Volume 60, Issue 4

Xylans were selectively removed from paper-grade pulps by nitren extraction to produce dissolving pulps. Extraction parameters were optimised for a birch kraft pulp regarding time, temperature, liquor/pulp ratio, and total nitren charge. Furthermore, the applicability of the method was investigated for two other kraft pulps obtained from eucalyptus and mixed softwood, and for one beech sulfite pulp. Extracted pulps were characterised regarding their carbohydrate content and Cuen viscosity. The nitren charge was a decisive factor for xylan removal and pulp purity. The combination of a high nitren concentration and low liquor/pulp ratio was most effective for xylan removal. However, a high liquor/pulp ratio with a lower nitren concentration proved to be more selective and minimised cellulose degradation as well. Glucomannans were almost insoluble under the extraction conditions investigated. Therefore, softwood pulps were not suitable for the upgrading of chemical pulps to dissolving pulps by nitren extraction. On the other hand, hardwood pulps obtained by kraft and sulfite processes contained 96–97% cellulose after nitren extraction.

De-esterification and sulfonation reactions, which create new anionic groups in the middle lamella and primary wall layers, are the key chemical reactions in chemithermomechanical pulping. The effects of these reactions on the resulting fibre dimensions, refining energy demand, hand-sheet bulk and strength properties were assessed by laboratory-scale chemical pre-treatments and refining of Norway spruce chips. After pre-treatments with alkaline, sulfite, alkaline sulfite and alkaline peroxide liquors, a Wing defibrator-type batch refiner was used. The refining energy was measured. The degree of alkaline hydrolysis of acetyl and methyl ester groups in galactoglucomannans (GGMs) and pectins, and the degree of lignin sulfonation were determined. Hand-sheets were prepared and their physical properties were tested. The data were subjected to multivariate analysis and the order of significance of the chemical reactions towards pulp and paper properties was estimated. Chemical pre-treatments were found to increase the fibre length and the energy demand considerably. The fibre length and width after refining were strongly influenced by lignin sulfonation and pectin demethylation. GGM deacetylation had little influence on preserving the fibre dimensions in CTMP refining. The bulk, on the other hand, was highly influenced by GGM deacetylation. Peroxide reactions in alkaline peroxide treatments had no effect on the pulp and paper properties.

The utilization of western red cedar mechanical pulp is limited by low brightness caused by a high chromophore content. In this paper we identify these chromophores and provide a possible mechanism for their formation during the mechanical pulping process. Diffuse reflectance ultraviolet (DRUV) and Fourier-transform infrared (DRIFT) spectra were recorded for western red cedar chemimechanical pulp treated with hydrogen peroxide, sodium borohydride and acetic anhydride. Treatment with hydrogen peroxide was conducted over different time periods. The spectra indicate that three carbonyl-containing chromophores contribute to light absorption in the visible region. Two conjugated ortho -quinones contributed most of the color. These quinones were formed by oxidation and polymerization of lignans during the refining process. The third chromophore was coniferaldehyde. There was a large initial time lag for the reaction of peroxide with coniferaldehyde relative to reaction time with the quinones. We ascribe this to differences in topochemistry. It was deduced that coniferaldehyde was mainly associated with lignin in the interior of the fiber wall, whereas the quinones were derived from lignans that had been deposited on the fiber surface. Identification of the three chromophores provides a basis for studies of the kinetics of brightening of western red cedar mechanical pulps.

Many chemical pulp mills use pulp viscosity as an indicator of pulp strength, and some mill customers stipulate a particular viscosity threshold for the delivered product. Nevertheless, the value of the viscosity-strength relationship is often questioned, particularly as it varies with the wood species and the pulping process. To provide some insight, the viscosity, degree of polymerisation and fibre length were measured for a bleached softwood sulfite pulp segregated into different fractions with respect to fibre length using a Bauer-McNett fractionator. It was demonstrated that fractions with a longer average fibre length also had a higher degree of polymerisation and higher viscosity. The cellulose chain length in chemical pulps is approximately three orders of magnitude shorter than the fibre length, and thus a relationship between these two properties should not be expected. The possible causes of the correlation between fibre length and viscosity are discussed. In this work, viscosity appears to be an indirect measurement of the average fibre length of a pulp, which would be the direct contributor to the strength of that pulp.

