Titanate nanotubes and nanosheets as a mechanical reinforcement of water-soluble polyamic acid: Experimental and theoretical studies

Titanate nanosheets (TiNS), titanate nanotubes (TiNT), and scrolled titanate nanosheets (STiNS) were used to synthesise polymer nanocomposites by solution processing. The hardness was found to increase by 90% on addition of 2% TiNS while the modulus (Er) increased by 103% compared to the pure polymer. Small angle X-ray scattering (SAXS) measurements of composite films were used to study alignment of nanostructures within the polymer. The obtained data on mechanical properties of composites have been tested against theoretical values and it was established that both nanostructures alignment as well as their mechanical properties affect the hardness and modulus of the polymer composites. At a low content of TiNS, the reinforcement behaviour matched well with Halpin-Tsai theory which assumes the filler has unidirectional orientation. After addition of 2 wt% TiNT, the hardness and modulus of the polyamic acid salt composites increased by 91% and 165%, respectively, and were higher than theoretical predictions, indicating that both TiNT and STiNS, prepared by hydrothermal synthesis, may have higher mechanical properties than bulk TiO2. At a high filler loading (>2 wt%), the mechanical properties of composites do not fit established theories due to agglomeration of titanate nanostructures.