Wood Cell Walls Research Articles

ОПРЕДЕЛЕНИЕ ПЛОТНОСТИ КЛЕТОЧНЫХ СТЕНОК ДРЕВЕСИНЫ И ДРУГИХ ПОРИСТЫХ МАТЕРИАЛОВ МЕТОДОМ ГАЗОВОЙ ПИКНОМЕТРИИ В СРЕДЕ АТМОСФЕРНОГО ВОЗДУХА

The article presents analytical and experimental studies to determine the density of the wood cell walls and other porous materials. From the literature, four main methods have been identified for determining the density of the cell walls of wood and porous materials. Of these, there are three direct methods: suspensions, mercury porosimetry and pycnometry, and one indirect - optical (planimetric). Helium gas pycnometry method is the most common of these ones. Based on the results of the critical analysis, a method for measuring the volume and determining the density of the cell walls of wood and porous materials in the atmosphere of atmospheric air was proposed. The method was theoretically substantiated and does not contradict the basic postulates and laws of thermodynamics. The functional suitability of the proposed method, as well as a high degree of reliability of the results obtained, has been determined experimentally. Volumes and densities of the cell walls of various wood species and other porous materials were measured under various modes of the system functioning using the developed experimental installation. The lowest density values were obtained at an overpressure of +70 kPa, the highest were seen at a vacuum of -90 kPa. The deviations in the results between the highest and lowest density values were, respectively: spruce – 7.02%, aspen – 4.12%, thermally modified (TM) linden – 2.95%, pine rot – 4.93%, shelf fungus – 5.12%, pine bark – 5.27%, birch charcoal – 14.6%.

Common sorption isotherm models are not physically valid for water in wood

Sorption isotherm models are frequently used to understand the interactions of water with cellulosic materials. Many commonly used models, such as the Guggenheim-Anderson-de Boer, Hailwood-Horrobin, and Dent isotherm models, are based on idealized physical systems. In the scientific literature, these models are often used to predict properties of wood such as the monolayer capacity, which is a representation of the number of available sorption sites in the material. Reporting such properties assumes that an idealized system adequately represents actual wood-water interactions. These models can be reduced to the same form, where the ratio of water activity, aw, to equilibrium moisture content (EMC), is a second-order polynomial function of aw. Here we review twelve models that have a parabolic form, fit these models to high quality water vapor sorption isotherm data for wood at multiple temperatures, and calculate physical properties from the model parameters. Moreover, variability in model predictions arising from measurement uncertainties in aw and EMC values is propagated using a Monte Carlo method. Predicted physical properties are tested against independently measured values of hydroxyl accessibility, relative amounts of primary and secondary water, and enthalpy of sorption. None of the models accurately predicts any of the physical properties, even when the reported measurement uncertainties are increased by a factor of three. Therefore, it must be concluded that parabolic sorption isotherm models are not valid for water in wood cell walls.

Characterisation of Moisture in Scots Pine (Pinus sylvestris L.) Sapwood Modified with Maleic Anhydride and Sodium Hypophosphite

In this study, the wood–water interactions in Scots pine sapwood modified with maleic anhydride (MA) and sodium hypophosphite (SHP) was studied in the water-saturated state. The water in wood was studied with low field nuclear magnetic resonance (LFNMR) and the hydrophilicity of cell walls was studied by infrared spectroscopy after deuteration using liquid D2O. The results of LFNMR showed that the spin–spin relaxation (T2) time of cell wall water decreased by modification, while T2 of capillary water increased. Furthermore, the moisture content and the amount of water in cell walls of modified wood were lower than for unmodified samples at the water-saturated state. Although the amount of accessible hydroxyl groups in modified wood did not show any significant difference compared with unmodified wood, the increase in T2 of capillary water indicates a decreased affinity of the wood cell wall to water. However, for the cell wall water, the physical confinement within the cell walls seemed to overrule the weaker wood–water interactions.