UV resonance Raman (UVRR) spectroscopy was used to study changes in the structure of reducing end groups of O -alkyl substituted celluloses under conditions simulating the initial phase of soda pulping. The derivatives studied were carboxymethyl cellulose (CMC) with a degree of substitution (DS) of 0.58 and methyl cellulose (MC) with DS of 1.64–1.95. Hot alkaline treatments were carried out in solutions of sodium hydroxide (0.1–1 M) at 95°C in the presence of creosol as a lignin model compound. Alkali-stable aromatic end groups were generated in both cellulose ethers. Moreover, the end groups of methyl cellulose were extensively condensed with creosol. The results demonstrate that aromatisation and condensation depend on the pH and reaction time.

This study evaluated the quality of kraft pulp from budworm-infested jack pine. The logs were classified as merchantable live, suspect, or merchantable dead. Raw materials were evaluated through visual inspection, analysis of the chemical composition, SilviScan measurement of the density, and measurement of the tracheid length. Unbleached pulps were then refined using a laboratory disk refiner. The mechanical and optical properties of handsheets made from the refined pulps were evaluated. Although budworm galleries may affect the physical integrity of the wood, they have no effect on pulp quality. Blue stain did not affect the handsheet brightness. The results indicate that merchantable dead jack pine trees are acceptable for kraft pulp production, with equivalent pulp yield.

Cellulolytic enzyme lignin (CEL) and milled wood lignin (MWL) were prepared by three different ball-milling methods. The structure of CEL at various yields was elucidated and compared with MWL using wet chemical analysis, FTIR and solution-state NMR techniques. Results show that ball milling of wood degrades β- O -4 structures in lignin. However, even after extensive ball milling, less than 25% of the β- O -4 structures were degraded. The extent of degradation was less for softwood than for hardwood lignin. Extractable lignin yield, either MWL or CEL, was the best way to assess the extent and effect of ball milling. CEL is preferred over MWL, as it can be isolated in higher yield with less degradation. CEL was isolated at yields ranging from 20% to 86%. Over this range the CEL had similar structures, suggesting that lignin in the secondary wall is uniform in structure. The residual enzyme lignin (REL) was structurally different from CEL and may originate mainly from the middle lamella. In this paper we propose a new procedure for the isolation of lignin for use in structural studies, whereby wood is sufficiently milled and successively extracted to produce three lignin fractions representing the total lignin in wood.

Evidence showed that acetyl groups introduced during acetic acid delignification was a primary cause of the poor enzymatic digestibility of acetic acid pulp. The inhibition by acetyl groups could be removed by saponification. Acetyl groups might inhibit the enzymes by interfering with the productive binding (hydrogen bonds) between cellulose and the catalytic domain of cellulases, by affecting the binding of CBD to cellulose, or by increasing the diameter of the cellulose chain.

Both spectral noise and reference method noise affect the accuracy and the precision NIR predicted values. The reference noise is often neglected, and the few reports dealing with it only consider random noise artificially added to the original sound reference data. A calibration for lignin content of maritime pine ( Pinus pinaster Ait.) wood meal was developed, but due to low precision and accuracy in the reference data set, NIR partial least-squares regression (PLSR) yielded a slope of 0.51 and an intercept at 14% Klason lignin. We demonstrate with an independent data set for external validation, obtained with higher precision and accuracy, that the NIR PLSR model based on the noisy reference data led to better results. The slope of the correlation between predicted and reference values was 0.89 and the intercept was 3.9. Thus, the model performed much better than expected from the cross-validation results. The predictability can be explained by the facts that the loadings of the first principal component (PC) of the calibration and test samples are very similar and dominated by lignin-related bands, and that most of the variation in the test set can be explained by the first PC. This only explains why the Klason lignin content could be predicted with the model without giving many spectral outliers, but not the good result of the external validation. We show that the latter can be explained by the inverse calibration used for PLSR and that predicted values can be more accurate and precise than the reference values used for calibration.

