Flax xylem as composite material reinforcement: Microstructure and mechanical properties

Abstract

Flax shives have been proven to be relevant injection-moulded reinforcement materials with a stiffness that reaches 90% of that obtained with cut flax fibres. Nevertheless, little is known of the reinforcing mechanisms of this material. In this study, deeper insight is sought on the mechanical properties of flax shives, which originate mainly from the xylem tissue of the flax stems. The microstructure of flax xylem is investigated by nanotomography and image analysis as a function of stem height, combined with AFM measurements of the cell walls in Peak Force Quantitative Nano Mechanical indentation mode (20–22 GPa were measured for the S2 layer). The bending stiffness of peeled flax stems was furthermore investigated, and finally, an estimation of the flax shive particle stiffness was carried out and tested with a micromechanical approach in order to evaluate their reinforcing potential in injection-moulded composites.