Chemorheology of aqueous-based alumina-poly(vinyl alcohol) gelcasting suspensions

A new gelcasting system based on aqueous-based alumina-poly(vinyl alcohol) (PVA) suspensions cross-linked by an organotitanate coupling agent has been developed. The chemorheological properties of this system exhibited a strong compositional dependence. A sol-gel phase diagram was established, which yielded the critical titanium concentration ([Ti]_c) required for gelation at a given PVA volume fraction as well as the minimum PVA volume fraction (φ_PVA^min = 0.0245) and titanium concentration ([Ti]_min = 9.984×10^-4 g of Ti/mL) below which gelation was not observed irrespective of solution composition. The gelation time of suspensions of constant PVA volume fraction (φ_PVA^soln) decreased with increased cross-linking agent concentration, temperature, and solids volume fraction. The steady-state viscosity and elastic modulus of polymer solutions (φ_PVA^soln = 0.05) of varying [Ti] were well described by the percolation model, giving scaling exponents of 0.84 and 1.79, respectively. The steady-state elastic modulus of gel-casting suspensions, which provided a measure of their handling strength in the as-gelled state, increased with increased solids volume fraction.