Microfibril Angle Research Articles

Genetic analysis of fiber dimensions and their correlation with stem diameter and solid-wood properties in Norway spruce

Adverse genetic correlations between growth traits and solid-wood, as well as fiber traits are a concern in conifer breeding programs. To evaluate the impact of selection for growth and solid-wood properties on fiber dimensions, we investigated the inheritance and efficiency of early selection for different wood-fiber traits and their correlations with stem diameter, wood density, modulus of elasticity (MOE), and microfibril angle (MFA) in Norway spruce (Picea abies L). The study was based on two large open-pollinated progeny trials established in southern Sweden in 1990 with material from 524 families comprising 5618 trees. Two increment cores were sampled from each tree. Radial variations from pith to bark were determined for rings 3–15 with SilviScan for fiber widths in the radial (RFW) and tangential (TFW) direction, fiber wall thickness (FWT), and fiber coarseness (FC). Fiber length (FL) was determined for rings 8–11. Heritabilities based on rings 8–11 using joint-site data were moderate to high (0.24–0.51) for all fiber-dimension traits. Heritabilities based on stem cross-sectional averages varied from 0.34 to 0.48 and reached a plateau at rings 6–9. The “age-age” genetic correlations for RFW, TFW, FWT, and FC cross-sectional averages at a particular age with cross-sectional averages at ring 15 reached 0.9 at rings 4–7. Our results indicated a moderate to high positive genetic correlation for density and MOE with FC and FWT, moderate and negative with RFW, and low with TFW and FL. Comparison of several selection scenarios indicated that the highest profitability is reached when diameter and MOE are considered jointly, in which case, the effect on any fiber dimension is negligible. Early selection was highly efficient from ring 5 for RFW and from rings 8–10 for TFW, FWT, and FC.

Analysis on Wood Quality, Geometry Factor, and Their Effects on Lathe Check of Samama (Anthocephalus macrophyllus) Veneer

Relatively little information is available regarding the correlation between wood and veneer quality, especially for Samama wood, an endemic wood species in eastern Indonesia. This study addresses the quality of 8 years old Samama wood and its effect on the veneer quality. Samama wood quality was determined by evaluating its specific gravity, moisture content, fiber dimensions, and microfibril angle from pith toward bark. Meanwhile, veneer quality was assessed by examining veneer thickness and lathe check characteristics. Geometry factor model was constructed to elaborate the quantities of lathe check from pith toward bark. Results show that fair variations of veneer thickness, ranging from 1.5 mm to 3.0 mm, could be obtained from Samama wood. The quantity, depth, and length of lathe check were noticeably decreasing toward bark. Further, in the same manufacturing process, geometry factor was determined as the dominant factor over other wood properties in affecting the frequency of lathe checks from pith towards bark. These facts should be put into consideration in producing veneer from Samama wood. Moreover, these results enlighten the potential of Samama wood as plywood and other excellent veneer-based products.

Measurement of microfibril angles in bamboo using Mueller matrix imaging.

The microfibril angle (MFA) giving the orientation of cellulose chains in hard sclerenchymatous bamboo fibers is one of the most important parameters determining the overall strength of the bamboo culm. In this work, Mueller matrix imaging polarimetry is implemented for determining MFA measured over a transverse section of group of fibers and parenchyma cells in bamboo of Dendrocalamus strictus species. The method, based on the Stokes-Mueller formalism, decouples the birefringence exhibited by crystalline cellulose from the clumped polarization parameters using 16 images taken with different polarization states at subcellular resolution. Retardance values, obtained from polar decomposition of the Mueller matrix, are extracted from different locations in the specimen, and distribution of MFA over the entire section is presented. The method permits simultaneous measurement of MFA in a transverse section of several fibers and parenchyma cells. The range of MFA obtained for bamboo fibers from Mueller matrix imaging is verified with the results obtained through x-ray diffraction using the pole figure method.

