Investigation of microstructure and tensile properties of porous natural coir fibre for use in composite materials

Natural coir fibres are studied for use as reinforcement in composite materials. In order to efficiently use the fibres and understand the composite properties, the microstructure and the mechanical properties of coir fibres are investigated in this study. X-ray microtomography in SEM (SEM-CT) and SEM image analysis are used to examine the fibre internal structure including the organisation of elementary fibres, microfibril angles and fibre porosity. Mechanical properties of coir fibres are determined by performing fibre tensile tests, in which an integrated optical strain mapping system is used to define fibre strain for producing more reliable values of E-modulus and strain at failure. The results show that technical coir fibres comprise plenty of elementary fibres and a lacuna at the centre. The elementary fibre is built up by two main cell walls which consist of bundles of microfibrils with a large misorientation with respect to the elementary fibre axis. Coir fibres appear to have a high porosity of 22 to 30%. The high microfibrillar angle in the coir fibres leads to the low stiffness in fibre direction and to high elongation to failure thanks to reorientation of the microfibrils under tensile loading.