Quantification of the variability of the geometric properties of fibres and impact on mechanical behaviour of short-vegetal-fibre reinforced PP

Short-fibre-reinforced thermoplastics (SFRT), processed by injection moulding, are commonly used in the automotive sector and the use of vegetal fibres in replacement of mineral glass fibres is booming. Yet, the great variability of the geometric and mechanical properties of the vegetal fibres, and the lack of knowledge about how this actually impacts SFRT’s mechanical behaviour is still a major obstacle to their more widespread use. In this article, the variability of geometric properties of vegetal fibres in the 3D microstructure of an injection-moulded short-vegetal-fibre reinforced polypropylene is thoroughly analysed. Then, its impact on SFRT mechanical behaviour is analytically computed by considering actual probability distributions of occurrence of geometric parameters. It appears that injection-moulding process tends to reduce the range of variability of fibres length. In addition, a comparison to short-glass-fibre reinforced PP demonstrates that similar distributions are observed for both kinds of fibres. Finally, at same fibre content, and all other parameters being fixed, the variability of SFRT mechanical behaviour caused by the variability of fibres length and diameter is greater with glass fibres than with vegetal fibres. These results constitute an important step towards an accurate prediction of envelop of variation of mechanical behaviour of injection-moulded short-vegetal-fibre-reinforced thermoplastics.