Erratum to: The effect of juvenility and veneer thickness on bending strength of Douglas-fir laminated veneer lumber

Most of wood industry requires well conformed logs and middle diameter trees to optimize primary processing yields. The raw material, mostly coming from monoculture plantations, contains a considerable proportion of juvenile wood. The objectives of present study were to identify the transition ring between juvenile and mature wood in Douglas-fir and to analyze the effect of juvenility and veneer thickness on bending strength of Douglas-fir laminated veneer lumber (LVL). Microfibril angle (MFA) and tracheid length from five Douglas-fir logs were measured from pith to bark. Veneers peeled with an instrumented lathe to produce LVL. Total of 140 LVL samples were mechanically characterized by measuring modulus of elasticity (MOE) and modulus of rupture (MOR). The results showed that transition rings from juvenile to mature wood at breast height, according to MFA and tracheid length, were at twentieth and twenty-first, respectively. According to analysis of variance, there was a significant effect of juvenility on LVL bending strength. The advantage of using veneers of mature compare to juvenile wood for LVL was due to an improvement of bending strength in the range of 7–22 %. LVL made of 3 mm veneers has lower stiffness (2.2 %) compare to LVL made of 5.25 mm veneers. High correlation between static and dynamic MOE was noted.

Identification of polymer matrix yield stress in the wood cell wall based on micropillar compression and micromechanical modelling

Based on a combination of micropillar compression experiments and modelling of the secondary cell wall (cw) using continuum micromechanics, the shear yield stress of the polymer matrix is identified for both normal and compression wood of Norway spruce. It is shown that the model is able to capture the differences in mechanical properties between the two tissues based on the knowledge of composition of the samples, microfibril angle, as well as phase properties on the nanometer scale. By testing an isolated piece of the cell wall with a homogeneous and uniaxial stress field on the micrometer scale and using the micromechanical model to determine average stress fields on the nanometer scale, it is possible to identify the shear yield stress of the polymer matrix in wood, which was found to be in the range of 14.9–17.5 MPa for normal and compression wood. It was shown that this corresponds to a stress in the lignin phase of approx. 17 MPa. This combined study thus demonstrates a new approach for validating multiscale models predicting yield properties with uniaxial experiments at the microscale and measuring phase properties of inhomogeneous materials by a combination of modelling and experimental approaches.

Quantifying size-dependent developmental trajectories of commercial-relevant fibre attributes within maturing black spruce plantations employing hierarchical linear models

The primary objective of this study was to quantitatively describe size-dependent developmental trajectories of commercially-relevant fibre attributes within maturing black spruce (Picea marina (Mill.) B.S.P.) plantations employing hierarchical linear models. A stratified random sample design was deployed within 5 density-stressed semi-mature plantations to obtain transverse breast-height radial xylem sequences from 47 trees representing 5 basal area size classes (quintiles). The cumulative annual ring-area-weighted moving average proceeding from the pith to the ith cambial age was calculated for density, microfibril angle, modulus of elasticity, fibre coarseness, tracheid wall thickness, tracheid dimensions (radial and tangential diameters) and specific surface area. Hierarchical linear regression models were used to quantify size-dependent effects on these developmental trajectories: (1) at the first hierarchical level, compound exponential models were specified following the assessment of a set of candidate functional forms; and (2) given (1), at the second hierarchical level, linear model specifications under fixed and random error structures were used to account for potential size-dependent effects on the first-level parameter estimates. In order to ensure statistically valid inferences regarding size-dependence by employing radial sequences devoid of serial correlation, and provide an independent data set for evaluating the parameterized models in terms of goodness-of-fit, lack-of-fit and predictive ability, the data set consisting of 1566 observations per attribute was systematically stratified into parameterization and valuation subsets. The results revealed that the parameters of the Hoerl-based compound exponential model varied by tree-size indicating the presence of significant (p⩽0.05) size-dependence in fibre attribute developmental trajectories. Statistical measures of model performance and associated graphical analysis of the final specifications indicated that the models performed well in terms of accounting for a relatively large proportion of variation (61–88%), unbiasedness and predictive ability (e.g., temporal invariant patterns in absolute and relative prediction errors). These results and related inferences demonstrated the utility of quantifying size-dependent fibre developmental trajectories employing hierarchical linear models.

