Water repellency in treatedHevea brasiliensis andMangifera indica wood

Samples of rubber (Hevea brasiliensis) and mango (Mangifera indica) wood treated with 2.5%, 5%, 7.5% and 10% aqueous solution of Chromic acid were assessed for water repellency and dimensional stability. Significant reduction in water absorption in treated samples was observed in initial five hours of soaking in water compared to untreated controls. It was found that effectiveness of water repellency was independent of concentration of solution under repeated cycles of wetting and drying. Degree of water repellency that could be achieved by chromic acid treatment appears to be dependent on constituents of wood.     

Effect of grain orientation and surface wetting on vertical density profiles of thermally compressed fir and spruce

The effects of grain orientation and surface wetting on wood densification by compression in a hot press were evaluated for two commercial Canadian wood species, balsam fir (Abies balsamea) and black spruce Picea mariana. The vertical density profiles (VDP) of wood densified at 180 °C could be engineered to achieve different properties depending on press closing rate, wood permeability and annual ring orientation. The lower permeability of spruce caused it to split frequently during hot pressing. For balsam fir, at a press closing time of 2 min, the compressed wood with an original grain angle of 0° (radial compression) shows widened high density bands due to collapse of low density earlywood adjacent to the dense latewood. All grain orientations show higher density areas close to the wood surfaces similar to those of wood-based composites. However, when wood was preheated without pressure for 5 min followed by a press closing time of 2 min, water migrated to and plasticized the board centre causing it to be densified while the surface density remained low. Wood surface plasticizing with water or urea solution causes some localized surface densification, but the effect was not great.     

The efficacy of commercial silicones against blue stain and mould fungi in wood

Scots pine (Pinus sylvestris L.) samples were vacuum pressure impregnated with quaternary ammonium (quat)-silicone micro-emulsion (<40 nm particle size), amino-silicone macro-emulsion (110 nm) and silicone macro-emulsion with alkyl modified side groups (740 nm). Quat-silicone micro-emulsion caused highest cell wall bulking (4.8%) and anti-swelling efficiency (21.8%) in wood when treated with 30% concentration of silicone in the treatment solution. All three formulations made wood hydrophobic which was evident from a capillary (longitudinal, tangential and radial) water uptake test. Amino-silicone macro-emulsion (10% silicone in treatment solution) resulted in strong resistance to blue stain attack with both pre-weathered and not pre-weathered wood samples. Signs of blue staining were more evident on the pre-weathered samples. Treatment with amino-silicone macro-emulsion (10% silicone in treatment solution) resulted in a certain resistance to mould growth on wood surfaces, whereas wood treated with the same concentration of quat-silicone micro-emulsion and alkyl-modified silicone macro-emulsion exhibited comparatively lower resistance.     

Effect of heat treatment on the wettability of white ash and soft maple by water

Heat treatment of wood has attracted a lot of attention both in Europe and recently in North America as an environmentally-friendly wood-protection method. The untreated wood is hydrophilic (high affinity for water). During the heat treatment, wood becomes more and more hydrophobic (low affinity for water) with increasing heat treatment temperature. As a result, it becomes more resistant to biological attacks. Furthermore, it becomes dimensionally more stable compared to untreated wood. Its hardness increases. As the wood becomes more hydrophobic, its wettability by water decreases. The effect of heat treatment is different for each species. Studying the wetting characteristics of heat treated wood gives a good indication of the heat treatment effects on certain wood properties which are related to its degree of hydrophobic character. The aim of this work was to study the characteristics of dynamic wetting process for two different heat-treated North American wood species white ash (Fraxinus americana) and soft maple (Acer rubrum). Contact angle measurements before and after heat treatment showed a significant increase in wood hydrophobicity. Advancing contact angles of a water drop were in all cases higher for heat-treated wood than for untreated wood.     

