Ubim Fiber (Geonoma baculífera): A Less Known Brazilian Amazon Natural Fiber for Engineering Applications

The production of synthetic materials generally uses non-renewable forms of energy, which are highly polluting. This is driving the search for natural materials that offer properties similar to synthetic ones. In particular, the use of natural lignocellulosic fibers (NLFs) has been investigated since the end of 20th century, and is emerging strongly as an alternative to replace synthetic components and reinforce composite materials for engineering applications. NLFs stand out in general as they are biodegradable, non-polluting, have comparatively less CO2 emission and are more economically viable. Furthermore, they are lighter and cheaper than synthetic fibers, and are a possible replacement as composite reinforcement with similar mechanical properties. In the present work, a less known NLF from the Amazon region, the ubim fiber (Geonoma bacculifera), was for the first time physically characterized by X-ray diffraction (XRD). Fiber density was statistically analyzed by the Weibull method. Using both the geometric method and the Archimedes’ technique, it was found that ubim fiber has one of the lowest densities, 0.70–0.73 g/cm3, for NLFs already reported in the literature. Excluding the porosity, however, the absolute density measured by pycnometry was relatively higher. In addition, the crystallinity index, of 83%, microfibril angle, of 7.42–7.49°, and ubim fiber microstructure of lumen and channel pores were also characterized by scanning electron microscopy. These preliminary results indicate a promising application of ubim fiber as eco-friendly reinforcement of civil construction composite material.

Influence of juvenile and mature wood on anatomical and chemical properties of early and late wood from Chinese fir plantation

The proportion of juvenile wood affects the utilization of wood seriously, and the transition year of juvenile wood (JW) and mature wood (MW) plays a decisive role in the rotation and the modification of wood. To find out the demarcation of JW and MW, the tracheid length (TL) and microfibril angle (MFA) of early wood (EW) and late wood (LW) from four Chinese fir clones were measured by optical microscopy and X-ray diffraction. Then the data were analyzed by the k-means clustering method. The correlation and the differences among wood properties between JW and MW were compared. Results indicated that the LW showed better properties than that of EW, but the anatomical differences between EW and LW did not influence the demarcation of JW and MW. The cluster analysis of TL and MFA showed that the transition year was in the 16th year and the transition zone of EW and LW was different among clones. The MW has longer and wider tracheid, thicker cell walls, and smaller MFA. In terms of chemistry, MW had a higher content of holocellulose, α-cellulose, less content of extract, but no significant difference in lignin content compared with JW. The stabilization of chemical components was earlier than that of the anatomic properties. Correlation analysis showed that there were strong correlations between the chemical composition and anatomical characteristics in JW and MW. In general, compared with chemical components, anatomical indicators were more suitable for JW and MW demarcation. The differences and correlations between JW and MW properties provide a theoretical basis for wood rotation and planting.

Mechanical Properties of Fibre-Reinforced Materials: the Wood-Water System

<p>The mechanical properties of wood are investigated from a "quasi-elastic point of view that makes allowance for variation in moisture content. The theoretical work is divided into three parts. The first part shows that wood may be regarded as a fibre-reinforced composite material and then builds up models of wood structure in terms of an assemblage of basic fibre-composite elements. The second part derives the constitutive relations for a fibre-reinforced composite consisting of, an inert fibrous phase embedded in a water reactive matrix; and the third part is concerned with the properties of the matrix of wood substance. The theoretical work is then tested against mechanical data from a set of specimens for which individual models have been devised. From this work, functions describing the behaviour of the matrix with moisture contest are obtained and the structural modelling procedures and the constitutive relation are shown to be not inconsistent with the observations. It was found that in addition to the mean cellulose microfibril angle, the matrix sorption properties are of great importance in correctly predicting Longitudinal shrinkage behaviour.</p>

