Volume 60, Issue 2

The variation in wood chemistry among aspen clones of similar age, harvested from a common site in northern British Columbia, Canada, was evaluated. The aspen clones were evaluated for ease of chemical pulping and differed by as much as 4.5% in pulp yield at a common H-factor. The results demonstrate both the need for understanding the resource and the substantial opportunities that exists in natural population of trees for selecting superior clones for reforestation and afforestation. The syringyl/guaiacyl ratio, as determined by nitrobenzene oxidation, was directly correlated with the ease of pulping, whereas thioacidolysis results were not as predictive. These results were supported by quantitative NMR analysis, which demonstrated differences in the amount of β- O -4/Ar groups and the degree of condensation. Furthermore, it was shown that, in addition to total lignin content, which differed by as much as 5%, structural differences in the lignin may influence pulping efficacy. Among the other parameters evaluated, the distribution of molecular mass and methoxyl content is relevant for pulping. More specifically, among the fractions isolated in this study [milled wood lignin (MWL), MWEL sol , and MWEL insol ], the insoluble fraction was the most indicative of the pulping efficiency.

Two laboratory high-lignin-content softwood (SW) kraft pulps with kappa values of 48.0 and 49.5, prepared by cooking at high and low active alkali (AA), were used for the study of fiber charge development during two-stage oxygen delignification with inter-stage washing (OwO). It was established that the first oxygen delignification (O) stage increased total fiber charge by 2–4%, and further O-delignification via a second O-stage led to a 3–18% decrease in total fiber charge. Carboxylic acid content in pulp holocelluloses decreased by 12–26% with respect to a 35–70% kappa number reduction due to an O and OwO stage of delignification for high and low AA cooked SW kraft pulps. After an OwO-stage delignification, the residual lignin was found to exhibit a 50–100% increase in carboxylic acid content. 13 C NMR spectral data for the residual lignin samples indicated that the unconjugated/conjugated acid ratio was approximately (3–4):1. Generally, the carboxylic acid content in low AA cooked softwood kraft pulp and the corresponding oxygen-delignified pulps was systematically higher (13–23%) than that in high AA cooked SW kraft pulp and the corresponding oxygen-delignified pulps. The experimental results also demonstrated that maximum acid-group content in total fiber occurred after 45–50% oxygen delignification of the SW kraft pulps studied.

In the presence of oxygen, radiolytically generated carbonate radical anions, CO 3 •– , were reacted with methyl β-D-cellobioside and methyl β-D-glucoside. From the ensuing product pattern, it was concluded that CO 3 •– abstracts hydrogen atoms predominantly from glucosidic C1–H bonds. This high intramolecular selectivity was rationalised mainly in terms of a polar effect on the transition state of the hydrogen abstraction reaction. The present findings are in sharp contrast to the relative inertness of CO 3 •– towards glucosidic C1–H bonds previously observed in cotton linters. The reasons for this discrepancy are discussed in light of a possible future role of CO 3 •– as a bleaching agent for pulp.

The finding that hexenuronic acid (HexA) groups can be selectively removed from kraft pulps by acid hydrolysis has provided an opportunity to reduce bleaching chemicals. However, there is evidence that the acid hydrolysis is not uniform. In this report, we evaluate the kinetics of acid hydrolysis of HexA in a xylan sample enriched with HexA, a conventional kraft pulp, and three modified kraft pulps: anthraquinone pulp (Kraft-AQ), polysulfide pulp (PS), and polysulfide-anthraquinone pulp (PS-AQ). We found that HexA present in the xylan and conventional kraft pulp behaved similarly toward the acid hydrolysis throughout. On the other hand, HexA present in the Kraft-AQ, PS-AQ and PS pulps was heterogeneous toward acid hydrolysis and the reaction can be separated into two pseudo-first-order kinetic phases, each of which has a different rate constant. The kinetic data provide evidence for the formation of lignin-HexA-xylan complexes during modified kraft pulping processes.

