Processing technical ceramics with maltodextrins: Crosslinking by acetalation

Technical ceramics are made by a sequential process of: (i) mixing ceramic powder with an organic carrier liquid (e.g.. organic solvents, polyethylene wax) to form a plastic slurry, (ii) molding the plastic slurry into a thre e-dimensional shape, (iii) thermal treatment to evaporate or pyrolyze the o rganic carrier, and (iv) kiln firing. In this paper, the use of aqueous pol ysaccharide solutions is examined as environmentally-friendly, economically -viable substitutes for organic carrier liquids in ceramic molding. The cen tral focus of the present study is to examine optimum conditions for crossl inking model slurries of maltodextrin and colloidal aluminum oxide by aceta lation of maltodextrin. Crosslinking is needed to prevent the common proble m of cracks that form in ceramic shapes during thermal treatment (stage iii above). Experiments involving rheology and differential thermal analysis r evealed that glyoxal and glutaraldehyde are effective crosslinkers, whereas formaldehyde and pyruvic acid did not exhibit measureable changes in slurr y rheology over a wide range of concentrations. Glutaraldehyde reacted fast er than glyoxal, however, glyoxal produced the strongest gels. Basic condit ions catalyzed acetalation. The sequence of blending the slurry components had no significant effect on slurry rheology.