A 3D micromechanical study of hygroscopic coiling deformation in Pelargonium seed: from material and mechanics perspective

The awned seeds of the family Geraniaceae are special seed-dispersal units. The awns can generate periodic coiling and uncoiling movement through interaction with the diurnal humidity cycle. To investigate how this natural actuator acquires the remarkable property, we determined the three-dimensional morphological features of the coiling awns of Pelargonium peltatum through X-ray microtomography (micro-CT). Many streaks with sharp corners were found distributed in the surface of the inner layer cells, indicating there are two different microfibril angles (MFAs) in the special tilted helix structure of each one cellulose fiber within the cell wall. A simplified mechanical model of the cell wall was developed. Moreover, finite element method was conducted based on the proposed model to analyze the basic mechanism of the coiling deformation. The results showed that stiff cellulose fibers with special tilted helix structures could direct the shrinkage forces resulted from the matrix, so as to generate torsional and bending movement simultaneously. Therefore, the inner layer cell could generate an anti-clockwise coiling deformation macroscopically. In addition, effects of other structural factors including fiber frequency of the cellulose fiber skeletons, modulus ratios between the fibers and matrix, and macroscopical combination among the cells on the degree of the coiling deformation were also studied. The results determined in this work may benefit the development of new kind of intelligent composites.

Variation in the Microfibril Angles in Resonance and Non-Resonance Spruce Wood (Picea abies [L.] Karst.)

Variation in microfibril angle (MFA) in the S2 of the tangent cell walls of resonance and non-resonance spruce wood (Picea abies [L.] Karst.) used in the manufacture of musical instruments was studied. MFA was measured directly after preliminary visualisation of microfibrils in the cell walls. In the tested samples the position of an annual ring in the samples had no significant influence on the MFA. In the resonance wood, MFA values were between two and three times smaller than in the non-resonance wood. In the resonance wood, the differences in the MFA between earlywood and latewood were smaller, and the MFA fluctuations were also smaller.

Mechanical properties of bamboo fiber cell walls during the culm development by nanoindentation

Bamboo fibers have excellent mechanical properties, and as such are a popular raw material in papermaking, textile, and various high-tech industries. In this study, the longitudinal mechanical properties of Moso bamboo (Phyllostachys Heterocycla Var. Pubescens) fiber cell walls during development were systematically investigated via nano-indentation technique at the sub-cellular level. Several influencing factors were also analyzed, particularly the effects of different locations within the vascular bundle and age. The results showed that the longitudinal nano-indentationmodulus (NI modulus) of the 1-month-old bamboo fiber cell walls was relatively high and changed very little in different locations of the vascular bundle, only fluctuating near 22GPa, while that at the interface between fibers and parenchyma cells (i.e., the edge of the vascular bundle) was smaller and less stable (15.61GPa on average); nano-indentation hardness (NI hardness) decreased from the center of the vascular bundle to the outside, ranging between 0.4665 and 0.5603GPa. Age had no significant effect on NI modulus from 1 month to 36 months, while NI hardness did increase with age (p<0.05), showing mean values of 0.5452–0.6142GPa across the samples. Our observations of longitudinal NI modulus and hardness were mainly affected by the microfibril angles and lignin content, respectively. These results may provide mechanical evidence for bamboo growth and lignin deposition, and also provide a scientific basis for the successful utilization of bamboo fibers.

Ecogeographic variation in black spruce wood properties across Quebec’s boreal forest

Ecogeographic variation in black spruce clear wood properties was investigated for the two main vegetation types of the managed boreal forest of the province of Quebec, Canada. In total, 409 co-dominant and dominant trees from 82 mature stands were sampled. Basic wood density, modulus of elasticity and microfibril angle were measured using SilviScan. Mature fiber length was determined using a high-resolution Fiber Quality Analyzer. Wood growing in pure black spruce stands had longer mature fibers, a significantly denser wood with better mechanical characteristics than the wood growing in mixed stands with balsam fir. All wood properties were clearly influenced by radial growth and species composition.Given the limited number of sample plots for mapping purposes, a two-stage modeling approach was assessed to predict stand-level estimates of black spruce clear wood properties. This scaling-up method, based on field measurements and ring data from 3350 inventory plots, has improved the performance of all models. Stand-level models explained 47%, 57%, 63% and 63% of variance in wood density, modulus of elasticity, microfibril angle and mature fiber length respectively with estimated root mean square errors of 8.9kg/m3, 0.52GPa, 0.60° and 0.06mm.An east-west gradient in black spruce clear wood properties was revealed as possibly the by-product of the change in relative proportions of both studied vegetation types across the study area. The results indicate that the black spruce wood from western regions of the managed boreal forest has a better potential for producing pulp and paper, lumber or engineered products due to its longer mature fibers and higher mechanical properties.

