Mechanical properties of wood swollen in organic liquids with two or more functional groups for hydrogen bonding in a molecule

The modulus of elasticity and the modulus of rupture during static bending in the radial direction, and the viscoelastic properties in the radial direction in the temperature range 20°–100°C of hinoki (Chamaecyparis obtusa) swollen in organic liquids with two or more functional groups in a molecule were compared with those of wood swollen by moisture. The wood swollen in organic liquids in or near the swelling equilibrium, but not that swollen in organic liquids distant from the swelling equilibrium, showed higher moduli of elasticity and rupture than the wood swollen to a similar degree by moisture. This suggests that wood exists in an unstable state as it approaches the swelling equilibrium, rendering it highly flexible and weak. During the first viscoelastic measurements for wood swollen in various organic liquids, thermal softening was observed in 40°–60°C range and above 80°C, though this softening disappeared during the second measurement. The softening observed in the 40°–60°C range and above 80°C was thought to have been caused by the redistribution of liquid toward the equilibrium state at a higher temperature and the swelling accompanying an elevated temperature, respectively.Part of this report was presented at the 49th Annual Meeting of the Japan Wood Research Society, Tokyo, April 1999     

Effects of moisture content and temperature on acoustic velocity and dynamic MOE of radiata pine sapwood boards

The effects of moisture content from 17 to 159% MC and temperatures from −71°C to +58°C on resonance-based acoustic velocity and dynamic modulus of elasticity (DMOE) were investigated using 36 boards of radiata pine sapwood. Acoustic velocity decreased with increasing moisture content and temperature, although effects differed noticeably below and above fibre saturation point (FSP). Below FSP, acoustic velocity decreased rapidly and linearly with increasing moisture; whereas above FSP changes in velocity were rather gradual and curvilinear with marked differences in velocity patterns between temperatures below and above freezing. Acoustic velocity decreased linearly with increasing temperature but there was an abrupt discontinuity at the freezing point for wood above FSP. Changes in moisture content and temperature affecting wood density and acoustic velocity led to changes in DMOE, although this relationship was not straightforward because changes of velocity with moisture were linear or curvilinear and depended on whether wood was frozen or unfrozen, whereas changes of density with moisture content were invariably linear. For practical work, it is important to estimate the relative effect of changing moisture content or temperature with respect to standard conditions on DMOE, thus general guidelines were devised to account for significant changes.     

Assessment of hygroscopic conditioning performance of interior decorative materials IV: Sorption characteristics of wood under high relative humidity condition

The equilibrium moisture content (EMC) of six wood species under desorption conditions of 20°C and 100% 0% relative humidity (RH), and the rate of adsorption at various depths of three wood species blocks under 98% RH at 22.5°C were studied. There were no significant differences among the EMC values for these six wood species over the RH range 40% 0%, but there were highly significant differences over the RH range 100% 50% at constant 20°C. The amount of moisture absorbed in the wood decreased curvilinearly with the increase of depth in the specimens as sorption time increased, and their relation could be represented by a semilogarithmic equation. Time-dependent adsorption behavior at various depths of the wood specimens could be represented by an exponential equation as a function of the product of the difference between moisture contents at equilibrium and initial conditions and the term (1 – e^–t/). The value of of various wood species was found to increase linearly with the increased depth of the specimen and showed the following trend: hard maple (Acer sp.) > China fir (Cunninghamia lanceolata) > Japanese cedar (Cryptomeria japonica D. Don).Part of this report was presented at the 47th annual meeting of the Japan Wood Research Society, Kochi, April 1997.     

The optimum temperature–humidity combination for the feeding activities of Japanese subterranean termites

Two species of Japanese subterranean termite, Coptotermes formosanus Shiraki and Reticulitermes speratus (Kolbe), were used in an investigation of the optimum temperature–relative humidity (RH) combination for their feeding activities. Daily wood consumption per worker and survivals were measured, and the protozoan fauna in the hindgut were observed under 15 temperature–RH combinations for 1 week. Five temperatures (20°, 25°, 30°, 35°, and 40°C) and three RH conditions (50%, 70%, and 90% RH) were examined. The activities of the workers were highest at around 30°C for both species, and workers died at 40°C within 5 days and 2 days for C. formosanus and R. speratus, respectively. The optimum RH condition for feeding activity was 90% RH for C. formosanus and 70%–90% RH for R. speratus. The optimum temperature–RH combinations for feeding activities were 30°C at 90% RH for C. formosanus and 30°C at 70%–90% RH for R. speratus.     

