mass change of CBPB at the various conditions tested - M_pj Mass change of cement paste at corresponding conditions - M_wj 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 - V_pf Volume fraction of cement paste in unit mass of CBPB - V_wf 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.     

Osmotic stress in wood — part II: on the computation of drying stresses in wood

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     

On movement of water through wood — The diffusion coefficient

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 - D_a 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 - D_f 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 - D_c 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 D_f/D_c 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     

Effects of quenching on relaxation properties of wet wood

A new relaxation property is discussed on the basis of creep behavior of wet wood specimens pretreated with heating at various temperatures followed by quenching. The treated samples showed more marked relaxation than that of an untreated sample. The relationship between relaxation time and heating history was represented by an equation ln() = –( _f – k ₁)T + [ln( _g) + k ₂], where ln() is the logarithmic relaxation time of wet samples after quenching, T is the difference between the heating temperature and the glass transition temperature (T _g), ln( _g) is the logarithmic relaxation time at T _g, is a constant, _f is the coefficient of thermal bulk expansion, and k ₁ and k ₂ are constants. It was concluded from the analysis of experimental results that the change in the relaxation property caused by heating and the following quenching is due to the temporary free volume created by freezing of molecular chain motion of wood components, most probably lignin, during quenching.This work was presented at the 52nd Annual Meeting of Japan Wood Research Society, Gifu, April 2002     

Non-steady state water adsorption of wood

Summary The validity of the following equation of water adsorption into wood substance which was derived in the previous report, is examined: d(W)/dt = k₀(1 – exp(-k₁/t))W(l – W), which can approximately be written as: d(W)/d(logt) = rW(l – W), where W is moisture content; t is time (t > 0); k₀, k₁ and r are constants. After measuring dimensional change with change in time under various relative humidities, the change of moisture content was indirectly calculated from the proportional relationship between dimensional change and moisture content. It was found that the theoretical equation satisfactorily agreed with the experimental results. These results lead to the conclusion that the equation was valid. Furthermore, the properties of the equation, whose constants are determined from experimental results, is discussed. The rate of water adsorption of wood shows interesting and systematical properties, especially near relative humidities corresponding to the fiber-saturation point.     

Bearing properties of engineered wood products I: effects of dowel diameter and loading direction

The embedment tests of laminated veneer lumber (LVL) with two moduli of elasticity (MOE; 7.8 GPa and 9.8GPa), parallel strand lumber (PSL), and laminated strand lumber (LSL) were conducted in accordance with ASTM-D 5764. The load-embedment relation for each of these engineered wood products (EWPs) was established. The directional characteristics of bearing strength (_e), initial stiffness (k _e), and effective elastic foundation depth were obtained from the tested results. The effective elastic foundation depth (=E/k _e,E = MOE), based on the theory of a beam on elastic foundation, was obtained from thek _e and MOE. An of 90° (perpendicular to the grain) was calculated by dividingE ₉₀ [MOE of 90° from the compression test, but MOE of 0° (E ₀), parallel to the grain, obtained from the bending test] byk _e90, the initial stiffness of 90°. This study aimed to obtain the bearing characteristics of each EWP, taking into consideration their anisotropic structures, for estimating the fastening strength of a dowel-type fastener. The relations between the bearing coefficients ( _e,k _e,) on the loading direction and dowel diameter were established from the load-embedment curves. Based on the results of the embedment test, tested EWPs showed different tendencies in all directions from wood and glued laminated timber.Part of this study was presented at the 49th Annual Meeting of the Japan Wood Research Society, Tokyo, April 1999     

Changes in the physical and chemical properties of six Japanese softwoods caused by lengthy smoke-heating treatment

