Effect of microstructure on the tensile and fracture properties of sisal fiber/starch-based composites

In this study, the effect of microstructure on the tensile and fracture properties of injection molded biocomposites consisting of starch-based matrix and short sisal fibers has been investigated. Tensile tests are carried out on samples cut in longitudinal (L) and transverse (T) directions with respect to the melt flow direction. An increasing trend in Young's modulus and tensile strength with fiber content is found, irrespective of the sample orientation. In addition, this reinforcing effect is more pronounced for L samples with many fibers mainly oriented longitudinally to the loading direction. Quasistatic fracture tests are also performed on SENB specimens with cracks propagating both parallel and perpendicular to the melt flow direction. The stress intensity factor is found to increase with fiber content, and it also depends on fiber orientation. The observed trend in fracture toughness with fiber content and microstructure is explained in terms of the fiber pullout mechanism. Puncture tests are carried out for all compositions. Injection molded composites exhibit higher values of total fracture energy than neat matrix. Furthermore, fiber orientation induces different patterns in the damage zone. Finally, several theoretical models are used in this study to predict the elastic properties of these composites.