Volume 63, Issue 4

In the structural analysis of lignins by 13 C-NMR, signal overlap limits definitive assignment and accurate intensity measurement. Selective labeling by 13 C-enrichment of a specific carbon in lignin enhances its signal intensity in the spectrum. Further enhancement of the specifically labeled carbons can be realized via difference spectra created from the enriched and unenriched samples. Difference 2D 13 C- 1 H correlation (HSQC) NMR spectra, derived from the spectra of specifically 13 C-enriched lignin model polymers (so-called dehydrogenation polymers) and their unenriched counterparts, take advantage of the enhanced dispersion afforded by both 13 C and 1 H chemical shifts, diminishing the difficulties arising from the signal-overlap problem and aiding in definitive signal assignments. In this research, protolignin in xylem cell walls was specifically 13 C-enriched at all of the individual phenylpropanoid side-chain carbons by feeding 13 C-enriched coniferins to growing stems of Ginkgo biloba . The whole xylem fractions containing 13 C-enriched and unenriched protolignins were dissolved in a mixture of N-methylimidazole and DMSO, and then acetylated. Solution state 2D-NMR (HSQC) spectra of the acetylated whole cell wall were acquired. Difference spectra between the walls containing 13 C-enriched and unenriched lignins afforded simplified 2D spectra in which well-separated signals were assigned exclusively to the specifically enriched carbons. This novel NMR technique provides a useful tool for elucidation of entire protolignin in the cell wall of ginkgo xylem.

Colour evolution and colour changes were analysed from surface images of small specimens of three thermally-modified timber species using the CIE L*a*b* colour space. Upon heat exposure, the wood substance became orange and then approached grey irrespective of species; this was accompanied by a steady reduction in lightness. Colour changes were similar in the three woods at any given level of heat-induced weight loss (WL), whilst changes in the three coordinates of the CIE L*a*b* space in function of WL were different regardless of the wood species. For ΔL *, the profile was curvilinear and monotonous, while Δa * and Δb * bear a complex, non-linear profile. In turn, ΔE * was found to be highly influenced by the behaviour of ΔL *. It is proposed that ΔE * in thermally modified wood originates from chemical changes in the main wood polymers, more so in lignin than in polysaccharides, due to the darkening of the lignin itself. This was associated with the generation of chromophoric groups, mainly the increase in carbonyl groups appearing in the Fourier transform infrared spectra of lignin between 1710 and 1600 cm -1 , particularly the emergence of quinone species.

In the woodworking industry, image analysis is routinely used for quality control and for matching and classification during various processes. An extension of these automated systems for the prediction of physical properties of thermally modified wood (TMW) is enticing, because to date there is no generalised procedure for the quality assurance of TMW. In this work, the feasibility of predicting 13 physical parameters from the analysis of colour changes is demonstrated using small thermally modified specimens of three wood species. Simple linear regression models for anti-swelling efficiency, nominal density, heat-induced weight loss and 10 strength parameters in six forms of stress were all very or highly significant, with R 2 statistics for the best predictor from 0.24 to 0.94. ΔE * was found to be a better predictor than ΔL * for most properties. Multiple linear regression with 11 colour variables increased the prediction ability of most models in terms of R 2 , although these improvements varied with the property and species concerned. The best models altogether were obtained by partial least squares regression, with relative prediction error values >0 in all cases. Our results demonstrate that physical properties of small specimens of TMW can be efficiently predicted with only one after treatment measurement of colour in the CIE L*a*b* colour space by means of image analysis of TMW surfaces. We anticipate that our approach would be a starting point for more refined modelling of physical properties of larger wood members and other properties of interest in TMW (e.g., decay resistance).

In this report, two softwood kraft pulps, one originating from chips and the other from sawdust, and a hardwood kraft pulp originating from chips were fractionated individually with regard to fibre length using a Bauer-McNett apparatus. The fibre length, the coarseness, the 0.5% viscosity and the intrinsic viscosity were measured on all fractions and whole pulps. For every pulp, there was a unique positive relation between fibre length and viscosity, and also between fibre length and coarseness. Since fibre length has a direct impact on pulp strength, viscosity measurement can provide an indirect method to predict pulp strength. This relationship between the two datasets increases the value of viscosity as an analytical tool.