The effect of the molecular structure of xylan on its assembly onto softwood kraft pulps was investigated. Various xylan-rich fractions were isolated from birch wood chips by different mild treatments using water (H 2 O), acetic acid (HAc) and sulfur dioxide (SO 2 ). The isolation involved prehydrolysis followed by alkaline extraction, with only the time, temperature and medium in the prehydrolysis step varied. After separation, the fractions were neutralised (pH 7) and some material agglomerated and became insoluble. Dynamic light scattering measurements revealed differences in aggregate size among the different fractions. The fractions that agglomerated to the greatest extent contained less glucuronic acid and a higher amount of lignin. Such fractions adsorbed to a significantly higher extent (25.5% compared to 5.0% for the lowest soluble fraction) onto bleached softwood kraft pulps in experiments performed in autoclaves. The adsorption was carried out with fixed process parameters (100°C, pH 10, 120 min). The adsorption of various xylan fractions resulted in different surface morphology on cellulose microfibrils, as observed by AFM. Pulps treated with xylans that were soluble at pH 7 showed small differences from the control sample, which was treated in an autoclave without the addition of xylan. Pulps treated with xylans that agglomerated at pH 7 showed a greater difference in the amount of nanosized aggregates covering the surface. ESCA analysis of the chemical surface composition indicated that samples containing more lignin showed a greater shift towards carbon-carbon bonds. A novel sequence for a pulping process is suggested.

Different methods for estimation of the surface coverage by extractives and lignin were critically compared. For data collection, four state-of-the-art X-ray photoelectron spectroscopy (XPS) instruments located in four different laboratories were used. Hand sheets of one mechanical and two chemical pulp samples were prepared in one laboratory and distributed among the other participants. The XPS results based on O/C ratios and curve fitting of the C 1s peak had very good intra- and interlaboratory variation for extracted and non-extracted pulp samples. The estimations of surface coverage by extractives and lignin also had acceptable intra- and interlaboratory variation. However, significant differences were observed between the results for the various methods. Estimation of surface coverage by extractives based on O/C ratios was much higher than that based on the C1 component analysis in the case of mechanical and unbleached chemical pulp. The surface coverage by lignin of mechanical pulp was reproducibly detected based on O/C ratios, C1 component analysis and by labelling with mercury acetate. The same data were, however, rather scattered if they were collected with these three methods for bleached and unbleached chemical pulp. In spite of the differences, similar trends regarding the pulp type could be observed. We interpret the results as indicating that the surface coverage for both extractives and lignin should not be considered as absolute “true” values, but rather as relative values, which are reliable only for comparison of samples for the same instrument. Even for relative comparisons, we recommend the selection of a strict experimental set-up for spectral acquisition and data treatment when applying any of the instruments and calculation models currently available.

A method for the quantitative isolation of lignin-carbohydrate complexes (LCCs) in a softwood is presented. The isolation steps involve partial enzymatic hydrolysis of cellulose, subsequent swelling in urea, and quantitative dissolution into four major fractions: (1) a galactoglucomannan LCC containing ∼8% of the wood lignin; (2) a glucane LCC containing ∼4% of the wood lignin; (3) a xylan-lignin-glucomannan network LCC (xylan>glucomannan) containing ∼40% of the wood lignin; and (4) a glucomannan-lignin-xylan network LCC (glucoman-nan>xylan) containing ∼48% of the wood lignin. Endoglucanase Novozyme 476, with only cellulase activity, and Ecopulp XM, with only xylanase and mannanase activities, were used as an enzymatic tool. From mildly ball-milled wood, all the lignin was isolated as LCCs. As a control, LCC was prepared from partially chlorite-delignified wood meal without ball milling, also in a mild procedure. The results were very similar to those obtained after ball milling. Thus, it can be safely concluded that the formation of new chemical linkages between lignin and carbohydrates during ball milling is improbable. Studies on isolated milled wood lignin (MWL) supported this conclusion and clearly showed that covalent linkages between lignin and carbohydrates are present. The study provide conclusive evidence of covalent linkages between lignin and carbohydrates in the native lignin in wood. It is concluded that carbohydrate-free lignin, i.e., lignin without covalent bonds to carbohydrates, probably cannot be present in spruce wood.

Lignin-carbohydrate complexes (LCCs) were isolated from unbleached acid sulfite pulp by selective enzymatic hydrolysis followed by fiber swelling and extraction. Approximately 80% of the lignin in the pulp was found to be chemically linked to carbohydrates in three major fractions, viz. as one glucan-lignin complex (with 8% lignin) and two hemicellulose-lignin complexes (with 72% lignin). The latter two were further separated into one glucomannan-lignin complex (with ∼25% lignin) and one xylan-lignin-glucomannan complex (with 45–50% lignin). Based on model experiments, it can be concluded that the lignin and carbohydrate moieties are probably linked together through benzyl ether linkages. Xylan is more stable towards acidic hydrolysis than galactoglucomannan, and this finding may explain the greater amount of xylan-rich LCC in the pulp.

