Showing papers in "Wood Science and Technology in 1983"

Hydrothermolysis -- a new process for the utilization of biomass.

Abstract: In the present paper a hydrothermolysis apparatus is described. The reaction vessel is of the percolator type with a volume of 560 cm3 and permits the hydrolysis of biomass materials up to 100 g. The optimum degradation conditions of pure cellulose (filter paper) were determined in dependence on temperature, flow rate of the eluting water and influence of stirring on the reaction mixture. Up to 52% glucose can be obtained by hydrolysing cellulose with pure water at 265°C at a flow rate of 12 cm3/min.

A wood densitometer using direct scanning with X-rays

Abstract: A computerised wood densitometer system using X-rays is described. The technique uses 5 mm increment core samples, machined to 2 mm thickness in the axial direction of the fibre, and an isotopic radiation source (Fe 55). Direct measurement of the intensity of radiation passing through the sample enables wood density variations to be recorded automatically and stored on disc file for subsequent analyses with an interactive computer program.

Chemical reactions in chlorine dioxide stages of pulp bleaching

Abstract: The hypochlorous acid formed intermediately during the bleaching of an oxygen-prebleached kraft pulp with pure chlorine dioxide (a D0-stage) was captured as N-chlorosulfamic acid by addition of sulfamic acid to the bleaching liquor The amount of hypochlorous acid captured corresponded to about 50 mol% of the consumed chlorine dioxide The amount of chlorite formed (20 to 30 mol%) was less than the amount of hypochlorous acid captured The excess of hypochlorous acid over chlorite suggests that chlorine dioxide is reduced initially not only by a one-electron mechanism to chlorite but also by a two-electron mechanism to monochlorine monoxide, which is then reduced by lignin or by chlorine dioxide to hypochlorous acid The routes for the further reactions of chlorite, monochlorine monoxide and hypochlorous acid are discussed

Dynamic sorption and hygroexpansion of wood wafers exposed to sinusoidally varying humidity.

Abstract: Round wood wafers, 4 mm thick along the grain and 2 cm in cross-sectional diameter, of green basswood (Tilia americana L.), yellow birch (Betula alleghaniensis Britton), and black cherry (Prunus serotina Ehrh.), and initially dried to equilibrium in air of 77% relative humidity and 25°C, were exposed to sinusoidally varying relative humidity between 77 and 47% at 25°C for many cycles at each of four different cycling periods, 5.33, 10.67, 16.0 and 25.33 hours. Moisture changes and radial and tangential dimensional changes in response to the imposed humidities, measured during initial drying and subsequent cycling, gave the following results: 1. The moisture and dimensional changes were generally sinusoidal but lagged behind the imposed humidity. The phase lag decreased and the amplitude increased with increasing cycling period. Both responses and phase lags approached repetitive or “steady-state” values as cycling was prolonged. 2. A numerical solution for moisture diffusion, assuming a constant diffusion coefficient and sinusoidally varying boundary moisture conditions, was used to simulate the average moisture content in the wafer at any time. The resulting curves were qualitatively similar to those obtained experimentally, the differences attributed primarily to the effects of hysteresis and stress relaxation. 3. The mean moisture diffusion coefficients, calculated from steady-state phase lag data combined with an analytical solution of the diffusion equation, decreased with increasing cycling period. The values obtained increased with decreasing wood specific gravity as anticipated, but their magnitudes were somewhat lower than theoretical values. 4. The dynamic moisture expansion coefficient was relatively constant during successive cycles, with no consistent effect of cycling period. The dynamic values were generally higher than the static values. 5. The dynamic humidity expansion coefficient increased with increasing cycling period. It was only about half that obtained from static experiments, presumably because of hysteresis. 6. The dynamic moisture sorption coefficient, which is the effective slope of the dynamic sorption isotherm, decreased with increasing number of cycles and decreasing cycling period. It was less than half the calculated static sorption isotherm in the same humidity range, presumably due to hysteresis.

Analysis of roll tensioning and its influence on circular saw stability.