Utilizing a novel fungal enzymatic cocktail as an eco-friendly alternative for cellulose pulp biobleaching

Enzyme cocktails can alter the lignin and hemicellulose content in wood cell walls, improving the bleaching process during pulp production and offsetting the need for toxic chemicals. In this study, brown pulp was biobleached with a mixture of crude fungal extracts rich in xylanase and laccase, respectively produced from Aspergillus tamarii Kita and Trametes versicolor on waste materials. The optimal conditions for biobleaching were a mixture of xylanase and laccase crude extracts (1 to 2 v/v), at a temperature of 36 °C and a pH of 5.5. The treated brown cellulose pulp showed a reduction in the Kappa number by 1.83 points, representing an efficiency of 20.3%. In addition, the brightness increased by 4.65 points in comparison to the control. Hence, studies involving the application of the standardized cocktail during the hydrolysis of lignocellulosic residues, e.g., barley residue and sugarcane bagasse, led to the formation of 85 g/L and 25 g/L of reducing sugars, respectively. Moreover, the standardized cocktail caused greater deinking of the recycled paper pulp.

Comparison of the time-moisture and time-temperature equivalences in the creep properties of Chinese fir

ABSTRACT The present study investigated how the applications of the time-moisture superposition principle (TMSP) under a moisture content (MC) range of 0–14.2% and the time-temperature superposition principle (TTSP) under a temperature range of 30–150 °C would affect to Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) creep behaviors across grain orientations via a dynamic mechanical analysis instrument. The results showed that both TMSP and TTSP could describe the evolution of creep in the radial and tangential directions. Master curves constructed by TMSP and TTSP overlapped at a reference condition (30 °C, 0% MC), regardless of the grain orientation. In addition, an equivalent relation between the effects of moisture and temperature on the creep behavior was assumed based on TMSP and TTSP. Under the tested temperature, the effect of the per unit MC was equivalent to that at ca. 33 and 44 °C for the radial and tangential specimens, respectively. These findings elucidate the effects of moisture and temperature on the rheological properties of wood cell walls and are helpful for better utilizing wood in civil engineering applications.

Hygromechanical mechanisms of wood cell wall revealed by molecular modeling and mixture rule analysis.

Despite the thousands of years of wood utilization, the mechanisms of wood hygromechanics remain barely elucidated, owing to the nanoscopic system size and highly coupled physics. This study uses molecular dynamics simulations to systematically characterize wood polymers, their mixtures, interface, and composites, yielding an unprecedented micromechanical dataset including swelling, mechanical weakening, and hydrogen bonding, over the full hydration range. The rich data reveal the mechanism of wood cell wall hygromechanics: Cellulose fiber dominates the mechanics of cell wall along the longitudinal direction. Hemicellulose glues lignin and cellulose fiber together defining the cell wall mechanics along the transverse direction, and water severely disturbs the hemicellulose-related hydrogen bonds. In contrast, lignin is rather hydration independent and serves mainly as a space filler. The moisture-induced highly anisotropic swelling and weakening of wood cell wall is governed by the interplay of cellulose reinforcement, mechanical degradation of matrix, and fiber-matrix interface.

Wood-Derived Composites with High Performance for Thermal Management Applications.

Fabricating advanced polymer composites with remarkable mechanical and thermal conductivity performances is desirable for developing advanced devices and equipment. In this study, a novel strategy to prepare anisotropic wood-based scaffolds with a naturally aligned microchannel structure from balsa wood is demonstrated. The wood microchannels were coated with polydopamine-surface-modified small graphene oxide (PGO) nanosheets via assembly. The highly aligned porous microstructures, with thin wood cell walls and large voids along the cellulose microchannels, allow polymers to enter, resulting in the fabrication of the wood-polymer nanocomposite. The tensile stiffness and strength of the resulting nanocomposite reach 8.10 GPa and 90.3 MPa with a toughness of 5.0 MJ m-3. The thermal conductivity of the nanocomposite is improved significantly by coating a PGO layer onto the wood scaffolds. The nanocomposite exhibits not only ultrahigh thermal conductivity (in-plane about 5.5 W m-1 K-1 and through-plane about 2.1 W m-1 K-1) but also satisfactory electrical insulation (volume resistivity of about 1015 Ω·cm). Therefore, the results provide a strategy to fabricate thermal management materials with excellent mechanical properties.

