New aspects in cationization of lignocellulose materials. VII. Modification of spruce wood meal with quarternary ammonium groups

Trimethylammonium-2-hydroxypropyl (TMAHP) derivatives of spruce wood meal (SWM) and holocellulose of this specia were prepared by the reaction of wood meal with 3-chlor-2-hydroxy-propyltrimethylammoniumchloride (CHMAC) in alkaline medium. The TMAHP samples were fractionated and yields and exchange capacity (Q) of individual fractions were compared with beech and aspen fractions obtained under the same conditions. As it is evident from ¹³C-NMR spectroscopy and GPC analysis the water soluble fraction from TMAHP–SWM consists only of lignin–saccharide degradation products. The NaOH extracts of TMAHP–SWM and TMAHP–holocellulose as well as the water-soluble fraction from TMAHP–holocellulose are polymeric materials. From TMAHP–SWM only 3.1% of alkali-soluble material could be extracted, while from TMAHP–holocellulose 15.7% of water-soluble and 7.9% of alkali-soluble materials were obtained.     

New aspects in cationization of lignocellulose materials. V. Modification of rotten aspen wood meal with quarternary ammonium groups

Holocelluloses prepared from clear and rotten aspen wood were gradually fractionated with 2.5% NH₄OH, 4.5% NaOH, and 17.5% NaOH, respectively. A higher yield of polysaccharides (24.4%) was obtained from the rotten sample in comparison with clear wood (20.9%). Trimethyl ammonium-2-hydroxypropyl (TMAHP) derivatives of rotten aspen were prepared by the reaction of wood with 3-chlor-2-hydroxypropyltrimethylammoniumchloride (CHMAC) in alkaline medium. The quantity of TMAHP—hemicelluloses (yield 14.1%) is only slightly lower in comparison with TMAHP—hemicelluloses (yield 15.8%) obtained by modification and subsequent extraction from clear aspen wood meal. The hemicelluloses isolated from the rotten aspen wood meal are contaminated with low molecular cellulose fraction, the degradation products of cellulose attacked by fungi. The lignin component of rotten wood is less intensively attacked by fungi than the polysaccharidic one.     

New aspects in cationization of lignocellulose materials. VI. Modification of steam-exploded aspen wood chips with quarternary ammonium groups

Holocellulose prepared from steam-exploded aspen wood was gradually fractionated with 2.5% NH₄OH, 4.5% NaOH, and 17.5% NaOH, respectively. Some residual polysaccharides were extracted from the material in this way, but their yield was only about 5%. Trimethylammonium-2-hydroxypropyl (TMAHP)-derivatives, exploded aspen wood (EXAW), were prepared by the reaction with 3-chlor-2-hydroxypropyl trimethylammoniumchloride (CHMAC) in alkaline medium. The quantity of water and alkali extracted TMAHP–polysaccharides (yield 2.6%) was lower than the yields from modified healthy beech and aspen, as well as rotten aspen. On the other hand, we can obtain more modified cellulose-rich and lignin-rich material than from previously mentioned species. The steam-explosion process is suitable for increasing the accessibility of cellulose component in lignocellulose material for chemical modification.     

Characteristics of Dioxane Lignins Isolated at Different Ages of Nalita Wood (Trema orientalis)

Abstract

Nalita (Trema orientalis) is one of the fastest growing trees in the tropical countries. The structural characteristics of lignin isolated at different ages of Nalita wood (Trema orientalis) by acidolytic dioxane method were examined by UV, FTIR, ¹H‐NMR and ¹³C‐NMR spectroscopy, alkaline nitrobenzene oxidation, molecular weight determination, elemental and methoxyl analysis. The data were compared with aspen lignin. The structural analysis revealed that Nalita wood lignin is syringyl‐guaiacyl type. The methoxyl content in Nalita wood lignin was lower than aspen lignin. The C₉ formulas for 30‐months‐old Nalita was C₉H_9.31O_3.13(OCH₃)_1.27, whereas that of aspen was C₉H_8.94O_3.15(OCH₃)_1.47. The weight average molecular weight of Nalita wood lignin was decreased from 36,500 to 25,500 with increasing tree age from 12 to 30 months, whereas weight average molecular weight of aspen was 20,000. Both alcoholic and phenolic hydroxyl group in Nalita wood lignin is lower than aspen lignin.     

