Graphite layer nano-composites with polyurethane matrix

The aim was to prepare expanded graphite oxide (GO, Graftech Inc.) and disperse it in a polyol (poly(oxypropylene glyceride), Dow Chemicals) using ultrasonication. The dispersion was polymerized and crosslinked with methane 4,4'-diphenyldiisocyanate to form a poly(ether-urethane). SEM showed relatively uniform dispersion of graphite oxide sheets and unexfoliated graphite oxide in the PU. X-ray data showed a single sharp diffraction peak for unexfoliated graphite at a scattering angle of 26°. Thermogravimetry demonstrated that the thermal stability of the PU was increased by GO. The increased thermal stability was due to retardation of volatiles emission by tortuous paths created by GO and absorption of both polymer and degradation products by GO. The modulus and yield strength of GO-PU nano-composites were increased, while the elongation at break was reduced. PU creep was reduced by GO, while recovery was slowed and the non-exponentiality (skewness of the exponential recovery curve) increased consistent to a greater distribution of relaxation times. The storage modulus in the glassy and rubbery regions was increased with PU-GO, while the damping factor was decreased. The glass transition of the flexible polyol phase was not significantly changed.