The wide-line 1 H nuclear magnetic resonance (NMR) spectrum of paper in equilibrium with ambient humidity consists of super-imposed relatively broad and narrow lines. The narrower line is of the order of 2 kHz wide at half the maximum height, while the broader line is of the order of 40 kHz in width at half height. On the basis of these line widths, the narrow line is assigned to water sorbed to the paper, and the broad line to the polymeric constituents of the paper. It was not possible to distinguish between the various polymeric components of paper contributing to the 1 H NMR spectra. A modified Goldman-Shen pulse sequence was used to generate a spatial magnetisation gradient between the polymer and water phases. The exchange of magnetisation between protons associated with water and those associated with the macromolecules in paper was observed. The exchange of magnetisation is discussed within a heat transfer model for homonuclear dipolar coupling, with exchange being characterised by a spin-diffusion coefficient. Consideration of the magnitude of the initial rate of the exchange process and estimates of the spin-spin relaxation times based on 1 H line widths indicate that some water must exist in a sufficiently immobile state as to allow homonuclear dipolar interactions between adjacent polymer and water protons. Thus, water sorbed onto paper must exist in at least two states in mass exchange with each other. This observation allows certain conclusions to be drawn about the ratio of free/bound water as a function of moisture content and the dispersal of water within the polymer matrix.

Correlations between process parameters and VOC emissions from an oriented strand board (OSB) made of Scots pine ( Pinus sylvestris L.) were demonstrated. Terpene and aldehyde emissions were affected by the pressing time factors in different ways: terpene emissions were lowered with elevated pressing times, whereas the formation of volatile aldehydes was accelerated. Drying temperature mainly affected the dynamics of aldehyde formation, with a clear rise and fall in aldehyde concentration after drying at elevated temperatures (170°C and >200°C). As a consequence of lower temperatures (120°C), aldehyde emissions from OSB constantly increased over the testing period. In spite of this context, a sustainable reduction in aldehyde emissions by adjusting the relevant process parameters does not seem to be feasible, as the concentrations released from all panels converged during emission testing.

The bulk and surface properties of blocks of nine Australian wood species of commercial importance were investigated to elucidate the factors affecting timber gluability with structural one-component polyurethane adhesives. Cross-lap joints were prepared from freshly sanded blocks and the joints were subjected to creep loading in a condensing humidity environment. The median tensile strength (MTS) of the joints was found to improve with decreasing phenolic extractives content, lower timber density and decreasing lipophilic surface extractives content. The latter was assessed from O/C atomic ratios of the timber surfaces determined by X-ray photoelectron spectroscopy (XPS). The content of bulk lipophilic extractives and lignins and wettability of the surface as determined by the sessile drop method did not reveal significant correlations with the adhesion properties. The adhesion tests indicated significant gluability differences between the species investigated.

The elastic modulus, hardness, and creep factor of wood cell walls in the interphase region of four different adhesive bonds were determined by nanoindentation. In comparison with reference cell walls unaffected by adhesive, interphase cell walls from melamine-urea-formaldehyde (MUF) and phenol-resorcinol-formaldehyde (PRF) adhesive bonds showed improved hardness and reduced creep, as well as improved elastic modulus in the case of MUF. In contrast, cell walls from the interphase region in polyvinylacetate (PVAc) and one-component polyurethane (PUR) bonds showed more creep, but lower elastic modulus and hardness than the reference. Considering the different cell-wall penetration behaviour of the adhesive polymers studied here, it is concluded that damage and loss of elastic modulus to surface cells occurring during the machining of wood is recovered in MUF and PRF bond lines, whereas damage of cell walls persists in PVAc and PUR bond lines.

Welding of wood is a well-known joining procedure that offers several advantages over traditional mechanical fasteners or gluing. During welding, extensive solid-state transformation phases occur in the so-called melting zone and the heat-affected zone. The nature and the extension of such transformations are correlated to the energy input and thus to the heat generated during the process at the wood joint interface. In the present work the influence of the welding parameters and wood grain orientation on the temperature profile and distribution and final strength of welded connections was investigated. For this purpose, the characteristics of the joints were evaluated with both destructive and non-destructive techniques. Non-destructive evaluation was performed with infrared thermography, which allowed measurement of the maximal and average peak temperature, temperature profile and distribution, and rate of temperature increase. Thus, this technique can also be used to detect welding defects and to provide information on material modification during welding.