Wood Fiber Quality and Kraft Pulping Efficiencies of Trembling Aspen (Populus tremuloides Michx) Clones

Abstract

The natural variation in wood and pulp fiber quality of 15 aspen (Populus tremuloides Michx) clones, represented by 47 trees, was assessed from 4 different sites in British Columbia, Canada. Kraft pulping trials revealed substantial variation in the pulping efficiencies, illustrated by differences of 6% in total pulp yield, ～30% differences in H‐factor required to attain a target kappa of 21, and differences of up to 2 ISO brightness units in bleachability of kappa 21 pulp. Clearly, enormous variation exists in the natural stands of aspen, and presents some exciting opportunities for selecting clonal aspen for targeted end‐product applications. A comprehensive characterization of wood chemical composition, wood density, and fiber properties indicated that pulp yield is directly related to syringyl lignin monomer composition, and not inherent wood density, regardless of geographic locations, whereas pulp bleachability and viscosity appear to be associated with the inherent cell wall thickness of the starting wood resources (fiber coarseness). These findings suggest that geographic location imparts influences on wood fiber coarseness traits, while substantial genetic variability exists on all sites.     

Identification and quantification of important steryl esters in aspen wood

Steryl esters make up a major portion of the total lipids in aspen wood, and contribute significantly to pitch deposit problems during pulping. Fungal treatment of aspen is an attractive method for removing these compounds because it is inexpensive and environmentally acceptable; however, the mechanism of steryl ester removal remains unclear. Identification of the steryl esters will lead to a better understanding of how they are removed by fungi. The steryl ester fraction from aspen wood was obtained by acetone extraction then further purified by silica gel column chromatography and argentation-silica gel column chromatography. This led to the isolation of three major fractions: fraction I, fraction II, and fraction III. The major steryl esters of fractions I and II were identified by gas chromatography, gas chromatography-mass spectroscopy, and proton nuclear magnetic resonance analysis of the intact fraction as well as sterol and fatty acid moieties obtained after base hydrolysis. Identification of the steryl esters was carried out by mass spectra comparisons with steryl ester standards synthesized in the laboratory and comparison with mass spectra libraries (Wiley and NIST) by mass fragmentography. Fraction I contained primarily the palmitate, stearate, and eicosanoate esters of α- and β-amyrin. Fraction II consisted mainly of the palmitate, stearate, and eicosanoate esters of tirucalla-7,24-dien-3β-ol and lupeol.     

Simulated autohydrolysis of aspen milled wood lignin in the presence of aromatic additives: Structural modifications

In a previous article the authors have described changes in molecular weight which occur when aspen milled wood lignin is subjecte to autocatalyzed hydrolysis (autohydrolysis) in the presence of three aromatic additives: 2-naphthol, resorcinol, and p-hydroxybenzoic acid. In the present work, the reactions of these additives have been studied from the viewpoint of their effect on the structure of the lignin. The use of milled wood lignin instead of aspen wood served to distinguish those reactions between the additives and the lignin, without involving the other wood components. The reaction products have been charactrized by elemental analysis and UV and IR spectroscopy. It was concluded that keto groups, generated on the lignin side-chain during autohydrolysis, condense with the additives, which become incorporated into the lignin. This occurs most probably through an aromatic eletrophilic substitution reaction. While 2-naphthol condensed primarily with the β-keto carbonyl groups, resorcinol attacked also the α-keto carbonyl groups. When p-hydroxybenzoic acid was the additive, its incorporation was accompanied by an increase in lignin carboxylic acid groups.     

Olfactory recognition of nonhosts aspen and birch by conifer bark beetlesTomicus piniperda andHylurgops palliatus

The field response ofTomicus piniperda (L.) andHylurgops palliatus (Gyll.) (Coleoptera: Scolytidae) to the attractant ethanol in combination with volatile wood constituents released from the nonhost tree speciesPopulus tremula L. (Salicaceae) andBetula pendula Roth (Betulaceae) was studied using flight barrier traps. The attraction of both species decreased when aspen or birch wood was added to the ethanol bait. The same was true forRhizophagus depressus (F.) (Coleoptera: Rhizophagidae), a predatory species associated with conifer bark beetles.Glischrochilus quadripunctatus (L-),Epuraea bickhardti St.-Claire Deville,E. unicolor (Oliv.) (Coleoptera: Nitidulidae), andRhizophagus parvutus (Payk.) (Coleoptera: Rhizophagidae) were caught in higher numbers in traps baited with both ethanol and wood of aspen or birch than in traps baited with ethanol alone. In a separate experiment, landings ofT. piniperda andH. palliatus on nonhosts (black plastic tubes) were demonstrated with sticky traps.     

