Volume 67, Issue 2

4- O -methylglucuronoxylans were isolated from the wood and pulp of different Eucalyptus species ( E. dunni, E. grandis, E. nitens, E. urograndis and E. urophylla) and characterized by 1 H NMR spectroscopy and size-exclusion chromatography (SEC). The content of 4- O -methylglucuronic acid (MeGlcA) varied between the eucalyptus species from 1.90 to 2.80 expressed as MeGlcA/10 xyloses, whereas in the pulp, the total uronic acid content was approximately 1.02, from which the half was hexenuronic acid (HexA). From the MeGlcA linked to the xylan chain 9–26% are substituted in position O -2 by hexose units. The M w of the xylans extracted from wood ranged between 26.1 and 28.4 kDa. The retention of 4- O -methylglucuronoxylans (51.3–58.7%) during kraft pulping was high, and the retention is related to the content of MeGlcA group, the content of MeGlcA group substituted at O -2, and the average molecular weight of the xylans. The parameters observed affect the overall pulp yield and pulp properties.

4- O -methylglucuronoxylans isolated from Eucalyptus grandis and Eucalyptus urophylla kraft black liquors (KBLs) were chemically characterized by Fourier transform infrared spectroscopy (FT-IR), size exclusion chromatography (SEC), and nuclear magnetic resonance (NMR) spectroscopy. Doses of alkali charge, expressed as active alkali (AA), were 16, 17, and 18% while the sulfidity was kept at 25%. Kappa numbers of 19.1, 17.5, and 16.1 for E. grandis and 20.4, 16.8, and 15.4 for E. urophylla were obtained. At higher alkali charges, the recovery of xylans from the KBLs was lower and the degree of substitution of xylans with uronic acids decreased. The average molecular weight ( M w ) of the recovered xylans was greater under conditions of mild pulping, i.e., in the case of pulps with higher kappa numbers. M w of xylans ranged from 16.1 to 19.1 kDa for E. grandis and from 15.4 to 20.4 kDa for E. urophylla . The xylans from KBL may be useful as pulp modifying agents or as a raw material for advanced applications.

Lignin, as the second most abundant biopolymer on earth, is one of the targets for plant biorefinery studies. Its complex chemical behavior is frequently studied by dimeric, trimeric, etc. model compounds, preferably with a β- O -4-type structure. In the present study, a convenient synthesis of a β- O -4-type trimeric model compound possessing a free syringylic hydroxyl has been investigated. Two key modifications were in focus: (1) Protection of the aliphatic hydroxyl groups of the starting phenolic dimer prior to the S N 2 displacement reaction before introducing the syringylic moiety with 2,2-dimethoxypropane. (2) The hydroxymethylation step to introduce the full side chain moiety. When this reaction was performed in dioxane/water in the presence of a catalytic amount of KOH instead of K 2 CO 3 , the formation of a side product via dehydration was markedly reduced. In addition, a convenient method for introducing an α,β-epoxide structure in acetophenone is recommended.

To broaden the knowledge about the chemical changes at the cell wall level of differently modified tropical hardwoods, heat-treated and N-methylol melamine (NMM)-treated samples of koto ( Pterygota macrocarpa ) and limba ( Terminalia superba ) were prepared. UV microspectrophotometry (UMSP) was applied at 278 and 240 nm as specific wavelengths to analyze chemical alterations of the samples caused by heat and NMM treatment, respectively. The absorbance of koto exceeded that of limba before and after treatment, potentially due to the higher extractive content of the former. Regardless of the wood species, the absorbance of the samples increased with increasing intensity of the NMM treatment. Additionally, the absorbance of lignin within the spectrum of 230–350 nm was altered due to the NMM treatment. The functionality of applying specific wavelengths for the analysis of different modification methods of wood was proven. However, the comparison with literature did not show differences in the absorbance, which could be assigned to the characteristics of tropical hardwoods.