In the present study, it was evaluated how two different culture conditions for the biotreatment of Eucalyptus grandis by Ceriporiopsis subvermispora affect a subsequent high-yield kraft pulping process. Under the varied culture conditions investigated, different extracellular enzyme activities were observed. Manganese-peroxidase (MnP) secretion was 3.7 times higher in cultures supplemented with glucose plus corn-steep liquor (glucose/CSL) as compared to non-supplemented (NS) cultures. The biotreated samples underwent diverse levels of wood component degradation as losses of weight and lignin were increased in glucose/CSL cultures. Mass balances for lignin removal during kraft pulping showed that delignification was facilitated when both biotreated wood samples were cooked. Delignification efficiency did not correlate positively with MnP levels in the cultures. On the other hand, biopulps from NS and glucose/CSL cultures saved 27% and 38% beating time to achieve 28° Schopper-Riegler freeness during refining, respectively. Biopulps disposed of decreased tensile and tear resistances, thus easier refining of the biokraft pulps seems to be a consequence of less resistant fiber walls. Improved beatability of biopulps was tentatively related to short fibers and fines formation during refining. We suggest that to some extent polysaccharide depolymerization occurred during the biotreatment, which also resulted in diminished pulp yields in the case of glucose/CSL cultures.

Alternative methods of enhancing water absorption of birch pulp fibers by crosslinking poly(methyl vinyl ether-co-maleic acid) and polyethylene glycol are briefly explored. While thermal initiated crosslinking is common, microwave initiated crosslinking of lignocellulosics is less studied. The thermal and microwave initiated crosslinking were compared through water absorption and retention. The microwave conditions were optimized to 105 s at 1600 W, while the thermal samples were placed in a 130°C oven for 6.5 min. Both methods resulted in successfully creating new superabsorbent fibers. The microwave initiated crosslinked fibers absorbed 45–413% more water and the thermal initiated fibers absorbed 210–582% more water than the control fibers (37.3 g/g and 29.4 g/g, respectively). This study demonstrated that it is possible to utilize microwave technology to enhance water absorption properties of lignocellulosics fibers and to reduce reaction times.

Eucalyptus wood chips were impregnated with various blends of fiber modifying enzymes prior to preconditioning refiner chemical-alkaline peroxide mechanical pulp processing. The process includes chemical pretreatment and two stages of refining. The energy consumption was compared at the same Canadian standard freeness level of 350 ml. Some enzyme treatments were found to reduce specific refining energy (SRE) by at least 24%. The enzyme hydrolysis within the cell wall was observed by transmission electron microscopy of impregnated chips with high spatial resolution. The enzyme blends that successfully reduced SRE requirements were found to selectively loosen the bonds between the S1 and S2 layers of the fiber wall. Enzymes which selectively attached the S2 layer did not impart any SRE reduction. All experiments for impregnation and pulp processing were conducted at the Andritz Pilot Plant in Springfield, OH.

β-Ether-type dimers, [1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1-propanol and 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1-propanol], and an α,β-diether-type trimer [1-(4-(3,4-dimethoxybenzyloxy)-3-methoxyphenyl) -2- (2-methoxyphenoxy) -1-propanol] were pyrolyzed in a closed ampoule reactor (N 2 /250–400°C/2 min). 1-Phenylpropenes (C α =C β ) and 1-phenylpropanones (C α =O) were obtained as the major β-ether-cleaved products. Radical chain mechanisms are proposed in which hydrogen abstraction at the phenolic O- H and C α - H s occurs, respectively. The former reaction which gives rise to three radical species was much more effective than the latter. As the effective reaction increases the radical concentration, cleavage of the β-ether linkage in the phenolic dimer is achieved at a much lower temperature (260°C) than that of the non-phenolic type (360°C). Radical chain reactions are initiated in the case of the trimer with a weak C α -O bond at lower temperature (320°C) than those of the non-phenolic (methylated) dimer, since homolysis of the C α -O bond produces the phenoxy type dimer and 3,4-dimethoxybenzyl radicals as initiators. However, some of the dimer phenoxyl radical was stabilized by H-abstraction (to form dimer) or by recombination with a 3,4-dimethoxybenzyl radical (to form C-benzylated products) so that the chain depolymerization via quinone methide intermediate was suppressed.