Improvement of physical and mechanical properties of poplar wood via immobilization of rosin by grafting of vinyl chains

Rosin is renewable biomass with the potential to enhance wood properties. However, its high leaching rate restricts the durability of rosin impregnation. To immobilize rosin in wood structure, polymeric rosin (R-GMA) with vinyl chains was synthesized by the chemical reaction between rosin and glycidyl methacrylate (GMA) in the present work. Poplar wood was impregnated by different concentrations of the R-GMA. Due to the initiator and high temperature, R-GMA polymerized both in wood cell lumens and cell walls through radical polymerization. The polymer loading gradually increased with the concentration increased. As a result, the ASE can reach 50% with a WPG of 54%. Compared with the control sample, the 7-day water uptake of treated wood (WPG was 54%) was reduced by 55%. At 20% R-GMA concentration, the MOR, MOE, and CS of wood were increased by 23.5%, 46.6%, and 66%, respectively. The dynamic wettability of wood was remarkably reduced by the R-GMA impregnation. The lightness of the wood surface was reduced and the surface color became reddish and yellowish after modification. Additionally, the thermal stability of wood was marginally improved by the filling of R-GMA polymers.

A Fungal Secretome Adapted for Stress Enabled a Radical Wood Decay Mechanism.

ABSTRACTBrown rot fungi release massive amounts of carbon from forest deadwood, particularly at high latitudes. These fungi degrade wood by generating small reactive oxygen species (ROS) to loosen lignocellulose, to then selectively remove carbohydrates. The ROS mechanism has long been considered the key adaptation defining brown rot wood decomposition, but recently, we found preliminary evidence that fungal glycoside hydrolases (GHs) implicated in early cell wall loosening might have been adapted to tolerate ROS stress and to synergize with ROS to loosen woody lignocellulose. In the current study, we found more specifically that side chain hemicellulases that help in the early deconstruction of the lignocellulosic complex are significantly more tolerant of ROS in the brown rot fungus Rhodonia placenta than in a white rot fungus (Trametes versicolor) and a soft rot fungus (Trichoderma reesei). Using proteomics to understand the extent of tolerance, we found that significant oxidation of secreted R. placenta proteins exposed to ROS was less than half of the oxidation observed for T. versicolor or T. reesei. The principal oxidative modifications observed in all cases were monooxidation and dioxidation/trioxidation (mainly in methionine and tryptophan residues), some of which were critical for enzyme activity. At the peptide level, we found that GHs in R. placenta were the least ROS affected among our tested fungi. These results confirm and describe underlying mechanisms of tolerance in early-secreted brown rot fungal hemicellulases. These enzymatic adaptations may have been as important as nonenzymatic ROS pathway adaptations in brown rot fungal evolution.

Impregnation of poplar wood with multi-functional composite modifier and induction of in-situ polymerization by heating

Herein, a modified wood with greatly improved mechanical properties and reduced hygroscopicity was successfully prepared. The effects of the impregnation of multi-functional composite modifier on the chemical, thermal and morphological properties of poplar wood were also studied by X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Thermogravimetric Analyzer (TGA) and Scanning Electron Microscopy- Energy-Dispersive X-ray Analysis (SEM-EDXA). The multi-functional composite modifier was fabricated by methylolurea, dimethylol dihydroxy ethylene urea (DMDHEU), carbamide and silica sol. Cross-linking reaction happened between the wood cell wall and the multi-functional composite modifier. The position peaks in the XRD pattern didn’t change obviously, which indicated the crystal structure of cellulose was not noticeably affected by the chemical modification. The FT-IR analysis showed that the intensity of hydroxyl (-OH) and carbonyl (C = O) absorption peaks decreased, which was attributed to the -NHCH2OH of the modifier reacted with the hydroxyl and carbonyl of the wood. Meanwhile the Si-O-Si bond and Si-O-C bond formed between the wood structure and silica sol by in-situ polymerization. The TGA curve showed the thermal stability of the modified wood. The micrographs and major elements of the untreated and modified wood were observed by SEM-EDXA.

Intrinsic kink deformation in nanocellulose

Sharp bends can be widely observed in isolated cellulose nanofibrils (CNFs) after mechanical treatment, referred to as kink dislocations that are previously found in wood cell walls under compression. The non-Gaussian distribution of kink angle implies some inherent deformation behaviors of cellulose nanocrystals (CNCs) hidden in the formation of kink dislocations in CNFs. We herein perform molecular dynamics simulations to investigate the kink deformation of nanocellulose. It is interesting to find an intrinsic deformation mode of Iβ CNCs under uniaxial compression, in which the metastable structure of kinked CNCs turns out to be the triclinic Iα phase with twin boundaries originated from interlayer dislocation-induced allomorphic transition. An intrinsic kink angle (~60°) is defined based on geometric traits of stable kinked CNCs. Moreover, the weakened intrachain hydrogen bonds in twin boundaries lead to exposed glycosidic bonds and damaged hydrogen-bonding networks, which would act as the origin of kink defects in nanocellulose.

