Water in Pinus Radiata Wood Secondary Cell Walls: An Investigation Using Nuclear Magnetic Resonance and Synchrotron X-Ray Diffraction

<p>The mechanical properties of wood allow it to be used for numerous purposes. For most purposes, drying of the wood material from the green state, sawn from the log, is first required. This drying step significantly improves the strength properties of wood. It is therefore clear that moisture in wood plays an important role in determining the bulk mechanical properties. Over the last century, many studies have been carried out to investigate the way in which the water content wood affects the bulk mechanical properties. More recent studies have focused to the individual chemical components that make up wood to understand the observed changes in bulk mechanical properties. Models of the nanostructure of wood contained; cellulose, hemicellulose, and lignin, and the arrangement and location of these components in terms of their mechanical properties was interpreted through what was described as the 'slip-stick' mechanism, by which wood, in its green state, maintained its molecular and mechanical properties under external stresses. This model, while insightful, failed to account for the presence and the role of water in the nanostructure of wood. In this work, synchrotron based X-ray diffraction and NMR studies, have been used to develop a new model, in which water plays a vital role in the determination of the mechanical properties of wood in its green, part-dried, and rewet states. X-ray diffraction showed that changes occur to the molecular packing of cellulose crystallites with change in moisture content, and that these changes begin to occur under mild drying conditions, i.e. drying in air at ambient temperatures. These changes depend on the severity of drying, whether ambient or forced oven drying, and are to some extent reversible. A spin-diffusion model was constructed using dimensions obtained from Xray diffraction, comparisons between predictions and experimental data from an NMR study showed that the location of water was dependent on the moisture history of wood. In the green state, at least some of the water in the wood cell wall forms a layer, between the cellulose crystals and the hemicellulose and lignin matrix. If dried and then rewet, this water associated with the cellulose crystals was not present to the same degree as in the green state, allowing a closer association of the hemicellulose with the cellulose. The effect of this change in water distribution in the wood cell wall on the bulk mechanical wood properties was shown in mechanical testing. The nanostructure of the wood cell wall therefore should be considered to contain cellulose, hemicellulose, lignin and water, where each component contributes, according to its molecular properties, dynamic mechanical properties which are reflected in the bulk material properties.</p>

Water in Pinus Radiata Wood Secondary Cell Walls: An Investigation Using Nuclear Magnetic Resonance and Synchrotron X-Ray Diffraction

<p>The mechanical properties of wood allow it to be used for numerous purposes. For most purposes, drying of the wood material from the green state, sawn from the log, is first required. This drying step significantly improves the strength properties of wood. It is therefore clear that moisture in wood plays an important role in determining the bulk mechanical properties. Over the last century, many studies have been carried out to investigate the way in which the water content wood affects the bulk mechanical properties. More recent studies have focused to the individual chemical components that make up wood to understand the observed changes in bulk mechanical properties. Models of the nanostructure of wood contained; cellulose, hemicellulose, and lignin, and the arrangement and location of these components in terms of their mechanical properties was interpreted through what was described as the 'slip-stick' mechanism, by which wood, in its green state, maintained its molecular and mechanical properties under external stresses. This model, while insightful, failed to account for the presence and the role of water in the nanostructure of wood. In this work, synchrotron based X-ray diffraction and NMR studies, have been used to develop a new model, in which water plays a vital role in the determination of the mechanical properties of wood in its green, part-dried, and rewet states. X-ray diffraction showed that changes occur to the molecular packing of cellulose crystallites with change in moisture content, and that these changes begin to occur under mild drying conditions, i.e. drying in air at ambient temperatures. These changes depend on the severity of drying, whether ambient or forced oven drying, and are to some extent reversible. A spin-diffusion model was constructed using dimensions obtained from Xray diffraction, comparisons between predictions and experimental data from an NMR study showed that the location of water was dependent on the moisture history of wood. In the green state, at least some of the water in the wood cell wall forms a layer, between the cellulose crystals and the hemicellulose and lignin matrix. If dried and then rewet, this water associated with the cellulose crystals was not present to the same degree as in the green state, allowing a closer association of the hemicellulose with the cellulose. The effect of this change in water distribution in the wood cell wall on the bulk mechanical wood properties was shown in mechanical testing. The nanostructure of the wood cell wall therefore should be considered to contain cellulose, hemicellulose, lignin and water, where each component contributes, according to its molecular properties, dynamic mechanical properties which are reflected in the bulk material properties.</p>

