Rigidity analysis of polypropylene/vegetal fibre composites after recycling

Polypropylene/hemp or sisal fibre composites exhibit interesting recyclability [Bourmaud A, Baley C. Investigations on the recycling of hemp and sisal fibre-reinforced polypropylene composites. Polymer Degradation and Stability 2007:92(6):1034-45]. The obtained results prove that the tensile modulus of these polypropylene/vegetal fibre composites is well conserved with the number of reprocessing cycles. In this work, we investigated the relationship between the mechanical properties of the fibres and those of the composites by taking the influence of the recycling into account. In the first part of this study we carried out nanoindentation and tensile tests on vegetal fibres to obtain transversal and longitudinal Young's moduli. The experimental values were then introduced into micromechanical models, taking the aspect ratio changes into account, to estimate the stiffness of the PP/vegetal fibre injected composites before and after recycling. The first results show an interesting correlation between experimental results and model predictions; however a general underestimation of tensile stiffness of composites can be noticed. (C) 2008 Elsevier Ltd. All rights reserved.