Dielectric Relaxation and Thermal Stability of Epoxy/Polyurethane -Carbon Nanofiber Composites

Abstract

The main purpose of this study is to improve the dielectric relaxation properties and thermal stability of epoxy/ polyurethane blend by dispersing carbon nanofibers, the EP/PU-CNF’s was fabricated by dispersing a weight fraction of (10%) of the CNF’s into EP/PU blend. The data of AC conductivity have been analyzed in the light of the correlated barrier hopping model (CBH) and percolation theorem. The dielectric measurements were carried out for all samples over the frequency range of (102-107) Hz and over temperature range of (293-463) K0. It is found that all samples displayed a wide dielectric dispersion, thus the values for dielectric constant and dissipation factor give a direct evidence of Debye relaxation existence which leaving a wide distribution of relaxation time. Eyring’s relaxation rate equation have been used to determine the thermodynamic parameters (Gibbs free energy of activations (ΔG), and entropy (ΔS)). The results (ΔG), and (ΔS) reviles a strong intermolecular interaction in all tested samples. The glass transition temperature (Tg) values were exhibited by deferential thermal analysis (DTA) and estimated by dielectric measurements (DM). The thermal stability of EP/PU blend and EP/PU-CNF’s composite was evaluated by thermal gravimetric analysis (TG) and deferential thermal gravimetric analysis (DTG), the results showed that the carbon nanofibers improve the thermal stability of the composite, hence the char yield at a temperature greater than (700) C0 reached to (31.08) %, while it is only (8.4) % for the EP/PU- blend.