Micro–macro mechanical relations in Palmetto wood by numerical homogenisation

In this paper we investigate micro–macro mechanical relations in Palmetto wood, a natural composite, by means of a computational homogenisation-based multi-scale modeling approach. The homogenisation procedure is solved sequentially at multiple length scales by following a bottom-up approach. The proposed strategy consists of homogenising the three length-scales by means of representative volume elements of material. The resulting effective macroscopic properties allow us to compute the mechanical response of individual macro-fibres and bulk wood specimens by means of a standard finite element procedure. The numerical predictions are compared successfully with experimental measurements. Following the validation, a parametric study is performed to investigate the micro–macro relations in Palmetto wood. The influence of several micro-structural features present at different length scales are investigated, such as the cellulose content and its crystallinity, the microfibril angle, the cell-wall thickness of micro-fibres, and the porosity of macro-fibres and their surrounding matrix, among others. The effects of such microscopic parameters are investigated on the Young’s modulus and density of Palmetto bulk wood. These results show that the present strategy can pave the way for further studies on complex microstructure–property relationships existing in different wood species, and on the possible development of more advanced bio-inspired composite materials.

Anatomical characteristics, microfibril angle and micromechanical properties of cottonwood (Populus deltoides) and its hybrids

Samples were prepared using stem xylem from cottonwood (Populus deltoides) and two cottonwood hybrids (P. deltoides × Populus maximowiczii and P. deltoides × Populus trichocarpa), which grew in Tennessee, United States. The anatomical characteristics, microfibril angle, and mechanical properties of the cell wall in juvenile wood (two-year-old) were investigated by means of microscopy image analysis system, X-ray diffraction, and nanoindentation (NI). The results showed that the double-wall thickness of the fiber cells in the hybrid poplars was thicker than that of the pure poplar, and the ratio of wall to lumen of fiber cell (0.40) of the P. deltoides × P. trichocarpa, which had the slowest growth rate, reached the greatest value among the three poplar clones. Their microfibril angles (MFA) of the cell wall in the investigated samples ranged between 11.5° and 16.7°, and they correlated positively with growth rates of the three poplar clones. The average hardness and reduced elastic modulus were 0.25 GPa and 8.58 GPa for P. deltoides, 0.28 GPa and 8.34 GPa for P. deltoides × P. maximowiczii, and 0.31 GPa and 12.2 GPa for P. deltoides × P. trichocarpa, respectively. P. deltoides × P. trichocarpa with the slowest growth rate had the greatest micromechanical values among the three poplar clones. In combination with growth characteristics of the three poplar clones, the findings of the analyses on their wood properties provided information-rich data that not only could describe juvenile wood properties but also could be used in selective breeding for the three poplar clones in Tennessee, USA.

IDENTIFICATION AND CHARACTERISATION OF DOUGLAS-FIR (PSEUDOTSUGA MENZIESII (MIRB.) FRANCO) JUVENILE AND ADULT WOOD GROWN IN SOUTHERN GERMANY

More than one-third of Germany s Douglas-fir resources, stock in age-classes from twenty-one to fifty-nine years. As such timber increasingly enters markets, detailed knowledge of the anatomy and properties of its wood is of importance to forest managers and wood processors. Anatomical and mechanical wood analyses in this study were carried out on twenty trees from four scientifically managed plantations in Southern Germany. The age of the trees selected was forty-two years whereby varying growth conditions were considered. Juvenile and adult woods were identified by segmented linear regression of radial profiles of anatomical characteristics, such as latewood percentage, tracheid wall thickness microfibril angle and density. Additionally, the width of earlywood, latewood and growth rings as well as bending modulus of elasticity were determined. Variance was dependent on the trait used for differentiation, j uvenile wood comprised of an eleven to thirty-one growth rings resp. radial amounts of fifteen to sixty-five percent. When compared to adult wood, juvenile wood showed corresponding features of approximately thirty percent wider growth rings, th irty four percent lower latewood percentage, fourteen percent thinner tracheid walls, and eighty percent larger microfibril angles, eleven percent lighter wood and fifty -seven percent lower bending modulus of elasticity. As the assortment features fast grown trees, adult heartwood characteristics were slightly inferior to the characteristics of European Douglas-fir.

