Effect of Elastomer Blend on High Temperature Dielectric Properties of Polypropylene

This paper presents investigation on dielectric properties of polypropylene (PP), binary blend (iPP/EOC=4.4:5.6), and ternary blend 1 (iPP/EOC/PPC=4:5:1), and ternary blend2 (iPP/EOC/PPC=3.6/4.6/1.8) at high temperatures up to 150°C. EOC and PPC stand for ethylene-octene copolymers and EPR dispersed in PP, respectively. The relative complex permittivity
${{{\bm{\varepsilon }}}_{\bm{r}}}^{\bm{*}} = \varepsilon_{r}^{\prime} - {\bm{j}}\varepsilon_{r}^{\prime\prime}$
and AC conductivity
${{{\bm{\sigma }}}_{{\bm{ac}}}}$
were measured in a temperature range from 30°C to 150°C at frequencies from 1 Hz to 10 kHz. Experimental results revealed that the real part
$\varepsilon_{r}^{\prime}$
of the relative permittivity of all kinds of material decreased with increasing temperature, though pristine PP exhibited a smallest decrease in
$\varepsilon_{r}^{\prime}$
with temperature. While the imaginary part
$\varepsilon_{r}^{\prime\prime}$
exhibited a linear decrease with the frequency in the log vs log plot below 1 kHz and above 100°C for binary blend, ternary blend1 and 2. The results indicate that the EOC addition to PP is contributed to the increase in the complex permittivity. It was also found that
${{{\bm{\sigma }}}_{{\bm{ac}}}}$
of binary blend, ternary blend1, and 2 remained constant below 1 kHz and above 110°C, while
${{{\bm{\sigma }}}_{{\bm{ac}}}}$
of all the samples increased proportionally with frequency above 1 kHz. The calculated activation energies derived from the temperature dependence of the DC conductivity of binary blend, ternary blend 1, and ternary blend 2 were 0.602, 0.849, and 0.791 eV, respectively, with ternary blend 1 having the largest activation energy. Ternary blend 1 with the largest value was considered the most likely to inhibit carrier transport.