Enhancement of Static and Fatigue Strength of Short Sisal Fiber Biocomposites by Low Fraction Nanotubes

Abstract Thanks to good mechanical performances, high availability, low cost and low weight, the agave sisalana fiber allows to obtain biocomposites characterised by high specific properties, potentially very attractive for the replacement of synthetic materials in various industrial fields. Unfortunately, due to the low strength versus transversal damage processes mainly related to the matrix brittleness and/or to the low fiber/matrix adhesion, the tensile performance of random short fiber biocomposites are quite low, and to date most of the fiber treatments proposed in literature to improve the fiber-matrix adhesion, have not led to very satisfactory results. In order to overcome such a drawback, this work in turn proposes the proper introduction of low fractions carbon nanotubes to activate advantageous improvements in matrix toughness as well as fiber-matrix bridging effects, that can both lead to appreciable increments of the tensile strength. Systematic experimental static and fatigue tests performed on high quality biocomposites obtained by an optimized compression molding process, have shown that the introduction of 1% of carbon nanotubes is sufficient to gives significant improvement in both stiffness and static tensile strength, respectively by approximately 28% and 30%. Furthermore, toughening the biocomposite with 1% of nanotubes results in an appreciable enhancement in lifetime of at least 3 orders of magnitude. Biocomposites with 2% of CNTs show instead more limited improvement of 13% in stiffness, 6% in strength and 150% in lifetime. Also, a thorough analysis of the damage processes by SEM micrographs, as well as of the main fatigue data, has allowed to determine the model that can be used to predict the fatigue performance of such biocomposites.