Physicochemical properties of new cellulosic Artisdita hystrix leaf fiber

ABSTRACTThe characterization of new natural fiber is increasing due to its excellent properties. This drives investigators to create high performance composites. The present investigation was designed to study the physicochemical properties of fibers obtained from the leaf of the Artistida hystrix. The Artistida hystrix fibers (AHFs) had crystallinity index (44.85%), cellulose (59.54 wt%), hemicellulose (11.35 wt%), lignin (8.42 wt%), and density (540 kg m−3). The tensile strength of AHFs was 440 ± 13.4 MPa with an average strain rate of 1.57 ± 0.04%. The calculated microfibril angle of AHFs was 12.64 ± 0.45°, which influenced the mechanical properties.

Genetic variation in growth and wood-quality traits of Corymbia citriodora subsp. variegata across three sites in south-east Queensland, Australia

Ten growth or wood-quality traits were assessed in three nearby Corymbia citriodora subsp. variegata (CCV) open-pollinated family-within-provenance trials (18 provenances represented by a total of 374 families) to provide information for the development of a breeding program targeting both pulp and solid-wood products. Growth traits (diameter at breast high over bark [DBH], height and conical volume) were assessed at 3 and 7 years of age. Wood-quality traits (density [DEN], Kraft pulp yield [KPY], modulus of elasticity [MoE] and microfibril angle [MfA]) were predicted using near-infrared spectroscopy on wood samples collected from these trials when aged between 10 and 12 years. The high average KPY, DEN and MoE, and low average MfA observed indicates CCV is very suitable for both pulp and timber products. All traits were under moderate to strong genetic control. In across- trials analyses, high (>0.4) heritability estimates were observed for height, DEN, MoE and MfA, while moderate heritability estimates (0.24 to 0.34) were observed for DBH, volume and KPY. Most traits showed very low levels of genotype × site interaction. Estimated age–age genetic correlations for growth traits were strong at both the family (0.97) and provenance (0.99) levels. Relationships among traits (additive genetic correlation estimates) were favourable, with strong and positive estimates between growth traits (0.84 to 0.98), moderate and positive values between growth and wood-quality traits (0.32 to 0.68), moderate and positive between KPY and MoE (0.64), and high and positive between DEN and MoE (0.82). However, negative (but favourable) correlations were detected between MfA and all other evaluated traits (−0.31 to −0.96). The genetic correlation between the same trait expressed on two different sites, at family level, ranged from 0.24 to 0.42 for growth traits, and from 0.29 to 0.53 for wood traits. Therefore simultaneous genetic improvement of growth and wood property traits in CCV for the target environment in south-east Queensland should be possible, given the moderate to high estimates of heritability and favourable correlations amongst all traits studied, unless genotype × site interactions are greater than was evident.

Radial and between-family variations of the microfibril angle and the relationships with bending properties in Picea jezoensis families

ABSTRACTWith emphasis on tree breeding for wood quality in Picea jezoensis, we aimed to evaluate radial and between-family variations in the microfibril angle (MFA) of the S2 layer in the latewood tracheids in 10 open-pollinated families of 43-year-old P. jezoensis trees. In addition, the relationships between MFA/wood density with the modulus of elasticity (MOE) or modulus of rupture (MOR) were investigated. Significant differences in MFA between families were found from the pith toward the bark. MFA showed higher values around the pith area, although some families showed relatively lower values than others around this area. In addition, due to a larger coefficient of variations of MFA near the pith, the potential for juvenile wood MFA improvement may be greater compared with mature wood. MOE was correlated with MFA in juvenile wood and with wood density in mature wood, whereas MOR was mainly correlated with wood density at radial positions in both woods. Therefore, to improve the MOE and MOR of P. jezoensis wood, both MFA and wood density would be factors to consider in both juvenile and mature woods. On the other hand, there are indications that, only wood density would be an important criterion for improving mature wood properties.

