Volume 71, Issue 2

The process named “sulfite pretreatment to overcome recalcitrance of lignocellulose” (SPORL) is designed for the digestion of softwoods within the framework of the biorefinery concept. “Hot water extraction (HWE)” is an environmentally benign and low-cost pretreatment, which only needs water as a reagent. In the present study, HWE has been investigated as a pre-process prior to SPORL with Douglas fir as feedstock. The SPORL parameters, namely, temperature and treatment time, were in the range 135–155°C and 40–120 min, respectively, while the sulfuric acid concentration was 0.2–0.4% (v/v). The aim was to maximize the enzymatic digestibility of the treated wood. The severity of SPORL at different pretreatment conditions was characterized by the combined severity factor (CSF). The HWE pre-process led to a two-fold increase in specific surface area of the substrate. More hemicellulosic-derived simple sugars were dissolved in the spent liquor (SL) as the CSF increased from 1.23 to 1.82. A maximum enzymatic digestibility of 64.3% was attained when SPORL was conducted at 155°C for 120 min with a sulfuric acid concentration of 0.4% (v/v). A considerably high enzymatic digestibility (~55–60%) is still achievable by incorporating HWE prior to SPORL, even if the SPORL severity is reduced, namely to a lower temperature (145°C), a shorter time (80 min), and a lower acid volume (0.3% v/v).

Pretreatment is one of the key steps for the utilization of lignocellulosic biomasses via biorefinery. Green liquor (GL) pretreatment has been considered as an effective approach to improve the subsequent enzymatic saccharification. For the better understanding of the structural changes of lignin in GL pretreatment, milled wood lignin (MWL) samples isolated from untreated and GL-pretreated poplar by the Björkman method were characterized by means of gel permeation chromatography (GPC), alkaline nitrobenzene oxidation (NBO), Fourier transform-infrared (FT-IR) spectroscopy, and quantitative 13 C and 2D heteronuclear single quantum coherence nuclear magnetic resonance (HSQC NMR). The results indicate that the average molecular weight of MWLs decreased after GL pretreatment. Surprisingly, more guaiacyl-propane units are extracted under mild alkaline conditions than syringyl-propane units, which results in a higher condensation degree and higher S/G ratios of MWLs isolated from GL-pretreated poplars. The amount of β–O–4 structures decreased, while the β–β and β-5 structures increased after GL pretreatment. The structure of esterified p -hydroxybenzoic acid was detected in poplar MWL sample and it degraded obviously after GL pretreatment.

Oxidation reactions of a non-phenolic β- O -4-type lignin model compound [4-ethoxy-3-methoxyphenylglycerol-β-guaiacyl ether ( 1 )] were conducted in an electrolytic mediator system (EMS) using 2,2,6,6-tetramethyl-1-piperidinyloxyl radical (TEMPO) or 4-acetoamido-TEMPO (AcNH-TEMPO) as mediators. The results revealed that the electrolytes strongly influenced the chemoselectivity between Cα-carbonylation and Cγ-carboxylation of compound 1 . The Cα-carbonylation proceeded preferentially in the EMS oxidation conducted in the LiClO 4 /CH 3 CN-H 2 O system, although the yield of the resulting Cα-carbonyl compound 2 was low (1.9%–11.1%). In contrast, Cγ-carbonylation was preferred, if the EMS oxidation reactions were conducted in the dioxane-carbonate buffer (pH 10.0), dioxane-borate buffer (pH 10.0), and dioxane-phosphate buffer (pH 7.0). Especially, the Cγ-carboxyl compound 3 was obtained in a high yield (72.0%–93.2%), when the dioxane-phosphate buffer served as the electrolyte. The catalytic efficiency of AcNH-TEMPO was higher than that of TEMPO for the EMS oxidation reactions. The conclusion is that AcNH-TEMPO-EMS oxidation reaction in dioxane-phosphate buffer could be used for the chemoselective Cγ-carboxylation of lignins.

X-ray computed tomography (XCT) was utilized to visualize and quantify the 2D and 3D microstructure of acetylated southern yellow pine (pine) and maple, as well as furfurylated pine samples. The total porosity and the porosity of different cell types, as well as cell wall thickness and maximum opening of tracheid lumens were evaluated. The wetting properties (swelling and capillary uptake) were related to these microstructural characteristics. The data show significant changes in the wood structure for furfurylated pine sapwood samples, including a change in tracheid shape and filling of tracheids by furan polymer. In contrast, no such changes were noted for the acetylated pine samples at the high resolution of 0.8 μm. The XCT images obtained for the furfurylated maple samples demonstrated that all ray cells and some vessel elements were filled with furan polymer while the fibers largely remained unchanged. Furfurylation significantly decreased the total porosity of both the maple and pine samples. Furthermore, this was observed in both earlywood (EW) and latewood (LW) regions in the pine samples. In contrast, the total porosity of pine samples was hardly affected by acetylation. These findings are in line with wetting results demonstrating that furfurylation reduces both swelling and capillary uptake in contrast to acetylation which reduces mostly swelling. Furfurylation significantly increased the cell wall thickness of both the maple and pine samples, especially at higher levels of furfurylation.

The effects of thermal treatment of bamboo at 130, 150, 170, and 190°C for 2, 4, and 6 h were investigated in terms of changes in chemical composition, cellulose crystallinity, and mechanical behavior of the cell-wall level by means of wet chemical analysis, X-ray diffraction (XRD), and nanoindentation (NI). Particularly, the reduced elastic modulus ( E r ), hardness ( H ), and creep behavior were in focus. Both the temperature and treatment time showed significant effects. Expectedly, the hemicelluloses were degraded and the relative lignin content was elevated, while the crystallinity of the cellulose moiety was increased upon thermal treatment. The E r and H data of the cell wall were increased after 6 h treatment at 190°C, from 18.4 to 22.0 GPa and from 0.45 to 0.65 GPa, respectively. The thermal treatment led to a decrease of the creep ratio ( C IT ) under the same conditions by ca. 28%. The indentation strain state ( ε i ) also decreased significantly after thermal treatment during the load-holding stage.