Abstract: In a typical sawmill, about 12% of the wood which is cut is reduced to sawdust. Further material is lost during subsequent planing. A substantial part of this large loss of a costly natural resource can be saved by the use of thin, stable sawblades, but only if proper saw tensioning conditions are developed. The thickness of a stable sawblade can be minimized through optimal tensioning, an increasingly urgent objective because of sharply rising raw material costs. A theoretical model is presented which accurately describes the development of residual stresses in a roll tensioned circular sawblade and the resulting changes in saw critical speed. This model is essential for the reliable prediction of optimal tensioning conditions for any given saw operating state, and for the development of automated control of the tensioning process. An example is presented of an optimally tensioned circular sawblade for which a 40% thickness reduction is achieved compared with an equivalent untensioned sawblade with the same critical speed.

Some physical properties of the coconut palm stem

Abstract: The purpose of this study was to assess the relationship of oven-dry density, initial moisture content, vascular bundles and shrinkage to stem height and diameter of Cocos nucifera L. High correlations were obtained between initial moisture content and stem height, initial moisture content and oven-dry density, oven-dry density and stem height, vascular bundles per cm2 and stem height, vascular bundles and oven-dry density for cross-sections and shrinkage and vascular bundles per cm2. The high correlations between vascular bundles per cm2 and oven-dry density on the one hand and to shrinkage on the other can be used for visual grading of coconut timber.

Polyelectrolyte swelling behavior of chlorite delignified spruce wood fibers

Abstract: A coarse thermomechanical Asplund pulp was prepared from Norway spruce (Picea abies). The pulp was delignified to different degrees using acidified sodium chlorite. The swelling behavior (measured as water retention value=WRV) of the resulting pulps was studied under various chemical conditions (pH and conc. of NaCl). It is shown that chlorite-delignified pulps have an appreciable polyelectrolytic character. Whereas the WRV of an Asplund pulp does not respond to changes in the chemical environment, the delignified pulp has a WRV of 155 at pH 3 and 250 at pH 9. Compared under the same chemical conditions, the WRV increases with increasing degree of delignification ( 70%).

Chemical potential as a driving force for nonisothermal moisture movement in wood

Abstract: An equation is derived to describe transverse nonisothermal moisture movement in wood, based upon a gradient of chemical potential. When compared with a previously derived equation based upon a gradient of activated moisture molecules, this new equation predicts an accentuated effect of the thermal gradient relative to the moisture gradient at high wood moisture contents and a decreased effect at low moisture contents. The two equations yield identical results at a moisture content in equilibrium with a relative humidity of approximately 53 percent.

Testing of poles by acoustic resonance

Abstract: An acoustic resonance technique has been evaluated as a means of detecting deterioration in wood poles. The basis of the technique is that degradation of the pole by rot or other agency will lead to an increase in the damping of longitudinal acoustic waves, which can subsequently be detected by an examination of the acoustic resonance characteristics of the pole. The technique was assessed in a series of field trials conducted on in-situ poles, which were subsequently removed and dissected. The results of the acoustic testing compared favourably with the gradings of the poles following dissection.

Deflection of wood under intermittent loading - Part 1: Fortnightly cycles

Abstract: SummaryDeflections of wooden beams loaded repeatedly for seven or two days in every 14 were compared with those of beams under constant load over a period of six months in a constant environment. Four load levels were applied to beams of three species. Loads ranged from 17 to 67 per cent of short-time failing load estimated from matched specimens. The deflections under intermittent loads were lower than the creep deflections under constant load and, with the exception of material under high stress, applicability of Boltzmann's principle of superposition of deformations was confirmed. Non-linearity at high stresses is linked with other signs of weakening after application of loads in excess of about 50 per cent of short-time ultimate.

A proposed theory for nonisothermal unsteady-state transport of moisture in wood

Abstract: Two equations are derived to describe the nonisothermal unsteady-state diffusion of moisture in one direction in parallel-sided bodies. One equation is based upon a gradient of activated moisture molecules and the other on a gradient of chemical potential.

Production of bleached softwood pulp by low pollution processes.

