Structure and dynamics of polypyrrole/chitosan nanocomposites

Polypyrrole/chitosan (PPy/Cs) nanocomposites with various amounts of polypyrrole nanoparticles (PPy-NPs) have been synthesized and afterwards exposed to UV irradiation for 240 min. Structure, dynamics and antibacterial activity of pure compounds and the corresponding nanocomposites were investigated by means of wide-angle X-ray scattering, Fourier transform infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis, broadband dielectric spectroscopy and antibacterial activity assay. The occurrence of a pronounced interaction between PPy-NPs and Cs has been verified. Broadband dielectric spectroscopy measurements revealed two relaxation processes at low and high frequencies. The low-frequency α-relaxation associated with the glass–rubber transition is attributed to the presence of hydrogen-bonded water (plasticizing effect) appearing at low temperature (<373 K). The high-frequency σ-relaxation is related to water molecules which become desorbed upon heating at T > 373 K and demonstrates Arrhenius temperature dependence with activation energy in the range 70–90 kJ mol⁻¹ in good agreement with previous reports. On the contrary, PPy-NPs do not show any structural relaxation process and the charge transport mechanism follows the correlated barrier hopping model. All PPy/Cs nanocomposites exhibit an improved antibacterial activity against both Staphylococcus aureus and Escherichia coli bacteria as compared with pure Cs and PPy-NPs.