Microfibril Angle Research Articles

Crystallinity as a Non-Destructive Indicator of Wood Hardness at Standing Trees

Wood hardness is an important property for flooring, furniture products and structural utilization. Currently wood hardness can only be measured using destructive testing. As there is no suitable method for predicting wood hardness from standing trees, developing a non-destructive technique to predict wood hardness from plantations trees would provide significant benefits for evaluating optimal silvicultural treatments, and for selecting trees for tree improvement programs. It is proposed initillay that a possible non-destructive test may be developed using „crystallinity“ characteristics (degree of crystallinity (DC), crystalite width (CW) and length (CL) and microfibril angle (MFA)) determined using X-Ray diffraction. The aim of this study was to test the feasibility of using crystallinity as a non-destructive indicator of wood hardness. Experimentally, nine trees were taken representing small, medium and large diameter from five-year old fast growing teak plantation forest in Ciampea, Bogor, Indonesia. Wood hardness and crystallinity were determined following a standard testing regime. The results showed that MFA was negatively related to all hardness directions. Crstallite width only influenced side hardness with negative correlation, while degree of crystallinity only affected the end-grain hardness with positive correlation. Different vertical positions within tree only influenced the end-grain hardness value, while different radial positions had no effect on wood hardness. The optimum sampling height was found to be 80 cm, 130 cm, and 100 cm for radial, tangential and end-grain hardness, respectively. The relationship was based on the height that provided the highest correlation with the whole tree hardness values. Proposed models involving density and „crystallinity“ for predicting wood hardness are presented. While the R2from the proposed models was mostly less than 0.50, however, the approach described provides a new way to predict wood hardness from 10 mm increment cores at standing trees.

Age trend of heritability, genetic correlation, and efficiency of early selection for wood quality traits in Scots pine

To examine the efficiency of early selection for wood quality traits in the Scots pine (Pinus sylvestris L.) breeding program in Sweden, a total of 778 wood increment cores were sampled from 179 full-sib families in a single progeny trial at 40 years of age. Age trend of inheritance, age–age genetic correlation, and early selection efficiency for eight wood traits including annual ring width, wood density, microfibril angle (MFA), modulus of elasticity (i.e., wood stiffness; MOE), and fibre dimensions were studied. Heritabilities for the eight wood traits reached a plateau between age 5 years and age 15 years, with the highest heritability for radial fibre width and fibre coarseness (∼0.6) and the lowest heritability for ring width (∼0.2). Heritability reached about 0.4 for both wood density and MFA but only reached about 0.3 for MOE. Genetic correlation from early to reference age 30 years reached a very high level (>0.8) for all eight wood traits at age 5 years. Early selection was effective for wood quality traits in Scots pine, and selection at age 8 years is recommended for MOE in Scots pine.

A model of stem growth and wood formation in Pinus radiata

A model of wood formation processes in pines predicted 80 % of mean wood density variation from inputs of carbohydrate allocation and tree water status from several varied sites. Numerous factors determine how wood properties vary as a tree grows. In order to model wood formation, a framework that considers the various xylogenetic processes is required. We describe a new model of xylem development and wood formation in pines (parameterised for the commercially important species, Pinus radiata D. Don). In this paper, we use as inputs simulated daily data from the CaBala stand growth model which, in turn, takes into account site and daily weather conditions, and silviculture. It incorporates a first attempt at predicting microfibril angle (the angle of cellulose microfibrils relative to the vertical axis of the cell, MFA) based on metrics of cambial vigour and carbohydrate allocation. It also predicts tracheid dimensions and wall thickness, and from these data, wood density. Pith-to-bark and intra-annual variation in predicted wood properties was realistic across a wide range of site types, although juvenile wood properties were weakly predicted. The model was able to explain 50 % of the variation in outerwood MFA and 70–80 % of the variation in outerwood and mean sample wood density respectively, from 17 study sites. The model, early results from which are very promising, provides a useful framework for testing concepts of how formation occurs, and to provide insights into areas where further research is needed.

Variation in Trembling Aspen and White Spruce Wood Quality Grown in Mixed and Single Species Stands in the Boreal Mixedwood Forest

The Canadian boreal forest is largely represented by mixed wood forests of white spruce (Picea glauca (Moench) Voss) and trembling aspen (Populus tremuloides Michx). In this study, a total of 300 trees originating from three sites composed of trembling aspen and white spruce with varying compositions were investigated for wood quality traits: one site was composed mainly of aspen, one mainly of spruce and a third was a mixed site. Four wood quality traits were examined: wood density, microfibril angle (MFA), fibre characteristics, and cell wall chemistry. Social classes were also determined for each site in an attempt to provide a more in-depth comparison. Wood density showed little variation among sites for both species, with only significant differences occurring between social classes. The aspen site showed statistically lower MFAs than the aspen from the mixed site, however, no differences were observed when comparing spruce. Fibre characteristics were higher in the pure species sites for both species. There were no differences in carbohydrate contents across sites, while lignin content varied. Overall, the use of social classes did not refine the characterization of sites.