Effect of thermal treatment of wood lumbers on their adhesive bond strength and durability

Wood used in outdoor applications needs to undergo either chemical or thermal treatment to improve its decay resistance. Thermal treatment permits to avoid the use of toxic chemicals, increases the dimensional stability and gives a dark color to the wood. However, this process deteriorates the mechanical properties of wood, i.e., the wood becomes more fragile and rigid. The chemical transformation of wood that takes place during the heat treatment changes the interaction between the wood surface and the adhesive. In this work, the interfacial bonding strength (the resistance to the shear stress by compression in parallel direction to the glued interface) and cyclic delamination (resistance to delamination during accelerated exposure) for different wood species and adhesives were tested in accordance with the ASTM D2559 standard. Four wood species: scott pine (Pinus sylvestris), aspen (Populus tremuloides), yellow poplar (Liriodendron tulipifera) and jack pine (Pinus banksiana) both treated and non-treated, and two structural adhesives, phenol resorcinol formaldehyde (PRF) and polyurethane (PUR), were used in the testing. Among the studied species, jack pine is found to be the easiest to bond, while aspen is found to be the most difficult. With the wood species and adhesives evaluated in this study, non-treated wood is found to provide a better bonding strength than the treated wood.     

Wood plastic composites by melt impregnation: Polymer retention and hardness

Wood plastic composites were prepared through impregnation of solid wood with polyethylene. The effects of impregnation parameters on polymer retention and hardness were investigated. A screening strategy of 16‐run resolution IV design for seven factors at two levels was adopted. The seven factors were: ratio of maleated polyethylene in formulations, ratio of polyethylenes with different molecular weights, four process factors (vacuum, pressure, time, and temperature), and wood species (red maple and aspen). Polymer retention (PR) and Brinell hardness (H_B) were investigated and discussed on the basis of the impregnation parameters. The present work showed that process parameters (pressure and temperature), polymer impregnants (different molecular weight polyethylenes), and wood species contributed significantly to PR and H_B. Increasing pressure and temperature resulted in a higher PR and H_B, whereas increasing the molecular weight of polyethylene and switching wood species from aspen to red maple gave a lower PR and H_B. This study was aimed at understanding how impregnation parameters affect the final properties of wood plastic composites and developing an optimal fabrication process for wood plastic composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1672–1680, 2006     

The Characteristics and Reactivity of Acid-Labile Aryl Ether Units in Wood Lignin

Wood lignin contains significant amounts of acid-labile aryl ether units, which play a significant role in lignin modification or delignification processes. We have evaluated the rate and reaction kinetics on the acid-catalyzed cleavages of aryl ether structures for wood lignin in situ based on the formation of phenolic hydroxyl groups. The content of acid-labile aryl ether units was quite uniform for a variety of softwood wood lignins (～4% per C₉ unit) and it varied appreciably among hardwood species, ranging from 4% for aspen to 9% for beech wood lignin. These variations, however, appear to be related to the content of syringyl units in wood lignin. The reactivity of these reactive aryl ether structures was noticeably higher for the spruce than for the aspen wood lignin. This difference in reactivity, based on the behavior of lignin model compound reactions, can be attributed to the influence of syringyl moieties in aspen wood lignin. It appears that most of the acid-labile aryl ether units in hardwood were associated with the syringy moiety being present as a benzyl unit, which is much less reactive than the corresponding guaiacyl moiety.     