The resistance drilling technique has been in focus for assessing the specific gravity (SG) of young Eucalyptus trees from plantations for pulpwood production. Namely, the data of 50 34-month-old and 50 62-month-old trees from Eucalyptus grandis × Eucalyptus urophylla clonal plantations was evaluated, while the relative resistance profiles were collected with the amplitude in a scale from 0 to 100% of each tree at the breast height. For laboratory determination of SG and moisture content (MC), 3-cm-thick disks were taken at breast height. The average resistance amplitude of a full drill penetration or a half-diameter penetration showed weak correlations with SG for both 34-month-old and 62-month-old trees. However, when the two age classes were combined, the strength of the relationship was improved significantly, with a correlation coefficient ranging from 0.71 to 0.77 with respect to SG determined from strip samples and from 0.59 to 0.72 with respect to SG determined from wedge samples. The drill penetration depth had a significant effect on the relationship between average amplitude and SG. A clear trend of weakening correlation was observed with increasing drill penetration. As a result, the average resistance amplitude of a half-diameter drilling (from bark-to-pith) is more advantageous for assessing the SG of young Eucalyptus trees than a whole-diameter drilling.

A novel device was conceived and built to measure the apparent gaseous permeability of porous media over a large range of permeability values (10 −10 –10 −18 m 2 ) and mean pressures (from 1 bar down to ca. 40 mbar). An extensive series of experimental data are presented and analysed for various porous media: (1) Norway spruce ( Picea abies ) and European beech ( Fagus silvatica ) in the three anatomical directions, and, for comparison, (2) three simpler porous media, i.e. an autoclaved aerated concrete (AAC, light concrete) and two wood-based panels. For all porous media, the intrinsic permeability, the gas slippage factor, and the effective pore size were determined from the variations of the apparent permeability as a function of mean pressure. These results are in good agreement with those of previous studies for spruce and bring new insights for beech and wood-based materials, in general. For all products, the effective pore sizes identified with the new instrument are closely linked to the medium morphology. In particular, it was found that in spite of the huge anisotropic ratios between wood’s longitudinal and tangential directions, the identified pore size is similar and corresponds to anatomical features: openings in margo for spruce and scalariform perforation plates for beech. Besides, the pore size identified for beech in the radial direction suggests that radial permeability is most probably controlled by the openings in ray cells (either pits or intercellular voids).

Wood flour (WF) was modified with sodium-montmorillonite (Na-MMT) and didecyl dimethyl ammonium chloride (DDAC) to form an organo-montmorillonite (OMMT) inside WF at different OMMT concentrations from 0.25 to 1%. The modified WF was blended with polypropylene (PP) to produce PP/WF composites at a weight ratio of 1:1 by compression molding. The composites were immersed in water and their stress relaxation behaviors were investigated at 26, 40, and 60°C, respectively. Results: (1) All composites show stress relaxation with increasing compression testing time, indicating that they have pronounced rheological properties. (2) The stress relaxation becomes more severe with increasing temperature and water immersion time. (3) OMMT improves the stiffness of the composites with slower stress relaxation, and the PP/WF 0.5% OMMT seems to perform best among all.

The hygroscopic properties of Pinus pinea L. wood at 35 and 50°C were investigated by the dynamic vapour sorption (DVS) technique. The sorption kinetic behaviour was studied through the parallel exponential kinetics (PEK) model, which is subdivided into a fast and a slow process. The parameters obtained by PEK were interpreted based on the Kelvin-Voigt (KV) model to determine elasticity and viscosity values of the wood cell wall. The PEK data perfectly fit the experimental data. The temperature-dependent transition between the fast and slow processes is fluent. The slow process contributes more to the total hysteresis of sorption. The kinetic properties varied in relation to the type of cycle and the temperature. The moduli of elasticity and viscosity were higher in the slow process than in the fast one. In both processes, the moduli showed a decreasing tendency in relation to relative humidity.

Auxins as phytohormons, responsible for coordination of growing processes, also contribute to the formation of tension wood (TW) in trees, but the mechanism of this process is still unclear. In this study, it has been tried to induce TW formation in erect hybrid poplar trees (in opposite to inclined or bended trees) by treatment with exogenous indole-3-acetic acid (IAA, as one of the auxins) or N-1-naphthylphthalamic acid (NPA) as an auxin transport inhibitor. The treatment with IAA resulted in TW formation and, as expected, NPA treatment did not. The gelatinous fiber formation and higher cellulose content in the cell wall were unambiguous indicators for TW formation. Real-time polymerase chain reaction (PCR) analysis revealed that genes of PIN1 , ABCB1, and AUX2 involved in polar auxin transport were highly expressed in trees treated with exogenous IAA. Moreover, expressions of cellulose biosynthesis related genes of UGP1 , UGP2 and CesA13 were strongly up-regulated. These observations indicate that the accelerated intercellular polar auxin transport caused by exogenous IAA is accounted for TW formation, i.e. the signal transduction of auxin is affected, which then facilitates cellulose biosynthesis. In contrast, the transcript abundances of PIN1 and all selected cellulose synthases ( CesAs ) were decreased after NPA treatment via inhibiting the cellular auxin efflux with negative effects on plant’s primary growth. These results are interpreted that TW formation is closely associated with the acceleration of intercellular polar auxin transport.