Initiator effect on the gelcasting properties of alumina in a system involving low-toxic monomers

Various low-toxicity gelling systems based on monofunctional monomers: methacrylamide, poly(ethylene glycol) methyl ether methacrylate, and 1-vinyl-2-pyrrolidone, difunctional monomers: N,N′-methylenebisacrylamide and poly(ethylene glycol) dimethacrylate were studied for powder dispersion and gel formation in 55 vol.% alumina suspensions. At optimum dispersant level the viscosity of aqueous slurries consisting of alumina and organic monomers at the shear rate of 20 s−1 was less than 1.5 Pa s, i.e., convenient for gelcasting slips. The storage and loss moduli, and complex viscosity of pure hydrogels were characterized as a function of initiator concentration. The effect of the initiator concentration on idle times of gelation of ceramic suspensions as well as on green flexural and tensile strengths of gelled bodies were determined. The idle times varied markedly, depending on the chemical character of monomer used. The monomers containing ester and ether groups exhibited shorter idle times than those containing amide groups. The green flexural and tensile strengths of gelled bodies for individual monomers were functions of initiator concentration. For each monomer system an optimum initiator concentration was found, at which the highest green strength was measured. This was due to more polymerization degree of hydrogel, as was revealed by dynamic rheometry.