Development and Characterization of Chemically Treated Unidirectional Flax Fibre Composites

Abstract

In order to reduce the use of conventional, petroleum-based Fibre Reinforced Polymer (FRP) composites in construction, natural alternatives are being explored such as natural fibres and bio-based resins. However, there are several known disadvantages to natural fibre reinforced composites such as lower mechanical properties and a higher affinity for moisture absorption leading to limited applications. In this study, three chemical treatments were chosen to address common issues associated with natural fibre composites: acetic anhydride, alkalization and amino-silane. These treatments were applied to unidirectional flax mats with a soaking time of 1 hour at low concentrations. Composite sheets were then fabricated with a commercial bio-based epoxy, and tested in standard tensile and lap-splice tests in order to evaluate their effect on mechanical properties. It was found that 2 % acetic anhydride for 1 hour produced the best results, with a 72 % increase in tensile strength and 2 % amino-silane with a soaking time of 1 hour, produced a 20 % improvement in shear strength. A single fibre fragmentation test (SFFT) was also performed on the chemically treated flax fibres in order to get a better understanding of the flax/matrix interface. It was found that 2 % Amino-Silane also showed the most improvement in micromechanical shear strength, supporting the lap-splice test results. Finally, a moisture absorption test was performed on fully fabricated chemically treated flax fibre composites in order to determine the effect on moisture absorption. 1 % acetic anhydride showed to be the most successful group with a 17 % moisture resistance improvement.