Fluorescence lifetime imaging as an in situ and label-free readout for the chemical composition of lignin

Important structures and functions within living organisms rely on naturally fluorescent polymeric molecules such as collagen, keratin, elastin, resilin, or lignin. Theoretical physics predict that fluorescence lifetime of these polymers is related to their chemical composition. We verified this prediction for lignin, a major structural element in plant cell walls and one of the most abundant components of wood. Lignin is composed of different types of phenylpropanoid units, and its composition affects its properties, biological functions, and the utilization of wood biomass. We carried out fluorescence lifetime imaging microscopy (FLIM) measurements of wood cell wall lignin in a population of 90 hybrid aspen trees genetically engineered to display differences in cell wall chemistry and structure. We also measured wood cell wall composition by classical analytical methods in the wood cell walls of these trees. Using statistical modelling and machine learning algorithms, we identified parameters of fluorescence lifetime that predict the content of S-type and G-type lignin units, the two main types of units in the lignin of angiosperm plants. Finally, we show how quantitative measurements of lignin chemical composition by FLIM can reveal the dynamics of lignin biosynthesis in two different biological contexts, including in vivo while lignin is being synthesized in the walls of living cells.

The Effect of High Lignin Content on Oxidative Nanofibrillation of Wood Cell Wall

Wood from field-grown poplars with different genotypes and varying lignin content (17.4 wt % to 30.0 wt %) were subjected to one-pot 2,2,6,6-Tetramethylpiperidin-1-yl)oxyl catalyzed oxidation and high-pressure homogenization in order to investigate nanofibrillation following simultaneous delignification and cellulose oxidation. When comparing low and high lignin wood it was found that the high lignin wood was more easily fibrillated as indicated by a higher nanofibril yield (68% and 45%) and suspension viscosity (27 and 15 mPa·s). The nanofibrils were monodisperse with diameter ranging between 1.2 and 2.0 nm as measured using atomic force microscopy. Slightly less cellulose oxidation (0.44 and 0.68 mmol·g−1) together with a reduced process yield (36% and 44%) was also found which showed that the removal of a larger amount of lignin increased the efficiency of the homogenization step despite slightly reduced oxidation of the nanofibril surfaces. The surface area of oxidized high lignin wood was also higher than low lignin wood (114 m2·g−1 and 76 m2·g−1) which implicates porosity as a factor that can influence cellulose nanofibril isolation from wood in a beneficial manner.

Fluid Flow of Polar and Less Polar Liquids through Modified Poplar Wood

Fast-growing species often have a low natural durability and can easily be attacked by fungi and insects, and therefore it is often better to preserve them before use. Permeability is a physical property in porous media that significantly affects the penetration of water- and oil-based preservatives into the texture of wood. In the present study, the specific gas permeability and liquid permeability to water and kerosene in poplar wood (Populus nigra var. betulifolia) were measured. The poplar trees were grown in plots with two spacings of 3 × 4 m and 3 × 8 m. Separate sets of specimens were also thermally modified in order to examinethe effects of this modification on gas and liquid permeability values. The results showed higher gas permeability in specimens grown in the plot with wider spacing (3 × 8 m), which was attributed to their larger vessel diameter. Kerosene demonstrated significantly higher permeability in comparison to water. This was attributed to the polar nature of water molecules, which tend to make stronger bonds with wood cell-wall polymers, ultimately delaying the movement of water through vessel elements. Thermal modification had an increasing effect on specific gas permeability. The increase was attributed to cracks that occur in the pits and wood cell wall during thermal modification, making way for the easier flow of fluids. Decreased wettability caused by thermal modification resulted in a significant increase in both water and kerosene permeability values.

