Volume 56, Issue 2

Knowledge about the moisture content of trees in the forest or wood yard is scarce. The variation of moisture content within and between 20 boles of sessile oak was investigated using 1543 measurements performed at three heights in each tree and along 4 radii. Five radial positions were defined: sapwood, outer, intermediate and inner heartwood, and the core piece including the pith. Results show that the average moisture content is highly dependent on the individual. The average moisture content was around 80%(oven-dried basis), but it ranges from 65% to 100%depending on the tree. This “tree” effect is discussed and examined using some general characteristics of the trees (region, stand structure, site quality, dendrometric and densitometric traits). Apart from age counted from pith, and the ratio of tree height vs. diameter, no strong correlation appears. Moderate variations in moisture content with radial position and height are also brought to the fore. The specific role of sapwood, which exhibits a more variable moisture content is discussed.

Two field test sites with different soil types were selected. Analysis showed that the two soils had considerable between-site variation in texture, base saturation, acidity, levels of metals, and cation exchange capacity. The sites also had moderate differences in average seasonal temperatures and rainfall. Stakes, made from defect-free southern yellow pine (SYP) sapwood and measuring 19×19×559mm, were treated to about 0.40 pcf (6.4 kg/m 3 ) with chromated copper arsenate (CCA-type C). The stakes were installed at the two sites and sets of ten or more samples pulled after 55 and 66 months of exposure. The depletion of the individual components (chromium, copper and arsenic, oxide basis) from below-ground sections of each stake was then determined. No significant site effect on depletion was observed despite the large contrasts in chemical and physical properties between the two soils. Of the individual components, copper generally had the least depletion on a pcf weight loss basis while the greatest loss was observed with arsenic in three of the four time/site sets. The exposure times examined had no influence on depletion.

Standing moso bamboo ( Phyllostachys pubescens Mazel) culm is attractive to many people for its green color, but it fades readily if it is not chemically treated. Chromated phosphate (CP)has beensuccessfully used to protect the green color of bamboo. In order to understand the mechanisms of such protection withCP, this study was performed using various surface analytical methods (FTIR,ESCA, and ESR) to examine the characteristic structures on the CP treated bamboo surface. The results revealed that pigments remaining in the bamboo epidermis did not affect the color of bamboo during subsequent green-color-protection treatment. After CP treatment, chromium and phosphorous from CP were located in the epidermisand cortical parenchymaofbamboo epidermaltissue. CPoxidized the chemical components on the bamboo surface and consequently generated a largenumber of carbonyl groups and radicals. Meanwhile, the valence states of Cr were reduced from Cr(VI) to Cr(V) and then to Cr(III).

Extractive-free cork from Quercus suber L. was submitted to organosolv fractionation and the effects of different process variables, such as ethanol/water ratio, temperature, time and the presence of acidic or alkaline catalysts, were studied. The variation of the relative proportions of extracted components, as a function of the processing conditions, could thus be established. Whereas the addition of 0.1Macetic acid only increased the yield of extracted materials from about 15 to 23 %, the use of sodium hydroxide, at the same concentration, produced a jump to 76 %. In the case of the alkaline organosolv fractionation, an increase in process temperature, time and catalyst concentration led to an increase in the extraction yield, although in some cases this increase did not follow a sustained trend, as in the case of reaction time. Increasing the ethanol/water ratio led to a higher selectivity in favour of suberin extraction. Residual cork from different organosolv processes was characterised by FTIR and 13 C solid-state NMR. The latter technique provided some valuable information about both process selectivity and cork morphology, particularly with respect to the positioning of suberin macromolecules in the cell wall.

The chemical composition of the dichloromethane extract of Eucalyptus globulus wood cultivated in Portugal was studied by gas chromatography-mass spectrometry, prior to and after alkaline hydrolysis. In addition to previously identified lipophilic extractives, 22 free or esterified compounds (14 fatty acids, 2 fatty alcohols and 6 aromatic compounds) were identified for the first time in E. globulus wood. One of these, ferulic acid, was esterified with three different fatty alcohols and with two α-hydroxyfatty acids. Some of the newly identified compounds, particularly the a-hydroxy-fatty acids are responsible for recently reported pitch problems during pulp production in a Portuguese mill. The differences found in the E. globulus chemical composition, when compared with published data, are expected to be related to variations in the location of growth and genetic factors.

The reaction activation energies and entropies have been determined for the catalysed reaction of pyridine swollen pine sapwood samples and phenolic model compounds (in solution) with a homologous series of carboxylic acid anhydrides. With wood samples, the activation energy (Ea) was largest for the reaction of ethanoic anhydride ( ca. 40 kJ mol −1 ), and decreased as the molecular weight of the anhydride increased (to ca. 10 kJ mol −1 with hexanoic anhydride). With the model compounds, there was no substantial evidence for such a relationship between molecular weight of anhydride and Ea. Values for the entropy of activation for reaction with wood were on the order of −300 J K −1 mol −1 , whereas values for reaction with the model compounds were generally on the order of −−220 to −260 JK −1 mol −1 . The activation energies of diffusion (Eadiff) for the anhydride series in Corsican and Scots pine have also been determined, these varied from ca. 7 to 19 kJ mol −1 . No correlation was found between Eadiff and anhydride, nor between Ea diff and wood species. The results are interpreted by considering the void space created around the reactive hydroxyl groups through swelling of the cell wall with pyridine.

