Measurement Of Microfibril Angle Research Articles

Measurement of microfibril angle in plant fibres: Comparison between X-ray diffraction, second harmonic generation and transmission ellipsometry microscopies

The orientation of cellulose microfibrils within plant fibres is one of the main factors influencing their mechanical properties. As plant fibres are more and more used as reinforcement for agro-composites, their mechanical properties have a strong influence on the final composite properties. It is, therefore, of interest to obtain reliable information about the microfibril angle (MFA) to better support the choice of fibres depending on the product requirements. In the present study, the reliability and specificities of three non-destructive methods that allow analysis on the same fibre glued on a holder; X-ray diffraction (XRD), second harmonic generation (SHG) and transmission ellipsometry (TE) microscopy; are investigated. Three types of plant fibres, with both low (nettle), and high (cotton, sisal) MFA values, are compared and their geometry and biochemical composition are characterised. The results obtained on the same fibre confirm that MFA analysis remains tedious and that despite their limitations, the methods are complementary depending on the information requested. Indeed, SHG is recommended for direct, qualitative and plane-selective mapping of heterogeneities in macrofibril orientations at various depths. However, reliable quantitative results with SHG depend on the initial image quality and could benefit from further image processing refinement. On the contrary, XRD and TE measure MFAs over the entire fibre thickness and provide variations along the fibres if a sufficient optical/spatial resolution is reached. Regarding the characterization of intrinsic defects in plant fibres, both SHG and TE suffer from uncertainties induced by the disorganization of the microfibril network and the lack of symmetry between the front and back fibre walls. Finally, all techniques prove to be dependant on the initial fibre alignment and geometry (i.e. twisting, double fibre configuration or form factor) which vary along the fibre length and should be carefully taken into account.

Measurement of Microfibril Angle Using X-Ray Diffraction and Light Microscope on 5-year-old Super and Conventional Teak Wood

The long harvest time causes the processing industry manufactured from teak wood (Tectona grandis L. f.) has experienced a lot of declines. To overcome this problem, currently, in Indonesia many types of fast-growing teak have been developed, one of which is Jati Unggul Nusantara (JUN). Trees that are accelerated in growth, are likely to cause changes in their anatomical structure. The anatomical structure of wood is one of the basic properties that greatly influences the use of wood as a raw material. Even small changes in cell shape and size can change the properties of wood as a raw material. One of the anatomical structures of wood, namely the ultramicroscopic structure that affects the quality of wood, is the microfibril angle (MFA). The purpose of this study is to determine the MFA of JUN at the planned cutting age of 5 years, compared to conventional teak at the same age. There are two methods used, namely using X-Ray Diffraction (XRD) and measuring the elongation of the pit apertures slope of the fiber cells using a light microscope, which was obtained from the maceration process. As a result, JUN's MFA is 22.09°, smaller than the conventional teak of 25.29°. This is because JUN was developed from top cuttings so although still young, it already reflects the characteristics of mature teak. The results of the MFA measurements on JUN using two methods (XRD and light microscope), resulted different values. It is different from the MFA measurement results on conventional teak. It is recommended to measure the MFA in JUN wood by using XRD, because possibly, due to accelerated growth, simple pits with an oval shape turn into circular. This difference causes the results of the JUN MFA measurement using a light microscope based on the pit apertures slope to be inconsistent, subjective, and different results in other pits contained in the fiber even though they are closely associated. However, in conventional teak, measurements using a light microscope are possible because the shape of the pit is oval so that the slope of the elongation of the pit aperture can be determined easily, and is more consistent with more uniform values in the same individual fiber

The spatial modulation of microfibril angle in the woody tissue of maturing tree stems studied with synchrotron radiation

Spatial variations in the microfibril angle (MFA) of cellulose are mapped on individual radial sections of wood from the maturing stems of Australian tree species (Acacia floribunda, Acacia suaveolens, Acacia doratoxylon, Acacia havilandiorum, Brachychiton populneus and Bertya cunninghamii) from different rainfall and soil nutrient availabilities using synchrotron wide angle X-ray scattering. For the three species with the smallest radial variation there is a clear linear relationship between the MFA with Young’s modulus and wood density with data published previously for these samples. The other three samples show a large radially symmetric variation in MFA across the radial section either having a continuous change from large MFA in the stem’s centre to small value close to the bark or the reverse, small MFA at the centre to larger values close to the bark. For these samples, a strong linear correlation between the Young’s modulus and density and the MFA is not apparent. We conclude that spatially localised measurements of MFA provide an important insight in the adaptation of wood tissue to environmental conditions.

