Résumé
Natural fibres are considered as ecological alternative reinforcements to glass fibres in polymer composites. However, the behaviour of biocomposites in service life and their durability are impacted by the great variability in dimensions and mechanical properties of plant fibres. Beyond the fact that each plant species has its own intrinsic properties, these variations can be explained in particular by a high sensitivity of plant fibres physical properties to hygro/hydrothermal conditions. In order to better understand and quantify these phenomena, we studied the effect of environmental conditions on the dimensional variations and the mechanical behaviour of fibre bundles extracted from several plant species from different botanical origins. All tests were conducted in both a climatic chamber or water immerged allowing to vary the relative humidity conditions between 20 to 100%. Our results revealed contrasted swelling and plasticization behaviour as a function of plant species, in relation with their specific biochemical composition and microstructure, influencing greatly their mechanical properties. This study highlights the need to characterize natural fibres under controlled hygro/hydrothermal conditions. In addition, the analysis of their swelling and mechanical properties as a function of RH opens interesting perspectives to better understand and estimate mechanical behaviour of biocomposites in service life.