Banana fibre filled natural rubber compounds: the effect of filler loading and the coupling agent

Banana plantation generates a huge volume of fibres as residues. The use of natural fibres as fillers in the rubber industry is a new trend. This is especially due to their availability, low cost and environmental friendliness. Of the commonly available natural fibres, banana fibre contains the highest cellulose content of 60-65%. Banana fibre has been incorporated into phenol formaldehyde and polyester resins as a reinforcing material. However, the use of banana fibre in dry rubber formulations is novel. The banana fibre can also be modified physically or chemically to enhance the properties of the rubber products. The objective of the present study is to investigate the effect of fibre loading on rheological properties and the physico-mechanical properties of a dry rubber compounds. In this study, banana fibres were extracted using a mechanical retting method, and were ground using a domestic grinder to prepare fibres in the size range 0.01 – 1.2 mm. The fibres were characterized and extracted fibres were examined under optical microscope. The ground fibres were incorporated into a natural rubber compound as a filler. Two series of filled natural rubber compounds were prepared by varying the fibre loading from 0 to 50 phr at 10 phr intervals; one with banana fibre alone and the other in the presence of a coupling agent (phenol formaldehyde and hexamethylene tetra amine), commonly used to enhance compatibility of natural rubber and biofibres. Cure characteristics, and physico-mechanical properties of the vulcanizates, were investigated according to ISO and BS standards. The properties of the banana fibre filled compounds were compared with the carbon black filled compounds. Cure time decreased gradually with banana fibre loading when banana fibre alone was incorporated into the rubber compound. However, the variation of cure time for all compounds was low and lie within the range of 4 to 5 min. Hardness increased with the banana fibre loading, while tensile properties such as tensile strength and elongation at break, and tear strength decreased. The property variations showed that the banana fibre alone behaves as a diluent filler. With incorporation of the coupling agent tensile strength elongation at break and tear strength improved for all banana fibre loadings. Tensile strength increase is limited to 25% maximum, but elongation at break increased by 200% at 50 phr banana fibre loading. This property enhancement suggested banana fibre with the coupling agent is a reinforcing filler to natural rubber