Weathering characteristics of wood treated with water glass, siloxane or DMDHEU

Specimens of Scots pine sapwood (Pinus sylvestris) and beech wood (Fagus sylvatica) were treated with a sodium water glass solution, an amino-alkyl-functional oligomeric siloxane and 1,3-dimethylol-4,5-dihydroxyethylene urea (DMDHEU). The specimens were exposed outside without ground contact for 24 months. Colour measurements during outside exposure showed a discoloration of all wood specimen surfaces. FTIR spectroscopy displayed lignin degradation of all specimens during the initial exposure time. Chemical treatments decelerated fungal infestation of wood, while their effect on lignin degradation was not discernible. SEM studies revealed that fungal infestation was affected by the different treatments. The untreated specimens showed radial penetration of fungal hyphae through the pits. Only superficial infestation and no radial penetration were visible at water glass and siloxane treated specimens. A significantly reduced radial penetration of fungal hyphae was exhibited at DMDHEU treated specimens. Fungal infestation through the pits was not visible.     

Enhancing the applicability of near infrared spectroscopy for estimating specific gravity of green timber from Eucalyptus tereticornis by developing composite calibration using both radial and tangential face of wood

Specific gravity is a very important factor in determining the economics of wood and wood products. This study is aimed to apply the near infrared spectroscopy technique with integrating sphere and fiber optic probe accessories for fast prediction of specific gravity of green timber (moisture content 27–30 %) of Eucalyptus tereticornis from 10 to 12 year old plantation. Specific gravity (basic density) was determined by conventional method (oven dry wt/green volume) and correlated with near infrared spectra using partial least square (PLS) regression. Calibrations using radial face, tangential face and composite face (both radial and tangential) were developed and compared. Coefficient of determination of cross validation ( $ {\text{r}}_{\text{cv}}^{ 2} $ ) for radial-longitudinal, tangential-longitudinal solid strips samples and composite face (both radial and tangential) was between 0.74–0.77 and 0.64–0.77 using integrating sphere and fiber optic probe, respectively. The coefficient of determination of prediction ( $ {\text{r}}_{\text{p}}^{ 2} $ ) was between 0.73–0.85 (with integrating sphere) and 0.69–0.83 (with fiber optic probe). The ratio of performance deviation (RPD) ranges from 2.06 to 2.46 for all models. Root mean square error of prediction (RMSEP) was higher than root mean square error of cross validation (RMSECV). For composite models with radial and tangential face $ {\text{r}}_{\text{cv}}^{ 2} $ / $ {\text{r}}_{\text{p}}^{ 2} $ was 0.74/0.76 using integrating sphere and 0.71/0.83 with fiber optic probe with Quant 2 automatic factors optimization process. The results indicate that the composite model is just as good as the radial and tangential face models and can adequately address the problem where it is difficult to obtain perfect radial or tangential surface, particularly in small girth plantation timber or where surface recognition is difficult.     

How far does a gaseous reagent penetrate into wood

The reaction between wood components and vaporous formaldehyde was applied to the evaluation of gas permeability and forecast of the extent where the reaction occurs. The structural changes of pre-compression wood, which is a new method to suck the liquid reagent by the recovery force, was also followed by the established method. The formaldehyde content (y) reacted with wood components decreased exponentially as according as the depth from the penetrating surface. It could be expressed by the distance from surface, x, for both longitudinal and tangential directions as follows; y=kexp(?ax) where, a and k are constants for individual wood samples. The half-interval (a definite distance of half reduction), d _1/2, was defined by (ln 2)/a. The reaction level at the arbitral inner portion of wood can be estimated by both the half-interval and the reaction level at the vicinity of surface region. The use of the structural changes of pre-compression wood is suggested.     

Reaction of wood with inorganic salts

Wood samples and veneers of Hevea brasiliensis (Rubber wood) and Acacia auriculaeformis treated with aqueous solutions of chromium trioxide, ferric chloride and ferric nitrate were studied for water repellency and their reaction with wood constituents. FTIR spectra obtained from wood surface treated with chromium trioxide indicate the formation of a water insoluble complex between chromium trioxide and aromatic ring of lignin, whereas no reaction takes place with ferric salts. Treatment of wood by chromium trioxide was found to be effective in imparting water repellency in wood.     