The quality of 8 and 10 years old samama wood (Anthocephalus macrophyllus)

In the near future, wood demand will be fulfilled by local fast growing woods from community forest. Among those, samama (Anthocephalus macrophyllus) is an endemic wood in Celebes and Moluccas. This species has been cultivated throughout Indonesia and usually harvested at age of less than 10 years. This research was conducted to examine the quality of samama wood at 8 and 10 years old. Each age group was represented by three healthy trees. Samples were made from 1 cm segmentation from pith to bark. Modified exponential curve was used to determine the transition of juvenile and mature wood in which maturity limit was achieved when growth parameter had reached the asymptote line. The quality parameters were specific gravity, moisture content, fiber length, fiber wall thickness and microfibril angle. The result showed that the first 6–8 segmentations from the pith were still juvenile, while the subsequent segments were mature wood. The 8 years old had 33.3–38.9 % of juvenile portion, while it was only 30.4–34.8 % in the 10 years old. This finding will be important in considering a proper technology for samama wood processing.

Effects of stand density and seedlot on three wood properties of young radiata pine grown at a dry-land site in New Zealand

Manipulation of stand density and choice of genetic material are two key mechanisms through which forest managers can influence tree growth and wood properties. Past silvicultural practices in New Zealand have been characterised by early thinning to relatively wide spacing, while tree improvement programmes have primarily focussed on growth and form. The aim of this study was to quantify the impacts of stand density and past genetic selections on the wood properties of radiata pine (Pinus radiata D. Don). Stress-wave velocity, wood density, microfibril angle (MFA) and modulus of elasticity (MOE) were measured on trees and wood samples taken from a 15-year-old silvicultural and tree breeds trial located in Canterbury, New Zealand. The focus of this study was comparison of seedlots with genetic ratings of GF6 and GF25. Data from pruned stands with final densities of 100, 200 and 400 stems ha−1 were compared as were data from unpruned stands with stand densities of 200, 400, 600 and 1000 stems ha−1. Stress-wave velocity of trees was affected by final stand density, with the lowest values recorded from trees in the 100 and 200 stems ha−1 treatments. Values for wood MFA and MOE both showed the greatest amount of change when final stand density was less than 400 stems ha−1. Trees from the GF25-rated seedlot had wood density that was approximately 34 kg m−3 lower than trees from the GF6-rated seedlot. Very high stand densities are not required in order to influence wood properties, but early thinning to low stand densities should be avoided. Such results are of practical importance to forestry managers.

The variation of microfibril angle in South African grown Pinus patula and its influence on the stiffness of structural lumber

Reduction in the rotation ages of softwood saw-log plantations in South Africa is causing increased proportions of low stiffness sawn lumber at final harvest. It has been shown for some species that the microfibril angle (MFA) of the S2 layer of tracheids is strongly related to the modulus of elasticity (MOE) of wood, even more so than wood density, especially in wood formed during juvenile growth. The objectives of this study were to describe the variation in MFA in young Pinus patula trees and to determine the relationship between MFA and the dynamic MOE of sawn P. patula lumber. Thirty 16- to 20-year-old trees from six compartments from the Mpumalanga escarpment were processed into discs and lumber. The MFA, density and ring width were measured at two height levels using Silviscan 3. The average annual ring MFA varied between 7° and 29°; the pattern of variation depended mainly on height level and the ring number from the pith. The MFA in P. patula followed the same within-tree variation trends as in New Zealand-grown Pinus radiata but the average MFA was lower in absolute terms and differences between height levels were less pronounced. The MFA and density exhibited highly significant Pearson correlations of 0.73 and 0.70, respectively, with board dynamic MOE. A multiple regression model, which included MFA, density and ring width, explained 71% of the variation in the dynamic MOE of boards. A sensitivity analysis on the model showed that MFA and density had approximately similar influences on predicting the dynamic MOE of Pinus patula boards.

Cellulose structure and lignin distribution in normal and compression wood of the Maidenhair tree (Ginkgo biloba L.).

