Mechanical properties of coagulated wet particle networks with alkali-swellable thickeners

Alkali-swellable thickeners (ASTs) such as Acusol 820 and Acusol 830, as we ll as poly(acrylic acid) homopolymers of various molar mass, have been used as additives in aqueous electrostatically stabilized alumina suspensions. These suspensions have been destabilized by internal enzyme-catalyzed react ions (a direct coagulation casting process) to form viscoelastic solids. Th e ASTs increase the strength and modulus of the wet green bodies on coagula tion. The effect of their molecular architecture on the mechanical properti es of wet particulate networks has been studied. At low pH (pH 4.5), ASTs a re small insoluble polymer particles that have only minor influence on the low viscosity of the high-solids-loading suspensions. After shifting the pH toward the isoelectric point of alpha -Al2O3, the suspension coagulates an d the AST polymer particles swell, thereby increasing the compressive stren gth and modulus of the alumina-particulate wet green bodies. The presence o f small amounts of ASTs (0.4 wt%, based on the solids loading) results in a 10-fold increase in the strength of the wet green bodies. The compressive strength of the wet green bodies that contain ASTs correlates with the size of the expanded AST molecules at pH 9. A possible explanation is that swel ling of the AST particles locally decreases the interparticle distance, whi ch leads to increased van der Waals forces between the ceramic particles.