The Accessibility of the Cell Wall in Scots Pine (Pinus sylvestris L.) Sapwood to Colloidal Fe3O4 Nanoparticles.

This work presents a rapid and facile way to access the cell wall of wood with magnetic nanoparticles (NPs), providing insights into a method of wood modification to prepare hybrid bio-based functional materials. Diffusion-driven infiltration into Scots pine (Pinus sylvestris L.) sapwood was achieved using colloidal Fe3O4 nanoparticles. Optical microscopy, scanning electron microscopy/energy-dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray powder diffraction analyses were used to detect and assess the accessibility of the cell wall to Fe3O4. The structural changes, filling of tracheids (cell lumina), and NP infiltration depth were further evaluated by performing X-ray microcomputed tomography analysis. Fourier transform infrared spectroscopy was used to assess the chemical changes in Scots pine induced by the interaction of the wood with the solvent. The thermal stability of Fe3O4-modified wood was studied by thermogravimetric analysis. Successful infiltration of the Fe3O4 NPs was confirmed by measuring the magnetic properties of cross-sectioned layers of the modified wood. The results indicate the feasibility of creating multiple functionalities that may lead to many future applications, including structural nanomaterials with desirable thermal properties, magnetic devices, and sensors.

In situ observation of shrinking and swelling of normal and compression Chinese fir wood at the tissue, cell and cell wall level

The shrinking and swelling of wood due to moisture changes are intrinsic material properties that control and limit the use of wood in many applications. Herein, hygroscopic deformations of normal and compression wood of Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) were measured during desorption and absorption processes. The dimensional changes were observed in situ by an environmental scanning electron microscope and analyzed at different hierarchical levels (tissue, cell and cell wall). The relationship between moisture variation and hygroscopic deformation was measured. During initial desorption periods from 95 to 90 or 75% RH, an expansion of the lumen and a shrinkage of the cell wall were observed, revealing a non-uniform and directional deformation of single wood cells. The variation of shrinking or swelling at different hierarchical levels (tissue, cell and cell wall) indicates that the hygroscopic middle lamella plays a role in the deformation at the tissue level. Higher microfibril angles and helical cavities on the cell wall in compression wood correlate with a lower shrinking/swelling ratio. Normal wood showed a more pronounced swelling hysteresis than compression wood, while the sorption hysteresis was almost the same for both wood types. This finding is helpful to elucidate effects of micro- and ultrastructure on sorption. The present findings suggest that the sophisticated system of wood has the abilities to adjust the hygroscopic deformations by fine-tuning its hierarchical structures.

Reaction mechanisms of furfuryl alcohol polymer with wood cell wall components

Abstract Wood properties of furfurylation can be altered by reaction mechanisms of furfuryl alcohol polymer (PFA) and cell walls. Although chemical reactions between PFA and lignin have been studied, reaction mechanisms between PFA and cell wall components, including lignin, cellulose and hemicellulose are still not comprehensively understood. In order to elucidate chemical reactions regarding PFA with wood cell walls, model compounds of main cell wall components were used to investigate its reactions with PFA by 13C NMR spectroscopy and differential scanning calorimetry (DSC). Results showed that there was no chemical bonding of PFA with either cellulose or hemicellulose. Condensations of uncrowded ring positions (meta, ortho and para) and side chains (α–C, β–C, β–OH, and γ–OH) of lignin with PFA did occur based on 13C NMR spectra. Reaction enthalpy and activation energy also confirmed the condensation reactions between lignin and PFA. This study could provide design guidelines to control the chemical reactions of PFA in cell walls and lignin and, therefore, improve the properties of furfurylated wood.

Solid-electrolyte interphase from nanowood for high-performance Li-metal batteries

Solid-electrolyte interphase from nanowood for high-performance Li-metal batteries

Influences of polysaccharides in wood cell walls on lignification in vitro

Influences of polysaccharides in wood cell walls on lignification in vitro

Temperature-Dependent Creep Behavior and Quasi-Static Mechanical Properties of Heat-Treated Wood

In this paper, Berkovich depth-sensing indentation has been used to study the effects of the temperature-dependent quasi-static mechanical properties and creep deformation of heat-treated wood at temperatures from 20 °C to 180 °C. The characteristics of the load–depth curve, creep strain rate, creep compliance, and creep stress exponent of heat-treated wood are evaluated. The results showed that high temperature heat treatment improved the hardness of wood cell walls and reduced the creep rate of wood cell walls. This is mainly due to the improvement of the crystallinity of the cellulose, and the recondensation and crosslinking reaction of the lignocellulose structure. The Burgers model is well fitted to study the creep behavior of heat-treated wood cell walls under different temperatures.