Swelling restraint of thermally modified ash wood perpendicular to the grain

The paper reports on creep of ash wood (Fraxinus excelsior L.) thermally modified at 180 and 200 °C, and subsequently subjected to compression in tangential and radial directions and simultaneously wetted, from the moisture content (MC) of 6% to above the fibre saturation point (FSP). The compressing load made 0.00, 0.25, 0.50 and 0.75 of impact stress at the proportional limit (R_c). The compression stress needed to restrain the swelling of wood, the so-called swelling pressure, was indirectly determined from isochrones of mechano-sorptive creep. The most important finding was that thermal modification reduces the strain of ash wood subjected to compression perpendicular to the grain to a degree proportional to the mass loss. The compression stress needed to restrain the swelling of thermally modified wood is ca. 10 and 20% smaller in the tangential and radial directions, respectively. This effect leads to a reduction in the anisotropy of swelling pressure of thermally modified wood perpendicular to the grain. Moreover, although upon thermal modification the mass loss of wood takes place, at the MC of 6% it shows practically the same modulus of elasticity (MOE) and Rc as the unmodified wood. After wetting to MC higher than the FSP, the thermally modified wood at 200 °C shows significantly higher MOE and Rc than the wood modified at 180 °C and untreated wood. Reduction of wood hygroscopicity, an inevitable effect of thermal modification, also reduces the range of changes in mechanical properties of wood caused by the increase in its MC to the FSP.     

Effect of drying method on the surface wettability of wood strands

An experiment was conducted to investigate the effects of drying methods, namely rotary drum, lab oven, microwave and air-drying, on the surface wettability of wood strands by the Wilhelmy plate method. The measurements included the surface contact angle, free energy, and liquid sorption capacity. Thirty industrial strands including southern yellow pine (Pinus spp.) and poplar (Populus spp.) were randomly collected for each drying method. The results from this study showed that the surface contact angle of a strand depends on the liquid used as well as the drying method and wood species. Liquid sorption capacity of the pine strands increased with decreasing surface contact angle, but this trend was not observed with the poplar strands. The total surface energy was almost the same for strands within species, regardless of the drying method, but it was higher on poplar strands than on pines. The polar and disperse components of surface free energy varied with both drying method and wood species. The surface polar energies of oven-dried pine strands and rotating drum-dried poplar strands were higher than on strands dried by other methods. For lower temperature drying methods (air and microwave), the lowest polar component was observed on the radial face of the pine strands. For the higher-temperature drying methods (oven and rotary-drum), the lowest polar component was found to on the tangential face of the pine strands.     

Observation of anisotropic water movement in<Emphasis Type="Italic"> Pinus radiata</Emphasis> D. Don sapwood above fiber saturation using magnetic resonance micro-imaging

Magnetic resonance micro-imaging has been used to visualise the movement of water during the drying of Pinus radiata D. Don (radiata pine) wood samples of varying annual ring orientation and dimension. The drying process has shown a strong influence of annual ring orientation for thin boards with drying deviating from the classical core-shell model. Diffusion tensor micro-imaging shows the direction of greatest restriction to diffusion being in the transverse radial direction. Similarly, anisotropic values for T₂ relaxation are observed, with values obtained when the transverse face is normal to the static magnetic field being higher than in the case when the radial or tangential faces are normal to the field.     

Influence of mechanical properties and mineral salts in wood species on tool wear of high-speed steels and stellite-tipped tools – Consideration of tool wear of the newly developed tip-inserted band saw

This paper is the third in a series of work done on a novel technique for bandsawing, which uses a tip-inserted saw, and is gaining increasing popularity in Japan. It builds up on previous reports on the novel technique for bandsawing, which considered cutting tool hardness, tool wear, accuracy of kerf width, washboarding, and surface profiles of the workpiece. In this paper, ash content analysis and three-point static bending tests were conducted to clarify the influence of mineral salts and mechanical properties of wood samples of Elais guineensis (Oil palm), Strombosia glaucescens (Afina), and Cryptomeria japonica (Sugi) on cutting tool wear. The cutting tools were made from Stellite and High Speed Steels (HSS) of designations SUS420J2 and TiN coated SKH 51 according to the Japan Industrial Standards (JIS). Among the tested wood samples, the highest cutting tool edge recession when machining with SUS420J2 and TiN coated SKH 51 tools were recorded in Oil palm in spite of Afina possessing the highest mechanical strength properties. On the contrary, Stellite in spite of possessing the smallest hardness (HV580) among all the tested cutting tools recorded the lowest cutting tool edge recession when machining wood samples of Oil palm. However, Stellite recorded the highest edge recession when machining Afina, a high density species. Ash content analysis and a scanning electron micrograph of wood samples of the tested wood species show the presence of high proportions of mineral salts in the transverse, radial and tangential sections of Oil palm. This could perhaps account for the high cutting tool edge recessions recorded in wood samples of the Oil palm. The studies have demonstrated that silica accumulation species could have significant effect on tool wear of high speed steels.     