We studied in detail the mean microfibril angle and the width of cellulose crystals from the pith to the bark of a 15-year-old Maidenhair tree (Ginkgo biloba L.). The orientation of cellulose microfibrils with respect to the cell axis and the width and length of cellulose crystallites were determined using X-ray diffraction. Raman microscopy was used to compare the lignin distribution in the cell wall of normal/opposite and compression wood, which was found near the pith. Ginkgo biloba showed a relatively large mean microfibril angle, varying between 19° and 39° in the S2 layer, and the average width of cellulose crystallites was 3.1-3.2 nm. Mild compression wood without any intercellular spaces or helical cavities was observed near the pith. Slit-like bordered pit openings and a heavily lignified S2L layer confirmed the presence of compression wood. Ginkgo biloba showed typical features present in the juvenile wood of conifers. The microfibril angle remained large over the 14 annual rings. The entire stem disc, with a diameter of 18 cm, was considered to consist of juvenile wood. The properties of juvenile and compression wood as well as the cellulose orientation and crystalline width indicate that the wood formation of G. biloba is similar to that of modern conifers.

Endo-β-1,4-glucanases impact plant cell wall development by influencing cellulose crystallization.

Cell walls are vital to the normal growth and development of plants as they protect the protoplast and provide rigidity to the stem. Here, two poplar and Arabidopsis orthologous endoglucanases, which have been proposed to play a role in secondary cell wall development, were examined. The class B endoglucanases, PtGH9B5 and AtGH9B5, are secreted enzymes that have a predicted glycosylphosphatidylinositol anchor, while the class C endoglucanases, PtGH9C2 and AtGH9C2, are also predicted to be secreted but instead contain a carbohydrate-binding module. The poplar endoglucanases were expressed in Arabidopsis using both a 35S promoter and the Arabidopsis secondary cell wall-specific CesA8 promoter. Additionally, Arabidopsis t-DNA insertion lines and an RNAi construct was created to downregulate AtGH9C2 in Arabidopsis. All of the plant lines were examined for changes in cell morphology and patterning, growth and development, cell wall crystallinity, microfibril angle, and proportion of cell wall carbohydrates. Misregulation of PtGH9B5/AtGH9B5 resulted in changes in xylose content, while misregulation of PtGH9C2/AtGH9C2 resulted in changes in crystallinity, which was inversely correlated with changes in plant height and rosette diameter. Together, these results suggest that these endoglucanases affect secondary cell wall development by contributing to the cell wall crystallization process.

Predicting wood fiber attributes using local-scale metrics from terrestrial LiDAR data: A case study of Newfoundland conifer species

Knowledge of wood fiber attributes (WFA) is important for evaluating forest resources and optimizing efficiency in the forest industry. To improve our ability to estimate WFA in the forest, we analyzed the relationships between structural metrics derived from terrestrial laser scanner (TLS) data and four key attributes of industrial significance: wood density, fiber length, microfibril angle, and coarseness. We developed a suite of structural metrics that relate to four aspects of the forest: canopy structure, competition, vegetation density, and local topography. We modeled WFA for sites dominated by black spruce (Picea mariana) and balsam fir (Abies balsamea) trees. For black spruce sites, R2 values ranged from 63% to 72%. Structural metrics that relate to competition were the strongest explanatory variables. For balsam fir sites, R2 ranged from 37% to 63% using structural metrics that relate mostly to canopy structure. Our results demonstrate that local structural variables are useful explanatory variables for predicting WFA of the dominant coniferous species in Newfoundland.

Influence of Gender on the Mechanical and Physical Properties of Hemp Shiv Fiber Cell Wall in Dioecious Hemp Plant

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.

The fasciclin‐like arabinogalactan protein family of Eucalyptus grandis contains members that impact wood biology and biomechanics

Fasciclin-like arabinogalactan protein (FLA) families have been identified and characterised in key plant species, with some members exhibiting functional specialization. Here we identify the FLA family of Eucalyptus grandis, and investigate the roles of three single-FAS domain FLAs, with particular focus on secondary cell-wall formation and wood properties. We use various in-silico approaches to identify and characterise E. grandis genome FLAs, and perform phylogenetic comparisons with other species. For three key FLAs, we perform functional testing including promoter-reporter and overexpression transgenic approaches using eucalypts, poplar and tobacco. Of the 18 eucalypt FLAs identified, several were specifically and highly expressed in stems. The specificity to stem xylem vessel and fibre development was demonstrated with EniFLA1promoter:GUS studies in several species. Testing of select eucalypt FLAs resulted in altered wood development and properties, for example 35S:EgrFLA2 led to a 3 degree reduction in cellulose microfibril angle in eucalypt xylem fibres, and 35S:EgrFLA3 to a reduction in tobacco stem flexural strength. These results indicate that the eucalypt FLA family contains diverse members, and particular members with single FAS domains that are functionally specialized for secondary cell wall growth and properties.