Direct measurement of surface adhesion between thin films of nanocellulose and urea–formaldehyde resin adhesives

When applying an adhesive to wood, the chemical heterogeneity of the wood cell walls makes it difficult to understand the contribution they make to the interfacial adhesion between the adhesive and the wood as the adhesion is a very complex physical and chemical phenomenon. This study, for the first time, directly measured the surface adhesion between cellulose, a major component of wood, and urea–formaldehyde (UF) resin adhesives. The adhesion between thin, smooth nanocellulose films, such as cellulose nanofibrils (CNFs), carboxymethylated nanofibrils (CM)–CNFs, and carboxylated cellulose nanocrystals (C–CNCs), and UF resins with two formaldehyde to urea (F/U) molar ratios of 1.0 and 1.6 was measured using two approaches: (1) direct measurement of the adhesion force between nanocellulose films and liquid droplets of the UF resins, and (2) calculation of the work of adhesion between films of the nanocelluloses and UF resins using the contact angle and the van Oss–Chaudhury–Good method. The results show that the total surface free energies, either between the different nanocelluloses or between the two UF resins are somewhat similar, indicating the similarity in their surface properties. However, the adhesion force and work of adhesion of 1.6 UF resins with different types of nanocellulose are higher than those of 1.0 UF resins, which shows that van der Waals forces are dominant in their molecular interactions. These results suggest that the adhesion between 1.6 UF resins and nanocellulose is stronger than that when 1.0 UF resins are used because the 1.6 UF resins have a more branched structure, smoother surface, and higher surface free energy.

Characterization of the structural and dynamic changes of cell wall obtained by ultrasound-water and ultrasound-alkali treatments

It is well-known that ultrasound has been studied for its cavitation, mechanical and thermal effects. As a pretreatment technology, ultrasonic alkali treatment has attracted much attention in the field of biomass biochemical transformation. In this study, the structural and dynamic changes of wood cell walls during ultrasound-water, alkali, and ultrasound-alkali treatments were investigated by stereoscopic microscopy, confocal Raman microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction. The results indicated that the ultrasound-water, alkali, and ultrasound-alkali treatments had the effect of removing extractives from conduits. The uniform self-shrinking samples with shrinkage conduits were obtained by the alkali and ultrasound-alkali treatments. All of the treatments affected the relative content, structure and distribution of the chemical components in the wood cell walls. Compared with water-immersion samples, the relative content of hemicellulose of the treated samples reduced from 32.31% to 7.02% for ultrasound-8% NaOH treated samples. For the signal intensity of lignin, ultrasound-water treated and ultrasound-alkali treated samples displayed a more significant reductions than the alkali treated samples in the cell wall region. The crystal zone and amorphous zone of cellulose coexisted before and after the treatment, for all of the treated samples, and particularly for the ultrasound-assisted treated samples, the crystallinity increased from 38.15% for water-immersion samples to 57.42% for ultrasound-8% NaOH treated samples.

Sustainable Wood Nanotechnologies for Wood Composites Processed by In-Situ Polymerization.

The development of large, multifunctional structures from sustainable wood nanomaterials is challenging. The need to improve mechanical performance, reduce moisture sensitivity, and add new functionalities, provides motivation for nanostructural tailoring. Although existing wood composites are commercially successful, materials development has not targeted nano-structural control of the wood cell wall, which could extend the property range. For sustainable development, non-toxic reactants, green chemistry and processing, lowered cumulative energy requirements, and lowered CO2-emissions are important targets. Here, modified wood substrates in the form of veneer are suggested as nanomaterial components for large, load-bearing structures. Examples include polymerization of bio-based monomers inside the cell wall, green chemistry wood modification, and addition of functional inorganic nanoparticles inside the cell wall. The perspective aims to describe bio-based polymers and green processing concepts for this purpose, along with wood nanoscience challenges.