Study of the flexural modulus of lignocellulosic fibers reinforced bio-based polyamide11 green composites

The stiffness of a material has high impact when its industrial use is considered. Moreover, this property has interest in the case of short fiber reinforced materials due to its dependence on the orientation of the fibers against the loads. Due to nowadays-environmental concerns, greener alternatives to oil-based composites are under study and development showing some promising results. In this work, a polyamide 11 reinforced with lignocellulosic fiber composite is evaluated as such sustainable alternative. Previous works showed the suitability of PA11-based composites to replace glass fiber reinforced polypropylene. Nonetheless, there is a lack of information about the flexural modulus behavior of these composites. This is of interest because, under some conditions, flexural modulus is more representative of a material behavior than Young's modulus. The flexural moduli of these composites were analyzed under a three point bending test and the results were evaluated from macro and micromechanical points of view. The increment of the modulus with the fiber contents implied a good dispersion of the reinforcements. Nonetheless, the results were lower than those observed for the tensile modulus. This was unexpected due to the anisotropy of the bending test. The micromechanics analysis showed a lower performance of the fiber during the flexural test. These lower results were related with a non-optimal interface or with the non-adequate compression of the fibers. Additionally, the calculus of the void volume showed low void contents.