Chemical and physical modifications of the surface of sisal agave fibre used as a reinforcement in epoxy resin - A Review

A combination of sisal fibers and bio-based epoxy resin offers good potential for producing environmentally friendly bio-composites with improved or equivalent mechanical properties compared to those obtained using 100% synthetic resins. However, the poor interaction between the two materials caused by the different distribution of electrical charge over the atoms joined by the bond in the functional groups of the chemical structure (polarity) necessitates the modification of one of the surfaces of the constituents through various techniques. The paper discusses available literature on several treatments to improve the adhesion between sisal fibers and thermoset epoxy matrices by achieving favorable wettability, mechanical interlocking, and improved interaction through chemical bonding. It is shown that fiber washing in an NaOH solution followed by rinsing and drying is the prevalent chemical treatment. With NaOH treatments, researchers observed cleaner fibers and this promoted better adhesion with the epoxy matrix. Coupling agents such as silane treatments showed an improved resistance to fiber moisture absorption. Thermal treatments affect the fiber's morphology by increasing the crystallinity of the cellulose leading to stiffer composites. It was also observed that the improvement in fiber-matrix adhesion had an adverse effect on the impact strength of the composite.