Measuring stiffness using acoustic tool for Scots pine breeding selection

Stiffness (modulus of elasticity, MOE) of conifer trees is the most important trait for structural wood products. Finding a fast, reliable and non-destructive way to measure MOE is a priority for screening large progeny trials in tree breeding programmes. For Scots pine, time-of-flight (TOF) velocity measured on standing trees accounted for 47% of the variation to the benchmark SilviScan-based clearwood MOE (MOEs), under the assumption of constant wood density. If wood density was included, 59% of the variation was accounted for. The TOF stiffness measurements on standing trees were, however, more related to the clearwood MOEs in the outerwood, and the prediction was the most reliable at breast height compared to the stem base and the top section. Microfibril angle (MFA) had higher correlation with acoustic velocity (VEL) of standing trees than wood density, and among the early, transition and latewood density, the latewood density had the highest correlation with stiffness measurements on standing trees. VEL measured at breast height in combination with wood density was the most reliable predictor of MOE of standing trees for selection and breeding in Scots pine.

Composition and structure of balsa (Ochroma pyramidale) wood

Balsa, with its low density and relatively high mechanical properties, is frequently used as the core in structural sandwich panels, in applications ranging from wind turbine blades to racing yachts. Here, both the cellular and cell wall structure of balsa are described, to enable multi-scale modeling and an improved understanding of its mechanical properties. The cellular structure consists of fibers (66–76 %), rays (20–25 %) and vessels (3–9 %). The density of balsa ranges from roughly 60 to 380 kg/m3; the large density variation derives largely from the fibers, which decrease in edge length and increase in wall thickness as the density increases. The increase in cell wall thickness is predominantly due to a thicker secondary S2 layer. Cellulose microfibrils in the S2 layer are highly aligned with the fiber axis, with a mean microfibril angle (MFA) of about 1.4°. The cellulose crystallites are about 3 nm in width and 20–30 nm in length. The degree of cellulose crystallinity appears to be between 80 and 90 %, considerably higher than previously reported for other woods. The outstanding mechanical properties of balsa wood in relation to its weight are likely explained by the low MFA and the high cellulose crystallinity.

Evaluation of Bast Fibres of the Stem of Carica papaya L. for Application as Reinforcing Material in Green Composites

Aims: The production of green composites based on natural fibres is rising with regard to increasing environmental problems and declining fossil raw materials. Bast fibres of papaya (Carica papaya L.) accumulate on plantations at a large scale but remain an unused resource. The characterisation of the bast allows a first evaluation of the potential of papaya-fibres for use in composites. Study Design: Material testing. Place and Duration of Study: Institute for Botany, Technische Universitat Dresden and Original Research Article Kempe et al.; ARRB, 6(4): 245-252, 2015; Article no.ARRB.2015.082 246 Fraunhofer Institute for Nondestructive Testing Dresden (IZFP-D), 2011 and 2013. Methodology: The anatomic structure of fibre cells and the microfibril angle of the cell walls were determined as well as a chemical analysis to determine the proportion of cellulose, lignin and hemicelluloses of the fibre cells. In addition, samples of fibres were subjected to static uniaxial tension tests revealing Young's modulus, tensile strength and breaking strain at different plant ages and of two origins. Results: Fibres of a two-year-old plant exhibited a Young's modulus of 10.7 GPa, a tensile strength of 101 MPa and a breaking strain of 1.2%, on average. Fibres from six-months-old plants, grown under greenhouse conditions had a mean Young's modulus of 4.4 GPa, tensile strength of 49 MPa and a breaking strain of 1.4%. Having one of the lowest fibre densities with ca. 0.85 g/cm3, papaya fibres exhibit noteworthy specific mechanical properties among all studied natural fibers. Conclusion: These data allow us a first estimation for a potentail use in green composites as reinforcing material.

Beyond tree-ring widths: stable isotopes sharpen the focus on climate responses of temperate forest trees.

[Extract] Tree rings provide an indispensable tool for assessing a tree's response to variability in its environment, oftentimes also pro¬viding a means of reconstructing that variability beyond instru¬mental records. The wood that trees produce is laid down sequentially, creating an archive of temporally ordered material that is rich in physiological and environmental information. This is made all the more useful because trees are globally distrib-uted, can live for thousands of years and in some cases remain intact long after they die. Tree-ring archives are used in a wide variety of studies, including, but not limited to, climate recon¬structions (Cook et al. 2010), archaeological dating of ruins (Cufar 2007), reconstructions of fire history and recurrence intervals (Swetnam et al. 1999), and assessments of tree physiological responses to drought (McDowell et al. 2010). The number of applications for tree rings has grown steadily in recent decades, and the variety of measurements that can be made on tree rings has grown as well (Speer 2010). The simplest measurement that can be made is in-series whole-ring widths. From this starting point, additional information can be gained from measuring early-wood and late-wood widths, wood density, elemental abundances, microfibril angles, radial diameters of xylem conduits and stable-isotope ratios of the organic material in tree rings. A tree-ring record based on a single sample from a tree is referred to as a series, whereas a composite of many series is referred to as a chronology.

