Determination of the Fibre Content of Natural Fibre Composites through Moisture Absorption

Volume fraction plays a vital role in determining the mechanical and thermal properties of fibre reinforced composites. Composites are strongly influenced by the ratio and the properties of the matrix and fibre reinforcement. The method traditional used to measure fibre content for glass fibre reinforced polymer composties is loss on ignition (LOI). High temperature is involved in removal of polymer matrix as glass fibre is stable at elevated temperatures but this cannot be used as natural fibres start to degrade at high temperatures. The aim of this work is therfore to find the fibre content of the sisal and flax composites which would be used to find the mechanical properties of the natural fibres.

A simple technique based on the tendency of natural fibres to absorb high levels of moisture in relation to their environment was utilised to estimate the fibre content in the composite samples. The composite moisture absorption is dominated by the high hydrophilic nature of the natural fibre compared to the matrix material therefore a higher fibre content leads to a higher amount of absorbed moisture in the composite. Unidirectional composites with various fibre orientations were manufactured by vacuum infusion process for fibre characterisation.  Monitoring the uptake of moisture in fibre, composites and resin samples under strict conditions allows us to determine the volume fraction of the constituent materials using the percentage weight gain. The results will show that the water absorption of the natural fibre composite at different orientation and by using the information from the water absorption technique and equations below the fibre content of the composites can be calculated.

Where the symbols are W_f , V_f, m_m, m_c,m_f, ρ_f and ρ_m are the weight fraction, Volume fraction, mass percent of the polymer matrix, composite, fibre and density of fibre and matrix respectively

This study will look at a technique using moisture absorption to calculate the fibre content of natural fibre composites and the effect of fibre orientation.