Mechanical Properties of Fibre-Reinforced Materials: the Wood-Water System

<p>The mechanical properties of wood are investigated from a "quasi-elastic point of view that makes allowance for variation in moisture content. The theoretical work is divided into three parts. The first part shows that wood may be regarded as a fibre-reinforced composite material and then builds up models of wood structure in terms of an assemblage of basic fibre-composite elements. The second part derives the constitutive relations for a fibre-reinforced composite consisting of, an inert fibrous phase embedded in a water reactive matrix; and the third part is concerned with the properties of the matrix of wood substance. The theoretical work is then tested against mechanical data from a set of specimens for which individual models have been devised. From this work, functions describing the behaviour of the matrix with moisture contest are obtained and the structural modelling procedures and the constitutive relation are shown to be not inconsistent with the observations. It was found that in addition to the mean cellulose microfibril angle, the matrix sorption properties are of great importance in correctly predicting Longitudinal shrinkage behaviour.</p>

Comparative studies on the mechanical properties and microstructures of outerwood and corewood in Pinus radiata D. Don

Twenty-year-old Pinus radiata trees imported from New Zealand were investigated, and a comparison was made between the outerwood (rings 16–20) and corewood (rings 4–6) in terms of mechanical properties, anatomical characteristics, microfibril angle (MFA), relative crystallinity, crystallite size and lignin content to determine the relationship between their mechanical properties and microstructures. The results demonstrated that the mechanical properties of the Pinus radiata outerwood were significantly better than those of the corewood. The outerwood had a modulus of rupture (MOR) of 106 MPa, a modulus of elasticity (MOE) of 11.4 GPa, and compressive strength parallel to the grain of 38.7 MPa, and the MOR, MOE and compressive strength parallel to the grain of the corewood were 78.9 MPa, 7.12 GPa and 29.3 MPa, respectively. The observed microstructures of the Pinus radiata outerwood and corewood were different, mainly due to differences in cell wall thickness, MFA, and relative crystallinity. The double wall thickness of the tracheid cells of the corewood and outerwood were 3.65 and 5.02 µm, respectively. The MFA data indicated that the average MFA of the outerwood was 14.0°, which was smaller than that of the corewood (22.3°). With X-ray diffraction, the relative crystallinity of the corewood was determined to be 35.7%, while that of the outerwood was 40.2%. However, the crystallite size of the outerwood cell wall shows no obvious difference from that of the corewood. Imaging FTIR spectroscopy showed a slightly higher relative content of lignin in the cell wall of the outerwood. The correlation between the microstructures and mechanical properties showed that the corewood with a thin cell wall, large MFA and low relative crystallinity had poor mechanical properties, while the outerwood with a thicker tracheid, smaller MFA and higher relative crystallinity had better mechanical properties. This means that the MFA, relative crystallinity and cell wall thickness synergically affect the mechanical properties of Pinus radiata in different radial locations.

Anatomical properties of Hibiscus macrophyllus and its mature wood development

The Hibiscus macrophyllus tree is widely planted in Indonesia especially on Java Island. It has several advantages to be developed commercially as a community or plantation forest compared to the famous introduced species Falcataria moluccana and Anthocephalus spp., including faster growth, higher wood density, and better stem morphology (straighter, more rounded, and lesser branches). However, information about the basic properties of this wood grown in plantations is limited. This study aimed to investigate the anatomical properties of H. macrophyllus and their variation at three ages (8, 12 and 16 years old), as well as to predict the mature wood development by using radial variation in fiber length, microfibril angle (MFA), and wood density from pith toward the bark as the indicators. The wood samples were obtained from a community forest area at Ciamis Regency, West Java Province. Furthermore, anatomical characteristics were examined through wood slides following the IAWA List, while fibre and vessel element dimensions were measured through macerated specimens prepared by modified Franklin’s method. The MFA was determined by X-Ray Diffraction, while wood density was measured in line with British Standard 373-57. The results showed that the anatomical structures were not influenced by tree age, except for wood porosity, and fibre and vessel element dimensions. The 16-year-old tree tended to be semi-ring-porous, the younger trees were diffuse-porous, while the fiber and vessel element length, as well as the diameter, were decreased. Meanwhile, the wall thickness was increased. The fibre length, MFA, and wood density were useful indicators for wood maturity that seemed to be developed at about 11 years of age.