Abstract: Some aspects of sulphur-free soda pulping with anthraquinone (AQ) additions and chlorine-free bleaching with oxygen-based treatments were investigated with the aim of producing bleached softwood pulp with kraft-like strength properties. The extent of soda-AQ pulping was studied by pulping to 32, 42 and 68 Kappa number. After oxygen delignification to 10, 15 and 20 Kappa number respectively, the extent of bleaching with ozone, alkali extraction, and hydrogen peroxide treatments (ZEP sequence) was studied. For comparison, oxygen delignified pulps were conventionally bleached with a sequential chlorine/chlorine dioxide, alkali extraction, and chlorine dioxide (D/CED) sequence. A reference kraft pulp at 45 Kappa number was similarly oxygen delignified and bleached. Kraft-like strength properties (as measured by tear/burst relationships) were attainable if soda-AQ pulping was terminated at high Kappa number and was followed by oxygen delignification and D/CED bleaching. This pulp had a 3% (on wood) higher total yield and consumed less active alkali (2.0% as Na2O) than the bleached reference kraft pulp. Soda-AQ pulping followed by oxygen delignification and ZEP bleaching produced pulp with strength properties that were at least 25% less than those of the reference kraft pulp after oxygen delignification and conventional bleaching with chlorine-based treatments. Although the combination soda-AQ pulping to low Kappa number and extended oxygen delignification adversely affected pulp strength properties, it was ZEP bleaching and ozone treatments in particular, which caused the majority of the strength loss.

A new approach to the formulation and application of CCA preservatives

Abstract: Three parameters have been found to be important to the long-term effectiveness and durability of CCA-treated timber: (i) the temperature during treatment, (ii) the initial pH of the CCA solution, and (iii) its concentration. Variation in the values of these parameters cause drastic differences in the distribution between lignin and holocellulose of the preservative chemicals, in particular of the chrome and of the part of copper and arsenic reacted with it. The massive differences in distribution which are obtainable will considerably affect the durability of CCA-treated timber. It is clear that the effectiveness of CCA types A, B and C is valid only within narrow limits of the parameters mentioned. New, more effective and more economical CCA formulations, both in chemical composition and requiring lower loads (Softwoods), in the timber without a drop in the durability of the treated timber can be devised from the results presented, as well as more rapid and economical timber treatment processes. CCA formulations giving better soft-rot resistant hardwoods can also be devised.

Ammonium sulfide organosolv pulping

Abstract: The use of ammonium sulfide in aqueous ethanol and methanol was investigated for pulping of wood. Hemlock chips required 21% ammonium sulfide (equivalent to 19% Na2O) at 180°C to become delignified to the kappa range 35–50. The yields exceeded those of conventional kraft pulps by 14% on dry wood basis. Over 75% of the original glucomannan was recovered in the pulp as the consequence of end group stabilization by ammonium sulfide. The intrinsic viscosity of the pulps, measured in cadoxen was 10.65 dl/g — approximately double the value for softwood kraft pulps. The pulps were readily bleached and possessed higher tensile and burst strengths but lower tear strengths than kraft pulps. Ammonium sulfide pulps from cottonwood were likewise obtained in high yields and with adequate strength properties.

Simultaneous inhibition and induction of compression wood formation by morphactin in artificially inclined stems of Japanese larch (Larix leptolepis Gordon)

Abstract: Morphactin IT3456, applied in a 2–3 cm band around the middle portion of 2- or 3-year-old internodes of artificially inclined 5-year-old Japanese larches, induced compression wood formation on both the upper and the lower sides of the inclined stem above the treated region, while it inhibited compression wood formation below this region. These results seem to suggest that a high concentration ratio of endogenous auxin to sugar (auxin/sugar) in the differentiating xylem tissue is necessary and sufficient for compression wood formation, and that compression wood formation under natural conditions requires polar transport of auxin which supplies and maintains high concentration of auxin along the undeside of the stem.