The effects of prolonged smoke-heating treatments on wood quality were investigated. Six Japanese softwoods were smoke-heated for 100 and 200h at a temperature of 75° ± 5°C, which was recorded inside the log. After smoke heating, wood quality, including moisture content, amounts of chemical components, relative degree of crystallinity (RDC) of cellulose, and sapwood color were examined. Moisture content decreased as a result of smoke heating, especially in sapwood, leading to a uniform distribution of moisture content within a log. Almost no difference was found in the amounts of chemical components between the control woods and the woods that were smoke-heated for 100h. However, in the wood that was smoke-heated for 200h, the amounts of holocellulose decreased, suggesting that thermal deterioration and/or degradation of hemicelluloses had occurred. We assume that the increase in RDC was caused by smoke heating with the crystallization of cellulose and/or thermal degradation of hemicelluloses. Almost no differences were found in sapwood color between the control woods and the woods that were smoke-heated for 100h. In the wood that was smoke-heated for 200h, however, L*decreased, whereas a* and b* increased. As a result, E*ab, showing the total color change, increased, resulting in a deeper color. These results suggest that thermal degradation of hemicelluloses was caused by smoke heating for over 100h. Therefore, smoke heating of softwood logs using a commercial-scale kiln should not exceed 100h.     

Absolute configuration of arylglycerol-β-aryl ethers obtained by asymmetric reduction of the correspondingα-ketonic compound with intactFusarium solani cells

When (±)--oxo-guaiacylglycerol--(vanillic acid) ether (1) is degraded byFusarium solani M-13-1, the-ketone is initially reduced to giveerythro andthreo guaiacylglycerol--(vanillic acid) ethers (2), arylglycerol--aryl ethers, both of which are enantiomerically pure. The absolute configuration in each2 was determined by Mosher's method; the products were converted to,-di-(R)--methoxy--trifluoromethylphenylacetates (MTPA esters) (3) oferythro (-)- andthreo (+)-veratrylglycerol--(methyl vanillate) ethers (3), whose¹H nuclear magnetic resonance (NMR) spectra were examined and compared with those of four di-(R)-MTPA ester (3) diastereomers from chemically synthesizederythro (±)-3 andthreo (±)-3. To assign the- and-MTPA-OCH₃ peaks, the¹H NMR scans of several compounds that have substructures of 3 and their 3,4,5-trimethoxyphenyl analogues were examined. When a racemic alcohol reacts with (R)-MTPA to give a pair of (R)-MTPA ester diastereomers, the value was defined as the absolute value of the difference in the¹H chemical shifts of the peak between the diastereomers. It was found that the values of-MTPA-OCH₃ were larger than those of-MTPA-OCH₃ owing to a shielding effect of the veratryl ring located on the-MTPA-OCH₃, and that the-MTPA-OCH₃ peaks in the 3,4,5-trimethoxyphenyl compounds shifted downfield relative to those in the veratryl compounds. On the basis of the¹h NMR data of (R)-MTPA esters, the absolute configuration of the four chemically prepared diastereomers (3) were determined. The catabolicerythro 3 [fromerythro (-)-3] andthreo 3 [fromthreo (+)-3] were identical to (R, S, R)-erythro 3 and (R, S, S)- threo 3, respectively. An hydrogen species in the fungal reduction would attack the-ketone fromre-face of both (R)-1 and (S)-1, givingerythro (S, R)-2 andthreo (S, S)-2, respectively.Part of this paper was presented at the 33rd Lignin Symposium, Tsukuba, November 1988     

Working mechanism of adsorbed water on the vibrational properties of wood impregnated with extractives of pernambuco (Guilandina echinata Spreng.)

