Volume 55, Issue 5

The green wood of twelve deciduous tree species was investigated regarding its radial and tangential moduli of elasticity measured in tension (E R and E T , respectively). In addition, the wood density and the volume fraction of rays were determined. A strong positive correlation was found between structural and stiffness properties. A simple two component model was derived for the relationship between the transverse elastic anisotropy factor (i.e., E R /E T ) of the green wood and the relative volume fraction of the axial and ray tissues. In the radial direction of the wood, the modulus of elasticity is influenced by the wood density and the volume fraction of rays; in tangential direction only the density seems to be important. However, the comparison between the elastic anisotropy and the volume fraction of rays indicates that the rays may have an indirect influence due to their shape.

The radial distribution of lignin content in a pine stem was compared to latewood proportion. With the exception of the innermost juvenile growth rings, a strong negative correlation was found. However, the cell-wall lignin content of low lignin growth rings was equal to that of high-lignin growth rings. Therefore, the difference in lignin content between individual growth rings was solely due to varying ratios of high-lignin compound middle lamella to low-lignin secondary wall in thin- and thick-walled tracheids.

The heartwood of sugi ( Cryptomeria japonica D. Don), one of the most important planted trees in Taiwan, has a pleasant yellow, yellowish red to red color. Unfortunately, its attractive appearance is susceptible to discoloration after environmental exposure. This degradation is a significant defect that decreases the value of sugi products. The objective of the present study was to evaluate the effects of environmental factors on the color of sugi yellowish heartwood. We found that the color eventually turned to brownish black in the presence of moisture. Under the combined influence of light and oxygen the color of heartwood changed from yellow to reddish blue. The effect of light wavelengths on the discoloration of sugi yellowish heartwood was also investigated. After irradiation with light of wavelengths above 600 nm, the color of sugi yellowish heartwood changed significantly from yellowish to red. Our findings show that red color enhancement, and hence the economic value of sugi yellowish heartwood, can be achieved by irradiating with light of wavelengths above 600 nm.

The mechanism of preservation by chemically modified tannin and tannin-ammonia-copper agents was examined. Wood decay by F. palustris was markedly suppressed by processing wood with agents made by mixing chemically modified tannins with ammonia and cupric chloride. When wood powder was treated with these agents, mycelial growth and generated protein increased to some extent. The preservative effects of the chemically modified tannins (RMT and CMT) or compound agents composed of the tannins and ammonia-copper were considered to be due to inhibition of the activities of xylanase, mannase and Cx-cellulase. In the culture medium in which treated wood powder was brought in with these agents, drop of pH by oxalic acid, which F. palustris produces, is not generated. The potency of the effect was thought to be due to chelation of copper, an essential trace element for wood decay by F. palustris , by the tannin, and/or neutralization or suppression of oxalic acid production by ammonia-copper.

Chromated copper arsenate (CCA) working solution is partially destabilized over time as a result of hexavalent chromium (Cr VI ) reduction by wood extractives and reactive additives such as water repellents and polyethylene glycol (PEG) wood softening agents. Hot water extracts of several softwood and hardwood species were used to prepare 2% CCA type C solutions. The softwoods included sapwood and heartwood of red pine ( Pinus resinosa Ait.), jack pine (Pinus banksiana Lamb.), black spruce ( Picea mariana Mill.), balsam fir ( Abies balsamea (L.) Mill.) and sapwood of southern yellow pine ( Pinus spp.). Hard wood samples were mixed sapwood and heartwood of red maple ( Acer rubrum L.), basswood ( Tilia americana L.), yellow poplar ( Liriodendron tulipifera L.) and red oak ( Quercus rubra L.). In a similar way, 2% CCA solutions were prepared containing 4% PEG and 1% paraffin wax formulated water repellent. The pH and hexavalent chromium content of the CCA solutions were monitored over time until sludge formation was observed. The obtained sludges were separated and analyzed by Fourier Transform Infrared Spectroscopy (FT-IR) in the mid-infrared range and by atomic absorption spectroscopy (AAS) for chromium, copper and arsenic contents. The results of FT-IR and AAS analyses of the sludges indicate that the products of sludging are of comparable chemical nature regardless of the agent responsible for the destabilization of CCA solutions. Arsenic and chromium are the major and copper the minor constituent of the sludges produced by destabilization of CCA solutions examined here.