Effect of pH on the autoxidation kinetics of vanillin

Abstract: The autoxidation kinetics of vanillin (4-hydroxy-3-methoxy benzaldehyde) have been investigated in aqueous media between pH 5.0 and 13.5. The results obtained clearly show two distinct reaction mechanisms are operative. At pH 7.3 the reaction orders with respect to vanillin concentration and oxygen partial pressure are 1.50 and 0.5 respectively, indicative of a free-radical chain process. A bimolecular ionic pathway is indicated at pH 11.0 and above since the reaction orders with respect to both vanillin and oxygen are 1.00. The formation of a hydroperoxide intermediate is believed to be the first step in both pathways. The energy of activation was found to be 14.2 kcal/mole at pH 7.3 and 13.6 kcal/mole at pH 11.0.

Small angle X-ray scattering measurement of porosity in wood following pyrolysis

Abstract: Changes in the submicroscopic porosity in southern pine latewood resulting from pyrolysis at temperatures through 600°C were measured using small-angle X-ray scattering. Two types of scattering curves were observed: the first was obtained for wood and for less intense heat treatment; and the second, for samples heated above 300°C. This change was found to be associated with the thermal degradation of crystalline cellulose in the sample. Specific surfaces and the average dimensions of macropores and micropores were calculated from the second type of scattering curve. The specific surface was found to increase from 1.2 to 2.3 m2/gm as the temperature and heating time increased. The average dimensions of the macropores calculated from the scattering curves was about 15 nm. The first effect of heating sufficiently to decompose the crystalline cellulose was found to be the production of micropores with average diameters of about 0.7 nm. Micropore volume increased from 0.06 cm3/gm for the lower heating temperatures to about 0.13 cm3/gm for samples heated to 600°C. The average micropore dimension increased as the temperature was raised and the samples were heated for longer times.

Permeability to water of the wood cell wall and its variation with temperature

Abstract: The permeability to water of the cell wall has been measured by applying a known osmotic pressure generated by PEG 6000 across wood samples containing water-swollen cell walls. In pine the void space was filled with silicone resin with the wood at near fibre saturation point. Permeability kx1021 as defined by the Darcy equation was 37.9 m2 for longitudinal flow and 0.96 m2 for tangential flow. Tangential permeability was also measured using water-saturated samples of spruce and lime, and allowance was made for the very high permeability of the water-filled cell cavities. The results were in satisfactory agreement with values obtained previously using wood filled with wax or resin. The variation of tangential permeability with temperature was measured over the range 10–55°C for pine and lime. The activation energy for flow through the cell wall was 6.8 kcal/mole for pine and 5.3 kcal/mole for lime. These values are much higher than the activation energy for viscous flow of water, presumably owing to hydrogen bonding of the water to the cell wall material.

Adhesive developments in forest products

Abstract: Historically, adhesive development has been a propelling force in the evolution of the forest product industry. The 1973 energy crisis has caused the wood industry to focus its attention on the necessity of adhesive self-sufficiency. Research in the use of bark, pulp waste liquor and foliage for adhesive application is rapidly spreading.

Evaluation on non-linear viscoelastic bending deflection of wood

Abstract: The viscoelastic deflection resulting from load increasing continuously from 30% stress level (linear range) to 60% stress level (non-linear range), i.e., within the proportional limit was measured over a period of 10 h. The experimental deflection could be predicted by a numerical method using model element constants which were an experimentally determined function of stress level. An 8-element model consisting of a Maxwell model and three Voigt models in series was used. The upper limit of stress level where a linear relation between creep strain and stress holds ranged from about 35% to 40%. Calculated deflections agreed well with experimental deflections.

Moisture and Transverse Dimensional Changes During Air-Drying of Small Green Hardwood Wafers *

Abstract: Round wood wafers, 4 mm thick along the grain and 2 cm in cross-sectional diameter, of green basswood (Tilia americana L.), yellow birch (Betula alleghaniensis Britton), and black cherry (Prunus serotina Ehrh.), were dried to equilibrium in air of 77% relative humidity and 25°C. Weight, and radial and tangential dimensions were recorded during the drying using a mean air velocity of 212 feet/minute.

