Polymer effects on the chemorheological and drying behavior of alumina-poly(vinyl alcohol) gelcasting suspensions

A new gelcasting system based on aqueous alumina (Al ₂O ₃)-poly(vinyl alcohol) (PVA) suspensions cross-linked via titanium ion complexation has been developed as a feedstock for bulk casting and solid freeform fabrication (SFF) routes. Its chemorheological properties, as measured by stress viscometry and oscillatory techniques, exhibited a strong dependence upon polymer hydrolysis and molecular weight. The gelation time of systems of constant PVA volume fraction (φ _PVA ^soln) and cross-linker concentration decreased with increasing degree of hydrolysis and molecular weight, whereas their steady-state elastic modulus (G′) exhibited the opposite dependence. Stress evolution during drying of gelcast layers was measured in situ using a controlled-environment, cantilever deflection apparatus. Both the maximum and residual drying stresses increased with increasing degree of hydrolysis, with only a modest molecular weight effect observed.