The lignin content in wood is generally determined with a standardized method. It is shown that with minor modifications, e.g., particle size, temperature and adherence to handling times, the standard deviation could be decreased substantially. Pooled standard deviations of 0.045 %, based on 30 determinations in immediate succession, and 0.11%, based on 400 determinations in randomized order, were obtained, which are well qualified for the calibration of secondary analytical methods such as NIR or Raman spectrometry. As a consequence of finer grinding, an identical sample can be used for lignin determination and for investigations in the mid infrared region without regrinding or fractionating.

Bark residues generated by the pulp and paper and wood industries represent a threat to the environment due to leaching of chemicals such as phenolics and resin acids which are being currently regulated by governments. Vacuum pyrolysis of resinous bark produces phenolic-rich oils which represent a potential raw material to replace petroleum-based phenol presently used in the formulation of wood adhesive resols. Resols with different levels of phenol replacement by phenolic pyrolysis oils, formaldehyde to phenolics molar ratios and sodium hydroxide to phenolics molar ratios were synthesized. Strandboards werepreparedandtheirmechanicalandphysicalpropertiessuchasmodulusofrupture(MOR),modulus of elasticity (MOE), dry and 2-hour boil internal bond (IB) and thickness swelling (TS) were evaluated. Homogeneous panels bonded with resins having 25 and 50% by wt of pyrolysis oils replacing phenol exhibited comparable mechanical properties to those of panels made with a commercial surface resin under the same pressing conditions. Three-layer panels made with resins having 50 % by wt phenol replacement in the surface and 25% by wt phenol replacement in the core had mechanical properties above the requirements specified by the Canadian Standards CSAO437.0-93 for OSB products.

The supermolecular structure of polysaccharides in unbleached sulphite pulps and kraft pulps was investigated by CP/MAS 13 C-NMR (Cross Polarisation Magic Angle Carbon-13 Nuclear Magnetic Resonance) in combination with spectral fitting. The cellulose crystallinity was found to be higher in the kraft pulps than in the sulphite pulps. Acellulose Iα to cellulose Iβ conversion was observed during kraft pulping but not during sulphite pulping. The sulphite pulps exhibited smaller lateral fibril aggregate dimensions than the kraft pulps. The spectral behaviour of the hemicelluloses in the sulphite pulps was different from that in the kraft pulps. The general observation is that the supermolecular structure of the polysaccharides in the investigated sulphite pulps is very similar to the structure observed in wood.

The fracture properties of unmodified and modified (heat treatments under various conditions and acetylation) sprucewood are investigated using the wedge splitting test. Fracture parameters measured include critical stress intensity factor and specific fracture energy under Mode I loading and specific fracture energy under Mode III loading. The Mode I fracture properties are reduced by all kinds of modification. However, acetylation leads to a reduction of only 20%whereas heat treatments reduce the properties to a much greater extent, approximately 50%to 80%. The Mode III fracture properties are influenced less. SEM pictures of the fracture surfaces support the described findings.

Polonowski type degradation reactions are a major reason for the frequently observed instability of solutions of cellulose in N -methylmorpholine- N -oxide monohydrate (NMMO, 1). The degradation is induced by degradation products of cellulose and NMMO generated in situ in the Lyocell system. The presence of both an amine component, such as morpholine or N -methylmorpholine, and an acid component is required for the decomposition process to proceed. The latter might be a low-molecular-weight compound, such as formic acid, acetic acid or gluconic acid, or also a high-molecular-weight acid, such as polyglucuronic acid or ion exchange resin.

This study investigates the effect of fire-retardant (FR) chemical retention and distributive percentage of FR chemical (DP) on FR performance of FR treated China fir ( Cunninghamia lanceolata ) wood. The specimens were treated with various concentrations of FR chemical solutions using a vacuum or full-cell process in order to obtain six different DP levels of FR treated woods with DP levels of 34 %, 48 %, 62 %, 76 %, 90%and 100 %.FR treated woods were tested in accordance with the third grade of surface FR performance as specified by the CNS 6532 standard. Results indicated that the minimum FR chemical retention for meeting the requirement of the third grade standard was 49.2 kg/m 3 and 56.6 kg/m3 for 100% and 90% of DP level specimens, respectively. However, when the specimens exhibited 62% ∼ 34% of DP level and a FR chemical retention up to 100.5–115.8 kg/m 3 they did not qualify for the third grade standard. The factors of surface FR performance were influenced significantly by the DP level of specimens, the factor of tl (flame lingering time index of material) of FR treated wood could be considered the most sensitive indicator for meeting the requirement of the third grade standard in this study.

The penetration behaviour of isocyanate-based wood resins was evaluated using x-ray microscopy. Aspen wood pieces were bonded together in a controlled manner. These were embedded in a methacrylate-based resinand thin sections were prepared, cut from the transverse face of thewoodcomposite. X-ray images of these sections were prepared at several selected x-ray energies to allow the isocyanate, cellulose, lignin and the embedding agent distributions to be mapped. The isocyanate resin was found to penetrate deeply into the wood. The resin enters large cell lumen, and wicks along the inner cell wall surfaces. The resin accesses connected cells via connecting pits, which become filled with the resin. The affinity of the isocyanate to the inner surfaces of the large cells is probably due to the hydrophobicity of these surfaces. Isocyanate resins do not penetrate into the smaller parenchyma and tracheid cells and indeed do not even wet the inner surfaces of these cells where isocyanate entry has been allowed due to damage of the cell at the macroscopic surface of the wood. If isocyanates penetrate into the wood-cell walls of the large cells, the concentration in the cell walls has been determined to be less than 2%of the bulk concentration. This lower limit is the sensitivity limit imposed by photon statistics in the data.