Damping loss in wood at mid kilohertz frequencies

Summary The dynamic moduli and logarithmic decrement of Rimu (Dacrydium cupressinum) were measured along the grain and perpendicular to it in the frequency range 45–85 kHz using a Marx regenerative oscillator system. The moduli and decrement were observed to exhibit strong dispersions between-20°C and-80°C, the actual temperature being dependent on measurement frequency and moisture content of the sample. The activation enthalpy of the dispersion mechanism varied from 3.9 kcal/mole at moisture contents in excess of 7 % to 6 kcal/mole at lower (1%) moisture content. Impregnation of the wood with solvents produced dispersion effects different from those associated with water impregnation. It is postulated that this mechanical dispersion observed in moisture-bearing wood results from the motion of the adsorbed water molecules.The author wishes to thank the Head of the Princes Risborough Laboratory, Building Research Establishment, for the hospitality and facilities provided during his year's residence, and also the Council of the University of New South Wales for their generous allowance of sabbatical leave.     

Wood tensile strength at temperatures and moisture contents simulating fire conditions

Summary The immediate tensile strength parameters for spruce parallel to the grain and for hardboard have been determined at equilibrium conditions at temperatures up to 250°C. Below 100°C the moisture content has been varied between 0 and 30%. Above 100°C dry samples have been studied. An increase in moisture content up to about 12% leads to a slight increase in the tensile strength of spruce whereas the modulus of elasticity remains constant. With a further increase in moisture content, both properties decrease significantly. At any given moisture content, both properties decrease with increasing temperature. The corresponding strain at rupture is constant. An increase in temperature leads to a more or less linear decrease in the tensile strength and in the modulus of elasticity up to about 200°C. Above 200°C there is a more rapid decrease due to thermal softening. It is most relevant to consider the relative strength decrease since the absolute levels may be quite high due to the fact that wood samples without any irregularities were used. Such relative strength data are compared with the small amount of similar data found in the literature. The effects on the modulus of elasticity are discussed in terms of thermal softening and of water as a softener for the cellulose/hemicellulose polymers. The glass transition temperature is determined as a function of the moisture content.A special thank to Ms. K. Bojadzijev for skillful experimental assistance, to Prof. E. L. Back for stimulating discussions and to the fund for research in woodworking industries for financial support     

Preparation of sulfuric acid-catalyzed phenolated wood resin

Summary Birch wood meal was phenolated in the presence of sulfuric acid used as a catalyst by changing several reaction conditions, such as, phenol-to-wood ratio, temperature, time, and catalyst concentration to make novolak-type resin. A phenol-to-wood ratio of 2–5, reaction temperature of 60–150 °C, time of 60–120 min, and acid concentration of 1–3% were found to be usable values for obtaining good enough amounts of combined phenol and less amounts of unreacted wood residue. The flow properties (flow temperature and apparent melt-viscosity) of the phenolated wood obtained increased with the increase in the amount of combined phenol, however, decreased with the increase in the moisture content and free phenol in the phenolated wood. Furthermore, it was found that the solubility of the phenolated wood in the organic solvents depended, greatly, on the hydrogen bonding strength of the solvents.     

Influence of moisture sorption on the tangential compression strength of Mahogany wood (<Emphasis Type="Italic">Swietenia macrophylla</Emphasis> King)

Moisture sorption tests and compression tangential tests at 25°C were carried out on specimens of mahogany (Swietenia macrophylla King) wood from Peru. The tests were performed over seven adsorption and five desorption moisture conditions, and differences in strength between adsorption and desorption curves at a given equilibrium moisture content were evaluated. The results showed that second-order effects in mahogany wood were not discernible in either the tangential compliance coefficient or for the stress at the proportional limit in tangential compression.     

Effects of artificial environmental conditions on anatomical and physiological ripening of Pinus sylvestris L. seeds

To determine suitable conditions for artificial ripening of Scots pine seeds, cones collected on seven occasions between August 6 and November 26, 1990, in northern Sweden, were subjected to artificial ripening at different temperatures (+5°–+15°C) and cone moisture contents for 3–9 weeks. Complete physiological ripening and improved seed vigour were attained after artificial ripening if collection occurred no earlier than the beginning of September. The highest germination percentage after artificial ripening, ca 90%, was achieved for seeds collected after the anatomical ripening in nature had ceased and was at least as high as for seeds ripened in nature. Temperature did not influence ripening, whereas a low cone moisture content impaired ripening of those seeds collected earliest. The germination percentage was not influenced by 2–6 months of cone storage subsequent to artificial ripening, but seed vigour was impaired. Anatomical ripening during artificial ripening was very limited.     