The bark and wood of an endemic oak species in Turkey, Q. vulcanica , were investigated with regard to main components, phenolics as well as extractives. About 66% of extract free wood consists of polysaccharides, i.e. cellulose and polyoses. Heartwood was found to be rich in ellagitannins, while in bark proanthocyanidins occurred in larger amounts. Extractives soluble in cyclohexane were divided into saponifiables and neutrals. Among saponifiables saturated acids made up the majority, while sterols and nonsteroidal triterpenes were the predominating compounds of the neutral fraction.

Suberin from extractive-free cork from Quercus suber L. was depolymerised by methanolysis using different sodium methanolate (NaOMe) concentrations. 1% and 3% NaOMe completely removed suberin from cork (54%–56% of extractive-free cork), but for lower concentrations there was incomplete solubilisation; with 0.05% NaOMe, only approximately 80% of total suberin was removed. The monomeric composition of the extracts differed significantly: for the 0.05% NaOMe, only alkanoic acids and diacids were found; the yield of v-hydroxy acids increased with reactant concentration, as well as alkanols and ferulic acid. Results from light scattering, SEC and MALDI-MS showed that soluble oligomeric fragments containing suberinic acids were present in the methanolysis mixture. The molecular weight of these oligomeric fragments decreased with higher sodium methanolate concentrations.

In this study we have shown that cellulose fibres can be coated with regular micron-sized particles by controlling the assembly process of xylans on the cellulose surfaces. When cotton linters were exposed to a 5% water solution of xylan from birchwood at 110°C, 2 h, pH 8, the substrates showed an increase in weight of approximately 6.5%, and visualization by AFM revealed regular particles on the fibre surfaces. The surface modification process was optimized using an experimental design where time, temperature, and pH were varied. The experiments showed that the amount of xylan deposited on the fibres could be varied from 2% up to 20% depending on treatment conditions. The temperature and time were the most important parameters, while pH was not important in the investigated region. The morphology of the deposited xylan layer, as shown by SEM, was dependent on the amount of xylan on the fibre surfaces. At low yield the fibres were coated with a homogenous layer, while at higher yields (20%) regular particles of micron size were identified by AFM analysis. The mechanism of this assembly process of xylan on cellulose fibre surfaces is discussed.

Solid state NMR spectroscopy was used to analyse the inhomogeneous structure of kraft fibre. Primary fines, isolated from the original kraft pulp, and secondary fines, isolated after refining, were compared with the corresponding long fibres. To fractionate fibre wall surface material, the kraft pulp was refined in stages. After each stage, the secondary fines and long fibres were separated and the long fibres refined again to peel off the surface material. It was found that the crystallinity of cellulose is lower in fines compared with the corresponding long fibres. When the fines fractions were compared with each other, the cellulose crystallinity was observed to increase towards the inner parts of the fibre surface. A very clear gradient was also seen in the amount of extractives, which was highest in the primary fines rich in ray cells. The contents of lignin and some hemicelluloses, mainly xylan and glucomannan, were also higher in fines. Residual lignin isolated from the fines was found to be slightly more condensed than residual lignin from long fibres.

Loblolly pine, separated into mature and juvenile portions, was refined at various pressures (4, 8 and 12 bar). Fiber surfaces were investigated using a Scanning Electron Microscope (SEM) and an Atomic Force Microscope (AFM). Refiner pressure had a significant effect on the fiber surfaces. SEM images showed an apparent increase in surface roughness with increased refiner pressure. This was shown quantitatively with data from the AFM that was analyzed using 5, 2.5 and 1.25 μm scan sizes. A scan size of 2.5 μm was found to be the most informative in terms of quantifying the effect of the different treatments on the two fiber types. The calculated surface roughness was greatest at 8 bar for both wood types. Juvenile fibers in general had higher surface roughness values than mature fibers. The results suggest that refining pressure may influence the failure mechanism of juvenile and mature wood differently.

Decomposition of cellulose crystallites in wood during pyrolysis was studied by X-ray diffraction using a tension wood of Populus maximowiczii (cottonwood), which contains highly crystalline cellulose. X-ray diffraction profiles were recorded at varied temperature up to 360°C. By one-hour isothermal treatments, the cellulose crystallites did not decompose at 300°C, but completely decomposed at 340°C. The change in equatorial diffraction profile was studied by temperature scan up to 360°C and by isothermal treatment at the critical temperature of 320°C. Along with the changes by thermal expansion, the changes in diffraction diagram revealed a characteristic discrepancy between the diminishment of crystalline order and the reduction in crystallite size; i.e., the intensity of crystalline reflections diminished steadily while the crystallite size decreased much more slowly. A model of highly heterogeneous decomposition is proposed to explain this behavior.