Perception of Aspen and Sun/Shade Sugar Maple Leaf Soluble Extracts by Larvae of Malacosoma disstria

We investigated the behavioral feeding preference and the chemoreception of leaf polar extracts from trembling aspen, Populus tremuloides, and from sun and shade sugar maple, Acer saccharum, by larvae of the polyphagous forest tent caterpillar, Malacosoma disstria, a defoliator of deciduous forests in the Northern Hemisphere. Three polar extracts were obtained from each tree species: a total extract, a water fraction, and a methanol fraction. M. disstria larvae were allowed ad libitum access to an artificial diet from eclosion to the fifth instar. Two-choice cafeteria tests were performed comparing the mean (±SE) surface area eaten of the total extracts, and the following order of preference was obtained: aspen > sun maple < shade maple. Tests with the other fractions showed that M. disstria larvae preferred the total aspen extract to its water fraction, and the latter to its methanol fraction. The response to sun maple was similar to aspen. However, for the shade maple experiment, there was no difference between the total extract and its water fraction. Electrophysiological recordings for aspen showed that the sugar-sensitive cell elicited more spikes to the water fraction, followed by the total extract, and finally the methanol fraction. Spike activity to stimulations of sun and shade maple extracts revealed a similar trend, where methanol fraction > water fraction > total extract. Our findings are discussed in light of previously known information about this insect's performance on these host plants.     

Fractionation and Characterization of Water-soluble Hemicelluloses and Lignin from Steam-exploded Birchwood

Abstract

Two crude hemicellulosic fractions, obtained by extraction of steam-exploded birchwood with hot water, were treated with 8% NaOH at 20[ddot]C for 1 and 4h, and subsequently sub-fractionated into four lignin and four hemicellulosic fractions. Acid hydrolysis, alkaline nitrobenzene oxidation, ultraviolet (UV), gel-permeation chromatography (GPC), Fourier transform infrared (FT-IR), and carbon-13 nuclear magnetic resonance (NMR) spectroscopies were used to investigate the chemical compositions and structural features of the fractionated hemicelluloses and lignins. The sugar analyses indicated that xylose was the predominant sugar component in the four hemicellulosic fractions. Due to the autohydrolysis at elevated temperature and lower in acidity during the steam treatment processes, all the four hemicellulosic fractions showed a low degree of polymerization (DP, 38–41), with molecular-average weights between 5620 and 6160. Assignments of all the signals in the NMR spectrum led to the conclusion that the four lignin fractions, which differ from the organosolv lignins obtained from steam-exploded aspen wood meals, are still mainly composed of β—O—4 ether bonds, together with small amounts of less common β—β and β—1 carbon-carbon linkages between the lignin structural units. The weight-average molecular weights were found to be 2250–2620 with the polydispersity of 1.5.     

WOOD DRYING MODELLING BASED ON THE WATER POTENTIAL CONCEPT: HYSTERESIS EFFECTS

ABSTRACT

The boundary absorption curve of the moisture content - water potential relationship of aspen sapwood was determined at 20°C. In order to quantify the impact of the hysteresis of the relationship on the results obtained with a wood drying model based on water potential, the results obtained were merged to the boundary desorption curve and hypothetical scanning curves were used to model the forced convection drying of aspen sapwood.

A strong hysteresis was found between the boundary desorption and absorption curves, the moisture content being higher in desorption than in absorption at a given water potential. The effect of the hysteresis on the simulation results was found to be significant. The results show that differences in the predicted drying time as high as 25% can occur depending on the moisture content - water potential curve used. This demonstrates that the sorption history of wood should be considered in the development of wood drying models.     

3D Numerical Simulation of Thawing Frozen Wood Using Microwave Energy: Frequency Effect on the Applicability of the Beer–Lambert Law

In this article, the frequency effect on the applicability of Beer–Lambert's law for thawing frozen wood using the microwave energy was analyzed. To this end, we use Maxwell's equations to determine the absorbed power and characterize the critical slab thickness L _crit of three Canadian eastern wood species: trembling aspen (Populus tremuloides Michx), yellow birch (Betula alleghaniensis), and sugar maple (Acer saccharum). The critical thickness L _crit above which the Beer–Lambert law is valid is estimated as a hyperbolic function in the frequency domain: L _crit = m/f ⁿ (f is the frequency of microwave radiation; m and n are adjustment constants). The nonlinear heat conduction problem involving phase changes such as wood freezing is solved by a three-dimensional volumetric specific enthalpy-based finite element method. The dielectric and thermophysical properties are functions of temperature and moisture content. The specific volumetric enthalpy approach is validated by experimental testing. For instance, we studied the frequency effect on the thawing of frozen trembling aspen wood.     