Enzymatic bleaching appears to be a promising approach for clean bleaching processes and the reduction of bleaching chemical consumption. In this work, the quality of the filtrates and the pulps has been characterized after enzymatic prebleaching stages of eucalyptus kraft pulp. Four different conditions with xylanase were investigated. Following each prebleaching stage, the properties of the pulp [kappa number, brightness, content of hexenuronic acid (HexA), xylan removal, and pulp yield lost], and of the resulting effluents (chemical oxygen demand (COD), biochemical oxygen demand (BOD), color, and conductivity) were determined. In addition, a complete bleaching sequence was performed to characterize the pulp quality at the end of the sequence. Finally, the pulp was refined in a PFI mill, and the mechanical and physical properties of the resulting paper were determined. The best pulp quality was achieved at pH 7, at which a lower kappa number, higher pulp brightness, and smaller amount of HexA were observed. Under this condition, however, a larger yield loss and a higher effluent COD load had to be accepted. After the complete bleaching sequence, the enzymatic treatments yielded pulps with higher brightness and viscosity as well as with a lower kappa number. The enzymatic treatments resulted in small changes in the mechanical and physical properties of the paper handsheets produced.

This work continues the introduction of the dynamic mechanical analysis (DMA) of wood in a novel stress mode, compressive-torsion. The glass/rubber transition in yellow-poplar ( Liriodendron tulipifera ) wood was measured under saturation in four organic solvents: N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), ethylene glycol, and glycerol. Systematic measurement of the linear viscoelastic response (LVR) revealed a complex relationship of LVR with grain orientation, temperature and solvent. This indicates that special care is required when analysis within the LVR is critical. Glass transition temperatures (Tgs) of swollen wood showed an inverse relationship with solvent induced volumetric swelling. DMF and NMP both caused volumetric swelling of ≥25%, and the corresponding Tgs were near 50°C. Ethylene glycol and glycerol caused volumetric swelling <25% and the corresponding Tgs were ≥100°C. Glycerol showed significantly higher solvolytic power than ethylene glycol. Glycerol plasticized wood underwent irreversible swelling when heated beyond the Tg, causing a reduction in the effective crosslink density and in the Tg. Consistent with the literature, the observed Tg grain dependency was highly varied. The weakest plasticizer, glycerol, produced a prominent Tg grain dependency, whereas grain dependency was variable in the stronger swelling agents. This study demonstrates the importance of researching lignocellulose rheology in a greater variety of organic liquids, to achieve new perspectives into the structure/property relationships of lignocellulose, and aspects of processing in organic media.

Ultra-lightweight foam core particleboards have been produced in a novel one-step process with resinated wood particles for the faces and expandable polystyrene (EPS) as core layer material. The mechanical and physical properties of panels were investigated in terms of the different foam core densities and press parameters (temperature, pressing and foaming time). The bending strength properties of the panels were not significantly changed with increasing foam core density from 80 to 120 kg m -3 . Panels produced at a press temperature of 130°C (1-EPS) have an improved core-face interface and also a denser surface layer, which positively influences the internal bond and thickness swelling. The panels produced at a press temperature of 160°C (2-EPS) have smaller and more foam cells and an improved fusion of foam beads and properties, which have a positive influence on the edge screw withdrawal resistance and water absorption.

Oriented strandboards were constructed from various combinations of mixed hardwood flakes. Fractal dimension of void size (FDVS) in the manufactured samples was studied by means of X-ray computer tomography images and a computer image processing technique. The FDVS value was high in the panel surface layers and decreased toward the panel center, and the FDVS decrement was linear to increased porosity. At the same overall porosity level, the FDVS varied as function of void distribution. FDVS could be a useful additional parameter for characterizing the internal void structure of strand-based wood composites.

The hygroscopic properties of thermally modified wood have been studied in terms of adsorption and desorption processes. Poplar ( Populus spp.) and European beech ( Fagus sylvatica L.) were in focus. The obtained isotherms were parameterized with the models of Hailwood-Horrobin, Guggenheim-Anderson-deBoer, generalized D’Arcy and Watt, and Yanniotis and Blahovec. The changes in equilibrium moisture content (EMC) were quantified, and the accessibility of water vapor to the sorption sites was determined. The monolayer and multilayer sorption was studied and the sorption isotherms were classified. All sorption isotherms were type II, and the type was not changed after the modification. The monolayer sorption was found to be responsible for the reduction in EMC after thermal modification. The observed increase in the hysteresis coefficient was explained by the reorganization of the wood ultrastructure.