To clarify the lowering mechanism of loss tangen (tan) of sitka spruce (Picea sitchensis Carr.) wood impregnated with extractives of pernambuco (Guilandina echinata Spreng. synCaesalpinia echinata Lam.), we examined the vibrational properties of the impregnated wood in relation to the adsorbed water. The results obtained were as follows: (1) The equilibrium moisture content (EMC) of impregnated sitka spruce decreased to some extent compared with untreated wood. (2) Frequency dependencies of tan a about 400–8000Hz showed that impregnated wood has much lower tan than untreated wood at around 9% mois ture content (MC), except for the high-frequency region. At high relative humidity, impregnated wood has a minimum tan (at around 4000Hz); and at other frequency ranges the tan of impregnated wood did not differ considerably from that of untreated wood. (3) The apparent activation energy of the mechanical relaxation process (E) concerned with adsorbed water molecules was higher for impregnated specimens than for untreated ones at moderately high relative humidity, whereas at high relative humidity the difference was not observed. Based on these results, it is thought that the tan of impregnated wood decreased at low rela tive humidity because of the formation of direct hydrogen bonds between impregnated extractives and wood components. However, when the specimen is at higher relativePart of this work was presented at the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 1998 humidity, the formation of direct hydrogen bonds are disturbed by the existence of a large number of water molecules, and some extractives act as a plasticizer.     

Applications of the capillary isotherm

The effect of temperature on the capillary isotherm is accounted for in a modified derivation. Some new equilibrium moisture content data for E. regnans are presented and fitted by the capillary isotherm. Some earlier data for Klinki pine are also fitted. It is shown precisely how reductions in the shear modulus of the cell wall material with increasing temperature give rise to reductions in equilibrium moisture content for a given relative humidity.Symbols A G₀/R, K - a₁ external radius of annulus, m - a₂ internal radius of annulus, m - a_f a₂ at fibre saturation, m - a a constant length, m - B a constant of integration - b₁, b₂ temperature parameters, K^1- - G rigidity of wood substance, Pa - G₀ G for dry wood, Pa - G_f G at fibre saturation, Pa - h isosteric heat, J/kg - latent heat, J/kg - p capillary pressure, Pa - P_s pressure of water vapour at saturation, Pa - R specific gas constant for water, J/kg K - r relative humidity - r_i inflection intercept - r_t tangent intercept - T temperature, K - t temperature, °C - X see equation (18) - x see equation (28) - , , ₁, ₁ coefficients, equations (27), (37) - y₁, y₂ see equations (25), (26), K - parameter, equation (9) - parameter, equation (33) - density of water, kg/m³ - _W density of wood substance, kg/m³ - equilibrium moisture content - _0.2 at r = 0.2 - _0.5 at r = 0.5 - _0.9 at r = 0.9 - _f at fibre saturation     

HTST hydrolysis of wood: Modelling of the kinetics and projections on reactor configuration

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 - G_e Glucose yield at equilibrium - G_{i, exp} Experimental glucose yield (Eq. (5)) - G_{i, th} Calculated glucose yield (Eq. (5)) - G_max 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 - m_g 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 - q_i Volume flow rate in reactor units, m³ · s^-1 - r_g Conversion rate of glucose, s^-1 - R Ideal gas constant, 1.987 cal · mol^-1 K^-1 - t Reaction time, s - T Temperature, K - V_i 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     

Influence of moisture content on the vibrational properties of hematoxylin-impregnated wood

The vibrational property of hematoxylinimpregnated wood was investigated from the aspect of moisture content dependence. The specific dynamic Young's modulus (E/) and loss tangent (tan) of hematoxylin-impregnated wood were determined in the relative humidity (RH) range of 0%–97%, and were compared with those of the untreated and some conventional chemically treated woods. The changes in theE/ and tan of wood with increasing RH were suppressed by acetylation and formaldehyde treatment because of a marked reduction in the hygroscopicity of the wood. Although the hematoxylin impregnation did not significantly affect the hygroscopicity of the wood, its influence onE/ and tan were similar to that of formaldehyde treatment at low RH and of acetylation at medium RH. It was supposed that at low to medium RH hematoxylin restrains the molecular motion of amorphous substances in the cell wall because of its bulkiness and rigidity. On the other hand, at high RH it seems to work as a plasticizer with adsorbed water molecules.     