Vibrational properties of Sitka spruce heat-treated in nitrogen gas

Sitka spruce (Picea sitchensis Carr.) wood was heated for 0.5–16.Oh at temperatures of 120°–200°C in nitrogen gas or air. The values for Young's modulus, shear modulus, and loss tangent were measured by free-free flexural vibration tests. X-ray diffractometry was carried out to estimate the crystallinity index and crystallite width. The results obtained are as follows: (1) Density decreased at higher temperatures and longer heating times. The specific Young's modulus, specific shear modulus, crystallinity index, and crystallite width increased during the initial stage and were constant after this stage at 120°C and 160°C, whereas they increased during the initial stage and decreased later when the temperature was high. Loss tangent in the longitudinal direction increased under all conditions, whereas that in the radial direction increased at 120°C and decreased at 160°C and 200°C. (2) From the relation between Young's modulus and moisture content, it can be safely said that Young's modulus is increased by the crystallization and the decrement in equilibrium moisture content, and that crystallization (rather than degradation) is predominant at the initial stage of the heat treatment, whereas the latter is predominant as the heating time increases. (3) It is implied that the specific Young's modulus, specific shear modulus, crystallinity index, and crystallite width decreased more in air than in nitrogen gas because of oxidation in air.This study was presented in part at the 43th Annual Meeting of Japan Wood Research Society at Morioka, August 1993, the 44th Annual Meeting of Japan Wood Research Society at Nara, April 1994, and the 45th Annual Meeting of Japan Wood Research Society at Tokyo, April 1995     

Prehydrolysis of beechwood

Summary The kinetics of the isothermal prehydrolysis of beechwood at 160°C and 170°C were investigated. It was shown that the hydrolysis of the hemicellulose portion was realised in two phases. The depth and rate of the first rapid prehydrolysis phase and the second slow phase depend on the temperature used. The lignin content in the prehydrolysed chips increased with the duration of the prehydrolysis due to the easily removable hemicellulose portion. The maximum amount of lignin extracted was gained after 45–60 minutes of isothermal prehydrolysis at 160°C with the yield decrease to 82–80 per cent and at 170°C with the yield decrease to 70–68 per cent. At the temperature of 160°C the amount of the lignin portion extracted was about 5 per cent and at 170°C at about 10 per cent of the whole lignin content in wood. The extraction of the whole hemicellulose portion present in wood was attained at 160°C after 5 hours prehydrolysis time, at 170°C after 80 minutes.By the prehydrolysis of hardwood to 30 per cent loss of the wood substance highly purified dissolving pulp was prepared by AQ catalysed sodium pulping. The pulp attained was characterised by a high alpha-cellulose content over 97 per cent and a low solubility in solutions of alkali. The sulphur-free delignification together with the low consumption of active chlorine (1.5–1.7 per cent) cause less environmental pollution.     

Influence of carboxyl group on the acid hydrolysis of cellulose

Cellulose isolated from wood is more susceptible than cotton cellulose to homogeneous hydrolysis in phosphoric acid. The influence of carboxyl group introduction at the C6 position on the hydrolysis rate of cellulose in 82.5% phosphoric acid was studied as a model of the oxidation of cellulose during pulping. The rate constant of hydrolysis for dissolving pulp was larger than that of cotton cellulose at temperatures of 25°–35°C. Mercerized cotton cellulose was partially oxidized regioselectively at the C6 position by a free radical system using 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO). The oxidized cellulose was obtained at a range of 1.7–12.7 mEq carboxyl content per 100 g of cellulose. The hydrolysis rate of the oxidized cellulose samples accelerated with increasing carboxyl content in the samples.Part of this work was presented at the 5th Annual Meeting of the Cellulose Society of Japan, Kyoto, July 1998     

Moisture content—water potential relationship of wood from saturated to dry conditions

Summary The water potential concept as applied to wood-water relations is presented. The gradient in water potential can be used as the driving force of moisture in wood in a model of drying in isothermal conditions provided the moisture content — water potential relationship is known. This relationship is established for aspen sapwood in desorption from saturated to dry conditions at 20, 35 and 50 °C for two specimen orientations. The tension plate, pressure plate and pressure membrane methods were used at high moisture contents and equilibration over saturated salt solutions was used at low moisture contents. The results obtained demonstrate that these methods can be used in combination in order to establish the relationship within the whole range of moisture contents. The equilibrium moisture contents obtained by the tension plate, the pressure plate and the pressure membrane methods for tangential desorption were slightly higher than those measured for radial desorption. The water potential increased with temperature at a given moisture content. This effect cannot be solely explained by the variation of surface tension of water with temperature.This research was supported by the Fonds pour la Formation de Chercheurs et l'Aide à la Recherche, Gouvernement du Québec, and by the Natural Sciences and Engineering Research Council of Canada     