Effect of Microstructures on the Shear Strength of Larix kaempferi

Shear strength is important for the application of Larix kaempferi (Lamb) Carr. The structural difference between earlywood and latewood of Larix kaempferi affects its mechanical properties, especially shear strength. The microstructures of earlywood and latewood in Larix kaempferi, however, are different. In this study, we investigated the shear strength and shear failure mode in the RL direction of 40 Larix kaempferi specimens. The results demonstrated that the initial crack appears in any location of a growth ring, whereas shear failure is concentrated in earlywood, as well as the junction between earlywood and latewood. The destruction of earlywood is the tear destruction, whereas when the destruction happened in the junction of earlywood and latewood, one to three earlywood cells usually adhered to latewood. At the cell wall level, the shear failure of earlywood was mostly observed in the direction of the microfibril angle (MFA). When the crack occurs in latewood, the destruction of latewood also occurs in the intercellular layer and preserves the complete morphology of tracheids. When destruction occurs in the wood ray, the ray cells detach intact from the tracheids. The failure mode is determined by the microstructure of earlywood and latewood. Our research suggests that the density, cell wall thickness, and MFA have significant differences between earlywood and latewood. The earlywood was found to have an MFA of 25.4°, a cell wall thickness of 6.36 µm, and a density of 0.39 g/cm3. The MFA, cell wall thickness, and density of latewood density were 17.60°, 12.37 µm, and 0.78 g/cm3, respectively. However, there was no significant difference found in the crystallinity between the earlywood (43.97%) and latewood (42.79%). The correlation between the microstructures and shear strength showed that earlywood with a thin cell wall, large MFA, and low density had poor shear performance, while the latewood with a thicker tracheid, smaller MFA, and higher density had better shear performance. Therefore, when shear failure occurred, it occurred in earlywood. We thus deduced that the MFA, cell wall thickness, and density of earlywood synergically affect the shear strength in the RL direction of L. kaempferi.

Radial variations to wood anatomical and chemical properties in eight poplar clones

Wood properties are crucial for the development and application of poplar clones. Here, the effects of clone and age on anatomical and chemical properties were analyzed in eight poplar clones (clone 50, Zhonglin46, 108, 36, N179, Danhong, Sangju, and Nanyang) from Henan province, China. The results showed that the effects of clone and age were both significant for these wood properties. Eight clones were grouped into three clusters according to their annual ring width, fiber quality, and chemical properties. For some properties including annual ring width, fiber length, and microfibril angle, all clones displayed the same radial variation trends. Whereas, for other ones, such as holocellulose content, the radial variation trends were different depending on clones. The culmination of the mean annual increment corresponded to the turning ages of wood properties such as annual ring width in eight clones and holocellulose content in partial clones except for fiber length, microfibril angle, and vessel length. The rotation age of the poplar clones could be determined as 8-9 years based on the fiber quality and chemical components. These results indicated strong genetic and age control of the wood properties and highlighted the rich source of variation for poplar clone selection.

Wide-angle X-ray Scattering studies on contemporary and ancient bast fibres used in textiles – ultrastructural studies on stinging nettle

Stinging nettle (Urtica dioica) among other bast fibres, is a potential fibre source material for industrial and manufacturing applications. However, systematic research on the ultrastructural properties of nettle fibres is lacking. Determining the ultrastructural parameters of the bast fibres could provide also new insights into the studies of archaeological and historical fibres and their usage. In this study, modern and ancient fibre samples of stinging nettle were studied using wide-angle X-ray scattering (WAXS) and compared to other well-studied plant fibre species. From the WAXS patterns, the mean microfibril angle, average cellulose crystallite width and relative crystallinity index were determined. Besides, the suitability of the WAXS method for fibre identification purposes was studied. The culturohistorical research material consisted of fibre samples of nettle, flax and hemp acquired from White Karelian textiles collected 1894 as well as of 800–900-year-old archaeological textile fragments from Ravattula Ristimäki burial site in Kaarina, Southwest Finland. The crystallite widths for all modern fibres were of the similar size, however subtle differences in the relative crystallinity values in descending order (from flax to nettle and finally hemp) were observed. For the culturohistorical fibres, the values for average crystallite width and relative crystallinity were larger compared to the modern references of the same fibre type. In addition, individual features due to the presence of other crystalline substances (noncellulosic, minerals e.g., calcium oxalates), were detected in the scattering patterns of all modern nettles. These features could potentially be used as a tool to identify modern nettle fibres.