Use of wax emulsions for improvement of wood durability and sorption properties

Waxes are used for treatment of wood surfaces for several decades predominately as surface treatments because they weakly penetrate into the wood. In order to overcome this issue, water emulsions were applied in the present experiment. Five water emulsions of various concentrations were used, namely montan wax, polyethylene, ethylene copolymer and oxidized polyethylene wax. Performance of wax treated beech (Fagus sylvatica) and Norway spruce (Picea abies) against white rot, brown rot and blue stain fungi was tested. In parallel, sorption properties of wax treated wood were determined. The treated specimens were more resistant to wood decay fungi. Polyethylene and oxidized polyethylene wax were found to be particularly efficient. Although this treatment does not improve resistance to blue stain fungi, it reduces the sorption of water.     

Effects of water glass and DMDHEU treatment on the colonisation of wood by Aureobasidium pullulans

Specimens of Scots pine sapwood (Pinus sylvestris) and beech (Fagus sylvatica) were treated with a sodium water glass solution and 1,3-dimethylol-4,5-dihydroxyethylene urea (DMDHEU). The pH-values of water glass treated specimens were between 9.7 and 12.0. Those of DMDHEU treated specimens were 3.8 (Scots pine) and 4.2 (beech). The resistance observed in an eight weeks laboratory test against the blue stain fungus Aureobasidium pullulans showed that treatments with water glass and DMDHEU reduced but not prevented the fungal growth. Wood specimens treated with water glass showed the lowest colonisation of blue stain. Both treatments inhibited fungal penetration through the ray cells. HPLC analysis showed that the amount of simple sugars was reduced due to water glass treatment. The amount of simple sugars in DMDHEU treated wood depended on the wood species. The amount of available sugar monomers did not indicate an influence of the colonisation of the sample surface.     

柞木弦／径切面胶合强度的试验研究

对柞木木材自身弦／径面强度及其水性高分子异氰酸酯(API)胶粘剂胶合试件弦／径面胶接强度进行了研究。结果表明:柞木木材API胶粘剂弦／径面胶合试件常态压缩剪切强度存在着差异;柞木径切面API胶合试件的常态压缩剪切强度比弦切面胶合试件的常态压缩剪切强度高;径切面API胶合试件的常态压缩剪切强度是弦切面的1.22倍;而柞木弦、径面API胶合试件的反复煮沸压缩剪切强度没有显著性的差别。柞木木材本身弦／径面顺纹抗剪强度试验结果表明:柞木木材径向的顺纹抗剪强度为14.41MPa,柞木木材弦向的顺纹抗剪强度为14.97MPa,尽管弦径向间差别不大,但经t-检验证明:柞木的弦／径向间顺纹抗剪强度有显著性的差别,柞木的径向顺纹抗剪强度比弦向顺纹抗剪强度小。     

Improving color stabilization in thermally modified wood by pretreatment with aluminum sulfate vacuum impregnation

The poor anti-weathering performance of thermally modified wood often influences the appearance and service life of wood exposed to an outdoor environment. In this study, wood samples exhibiting ultraviolet (UV) resistance were successfully fabricated by joint aluminum sulfate (Al₂(SO₄)₃) impregnation and thermal modification, and the samples were subjected to accelerated weathering reaching 144 h. Time–dependent changes in the surface color of the control samples and treated samples during weathering were evaluated. Chemical and morphological alterations were analyzed by UV spectrophotometry, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The results showed that incorporating Al₂(SO₄)₃ into the specimens helped prevent both the photooxidative degradation of lignin and the formation of degradation products. The anti-weathering performance of thermally modified wood pretreated by Al₂(SO₄)₃ impregnation improved because the negative effects of ultraviolet light and water on the wood surface were controlled by the high temperature resistance and encapsulation of the hydrolyzed aluminum flocs. The thermal stability also improved in the impregnated–thermally modified samples, as confirmed by the TG results.

