Effect of sisal fibre orientation on electrical properties of sisal fibre reinforced epoxy composites

Different directionally oriented sisal fibre reinforced epoxy resin composites have been prepared by compression moulding. The effect of temperature and frequency variation on dielectric constant (epsilon'), dielectric dissipation factor (tan delta) and on a.c. conductivity (sigma(a.c.)) of the samples was measured. Measurements were in the temperature range 24-180 degrees C and in the frequency range 1-20 kHz. The sisal fibre epoxy composites were oriented parallel and perpendicular to the electric field. It was found that the dielectric constant, tan delta and a.c. conductivity increased with increasing temperature. The dependence of dielectric constant, tan delta and a.c. conductivity with frequency has also been studied and it was found that epsilon' and tan delta of the epoxy and 0 and 90 degrees oriented sisal fibre epoxy composites decreased with increasing frequency and a.c. conductivity increases with increasing frequency. Near the transition temperature of the epoxy the observed properties showed anomalous behaviour. Peaks for dielectric constant, tan delta and a.c. conductivity were observed. Clear relaxation peaks for tan delta around 169 degrees C were observed in epoxy resin, shifting to the lower temperature side with increasing frequency. The relaxation time of epoxy and 0 and 90 degrees oriented sisal fibre epoxy composites has been calculated and it was found that tau(s) was 4.09 x 10(-5), 5.52 x 10(-5) and 5.47 x 10(-5), respectively at 100 degrees C. Semi log plots show that epsilon'(T)/epsilon'(P) tan delta(T)/tan delta(P) and sigma(a.c.T)/sigma(a.c.P) can be represented as follows epsilon'(T)/epsilon'(P) = k log f + c, tan delta(T)/tan delta(P) = a log f + b and, sigma(a.c.T)/sigma(a.c.P) = l log f + m. (c) 2004 Elsevier Ltd. All rights reserved.