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.

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.

Microfibril angle of Eucalyptus grandis wood in relation to the cambial age

The microfibril angle (MFA) of wood is an important feature, which helps to explain the physical and mechanical behaviour of wood in use. It has been little investigated for wood produced in Brazil, mainly for mature trees. Thus, the objective of this study was to analyze the MFA of Eucalyptus grandis at age 25 years in relation to the cambial age. One disk was cut from the base of the stem from each of three trees, where growth rings were marked. From a central strip 3,0 cm wide, 1 cm3 blocks were removed from each growth ring. After sectioned on the tangential face with a sliding microtome, sections of 8 μm thick were macerated. The individual fibres were observed by polarized light microscopy for measurement of MFA. According to the results, i) the MFA decreased from 29,3° (ring no 1) to 18,9° (ring no 25); ii) MFA can be estimated by the cambial age – a, according to the equation MFA = 28,1 – 0,35 × a, with R2 = 94,7%.

Evaluating growth strain of Eucalyptus globulus Labill. from SilviScan measurements

Abstract Longitudinal surface strain was measured or estimated using three different methods along the stems of nine trees of 10-year-old Eucalyptus globulus Labill. Wood samples were collected close to the location where the strain was measured or estimated. Microfibril angle (MFA), cellulose crystallite width (Wcryst), microdensity and Young's modulus along the grain (EL) were determined using the SilviScan-2 technology at high spatial resolution. Relationships of measured strain and estimated strain to wood properties were established. The quality of the relationships depends on a particular wood property. Strain was more closely related to mean Wcryst than to any other wood properties. Its relationship with MFA was the next closest. Based on the results of regression analysis, we propose that Wcryst may be suitable for the prediction of surface strain at a moderate level of reliability. Adding measurement of MFA, microdensity and EL does not significantly improve the prediction quality. The strain measurement method also affects the results. The best relationships were obtained with longitudinal displacement measured by the CIRAD method. Strain measured by the strain gauge method gave weak relationships, possibly owing to variation in the cambium age of the specimens.

Cellulose microfibril angle in the cell wall of wood fibres.

The term microfibril angle (MFA) in wood science refers to the angle between the direction of the helical windings of cellulose microfibrils in the secondary cell wall of fibres and tracheids and the long axis of cell. Technologically, it is usually applied to the orientation of cellulose microfibrils in the S2 layer that makes up the greatest proportion of the wall thickness, since it is this which most affects the physical properties of wood. This review describes the organisation of the cellulose component of the secondary wall of fibres and tracheids and the various methods that have been used for the measurement of MFA. It considers the variation of MFA within the tree and the biological reason for the large differences found between juvenile (or core) wood and mature (or outer) wood. The ability of the tree to vary MFA in response to environmental stress, particularly in reaction wood, is also described. Differences in MFA have a profound effect on the properties of wood, in particular its stiffness. The large MFA in juvenile wood confers low stiffness and gives the sapling the flexibility it needs to survive high winds without breaking. It also means, however, that timber containing a high proportion of juvenile wood is unsuitable for use as high-grade structural timber. This fact has taken on increasing importance in view of the trend in forestry towards short rotation cropping of fast grown species. These trees at harvest may contain 50% or more of timber with low stiffness and therefore, low economic value. Although they are presently grown mainly for pulp, pressure for increased timber production means that ways will be sought to improve the quality of their timber by reducing juvenile wood MFA. The mechanism by which the orientation of microfibril deposition is controlled is still a matter of debate. However, the application of molecular techniques is likely to enable modification of this process. The extent to which these techniques should be used to improve timber quality by reducing MFA in juvenile wood is, however, uncertain, since care must be taken to avoid compromising the safety of the tree.