Dielectric properties of hardwood species at microwave frequencies

Dielectric measurements at 9.8GHz and 2.45GHz were made for the three hardwoods Euramerican hybrid poplar, alder, and oriental beech. The method used was based on Von Hippels transmission line method. The measurements were carried out at room temperature of 20°–24°C. The dielectric properties of the wood species were determined for the three principal structural directions at six different moisture conditions, covering the range of 0% to 28% moisture content. Results indicated that the behavior of all wood species studied is quantitatively similar. In general, the dielectric properties increase within the range studied with rising moisture content. The grain direction of the wood also plays a significant role.     

Compressive deformation of wood impregnated with low molecular weight phenol formaldehyde (PF) resin III: effects of sodium chlorite treatment

To obtain high-strength phenol–formaldehyde (PF) resin-impregnated compressed wood at low pressing pressure, we investigated the effects of sodium chlorite (NaClO₂) treatment on wood prior to low molecular weight PF resin impregnation. Sawn veneers of Japanese cedar (Cryptomeria japonica) were treated with 2% aqueous NaClO₂ solution at 45°C for 12 h to remove lignin, and the process was repeated up to four times, resulting in weight loss of 21%. NaClO₂ treatment has shown considerable potential for high compression of PF resin-impregnated wood at low pressing pressure, especially after adding moisture to a content of 10%–11%. This deformation is further enhanced during pressure holding by creep deformation. The density, Young’s modulus, and bending strength of PF resin-impregnated veneer laminated composites that were treated with NaClO₂ four times and compressed at 1 MPa, reached 1.15 g/cm³, 27 GPa, and 280 MPa, respectively. The values in untreated PF resin-impregnated wood reached 0.8 g/cm³, 16 GPa, and 165 MPa, respectively.     

Wood fracture, acoustic emission, and the drying process Part 2. Acoustic emission pattern recognition analysis

Summary Signal features were extracted from AE signals collected during mixed mode fracture tests of ponderosa pine and California black oak conducted at 12 and 18 percent moisture content and temperatures of 20, 40 and 60 °C. Five features in the time domain and three in the frequency domain were selected for further analysis. Signal features were found to be significantly affected by both temperature and moisture content. Cluster analysis showed that while signals could be successfully classified, the resulting patterns showed little relationship to wood fracture. Only load levels well beyond maximum load could be consistently distinguished from lower load levels. It was concluded that pattern recognition analysis would have only limited application to control the wood drying process.This study was supported in part by USDA Grant No. 90-37291-5762     

Untersuchungen zur Wirkung von Methylbromid besonders bei niedrigen Temperaturen gegen Khaprakäfer-Larven (Trogoderma granarium Everts (Dermestidae,Coleoptera)

Tests on the efficiency of methyl bromide especially at lower temperatures in controlling Khapra Beetle Larvae (Trogoderma granarium Everts), Dermestidae, Coleoptera In the laboratory, experiments were carried out to investigate the efficiency of methyl bromide in controlling the Khapra Beetle (Trogoderma granarium Everts) in a specially developed fumigation apparatus at 30, 25, 20, 15, 10, 5, 0, –6, and –10 °C as well as 40 – 70% relative humidity. The lethal dosis as c. t. products in mg.h/l were estimated at different temperatures from the dosis-mortality regression lines. The treated larvae were divided after the fumigation into two series (1 and 2). The larvae of serie 1 were held immediately after the fumigation time at 28°C, while the larvae of serie 2 were kept for another 10 days at the same fumigation temperature, then removed to 28°C until final control. Experimental results of both series showed that, for a given mortality the c. t. product required at low temperatures considerably increased and accordingly the tolerance of the larvae decreased with a rise in temperature (in range 0–30°C). A maximum in the tolerance of the larvae to methyl bromide was found at 0°C. At lower trial temperatures –6 and –10°C the required c. t. product subsequently decreased. This result was caused through the combined harmful effect of the low temperatures and the methyl bromide. It is evident from the estimated values that the c. t. products of methyl bromide required for a given mortality in serie 2 especially at lower temperatures (from +10 to –10°C) are lower than that in serie 1. For example in serie 2 the c. t. product required to kill the larvae decreased at 5°C to less than 50%. This effect of the post-treatment temperature was also examined to obtain the shortest holding time for maximum mortality, which was observed after 3–4, 7–8, 7–8 and 8–9 days at 10, 5, 0, and –6°C respectively. From a practical aspect this result is of great importance, because it proves the influence of the factors prevailing after a quarantine fumigation.     