Effect of Thermal Modification on the Nano-Mechanical Properties of the Wood Cell Wall and Waterborne Polyacrylic Coating

Masson pine (Pinus massoniana Lamb.) samples were heat-treated at different treatment temperatures (150, 170, and 190 °C), and the nano-mechanical properties of the wood cell wall, which was coated with a waterborne polyacrylic (WPA) lacquer product, were compared. The elastic modulus (Er) and hardness (H) of wood cell wall and the coating were measured and characterized by nanoindentation, and the influencing factors of mechanical properties during thermal modification were investigated by chemical composition analysis, contact angle analysis, and colorimetric analysis. The results showed that with the increase in the heat treatment temperature, the contact angle of the water on the wood’s surface and the colorimetric difference increased, while the content of the cellulose and hemicelluloses decreased. After thermal modification of 190 °C, the Er and H of the wood cell wall increased by 13.9% and 17.6%, respectively, and the Er and H of the WPA coating applied to the wood decreased by 12.1% and 22.2%. The Er and H of the interface between the coating and wood were lower than those near the coating’s surface. The Er and H of the cell wall at the interface between the coating and wood were lower than those far away from the coating. This study was of great significance for understanding the binding mechanism between coating and wood cell walls and improving the finishing technology of the wood materials after thermal modification.

Improvement of interfacial interaction in impregnated wood via grafting methyl methacrylate onto wood cell walls

Improving the interaction between the wood cell wall and a modifying agent is fundamental to enhancing the efficacy of wood modification. The extent of interaction is, nevertheless, difficult to evaluate due to the highly heterogeneous nature of the modified wood. In this study, methacryl groups were grafted onto the wood cell wall polymers, via the reaction between 2-isocyanatoethyl methacrylate (IEMA) and hydroxyl groups, to improve their compatibility and reactivity. Subsequently, methyl methacrylate (MMA) was introduced into methacrylated wood and copolymerized with the bonded methacryl groups. The distribution of IEMA and poly MMA (PMMA) in the wood cell walls was investigated by scanning electron microscopy (SEM) and confocal Raman microscopy. The results showed that MMA penetrated the wood cell walls and formed strong interfacial interaction, which was confirmed by confocal Raman microscopy combined with principal component analysis (PCA). With copolymerization, the highest anti-swelling efficiency (ASE) (57%) was achieved, because of the effect of methacrylation. Compared to the reference, the water resistance and hardness were significantly improved. In addition, the dynamic wettability was also altered largely due to copolymerization.

Enhancement of the physical and mechanical properties of wood using a novel organo-montmorillonite/hyperbranched polyacrylate emulsion

In this work, a novel waterborne hyperbranched polyacrylate (HBPA) dispersed organo-montmorillonite (OMMT) emulsion was synthesized and used for the treatment of wood in a vacuum environment in order to enhance the physical and mechanical properties of the wood. The sapwood of Cathay poplar (Populus cathayana Rehd.) and Radiata pine (Pinus radiata D.Don) were used as the samples for experimentation. The results showed that the physical and mechanical properties of the wood improved significantly due to the successful penetration of the OMMT and HBPA into the wood cell wall. From it was also observed that OMET completely exfoliated from the HBPA matrix and formed a hydrophobic film covering on the inside walls of the cell lumen. Further, it was observed that the poplar sample displayed better mechanical properties than the pine sample because the pine has a more compact structure when compared to poplar and contains rosin. Furthermore, it was also observed that the mechanical properties of the modified wood sample gradually improved with an increase in the concentration of the emulsion. However, excessive concentration (>4 wt%) did not lead to further improvement.