     

Quantitative determination of bound water diffusion in multilayer boards by means of neutron imaging

Diffusion processes into multilayered samples of Norway spruce (Picea abies [L.] Karst.) exposed to a differentiating climate (dry side/wet side) were determined and quantified by means of neutron imaging (NI). The experiments were carried out at the neutron imaging facility NEUTRA at the Paul Scherrer Institute (PSI) in Villigen (Switzerland). With NI the influence of different adhesives (polyvinyl acetate (PVAc), urea formaldehyde resin (UF), epoxy resin (EP), one-component polyurethane (1C PUR)) on the diffusion process could be determined by varying the layer number and the thickness of adhesive joints of the samples. Thereby, neutron transmission images were used to measure time dependent water profiles in the diffusion direction. Using Fick’s second law, diffusion coefficients for radial and tangential water transport in spruce wood and in the adhesive joints were calculated depending on moisture content (MC). It was found that the diffusion coefficients of the adhesives (1C PUR, EP at high MC) were up to three orders of magnitude lower than those of spruce wood. PVAc and UF had a smaller barrier effect compared to wood, which in contrast to 1C PUR and EP, clearly depends on the MC.     

Quality assessment of heat-treated wood by NIR spectroscopy

NIR spectroscopy was tested for predicting the properties of heat treated wood using pine (Pinus pinaster) and eucalypt (Eucalyptus globulus) woods with two types of treatment: in oven and in a steam autoclave. Mass loss, equilibrium moisture content, dimensional stability, MOE, bending strength, colour CIELAB parameters and extractives content were determined. NIR spectra were obtained using a fibre probe on the radial surface of the samples. NIR models for mass loss showed very high coefficients of determination (R²) for cross validation ranging from 96–98%. The models obtained for wood properties were in general good with coefficients of determination ranging from 78–95% for equilibrium moisture content, 53–78% for dimensional stability, 47–89% for MOE, 75–77% for bending strength and 84–99%, 52–96% and 66–98% for colour parameters L, a^* and b^*, respectively. R² of the models for extractive content varied between 41.9–79.8% for pine and between 35.3–82.2% for eucalypt wood. NIR spectroscopy showed a good potential for quality control and characterization of heat treated woods.     

Wood–water relations of chestnut wood used for structural purposes

Hygroscopic properties and water vapour permeability of chestnut (Castanea sativa Mill.) wood were studied using saturated salt solutions, and the results were analyzed using the Hailwood–Horrobin model. At 20 °C/65 % the equilibrium moisture content (MC _eq ) and density were 11.5 ± 0.1 % and 576.6 ± 10.2 kg m^?3, respectively, and the fiber saturation point was 20.83 %. The average water vapour permeability was 0.320 kg m^?1 s^?1 Pa^?110⁸, lower than that of Radiata pine (0.726 kg m^?1 s^?1 Pa^?110⁸). Furthermore, there was no difference in permeability between tangential and radial cuts. This low permeability is explained by the scant development of the multilayer of the Hailwood–Horrobin model. This is attributed to the wood extractives, which reduce the void space and hindered condensation. Chestnut wood has different vapour sorption and vapour permeability than conifers normally used in construction.     

Observation of anisotropic water movement in Pinus radiata D. Don sapwood above fiber saturation using magnetic resonance micro-imaging

Magnetic resonance micro-imaging has been used to visualise the movement of water during the drying of Pinus radiata D. Don (radiata pine) wood samples of varying annual ring orientation and dimension. The drying process has shown a strong influence of annual ring orientation for thin boards with drying deviating from the classical core-shell model. Diffusion tensor micro-imaging shows the direction of greatest restriction to diffusion being in the transverse radial direction. Similarly, anisotropic values for T ₂ relaxation are observed, with values obtained when the transverse face is normal to the static magnetic field being higher than in the case when the radial or tangential faces are normal to the field.