Dielectric properties of short sisal fibre reinforced SBR composites

Short sisal fibre reinforced SBR(styrene-butadiene rubber) composites were prepared by reinforcing SBR with short fibres in an open mixing mill. The dielectric constant, volume resistivity and dissipation factor (tan delta) of these composites have been monitored as a function of frequency, fibre length, fibre concentration and chemical treatment. Dielectric constant values were found to increase with fibre loading. Fibre treatments such as hydration, salt water, mercerization, acetylation and benzoylation were carried out to improve the adhesion between the fibre and the matrix. A two component dry bonding system consisting of HMT (hexamethylene tetramine) and resorcinol was incorporated into the mixes in order to impart greater interfacial adhesion between fibre and matrix. The influence of chemical modifications of fibres on the electrical properties of the composites has been studied. The fibre filled system showed higher dielectric constant values than pure gum due the polarization exerted by the presence of short fibres. Volume resistivity is found to be greater for treated composites due to the increased hydrophobicity of fibres after chemical modification. A percolation threshold is obtained at 8% volume loading of fibres. The estimated value of filling factor and effective co-ordination number is 0.95 and 22.5, respectively. SEM studies were conducted to explain the morphology of the treated fibres and the composites.