AC conductivity and dielectric relaxation of chitosan/poly(vinyl alcohol) biopolymer polyblend

Polyblend samples of chitosan/poly(vinyl alcohol) (PVA) have been prepared using a casting technique. Scanning electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis measurements revealed that chitosan and PVA are compatible with each other. Alternate current (AC) conductivity and dielectric relaxation features of pure and polyblend samples are analysed in the frequency range of 0.1 Hz to 100 kHz covering a broad temperature range from room temperature to 423 K. Variation of AC conductivity,sigma(AC), of pure and chitosan/PVA polyblend samples is found to be characterized by a plateau region at low frequency and high temperature, and this plateau region increases with increase in temperature. Based on the behaviour of the exponents vs.temperature, AC conductivity dependence on frequency is found to be correlated with overlapping-large polaron tunnelling (OLPT) model. The polyblend samples showed an improvement in their dielectric properties compared to the pure materials. The dielectric constant,epsilon ', of polyblend samples was increased by increasing the content of PVA. The dielectric dispersion was observed in the variation of epsilon ' against frequency for all samples. The high values of epsilon ' for all samples at high temperature and low frequency are attributed to space charge polarization. Also, loss tangent-frequency behaviour of pure chitosan, PVA and all polyblend samples showed two distinguished relaxation peaks with different values of activation energies. The first relaxation peak is termed as interfacial polarization or Maxwell-Wagner-Sillars polarization due to heterogeneity of the polyblend samples, whereas, the second relaxation peak is termed as delta-relaxation and alpha-relaxation, for pure chitosan and PVA, respectively.