Relaxation phenomena in chitosan-carbon nanotube bionanocomposites

For the first time, thermal relaxation properties of chitosan films with carboxy-functionalized multiwall carbon nanotubes MWCNTs (0.5, 1, 3, 5 and 10 wt. %) composites have been investigated. Depending upon MWCNT concentration three relaxation processes can be observed as a function of temperature and water content using dynamical mechanical analysis and dielectric spectroscopy in the temperature range of 25-330°C. Low temperature relaxation process, in the range 25-70 °C, can be related to the α-process associated with the glass-rubber transition and can be described by the Vogel-Fulcher-Tammann dependence of the relaxation time versus reciprocal temperature. The glass transition temperature is strongly affected by water content such that it vanishes in a dry material. The second relaxation was observed in the temperature range 70-190 °C and it is identified as the σ-relaxation which it is often associated with the hopping motion of ions in the disordered structure of the biomaterial. This relaxation exhibits a normal Arrhenius-type temperature dependence with activation energy of 81-86 kJ/mol and it is independent of water content. In the temperature region of 200-300°C we have observed a relaxation process that is associated to film degradation.