A chemistry-based parameter has been sought for determining the gradation of compression wood (CW), i.e., the severity, in tissues of Pinus radiata wood. Fluorescence microscopy was the reference for characterisation of the tissues containing CW. The collected material contained CW of varying severity, beginning with normal wood (NW containing no CW), continuing with material with some features of CW (CW of mild severity, MCW) and ending up with a material with pronounced features of CW (CW of high severity, SCW). Matching opposite wood (OW) was also included in the study. The chemical analyses included lignin determination, sugar analysis in the acid hydrolysate, thioacidolysis, 31 P-NMR spectroscopic analysis and steric exclusion chromatography of thioacidolysis products. As the severity of CW changed progressively from NW through MCW to SCW, all chemical parameters changed concurrently. In particular, levels of galactose and lignin increased, while those of glucose and mannose decreased. The amounts of p -hydroxyphenyl β-ethers released by chemical degradation and uncondensed p -hydroxyphenyl C-9 units also increased at elevated CW severity levels. The amounts of galactose and the p -hydroxyphenyl content of the lignin correlated linearly with lignin for CW samples. The chemical differences between CW and OW in the stem, branch and seedling were similar, i.e., they are independent of the morphological origin of the sample. Parameters based on the p -hydroxyphenyl unit content appear the most suitable chemical indicators of CW severity, as they are least sensitive to the sample's morphological origin and their response to CW severity is high.

Thermal modification is a well established method to improve the dimensional stability and the durability for outdoor use of wood. Unfortunately, these improvements are usually accompanied with a deterioration of mechanical performance (e.g., reduced strength or higher brittleness). In contrast, our investigations of the hardness properties in the longitudinal direction of beech wood revealed a significant improvement with thermal modification. Furthermore, we applied instrumented indentation tests on different hierarchical levels of wood structure (growth ring and cell wall level) to gain closer insights on the mechanisms of thermal treatment of wood on mechanical properties. This approach provides a variety of mechanical data (e.g., elastic parameters, hardness parameters, and viscoelastic properties) from one single experiment. Investigations on the influence of thermal treatment on the mechanical properties of beech revealed similar trends on the growth ring as well as the on the cell wall level of the wood structure.

In an attempt to examine the dynamic inter-relationship among wood density and fibre traits [tracheid length and microfibril angle (MFA)] in lodgepole pine ( Pinus contorta ), 60 trees were sampled in three age classes from four sites in central British Columbia. Breast height discs were taken and relative wood density was measured along two radii. Tracheid length was assessed on isolated 5-year increments from pith to bark at breast height for each tree. MFA was determined every 50 μm and the 5-mm composite intervals from pith to bark per disc at breast height were used in the analysis. Segmented regression was employed to identify the “juvenile to mature wood” transition point, which revealed transition ages of 31, 18 and 15 for wood density, fibre length and MFA, respectively. These traits were related to primary growth, expressed as area increment, ring width, percent earlywood and height increment during the juvenile wood phase. Comparisons of wood and fibre traits showed a higher congruence between the time of transitions for fibre length and MFA (Pearson correlation coefficient 0.52) than that between fibre length and wood density (0.07), and MFA and wood density (0.16). The cessation of early rapid radial increment growth terminated before wood and fibre transitions to mature wood occurred. Fibre length was significantly, but not strongly, related to ring width and percent earlywood (0.35 for both). The duration of juvenile fibre production was not significantly related to height growth.

A total of 30 Caesalpinia echinata (pernambuco) sticks were ranked based on their suitability for making high quality bows and were assigned to one of the three following categories: 0=very poor to poor, 1=good to very good, and 2=excellent. From the end of each stick a sample was cut for wood property and near infrared (NIR) spectroscopic analysis. Wood properties measured included air-dry density, extractives content, microfibril angle, stiffness and wood color. NIR spectra were evaluated by principal component analysis (PCA) and on the PC scores. Poor quality samples were discriminated from those of good to very good and excellent quality; however, samples from the two higher quality groups were mixed. Based on relationships observed between PC scores and wood properties, we suggest that, of the measured properties, density and stiffness were the most important in sample discrimination based on quality. Samples ranked in the excellent category had high average density (1119 kg m -3 ) and stiffness (25.2 GPa) and relatively low extractives content (21.2%) compared to samples in the very poor to poor category (density= 938 kg m -3 , stiffness=18.9 GPa and extractives content=24.9%).

