Relationships between micro-fibrillar angle, mechanical properties and biochemical composition of flax fibers

An elementary plant fiber could be assimilated to a laminate, mainly constituted of the secondary wall S2 layer, made of a few non-crystalline polysaccharides reinforced by cellulose fibrils organized in a helix, with a microfibrillar angle (MFA) around 10° relative to the longitudinal fiber axis. This paper investigates the relationships between the MFA, the mechanical properties and the biochemical composition of different varieties of flax. To conduct this study, tensile tests on elementary flax fibers, X-ray diffraction, and solvent extractions have been carried out. Within the different varieties of flax, Young's modulus was found to be negatively correlated with the MFA. The results showed that the ratio between hemicelluloses (matter extracted with alkali) and pectins (hydrolyzed with acids) is highly correlated with the tensile properties; concurrently, we showed the great influence of pectic acids on the fiber’ Young's modulus, and on the orientation of the microfibrils.

► The microfibrillar angle of flax fibers was obtained by X-ray diffraction.
► Lower is the micro fibrillar angle, higher is the Young's modulus.
► The amount of coating and matrix polymers is correlated with tensile properties.
► Pectic acids have a structuring role and influence the microfibrils orientation.