Continuously varying schedule (CVS) —A new technique in wood drying

Abstract: The high potential of marketing dry wood encourages the study of the possibility to kiln dry green hardwood. Description of the technical details of three drying processes and their differences are discussed. One of the processes is recently developed, and is called “Continuously Varying Schedule”. Three drying tests were carried out using each process to dry green 100×50 mm quarter and back sawn Eucalyptus laevopinea and E. agglomerata. The Continuously Varying Schedule and the Continuously Rising Temperature processes reduced the drying time to one third that of the Conventional process. Recovery in volumetric shrinkage for samples dried by the Continuously Varying Schedule was not significantly different from those dried by the conventional Schedule, but different at the 5% confidence level from those dried by the Continuously Rising Temperature.

Evaluation of linear and non-linear viscoelastic bending loads of wood as a function of prescribed deflections

Abstract: Viscoelastic bending loads resulting from prescribed deflections increasing continuously or stepwise from 0, 20, or 30% initial stress level (linear range) to 55 or 65% final stress level (non-linear range), i.e., within the proportional limit, were measured over a period of 10 h. Loads could be predicted by a numerical method using model element constants which were an experimentally determined function of deflection. An 8-element model consisting of a Maxwell model and three Voigt models in series was used. The upper limit of stress level where linear relation between creep strain and stress holds ranged from about 35 to 45%. Calculated load changes agreed well with experimental load changes.

The periderms of three north American conifers: Part 2: Fine structure

Abstract: SummaryThe fine structure of inactive eastern white spruce phellogen (Pg) and phelloderm is briefly described. Phellogen cells resemble dormant cambium but contain larger tannin vacuoles. Phelloderm cells contain even more tannin and have much thicker primary walls. Three types of phellem are described: crystalliferous phellem (CP), thin-walled phellem (TnP), and thick-walled phellem (TkP). All three occur in spruce, but only the latter two in balsam fir and eastern hemlock. The TnP cells have thin shared common walls overlain by suberinic and wax extractive layers. True pits are lacking, but plugged plasmodesmatal canals sealed over by the wax extractive layers cross the suberinic layers. Spruce CP and fir and hemlock TnP cells have adaxially-thickened suberinic and wax extractive layers when adjacent to TkP or inactive Pg. The suberin lamellae are much thickened in these suberinic layers, at least in spruce. Spruce CP has a thick wax extractive layer which also sheaths the crystals. The TkP cells of all three species have thick polylamellate abaxial cellin walls perforated by simple pits. The lamellae differ both in structure and composition. Polylamellate wall construction is discussed and a model proposed. The TkP cells have both suberinic and wax extractive layers in fir and hemlock, but only wax extractive layers in spruce. These cells are therefore true phellem cells, not phelloids.

A sampling strategy useful in full-distribution simulation.

Abstract: Inherent in most simulation processes is a mechanism to sample from known probability distributions. This is most often accomplished with the aid of pseudo-random generation systems. Though, these generators produce sets of numbers which are usually statistically indistinguishable from a uniform distribution, the actual distribution of any individual one of these data sets exhibit peaks and valleys which, when used in simulations, somewhat misrepresent the desired probability distribution. A stratified approach to fulldistribution sampling is presented which represents a marked improvement over random number generated sampling in certain types of simulation procedures.

Debarking of fibrous-barked hardwoods by ultra-high pressure water jets

Abstract: Ultra-high pressure water jets, operating at 48 300 kPa through a ring-type No. 6 nozzle with 15° fan and 1.57 mm diameter opening, were used in practical trials for debarking several hardwood species. Eucalyptus paniculata, E. agglomerata, E. acmenioides, E. pilularis and Syncarpia glomulifera were tested, as they are known to be difficult to debark. The effects of these jets on the configuration of the detached bark, were also assessed. Except for E. pilularis, all species were effectively debarked, and a classification was made of the relative difficulty with which various barks were removed. In E. pilularis the bark adhered strongly to the timber, the surface of which was extensively damaged by the water jets. The high pressure water often broke and shattered the bark, which sometimes underwent pronounced defibration. In particular, the bark of E. acmenioides and E. paniculata was broken down into a material, which should be readily utilisable without further processing. Finally, these trials have shown that the design of a small-size hydraulic debarker is feasible and should eventually be a commercially viable proposition.