Résumé
Flax shive is the main by-product for flax fiber production. It represents about 50% of the weight of the dry flax stem. Its low price (around 100 €/t) and its very low bulk density (100 to 140 kg/m3 [1]) attracts its use as? an alternative bio-based filler in bio-composite materials. Recent studies have shown a significant effect of flax shives granulometry on the tensile properties of the composite. Therefore, this study aims to further investigate the influence of the size and shape distributions of flax shives on the mechanical behavior of the composite and interpret the results through microstructural analysis. Different fractions were prepared by grinding and sieving to obtain these particle sizes: less than 200 µm, 200-500 µm, 500-800 µm and 800-1600 µm. Flax shive / polypropylene (PP) composites were prepared using twin-screw extrusion and injection molding with fiber weight fractions of 10%, 20%, 30%, and 40%. Maleic anhydride grafted polypropylene (MAPP) was used as a compatibilizer with an optimized ratio. Figure 1a presents the tensile properties of the resulting composites, revealing that flax shives sieved between 200 and 500 µm provide the optimal tensile properties. Microstructure analysis showed that better fiber dispersion and higher interfacial area (shown in Figure 1b) are obtained for composites reinforced with low fiber granulometry. The aspect ratio of the particles was determined after solvent extraction of flax shives from the composite. X-ray tomography (shown in Figure 1c) provided additional data regarding the orientation and the distribution of the flax shives in the composite. Microstructural data were then used to predict the mechanical behavior of the composites and estimate the Young’s modulus of the flax shive through both Mori-Tanaka analytical model and finite element analysis.