Modelling the long-term strength of timber columns

Summary This paper studies the influence of the used creep function, and the duration of the experimental sustained loading from which the creep function was derived, in modelling the long-term buckling strength of timber columns. The sensitivity of this buckling strength to creep and initial deflection is numerically studied using an energy approach that takes into account the initial deflection. Various creep functions — power laws as well as exponential laws — derived from bending experiments of different durations are used for the numerical simulation. The crucial need for experimental results issued from very long load period experiments is identified. Such experiments may lead to a more credible creep analysis of timber structures.Symbols i radius of giration - s stress level - E_L effective MOE - E₀ instantaneous MOE - I inertia moment - K,K geometrical matrices - L length of beam or column - L_f effective length - N_cr axial force, buckling load - U elastic strain energy - W external forces work - t time variable - u moisture content (m.c.) - v total deflection - v_c, v_e, v₀ creep, instantaneous elastic and initial deflections respectively Greek Letters (t) time function - , _e, ₀ total, instantaneous and initial strains respectively - twist rotation - (t) creep coefficient or fractional creep or relative creep - (x) shape function - load factor - longitudinal shortening - total potential energy - creep factor - relaxation time     

Postbuckling of thin wood-based sandwich panels due to hygroexpansion under high humidity

This study was carried out to investigate the postbuckling behavior of thin wood-based sandwich panels under high humidity. Using the Rayleigh-Ritz method based on the von Karman nonlinear theory for the panel, the solutions for both the approximate and the closed form for postbuckling of orthotropic panels were derived to evaluate the deflection for the boundary condition of all clamped edges. The results suggested that the edge movement be considered for evaluation of a critical moisture content and deflection of thin wood-based panels fixed on the core with an adhesive. The numerical solution obtained from the derived model showed some discrepancy with the experimental results. The predicted results overestimated the center deflection of the panels because creep and plastic deformation might be caused by considerable in-plane stress on panels.Appendix: Abbreviations and symbols total potential energy of panel - A _ij ,D _ij extensional and bending stiffness, respectively - _x , _y midplane strains inx andy directions, respectively - _xy midplane shear strain inxy plane - N _x ^M , N _y ^M hygroscopic forces inx andy directions, respectively - h panel thickness - a, b panel length inx andy directions, respectively - x, y, z coordinate system - u, v, w displacement inx, y, andz directions, respectively - MC moisture content change - a _x ,a _y coefficient of linear expansion inx andy directions, respectively - LE linear expansion (MC) - s arc length - R radius of curvature - N _x ,N _y resultant in-plane forces per unit length inx andy directions, respectively - N _n nondimensional loadN _x ^M b ²/E ₂ h ³ - N _cr nondimensional critical load,N _x,cr ^M b ²/E ₂ h ³ - ratio of the core to the total width,a _c /a + a _c - E _c effective core MOE,E +E (i.e., the summation of MOE parallel to the grain and perpendicular to the grain) - h _c core thickness     

Ultrastructure—Critical domain for wood behavior

Summary That the behavior of wood in service results from its structure is generally accepted by wood scientists. No doubt this acceptance is due to the broad interpretation of such a term. Structure can refer to the organization of elements on a macro scale, such as in a laminated beam, as well as to the arrangement of cellulose molecules in the crystalline region of an elementary fibril.This presentation focuses on a structural domain that appears increasingly to be a critical one in wood behavior-ultrastructure. The spectrum of terminology that has been used in profusion during the electron microscopic era must first be defined so that confusion is minimized. Then a historical evolution of the field of wood ultrastructure can be presented to provide perspective. Structures that have been shown to affect or indeed to control certain processes can be identified. The role of a non-structure, the elusive transient capillary, can be illustrated. Microfibrillar organization and cell wall archictecture fall into the realm of ultrastructure as well.The past decade of research in wood science has been productive to a significant extent because of scanning electron microscopy and its accessory tools and techniques. The exploration of wood penetration by wood preservatives, pulping liquors and coatings using this approach has yielded much new evidence. One can speculate about the anticipated contributions of computer-driven SEM, stereology, STEM, and even higher resolution microscopy in the near future.