Wood specimens of fir ( Abies alba Mill) and beech ( Fagus sylvatica L.) were chemically modified using polycarboxylic acids (PCA), cured by convection heating or microwave treatment and analyzed by HPLC. A new non-formaldehyde cross-linking system was composed of citric acid (CA) and 1,2,3,4-butanetetracarboxylic acid (BTCA), which are representative polycarboxylic acids (PCAs). These reagents require phosphono-based catalysts, so a sodium hypophosphite (SHP) catalyst was used in this study. The effects of PCA treatment were compared with a previously introduced 1,3-dimethylol 4,5-dihydroxy ethylene urea (DMDHEU) treatment. The dimensional stability of the modified wood was determined in terms of the anti-swelling efficiency (ASE) using the water soak/oven dry method. The results revealed an improvement in ASE for wood modified with PCA compared to modification with DMDHEU. Qualitative and quantitative determinations of bound acids were performed by HPLC. Further intensification of the wood modification process and an increase in the quality of wood-based materials were achieved using microwave treatment. Among other benefits, the formation of cross-links between the wood and the reagent components led to an improvement in the tensile strength retention, particularly in combination with the microwave treatment.

This study considered the influence of variations in the modulus of elasticity (MOE) on the mechano-sorptive (MS) creep of wood. MOE in the radial direction ( E R ) was investigated as a function of changes in moisture content (MC). E R values were lower during both adsorption and desorption processes than under constant MC, despite the same MC values. However, the effects observed were small and are thus not of great practical importance.

The present study shows that isolates of P. vitreus have an extraordinary capacity to induce substantial permeability changes in heartwood of P. abies without causing significant losses in impact bending strength. The degradation of pit membranes by P. vitreus is an important aspect that could also have significant benefits in wood protection processes. Further studies are currently in progress with the objective of optimising the uniformity of wood colonisation and duration of incubation, so as to improve the permeability of water-borne wood preservatives or hydrophobic substances applied by brushing, dipping and impregnation.

The decay and termite resistance of boric acid (BA)- and di-sodium octoborate tetrahydrate (DOT)-treated sugi sapwood was tested in the context of additional heat treatments at two temperature levels. Heat treatments had no effect on boron release and almost all boron was leached from specimens during a 10-day weathering period. Decay tests with the brown-rot fungus Fomitopsis palustris and the white-rot fungus Trametes versicolor and a 3-week termite resistance test with the subterranean termite Coptotermes formosanus were performed. Heat treatments did not increase the decay resistance of either BA- or DOT-treated specimens against the brown-rot fungus. However, the decay resistance of BA-treated specimens against the same fungus increased after heat treatment at 220°C for 2 h. Heat treatments at 180°C for 4 h and 220°C for 2 h also resulted in increased decay resistance of DOT-treated specimens against T. versi-color . Increased resistance against termite attack was observed only in DOT-treated specimens heated at 180°C for 4 h or at 220°C for 2 h. Accordingly, a synergistic effect between heat and DOT treatments was observed for resistance against white-rot decay and termites.

The bark of Chamaecyparis lawsoniana (A. Murray) Parl. was extracted with methanol and sequentially partitioned with n -hexane, ethyl acetate, n -butanol and deionized water. The antioxidant activities of the four extracts were evaluated using the DPPH• and ABTS +• methods. The total phenolic content of the extracts was determined using the Folin-Ciocalteu method and expressed as gallic acid equivalents (GAE). Butylated hydroxytoluene was used as a positive control in the radical-scavenging activity tests. All the bark extracts showed significant radical-scavenging activity. In the ABTS +• assay, n -butanol extracts exhibited the strongest radical-scavenging activity, followed by ethyl acetate, water, and n -hexane extracts. The greatest total phenolic content was 428.54 mg GAE per gram of dry extract and was detected in the n -butanol extract, followed by the ethyl acetate and n -hexane extracts. The antioxidant activities correlate with the amount of phenolics present in these extracts. The ethyl acetate and n -butanol extracts were rich in phenolics and may represent a good source of antioxidants.