Variations in compression strength and surface roughness of heat-treated Turkish river red gum (Eucalyptus camaldulensis) wood

This article reports the effects of heat treatment on compression strength parallel to the grain, the surface roughness [average roughness (R_a)], and the air-dry den-sity of wood from the river red gum tree (Eucalyptus camaldulensis Dehn.) planted in Turkey. Eucalyptus wood was heat-treated at temperatures varying from 120° to 180°C for durations of 2–10 h. Samples cut from the heat-treated wood were tested for air-dry density, compression strength parallel to grain, and surface roughness properties. Roughness measurements by the stylus method were made in the direction perpendicular to the fiber. Based on the findings in this study, the results showed that density, compression strength, and surface roughness values decreased with increasing treatment temperature and treatment times. Eucalyptus wood could be utilized by using proper heat treatment techniques without any losses in strength values in areas where working, stability, and surface smoothness, such as in window frames, are important factors.     

Advantages of prefreezing for reducing shrinkage-related degrade in eucalypts: General considerations and review of the literature

Summary Difficulties associated with the drying of ash eucalypts including collapse and internal checking, are discussed briefly. Prefreezing is one method that has been used successfully as a pretreatment for the drying of both hardwoods and softwoods from temperate and tropical regions.Prefreezing has produced marked reductions in shrinkage, collapse and drying degrade of the heartwood in the following species: California redwood, black walnut, black cherry, tanoak, toon, bamboo, and eucalypts. Little or no collapse reduction has been observed in New Zealand red beech, Pacific madrone, white birch, sitka spruce, and white ash. Limited response has been observed for numerous other species notably red oak and white oak.Reduced drying time in response to prefreezing has been observed in jarrah, karri, black walnut, Asian oak, toon, and California redwood; in Pacific madrone and tanoak the drying time increased. Not all species which respond with a reduction in shrinkage show reduced drying rates.Prefreezing wood at -20°C appears to be the most practicable temperature, although some species respond better at lower temperatures. However, in all cases, it is critical to ensure that the wood freezes and remains frozen for a number of hours. Indications are that the effect is retained for days to weeks and that the length of time of freezing need not exceed 12–24 hours.A number of explanations have been put forward to explain the behaviour of prefrozen wood. It is suggested that the main mechanism responsible for reduced shrinkage is due to the migration of moisture from the cell wall onto frozen lumen water. The moisture loss from the cell wall produces a cold shrinkage; water to ice transformation leads to an expansion of liquid water in the lumen, thus imparting a compressive stress to the cell wall, which together with the moisture loss, make the cell more rigid, and therefore likely to shrink less. There is some evidence that certain types of wood extractives migrate into the cell wall during freezing and may play a role in the reinforcement of the wall. Reduced shrinkage after prefreezing has also been attributed to a reduction of the plasticising effect of wood extractives in wood dried at higher temperatures and low humidities; this effect does not occur at low temperatures.Many suggestions and discussion from Dr. W. E. Hillis are gratefully acknowledged     

The effects of a heat treatment on the behaviour of extractives in softwood studied by FTIR spectroscopic methods

Scots pine battens were heat-treated at 100–240º C under saturated steam. Cross-sections of heat-treated battens were analysed using ATR and reflection FTIR microscopies. A typical absorption band of fats and waxes at 1740 cm^-1 was detected on the sapwood edges in the temperature range of 100–160º C, indicating that fats and waxes moved along the axial parenchyma cells to the surface of the sapwood during the heat treatment. At the elevated temperatures (above 180° C) fats and waxes disappeared from the sapwood surface and were no longer detected with FTIR spectroscopy. Resin acids were detected at temperatures between 100 and 180º C in the middle of the battens. IR spectra of these spots showed a characteristic absorption band of resin acids at 1697 cm^-1. At 200º C resin acids were not detected in the middle of the battens; however, resin acids were detected at distances of 500 and 600 mm from the midpoint of the battens and on the edges of battens. At temperatures above 200° C, resin acids had disappeared from the wood.