Natural fibres are poised to replace currently used synthetic reinforcing fibres such as E-glass due to their lower weight, cost and bio-degradability. However, a significant factor retarding the growth of natural fibre usage is the poor performance of natural fibre composite materials. It is of particular interest to determine if the moisture content and surface quality of the natural fibres are causing the lack of strength in the resulting composite.
In this project, bundles of Flax fibre were subjected to four different treatment methods, cooked sets with the intention of either reducing fibre moisture content and chemically washed sets with the intention of removing the surface impurities. They were then used to develop a composite using epoxy resin, which featured the treated end of the fibre bundle embedded 0.4mm deep into the epoxy matrix.
The samples then underwent pull-out testing using an Instron machine to record the force required to pull the fibre bundle out of the matrix. The data from the testing was then used to calculate the interfacial shear strength between the fibre and matrix for each sample, obtaining an average value for each treatment type.
It was concluded that none of the fibre treatment methods increased the interfacial shear strength of the Flax fibre composites. Evidence was found in the set washed in acetone that suggests surface impurities can increase the interfacial shear strength due to increased interface area, while increasing uncertainty due to the inconsistency of the impurities.
Upon investigation of the samples that failed by fibre breakage and partial pull-out, it was determined that an excess in embedded length of the fibre bundle was the primary cause of these failure modes due to the interface becoming stronger than the fibres.
Ultimately, while no conclusions were drawn about the relationship between moisture content and shear strength, evidence was found suggesting that surface impurity is not the primary cause of interfacial weakness.