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Bamboo fiber cell wall structure, including cellulose microfibril morphology, endows fibers with excellent and stable mechanical strength and toughness. Due to the imaging resolution limitations, the ultra-structure of bamboo fiber cell walls remains elusive. Here we characterized the fiber cell wall's inherent structure and the cellulose microfibril's cross-sectional shape from native and delignified inclined samples, and the tangential sections of moso bamboo using atomic force microscopy. The secondary cell wall sublayer was composed of multiple microfibril layers, 20 nm in thickness each. The 18 nm in diameter spherical particles between microfibrils were lignin. The bamboo fiber cell wall's microfibrils were composed of various numbers of individual cellulose elementary fibrils (CEFs), including one, two, three, four, and multiple CEFs (up to 7 CEFs). The microfibrils' dimensions varied from 3.5 to 40 nm. Additionally, branched microfibrils are described for the first time in the bamboo plant. The study provides insight into the nanometer-scale structure of the fiber cell wall in the bamboo plant. [ABSTRACT FROM AUTHOR]

The plant cell wall is a complex structure consisting of a polysaccharide network. The rearrangements of the cell wall during the various physiological reactions of plants, however, are still not fully characterized. Profound changes in cell wall organization are detected by microscopy in the phloem fibers of flax (Linum usitatissimum) during the restoration of the vertical position of the inclined stems. To characterize the underlying biochemical and structural changes in the major cell wall polysaccharides, we compared the fiber cell walls of non-inclined and gravistimulated plants by focusing mainly on differences in non-cellulosic polysaccharides and the fine cellulose structure. Biochemical analysis revealed a slight increase in the content of pectins in the fiber cell walls of gravistimulated plants as well as an increase in accessibility for labeling non-cellulosic polysaccharides. The presence of galactosylated xyloglucan in the gelatinous cell wall layer of flax fibers was demonstrated, and its labeling was more pronounced in the gravistimulated plants. Using solid state NMR, an increase in the crystallinity of the cellulose in gravistimulated plants, along with a decrease in cellulose mobility, was demonstrated. Thus, gravistimulation may affect the rearrangement of the cell wall, which can enable restoration in a vertical position of the plant stem.

Hemp (Cannabis sativa L.) shiv has great potential for the production of bio-composites as a reinforcement material. To gain more information about hemp shiv, this research studied the influence of gender on the physical and mechanical properties of the fiber cell wall in the shiv of three dioecious hemp plant varieties by optical microscopy, image analysis software, WXRD, and nanoindentation. The results show that a hemp plant’s gender greatly influences the properties of hemp shiv. While long and thin in female hemp shiv, the fibers are shorter with a larger diameter in male hemp shiv. In addition, the cell walls in female shiv are thinner than those in male shiv. The microfibril angle (MFA), relative degree of crystallinity, elastic modulus, and hardness values of fiber cell walls as well as the lignin content in male hemp plants are higher than those in female hemp plants. Besides, the relationship between mechanical properties and MFA do not align with those observed in previous research, which shows that the gender of an individual plant has a greater effect on the mechanical properties of the fiber cell wall than does its MFA. Thus, when the fiber from this dioecious plant is investigated or used, the sex of the plant should be known and considered.

Castor (Ricinus communis L.) stalk is a byproduct of the production of castor oil. As a natural material, castor stalk has great potential in the production of bio-composites as reinforcement materials. To provide more information about the castor stalk for using it better, the structure, microfibril angle (MFA), relative degree of crystallinity (%), and mechanical properties of castor fiber cell walls were investigated using X-ray diffraction (XRD) and nanoindentation. The influence of chemical composition and MFA on the mechanical properties of fiber cell wall was studied as well. The cortex of castor stalks primarily contains long fibers, while the xylem of castor stalk, an excellent wood-type material, comprises most of the castor stalk (83.95% by weight); the pith of the stalk is composed of parenchyma cells. The average elastic modulus of fiber cell wall in lower, upper, and branch parts are 16.0 GPa, 18.6 GPa, and 13.2 GPa, respectively. The average hardness of fiber cell wall in lower, upper, and branch parts are 0.50 GPa, 0.54 GPa, and 0.43 GPa, respectively. As lignin content increases from 15.57% to 17.41% and MFA decreases from 21.3˚ to 15.4˚, the elastic modulus increases from 13.2 GPa to 18.6 GPa and the hardness increases from 0.43 GPa to 0.54 GPa. The mechanical properties, including the elastic modulus and the hardness of the fiber cell wall in the upper region of the castor stalk, are higher than those in the lower region, while the mechanical properties of the fiber cell wall in the branches are lower than those in either the upper or lower regions.