Effects of application of trans-zeatin on tracheid differentiation in mature sugi (Cryptomeria japonica) trees

The mechanism of differentiation of tracheid (earlywood or latewood) should be elucidated to improve the wood properties of sugi trees (Cryptomeria japonica). Water deficit affects tracheid differentiation in conifers. However, the signals, which transmit the information of water contents in the soil to the differentiating tracheid, remain unknown. Plant responses with deficits of macronutrients or water showed some differences but also similarities, mostly involving hormonal long-distance signaling. In Arabidopsis, trans-zeatin (tZ)-type cytokinins play a role as a root-to-shoot acropetal signal. In this study, we report the effects of applying tZ alone or in combination with other phytohormones on tracheid differentiation in mature sugi trees forming latewood. The application of tZ induced the formation of earlywood-type tracheids with significantly smaller cell wall ratios and larger microfibril angles than those of controls in July, August and September. The application of indole acetic acid (IAA) in combination with tZ inhibited the effects of applied tZ, although gibberellic acid (GA3) did not. In October and November, application of tZ could not affect the xylem formation or dormancy of cambium. We hypothesized that tZ might play a role in the differentiation of earlywood tracheid.

Variation in physical and mechanical properties from three drought tolerant Eucalyptus species grown on the dry west coast of Southern Africa

Southern Africa, and specifically its western parts is dominated by low rainfall areas, and it is expected that the rainfall in most of these parts will in future decrease further due to climate change. Woodlots of fast-growing, non-invasive tree species can provide the opportunity to produce wood and release the pressure on natural woodlands, while creating much needed income to inhabitants. Over the last two decades several trials of Eucalyptus species that could potentially withstand arid conditions were established on the South African west coast. The three most promising genotypes according to their volume growth were selected among 46 pure and hybrid species from two 20-year-old trials for further evaluation. These included 10 Eucalyptus grandis × Eucalyptus camaldulensis hybrid trees, 9 Eucalyptus gomphocephala trees, and 9 Eucalyptus cladocalyx trees for a total of 28 trees. The objective of the study reported here was to investigate the within-tree and between species variability of selected physical and processing properties determining the suitability of these three species for lumber production. The density, microfibril angle, spiral grain angle, MOE, MOR, radial and tangential shrinkage, twist, bow, splitting, and collapse were measured in a radial and longitudinal gradient. Valuable insights were gained which could provide decision support for planting, processing and further research on these species when grown in arid conditions. The E. grandis × camaldulensis hybrid was inferior in terms of most relevant properties to the other two species evaluated. The main shortcoming of both E. gomphocephala and E. cladocalyx was the high levels of twist in lumber.

Micromechanical modeling of the wood cell wall considering moisture absorption

Abstract This paper constructs a micromechanical framework to study the modulus loss of the wood cell wall induced by moisture absorption. The wood cell wall is modeled as an infinite matrix containing circular cylindrical inhomogeneity. The matrix, composed of hemicellulose and lignin, can uptake large amounts of water and as a result cause remarkable modulus loss below fiber saturation point. Considering the swelling strain distributed in the matrix rather than in the inhomogeneity, two sub-problems are constructed. One is an equivalent eigenstrain problem where the eigenstrain is distributed in the inhomogeneity, and another is a uniform swelling strain distributed in both matrix and inhomogeneity. The modulus loss of the matrix is treated as a damage process that correlates with the moisture content. Based on the Mori-Tanaka method, the proposed micromechanical framework is employed to predict the effective stiffness of the wood cell wall under different moisture contents. Theoretical predictions of the tensile modulus under different microfibril angles (MFAs) and moisture contents agree well with available experimental results.

Analysis of creep and modulus loss of the wood cell wall

This paper proposes a nonlinear constitutive model for the wood cell wall based on the nonequilibrium thermodynamics. The wood cell wall is modeled as a long fiber-reinforced composite with cellulose microfibril enclosed by hemicellulose and lignin. An internal variable is introduced into the Helmholtz free energy of the cell wall system, to describe the modulus loss of hemicellulose due to moisture absorption. The viscoelastic behavior of the wood cell wall changes with its moisture content, which leads to different creep evolutions even under the same loading level. To account for this phenomenon, another internal variable is introduced to depict the creep behavior of the wood cell wall, which is correlated with the irreversible energy dissipation processes such as stick–slip mechanism in the wood cell wall. Based on five elastic coefficients of transverse isotropy predicted by the present model, the creep behaviors of the wood cell wall with different microfibril angles are theoretically analyzed and show good agreements with experiment results.