Influence of lignin content on the intrinsic modulus of natural fibers and on the stiffness of composite materials.

Agricultural wastes are an alternative to the use of wood in plastic composites, thanks to their abundance, easy availability and other environmental and economic advantages. Agricultural wastes can be processed to obtain lignocellulosic fibers of different compositions that will allow better performance of their composites and the final desired residues' valorization. In this context, the current investigation aims at the management of corn stover wastes to be applied as reinforcement of polypropylene (PP). Four types of lignocellulosic fibers were obtained by submitting the wastes to mechanical, thermomechanical, semi-chemical or chemical processes. Corn fibers were characterized in terms of chemical composition, morphology and mechanical properties. In addition, PP was reinforced with corn fibers and the composites' stiffness evaluated. An assessment of the influence of the fiber composition on the mechanical performance of the composites is conducted. It is observed the key role of lignin content on the intrinsic modulus of the reinforcing fibers, which directly affected the final stiffness of composites. The best performance was achieved for an optimal kappa number between 40 and 50, corresponding to the semi-chemical fibers. The intrinsic modulus of the fibers, as well as the efficiency factor, length and orientation factors in composites were determined via micromechanical models.