Polyurethane latex/water dispersible boehmite alumina nanocomposites: Thermal, mechanical and dielectrical properties

Boehmite aluminas that become nanosize-dispersed in water were mixed with polyurethane (PU) latex. The produced nanocomposites were investigated upon their mechanical performance, thermal stability, water uptake and dielectric response as a function of the nominal nanoparticle size of the boehmites. The stiffness, determined by tensile experiment and dynamic mechanical thermal analysis (DMTA), was enhanced with decreasing particle size at the same filler content. The 25 nm alumina caused the highest modulus improvement, however, at cost of the thermal stability compared to the 90 nm and 220 nm boehmite aluminas. The water uptake increased by filling, however, decreased with increasing size of the alumina particles. The dielectric response of the nanocomposites was examined by means of broadband dielectric spectroscopy in the frequency range 10−3–107 Hz, at ambient temperature. Three distinct relaxation modes were recorded in the spectra of all systems. They were attributed to interfacial polarization, glass transition (α-relaxation) and movement of polar side groups (β-relaxation). The intensity and position of these relaxations varied as a function of the size of the water dispersible boehmite.