The antioxidative behavior of various lignin preparations derived from chemical wood treatment for paper production was examined. All lignin samples exhibited higher antioxidant activity than Trolox. The protective effect of lignin antioxidants against H 2 O 2 -induced oxidative damage of DNA in human carcinoma cells and male rats was evaluated. Moreover, lignin was tested as a stabilizer in the processing of polypropylene composites, as well as in thermo-oxidative aging of styrene-butadiene vulcanizates. The results indicate that the lignin preparations show great potential as antioxidants in human diets and polymer blends. Lignin has the potential to protect living organisms against cancer diseases and contributes to the protection of polymers against degradation.

Cork suberin was partially depolymerised by methanolysis catalysed by Ca(OH) 2 . The solubilised depolymerisate was analysed by ESI-MS/MS. The compounds identified included monomers and “dimeric” and “trimeric” oligomers. Among the latter, an oligomer of glycerol esterified to a ω-hydroxyacid esterified to ferulic acid was identified. The “dimeric” structures of glycerol esterified to a ω-hydroxyacid and of a ω-hydroxyacid esterified to ferulic acid were also found in the partially depolymerised fraction. The identification of these molecules was confirmed by synthesis of model compounds and comparison of their ESI-MS/MS spectra. The glycerol-ω-hydroxyacid-ferulic acid trimeric oligomer could be an important constituent block in the suberin structure. Its function is probably to link the two main polymers present in suberised cell walls, namely, polyaliphatic polyesters and lignin-related polyaromatics. The glycerol-ω-hydroxyacid moiety is part of the polyaliphatic polyester and the ferulic acid moiety is esterified to the polyaromatics. These oligomers provide a new insight to understanding of the macromolecular structure of suberin, since they could allow cross-linking of the two structurally different biopolymers.

Condensed tannins have formaldehyde gas-scavenging ability. Tannins consisting of phloroglucinol-type A-rings, such as prodelphinidin and procyanidin, had higher formaldehyde-scavenging ability than those consisting of resorcinol-type A-rings, such as prorobietinidin and profisetinidin. This ability was markedly improved by ammonia treatment. The increase in formaldehyde-scavenging ability was especially notable in the case of condensed tannins with a high ratio of pyrogallol-type B-rings, such as prorobietinidin and prodelphinidin. To clarify the factors affecting improvement of the formaldehyde-scavenging ability by ammonia treatment, the reaction behavior of condensed tannins during ammonia treatment was studied. Analyses using 13 C-NMR and on-line methylation pyrolysis/gas chromatography/mass spectrometry revealed that on treatment of condensed tannins with ammonia, amino-substitution at C-4′ of the pyrogallol-type B-ring occurred to form a 4′-amino-3′,5′-dihydroxybenzene-type B-ring. It can be assumed that the introduction of a 4′-amino-3′,5′-dihydroxybenzene-type B-ring into the tannin molecule results in improved formaldehyde-scavenging ability.

The lipophylic extracts of yellow birch ( Betula alleghaniensis ) have been investigated to detect the effect of tree age and wood storage time on extract composition. A total of 17 wood disks were cut from trees belonging to different age groups at 1 m above ground and the wood was milled as usual for extraction (laboratory samples). In addition, 49 sawdust samples were collected in a lumber mill to study the effect of industrial processing on the extractives (industrial samples). All laboratory and industrial samples were extracted with dichloromethane under sonication. The chemical composition of the lipophilic extracts obtained was analyzed by GC-MS. A systematic (quasi-linear) relationship was found between the lipophilic extract yield and specimen age. A total of 30 constituents from yellow birch extracts have been identified, 26 of which have never been previously reported for B. alleghaniensis wood.

