AC conductivity and dielectric spectroscopy of poly (3-hydroxybutyrate-co-3-hydroxyvalerate)

AC conductivity of pure (3-hydroxybutyrate), PHB and its copolymers (3-hydroxybutyrate-co-3-hydroxyvalerate), PHB-HV, is investigated in wide range of frequency. The Arrhenius plots of AC conductivity showed a remarkable change in the conduction mechanism in glass transition temperature region of pure PHB. Broadband dielectric spectroscopy for all samples has been investigated in the frequency range from 1x10^-3 to 10⁷ Hz and a temperature range from 273 K to 353 K. The remarkable increase in dielectric constant (ε^/) at low frequency with increasing temperature is attributed to the enhanced dipoles and interfacial polarization, (Maxwell-Wagner-Sillars) polarization. Dielectric loss tangent spectrum of all samples is characterized by a broad relaxation peak in the high frequency side. This peak is assigned as dipolar peak and is attributed to the micro-Brownian cooperative motions of the main chain backbone. The behavior of imaginary part of electric modulus (M^//) as a function of frequency for the samples is characterized by two different relaxation peaks. The first one is positioned in the region of T_g of pure PHB, whereas, the second peak at temperature ~ 338⁰K, and is assigned as Maxwell-Wagner- Sillars (MWS) relaxation.