Reed (Phragmites australis) is a natural biological material that has great potential as reinforcing material in bio-composites. In order to evaluate the potential of reed stalk for reinforcement, the microstructure, elemental composition, microfibril angle (MFA), and mechanical properties of fiber cell walls were investigated by means of scanning probe microscopy (SPM), energy dispersive analysis of X-rays (EDAX), X-ray diffraction (XRD), and nanoindentation, respectively. The effects of elemental composition and microfibril angle of reed fibers on the mechanical properties were also considered. The results indicated that reed fiber cells have a multilayered structure. The observed increase in lignin content and decrease in MFA may contribute to the increase of mechanical properties. The elastic modulus and hardness of fibers in the upper part of the reed stalk were higher than those of the lower part. Based on nanoindentation results found in the literature, reed fibers have higher elastic modulus and hardness than poplar and spruce fibers. [ABSTRACT FROM AUTHOR]

Abstract: Arborists and managers of amenity trees could benefit from an improved understanding of how tree canopies withstand loading events such as wind, snow or ice. Knowledge of how material properties change along tree branches is important in understanding how a branch tips can bend in the wind yet resist displacement at the base which could lead to branch failure. Limited knowledge of modulus of elasticity (E or stiffness) in branch wood is available in the literature and is typically measured at only one location on a branch. This study investigated variation of E and density-specific E (E/ρ) at five locations along the axis of 20 branches from seven trees. E and E/ρ were found to be 70% lower at the branch tips than in the proximal locations. The variation in E was negatively correlated with the percentage of tissue area composed of vessels and positively correlated with mean fiber cell wall size, suggesting a balance between the two principle functions of hydraulics and mechanics. Reaction wood was observed in the form of gelatinous layers in fibers along the branch tops, but did not result in a difference in E between the top and bottoms at each branch location. It is proposed that differences in material properties are probably related to wood development type, as juvenile wood is considered to have lower stiffness than mature wood. [Copyright &y& Elsevier]

Abstract: Bamboo is a natural biological composite with superior mechanical strength and toughness. What is the secret recipe that Mother Nature uses to fabricate bamboo? Here we report discovery of cobble-like polygonal cellulose nanograins with a diameter of 21–198 nm in the cell wall of bamboo fibers. These nanograins are basic building blocks that are used to construct individual bamboo fibers. Nanoscale mechanical tests were carried out on individual fiber cell walls by nanoindentation. The nanograin-structured bamboo fibers are not brittle in nature but somewhat ductile. The bamboo fiber reinforcing mechanisms are discussed with reference to the hierarchical structure and mechanical properties of individual bamboo components. [Copyright &y& Elsevier]

The plant cell wall is a complex structure consisting of a polysaccharide network. The rearrangements of the cell wall during the various physiological reactions of plants, however, are still not fully characterized. Profound changes in cell wall organization are detected by microscopy in the phloem fibers of flax (Linum usitatissimum) during the restoration of the vertical position of the inclined stems. To characterize the underlying biochemical and structural changes in the major cell wall polysaccharides, we compared the fiber cell walls of non-inclined and gravistimulated plants by focusing mainly on differences in non-cellulosic polysaccharides and the fine cellulose structure. Biochemical analysis revealed a slight increase in the content of pectins in the fiber cell walls of gravistimulated plants as well as an increase in accessibility for labeling non-cellulosic polysaccharides. The presence of galactosylated xyloglucan in the gelatinous cell wall layer of flax fibers was demonstrated, and its labeling was more pronounced in the gravistimulated plants. Using solid state NMR, an increase in the crystallinity of the cellulose in gravistimulated plants, along with a decrease in cellulose mobility, was demonstrated. Thus, gravistimulation may affect the rearrangement of the cell wall, which can enable restoration in a vertical position of the plant stem. [ABSTRACT FROM AUTHOR]

Self-bonded natural fiber material (SNFM) is a promising alternative for plastic and wood owing to its abundant raw material resources and low environmental impact. In this study, a high-performance SNFM was developed by the comprehensive treatments for the plasticity and structure of fiber cell walls. The cell wall structure was treated by a progressive chemical etching process for selectively removing surface lignin, internal lignin and hemicelluloses, respectively. The cell wall plasticity was tuned by controlling the fiber moisture content during compression molding process. The results showed that the increase in fiber plasticity improved the tensile strength from 38.0 to 83.5 MPa and the flexural strength from 31.2 to 73.3 MPa. The selective removal of surface lignin increased the flexural strength from 101.3 to 122.1 MPa. The functional relationships among mechanical strength, lignin content, hemicellulose content and moisture content were established. The self-bonded mechanism for natural fiber materials was also discussed. The SNFM products showed excellent mechanical performance (tensile strength: 21.5–83.5 MPa; flexural strength: 31.2–127.3 MPa), which was superior to that of natural wood (46.5–55.6 MPa; 70.7–92.4 MPa) and plastic (15.9–51.0 MPa; 21.7–73.0 MPa) (e.g., HDPE, PP, PVC, and ABS). Unlabelled Image • High-performance self-bonded natural fiber material was developed using pulp fibers that were made from hardwood wastes • Mechanical property was enhanced through comprehensive treatments on fiber cell wall plasticity and structures • Establishment of functions among mechanical strength, lignin content, hemicellulose content and mat moisture content • Comparison with plastic and wood confirmed the mechanical strength superiority of self-bonded natural fiber material [ABSTRACT FROM AUTHOR]