Previously reported drying experiments on highly impermeable hardwoods have shown that bell-shaped within-board moisture content profiles develop as drying proceeds, with a change in concavity around the fibre saturation point. However, drying models based on Fick's second law of diffusion with an Arrhenius temperature dependency for the diffusion coefficient predict a parabolic form. The present work showed that the influence of moisture content on the diffusion coefficient must also be considered to improve these drying predictions. A drying model that includes both temperature and moisture content effects on the diffusion coefficient was developed. This model is able to accurately predict the drying rates and within-board moisture content profiles of New Zealand's indigenous red and hard beech timbers for various timber thicknesses over a range of temperatures, relative humidities and air velocities used in practice.

Attenuation coefficients and mass attenuation coefficients of wood were determined theoretically and experimentally for thermal and cold neutrons. Experiments were carried out at the neutron imaging facilities at the Paul Scherrer Institute, Villigen (CH). For the calculation of theoretical attenuation coefficients, only the three main elemental components (carbon, oxygen and hydrogen) were taken into consideration. While hydrogen accounts only for 6% (by wt) of wood, over 90% of the attenuation can be attributed to this element. Nitrogen and other trace elements were estimated to have a negligible impact on the theoretical attenuation coefficient. For the experimental determination of the attenuation coefficients, samples from different European and tropical wood species were tested in order to examine the influence of density and extractives content. Experimental results show a very strong linear correlation between attenuation coefficient and wood density irrespective of the tested species and extractives content that play only a minor role. As neutrons are very susceptible to scattering, it is necessary to apply a scattering correction if a quantitative evaluation is intended.

Formation and lignification of xylem cells in mature beech ( Fagus sylvatica L.) trees growing in a forest site in Slovenia (46° N, 14°40′ E, 400 m a.s.l.) were studied on the cellular and subcellular level. Samples containing the cambial zone and developing xylem were taken from six beech trees every week throughout the 2006 vegetation period. Cell wall thickening and lignification in individual cell wall layers and cell types were determined by light microscopy, cellular UV-microspectrophotometry and transmission electron microscopy, respectively. Cell division started between the 18th and the 24th of April 2006. Lignification began in the newly formed xylem tissue on the 2nd of May. After 1 month, the developing earlywood portion contained fully differentiated vessels with completed wall deposition and lignification, and differentiated fibres and axial parenchyma became visible after 2 months. At the end of cambial cell division on the 9th August, the differentiation of the most recently formed fibres in the terminal zone of the growth ring continued for approximately 4 weeks. This indicates that the process of lignification in earlywood is slower than in latewood. The high temporal resolution of the investigated processes and the combination of the above-mentioned microscopic techniques provides a detailed insight into the process of cell wall thickening and lignification of woody tissue in beech.

Spalting is the coloration of wood caused by fungal colonization. Woodturners, craftspeople, and artists appreciate spalted wood for its aesthetic appeal and uniqueness. Laboratory-induced spalting aims at a repeatable procedure in which wood is inoculated with selected fungi to obtain natural color with high aesthetic appeal, low weight loss and good machinability. Vermiculite (a natural clay with a high capacity for water holding and cation exchange) has been the primary incubation substrate for spalting research despite soil being the standard substrate for soil block decay testing. In this research, we explored the differences between these two substrates and their effects on the growth of spalting fungi on sugar maple ( Acer saccharum ) wood. Five fungi, Trametes versicolor , Xylaria polymorpha , Arthrographis cuboidea , Ceratocystis pilifera , and Ceratocystis virescens , were tested for their weight loss and spalting abilities on 14-mm sugar maple cubes incubated in both soil and vermiculite. Weight losses from all fungi were either unaffected or reduced by incubation in vermiculite compared to soil. In vermiculite, X. polymorpha produced more zone lines and A. cuboidea produced more pigment than blocks incubated in soil. Growth in vermiculite decreased weight loss of blocks inoculated with T. versicolor and X. polymorpha , while bleaching was unaffected regardless of substrate. External blue stain was higher on blocks inoculated with either Ceratocystis species and incubated in soil. These results indicate that vermiculite is a better substrate for spalting regardless of fungus due to the higher external pigmentation, lower weight loss, and better color contrast on the sugar maple blocks incubated in this substrate.

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