Analysis of morphological variations of flax fibre bundles by Fraunhofer diffraction

Abstract

The increasing use of plant fibres in industrial applications requires a better understanding of their morphologies. Experimental observations have shown that these fibres are characterized by a complex geometry which could affect their mechanical behaviour. Indeed, it is well known that the size and shape of plant fibres cross-section vary from bundle to bundle and along their length. In this study, the technique of Fraunhofer diffraction was used to characterize this morphological heterogeneity of flax fibre bundles. The analysis of the results showed a large scattering of the cross-section area (CSA). Lengthwise morphological variations of the bundles were examined and reveal that the CSA varies by a factor of 3.4 over a length of 75 mm. It also appears that the cross-section shape of flax fibre bundle can be better approximated by an elliptical model than by a circular model. The ratio between the maximum and minimum cross-section shape factor was found to be approximately 2 over a length of 75 mm. Moreover, the occurrence of cross-section rotations has been shown in case of fibre bundles, i.e., the orientation of the major-axis of the ellipse corresponding to the cross-section may be different from one point to another, causing sometimes visible twists along the bundle. These different results allowed us to build a numerical 3D volume considering the evolution of flax fibre bundles outer contour.