Tests under mode I and mode III loading were performed on side grooved Compact-Tension specimens of larch and beech under steady state crack propagation to study the damage and fracture behaviour and the influence of two fibre orientations. From the complete load-displacement diagram, all important damage and fracture mechanical values (stiffness/compliance, microstructural damage, crack initiation energy, specific fracture energy, etc.) have been determined. Crack initiation energy and specific fracture energy are approximately ten times higher for mode III loading than for mode I loading in both wood species. Crack initiation occurs in mode III under external mode III loading, crack propagation, however, takes place under mode I, owing to crack surface interference. The influence of fibre orientation on the (fracture) mechanical properties of beech and larch is different. This difference may be explained mainly by the high number of rays in beech.

A near infrared auto-goniophotometer was designed to acquire detailed information on optical characteristics of a biological material which had a cellular structure, such as wood. The reflected light, which originated from the irradiation of polarized near infrared light, was separated into an unpolarized and a polarized component by using two polarizing filters. The standardized reflected intensities of each component at various incident angles θ and observation angles η , ρ up ( θ, η ) and ρ p ( θ, η ), were measured. Sitka spruce samples with various thicknesses were used. The measurements showed that the directional characteristics of the unpolarized component were affected significantly by the irradiation conditions and the sample thickness. Particularly, these varied with the wavelength of incident light λ . This shows that the directional characteristics models we proposed previously are reasonable. On the other hand, matrices of the directional characteristics for polarized components typically show an elliptical shape which is strongly affected by incident angle and only slightly by λ . Based on these results, the effects of sample thickness on the spectral directional characteristics were determined.

Wettability of sanded and non-sanded transverse and tangential sections of 22 southern hardwoods species was judged by measurement of contact angles using phenol formaldehyde resins. As expected, contact angle values on transverse sections were higher than those on tangential sections for both sanded and non-sanded surfaces. On sanded surfaces, hackberry had the highest mean contact angle (64.7°), and black oak had the lowest mean contact angle (50.1°). On non-sanded surfaces, winged elm had the highest mean contact angle (59.1°), and sweetgum had the lowest mean contact angle (45.9°). In addition, 4 of the 22 species (southern red oak, sweetgum, white oak, and post oak) were selected to investigate the effect of oven-drying, air-drying, and free-drying on wettability. The mean transverse contact was 2.1°–29.0° and 5.1°–31.5° higher than radial and tangential values, respectively. The contact angle pattern typically displayed for a given species and plane was generally oven-dry > air-dry > freeze-dry. The species pattern for most methods and planes was: sweetgum > white oak > post oak > southern red oak. White oak and post oak gave similar contact angle values.

The mechanical properties of wood are highly related to its structure, and knowledge regarding the influence of, for instance, density and fiber wall structure is needed for a better utilisation of the wood material. In this work, the Iosipescu method was used to test wood in rolling shear in order to establish the intra-ring variations in the wet shear modulus of spruce wood. The shear modulus increased from the earlywood to the latewood within the annual rings. This increase in the wet shear modulus was explained to 80% by the variations in the density of the wood.

An approach to a chromophore composition study using the direct size-exclusion chromatography (SEC-UV) analysis of an alkaline extract of pulp fibre walls is described. Absorbance in the 290–405 nm range of 2% and 18% NaOH extract from unbleached pulps obtained by conventional and extended kraft delignification of black alder wood is compared. The effect of cooking conditions on the localisation and accessibility of chromophores is elucidated. The alkali-soluble lignin from pulp produced by extended cooking was less oxidised, less conjugated, and less coloured as compared with the conventional kraft lignin. A chromophore accessibility index is proposed. The chromogenic structures in pulps obtained by extended cooking were more resistant to alkali solutions than those in conventional kraft pulps.

This study aims at the optimization of the durability of Laminated Veneer Lumber (LVL) panels by adding borates to the gluing formulation. Poplar veneers measuring 2.6 mm thickness were used for the manufacture of LVL by Isoroy, a French company located in Lisieux. The melamine-urea-formaldehyde (M.U.F.) glue formulations were mixed with various concentrations of boric acid. A 0.8% retention of boron was measured in the LVL panel after intensive water leaching. The mechanical properties of finished LVL panels and their bonding strength properties were evaluated. The influence of the glue bonding on leaching was also evaluated. The amount of boron in LVL was measured by spectrocolorimetry using the CIELAB system. Results demonstrated that the incorporation of boron in the glueline may improve LVL durability.