Effect of the measurement contact scale on the thermomechanical characterization of biocomposite surfaces

Abstract

This paper proposes a multiscale surface characterization of biocomposites using the nanoindentation technique to identify the functional relationship between the measurement contact scale and the thermomechanical response of each biocomposite component, typically natural plant fibers and the polymer matrix. Flax fiber reinforced polypropylene composites are considered in this investigation. The measurement contact scale in nanoindentation is monitored by the tip indenter radius that ranges from ∼ 10 nm to ∼ 400 nm using different nanoindentation devices (AFM and commercial triboindenters). The thermal contribution is considered by heating the samples during the nanoindentation experiments. Finally, the outputs from multiscale nanoindentation experiments are confronted with the thermomechanical properties reported in the literature with conventional tensile tests as a reference. The results of this paper show the fundamental importance of considering contact scale measurement when characterizing the mechanical properties of biocomposites. Indeed, flax fibers are highly affected by the geometrical contact scale of indentation, while polypropylene does not show a significant dependence on the contact scale. On the other side, flax fibers show a specific multiscale thermomechanical behavior that is related to their hygrometric properties.