Characterizing compression wood formed in radiata pine branches

The formation of reaction wood is an adaptive feature of trees in response to various mechanical forces. In gymnosperms, reaction wood consists of compression wood (CW) and opposite wood (OW) that are formed on the underside and upperside of bent trunks and branches. Although reaction wood formed in bent trunks has been extensively investigated, relatively little has been reported from conifer branches. In this study SilviScan® technology was used to characterize radiata pine branches at high resolution. Compared to OW formed in the branches, CW showed greater growth, darker colour, thicker tracheid walls, higher coarseness, larger microfibril angle (MFA), higher wood density, lower extensional stiffness and smaller internal specific surface area. However, tracheids of CW were similar to those of OW in their radial and tangential diameters. These results indicated that gravity influenced tracheid cell division and secondary wall formation but had limited impact on primary wall expansion. Furthermore, seasonal patterns of CW formation were not observed in the branches from cambial age 4 while earlywood and latewood were clearly separated in all rings of OW. The marked change of MFA during reaction wood formation suggested that branches could be ideal materials for further study of cellulose microfibril orientation.

Investigation of microstructure and tensile properties of porous natural coir fibre for use in composite materials

Natural coir fibres are studied for use as reinforcement in composite materials. In order to efficiently use the fibres and understand the composite properties, the microstructure and the mechanical properties of coir fibres are investigated in this study. X-ray microtomography in SEM (SEM-CT) and SEM image analysis are used to examine the fibre internal structure including the organisation of elementary fibres, microfibril angles and fibre porosity. Mechanical properties of coir fibres are determined by performing fibre tensile tests, in which an integrated optical strain mapping system is used to define fibre strain for producing more reliable values of E-modulus and strain at failure. The results show that technical coir fibres comprise plenty of elementary fibres and a lacuna at the centre. The elementary fibre is built up by two main cell walls which consist of bundles of microfibrils with a large misorientation with respect to the elementary fibre axis. Coir fibres appear to have a high porosity of 22 to 30%. The high microfibrillar angle in the coir fibres leads to the low stiffness in fibre direction and to high elongation to failure thanks to reorientation of the microfibrils under tensile loading.

Stem damage of lodgepole pine clonal cuttings in relation to wood and fiber traits, acoustic velocity, and spiral grain

Eight clones from a 16-year-old field trial of clonal cuttings of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) were analyzed for growth, growth pattern, and stem damage in the field. In addition, wood and fiber traits (acoustic velocity [AcVel] and spiral grain) were analyzed and wood density, microfibril angle, modulus of elasticity, and radial fiber diameter (FibDR) determined from SilviScan analyzes. Two clones with considerably more bent, broken, and leaning stems differed from the other clones in terms of microfibril angle and modulus of elasticity (MOE) in the outermost annual rings. FibDR and, to some extent, MOE in the outermost annual rings were negatively correlated with the frequency of bent, leaning, or broken stems, while microfibril angle (MFA) was positively correlated. AcVel was negatively correlated with both MFA and the frequency of bent, broken, and leaning stems. We conclude that AcVel could be used as an effective tool to predict severe stem damage and determine stem strength in the field instead of using costly lab-based SilviScan measurements of microfibril angle. If developed further, this approach could be used for large-scale screening of progeny tests when selecting for stem strength.

The S3 layer isolated from carboxymethylated cellulose wood fibers

The innermost S3 layer is isolated from highly swollen, carboxymethylated cellulose wood fibers (CMF). The isolation is attempted by applying gentle magnetic stirring, ultrasonication, and acid hydrolysis, where each treatment has caused the formation of largely variable fiber morphologies. The S3 layer can be partially or completely isolated from CMF by applying gentle shear or a mild acid hydrolysis. The S3 layer isolated from CMF is highly swollen with a volume 5–10 times its original value, and has microfibril angles between 50° and 90°. Surface carboxylates on the S3 microfibrils are available for further chemical modifications. Dominant right handedness is observed from 3D reconstructed confocal microscopic images. When air-dried from water, the S3 layer collapses completely onto the substrate, giving an average layer thickness of 83–140 nm.