The mechanical behaviour of European oak ( Quercus robur L.) was studied in radial and tangential compression. Young's modulus and the yield strength were approximately 1.7- and 1.6-fold higher, respectively, in the radial direction. Strain fields were determined by digital speckle photography (DSP). Strains and the effective Poisson ratio could be determined separately in earlywood and latewood during deformation and failure events. In radial compression, strain data showed that rays contributed significantly to the high modulus. In addition, multiseriate ray microbuckling was observed to control yield strength. The microbuckling was localised in the low-density earlywood. In tangential compression, yield strength was controlled by vessel collapse in the low-density regions of the latewood. The strain field data provide direct evidence that the rays are the main micro-structural factor controlling transverse anisotropy in European oak.

Conventional lumber drying is carried out by forcing hot air to flow across a pile of lumber layers separated by wood strips. The airflow provides the heat required to warm up the lumber and produce the moisture evaporation and, in theory, the difference in temperature at each side of the load can be used to estimate the evaporation rate. The main problem with this approach is that typical temperature sensors that are installed in conventional kilns are not accurate enough to measure the temperature drop across the load during periods of low evaporation. In this paper, a new sensor to measure the temperature drop across the load is proposed and tested in three experimental drying runs of 2″×6″ spruce-pine lumber. The results demonstrate that after calibration, the temperature drop across the load can be used to determine drying curves in conventional lumber drying. In the particular case of this study, calibration was performed by multiplying the experimental temperature drop across the load by a constant factor, which was adjusted by identifying the correction factor that best simulated the experimental green moisture content of the three lumber charges.

Acetoacetylated wood meal (AAWM) was prepared and a preliminary evaluation of its antifungal activity was carried out. Acetoacetylation of wood meal proceeded almost quantitatively with diketene under optimal reaction conditions, even as a heterogeneous reaction. Diketene concentration was the most important governing factor for this reaction. AAWM with a high weight percentage gain inhibited the fungal growth of Fomitopsis palustris .

Fixation of copper ions to acetoacetylated wood meal (AAWM) was conducted in Cu(OAc) 2 -MeOH solution. The maximum amount of copper fixed to AAWM was 147.9 mg g −1 under optimum conditions. From FT-IR analyses of AAWM containing copper ions (AAWM-Cu), it was concluded that a chelate was formed between copper and the acetoacetyl group of AAWM. In a leaching test, half of the copper in AAWM-Cu was retained, even at pH 4.0.

Different aminofunctional silanes were tested for their suitability to preserve wood against basidiomycetes in a mini-block experiment according to EN 113. High effectiveness against the brown rot fungus Coniophora puteana was maintained over prolonged exposure times of up to 18 weeks. Resistance against the white rot fungus Trametes versicolor was only enhanced in the initial phase of exposure (6 weeks); after longer exposure times of 18 weeks, considerable mass losses were observed. It was shown that the antifungal resistance was caused by the amino groups of the oligomeric silane systems, while alkyl groups, which influence the water uptake of wood, only had a minor impact. For effective protection, acidic conditions of the treatment solution were important; this promotes the formation of cationised amino groups (ammonium). The silane quaternary ammonium compound (Si-QAC) 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride was applied in combination with an oligomeric silane system to incorporate quaternary ammonium sites into a SiO 2 matrix via a sol-gel process. This combined treatment significantly enhanced the decay resistance of pine wood against C. puteana.

The suitability of a previously described high-energy multiple impact (HEMI) test for the detection of early fungal decay was examined. The HEMI test characterises the treatment severity of thermally modified wood by stressing the treated material by thousands of impacts of pounding steel balls. This method differentiates between heat treatment intensities, which are manifest as structural changes in the wood. Similar changes in wood structure are known for wood decayed by fungi. Pine ( Pinus sylvestris L.) decayed by brown rot and beech ( Fagus sylvatica L.) decayed by white rot were tested. Mass loss caused by fungal decay and resistance to impact milling (RIM) determined in HEMI tests were found to be highly correlated. Testing of non-degraded pine, beech, and ash ( Fraxinus exelsior L.) showed only marginal effects of wood density on RIM. Furthermore, annual ring angles and RIM of spruce ( Picea abies Karst.) were not correlated. Accordingly, the detection of RIM reduction in decayed wood is not masked by variations in density and orientation of the annual rings. Previous results showed no adverse effects of weathering on RIM. Thus, the detection of fungal decay with HEMI tests is feasible not only for laboratory purposes, but also for wood in outdoor applications that has already undergone weathering.