Rheology of Cross‐Linked Chitosan–Alumina Suspensions Used for a New Gelcasting Process

The rheological behavior of a low‐toxicity, aqueous, Al 2 O 3 –chitosan–2,5‐dimethoxy‐2,5‐dihydrofuran (DHF) system was examined over a temperature range of 20°–98°C. At room temperature, a high‐volume‐fraction solids, shear‐thinning suspension was produced. The suspension remained in a liquidlike state for ∼24 h. By contrast, at elevated temperatures, DHF became active as a cross‐linking agent for chitosan, and a rapid transition from liquidlike to solidlike suspension behavior was apparent. The rate of gelation and the gel strength increased with increased temperature and increased DHF concentration. Gelation occurred at pH 1.4–4.5, which is a complex function of pH. At pH above ∼4, rapid gelation was not possible because of the low‐pH solution conditions required for the cross‐linking reaction. An examination of the strength and shape‐forming properties of several Al 2 O 3 –chitosan–DHF systems showed them to be suitable for production of strong, reliable, complex‐shaped ceramic components. In particular, small, dense Al 2 O 3 pseudorotors were formed and found to be of sufficient strength for mold removal and subsequent handling. In all formulations examined, chitosan concentrations of <0.5 wt% (by weight of ceramic) were required; therefore, the need for a discrete binder burnout process was eliminated.