Undebarked ponderosa pine chips were treated by hot water extraction to modify the chemical composition. In the treated pine (TP), the mass was reduced by approximately 20%, and the extract was composed mainly of degradation products of hemicelluloses. Wood flour produced from TP and unextracted chips (untreated pine, UP) was blended with high-density polyethylene (HDPE) and polypropylene (PP) and was extruded into wood plastic composites (WPCs). Formulations for WPCs consisted of 58% pine, 32% plastic, and 10% other additives. WPC based on HDPE+TP and PP+TP absorbed 46–45% less water than did WPC based on HDPE+UP and PP+UP, respectively. Thickness swelling was reduced by 45–59%, respectively, after 2520 h of immersion. The diffusion constant decreased by approximately 36%. Evaluation of mechanical properties in flexure and tension mode indicated improvements in TP-WPC properties, although the data were not statistically significant in all cases. Results showed that debarking of ponderosa pine is not required for WPC production.

The failure of adhesive bondlines has been studied at the microscopic level via tensile tests. Stable crack propagation could be generated by means of samples with improved geometry, which made in situ observations possible. The interaction of cracks with adhesive bondlines under various angles to the crack propagation was the focus of this study, as well as the respective loading situations for the adhesives urea formaldehyde (UF), polyurethane (PUR), and polyvinyl acetate (PVAc), which have distinctly different mechanical behaviors. It has been shown how adhesive properties influence the occurrence of certain failure mechanisms and determine their appearance and order of magnitude. With the observed failure mechanisms, it becomes possible to predict the propagation path of a crack through the specimen.

Dimensions of dated tree rings are an important tool of dendroclimatology. However, the relationships between climatic variables and cell diameter and cell wall thickness are not yet clearly elaborated. In the present article, year-to-year cell characteristics, ring width, and wood density of Picea crassifolia trees growing in northwestern China have been measured with high resolution by means of the instrument SilviScan-3. The response function analysis showed that climate explained 51% of the variation of cell radial diameter chronology, 48% of wood density, 40% of cell wall thickness, and 37% of ring width. Cell wall thickness and wood density responded significantly and positively to temperature, and the response to precipitation was negative, while the opposite was true for cell radial diameter and ring width. Cell wall thickness and wood density were pronounced (statistically significant) to temperature in September and precipitation in May and August. Cell radial diameter responded significantly to temperature in June and July, and precipitation, in August. For ring width, the temperature in July was important. Accordingly, cell characteristics are sensitive to climate, and the findings could be useful in the field of dendroclimatology.

Visual appeal of wood is as important as its structural integrity in outdoor applications. Discoloration and checking of wood favor the utilization of alternative materials for outdoor cladding and decking. Lignin depolymerization is one of the critical processes leading to weathering. In the present paper, the potential of different classes of surface protection agents has been assessed on loblolly pine ( Pinus taeda ) impregnated with water repellents, organic UV inhibitors, and an organic biocide. The treated samples were exposed to predetermined doses of solar radiation in Eastern Oregon, and the chemical changes occurring on the surfaces were evaluated by FTIR spectroscopy. After 1-year exposure, lignin loss was complete on all surfaces; however, some treatments provided longer term protection than others. Organic UV light inhibitors were most effective in this regard. A petroleum-based water repellent with a melting point of 54–58°C also provided protection against lignin degradation.

Local variability in the thermal conductivity of the cell wall of beech wood fibers was studied by means of scanning thermal microscopy (SThM). In the cross section, the thermal conductivity of the secondary cell wall was essentially higher than that of the compound middle lamella (CML). In sections parallel to the cell axis, the overall conductivity of the S1 layer was lower than that of the secondary cell wall, but the S2 layer and the CML showed similar conductivities. This is attributed to the orientation of the cellulose microfibrils playing a key role in the observed anisotropies concerning the thermal conductivity. The deviating thermal conductivities on different sections are attributed to the depth effect of the thermal scanning. SThM proves to be a technique with considerable potential for wood research.

The shrinkage behavior of European beech wood was successfully observed on a time series of images obtained by high resolution X-ray computed tomography (μXCT). The calculated measures for shrinkage and shrinkage anisotropy are consistent with published data. Evidence was provided for the ‘ray restraint’ theory of shrinkage anisotropy. This technique has a high potential for the study of dynamic processes in wood at the micro-scale, though the resolution of the images is lower and the measurement times are longer in comparison to synchroton radiation μXCT.

No abstract available.