Production of biocatalysts on the basis of recombinant heterologous xylanase producer strains in the Penicillium verruculosum fungus: Their application in the hydrolysis of timber and wood processing industry wastes

The aim of this work was to create biocatalysts with an increased heterologous expression of endo-β-1,4-xylanase of P. canescens using recombinant P. verruculosum strains, to analyze the properties of new enzyme preparations, and to study the saccharifying activity of these preparations in the hydrolysis of plant raw materials, such as hogged aspen and detarred pine wood wastes of the timber and wood processing industries. The xylanase activity of the existing enzymatic preparations is insufficiently high to hydrolyze a xylan-rich biomass. The creation of increasingly xylanolytically active P. verruculosum-based recombinant strains containing homologous or heterologous genes of xylanase and mannanase is therefore a problem of great interest. Using the methods of genetic engineering, we obtained enzymatic preparations that are biocatalysts for the hydrolysis of plant raw material wastes of the sawmilling and wood processing industries and, according to the data of chromatographic fractionation, have compositions of 45–60% cellulase and 20–50% xylanase (which is optimal for the saccharifying of bagasse, along with aspen and pine wood). The originality of our technique lies in the creation of biocatalysts with predetermined properties, thus reducing appreciably the cost of enzyme preparation by eliminating the need to mix components of the carbohydrase complex for the hydrolysis of plant raw materials, e.g., aspen and pine wood.     

The effect of moisture on the dynamical mechanical properties of bacterial cellulose/glucuronoxylan nanocomposites

The plant cell wall possesses unique material properties due to its hierarchical organisation. In order to biomimic a native structure like a plant cell wall, a model system consisting of microfibrillar cellulose, produced by the gram-negative bacteria Acetobacter xylinum, and a glucuronoxylan matrix derived from aspen holocellulose was constructed. The glucuronoxylan was extracted from delignified aspen (Populus tremula) wood chips using DMSO to preserve its native chemical composition. Dynamic mechanical analysis (DMA) measurements performed with moisture scans showed a moisture-induced softening of delignified aspen wood fibres due to the plasticization of glucuronoxylan. A similar result was observed for the model system. However, the softening behaviour of the delignified aspen fibre and the model system was not identical, most probably due to differences in spatial organisation of the components. Dynamic FTIR-studies indicated that interactions between the cellulose and the glucuronoxylan exist in the aspen holocellulose while the components in the nanocomposite appear to be more isolated.     

原位复合纳米SiO2改性脲醛木塑复合材料制备

以原位复合纳米SiO2改性脲醛树脂为填充体，人工速生杨木为基体，通过真空加压浸渍法制得木塑复合材料。各种木塑复合材料的主要性能——增重率、抗吸水性、顺纹和恒纹压缩强度分别提高49％、38％、68％和83％。扫描电镜照片显示纳米SiO2改性脲醛完整地填充在杨木基体导管以及孔状结构中。傅立叶红外光谱（FTIR）分析纳米SiO2改性脲醛与杨木基体的固化反应表明，木塑复合材料中木质素C=O吸收峰1750cm^-1完全消失，木质素COO-吸收峰1645cm^-1增强而且发生偏移，充分证明纳米SiO2改性脲醛树脂填充体与木材基体之间发生了化学键合作用而使木塑复合材料各项力学性能得以增强。     

Quantitative Phosphorus-31 NMR Analysis of Six Soluble Lignins

By using a set of lignin samples, which have been subjected to thorough analyses by the international wood chemistry community, the recently developed quantitative method of ³¹P NMR spectroscopy was comprehensively examined. The values of total phenolic hydroxyl groups and those of total hydroxyl groups were found to favourably compare with those obtained by other laboratories, applying independent methods of analysis. Furthermore, the application of quantitative ³¹P NMR spectroscopy offered additional detailed structural information for the examined lignins which was in accord with literature accounts for similar wood species and lignin preparations. More specifically, the steam explosion lignins from aspen and yellow poplar woods and that produced by ball milling/enzyme hydrolysis of cottonwood were found to contain relatively high amounts of β-O-4 structures. In contrast, the kraft, organosolv, and the acid hydrolysis processes were found to induce significant chain scission on the resulting lignins. Ball milled cottonwood lignin contained the highest frequency of β-O-4 bonds and the lowest amount of free phenolic hydroxyls. The erythro form of β-O-4 structures were invariably predominant in the lignins from aspen, yellow poplar and cottonwood, in accord with the conclusions of previous reports on hardwood lignins. Thus, the application of quantitative ³¹P NMR spectroscopy offered the detailed chemical composition of the examined lignins.