Effect of ethylene-vinyl acetate copolymer on the rheological behaviour of alumino-silicate/polyethylene wax suspensions

Ceramic suspensions were prepared from an alumino-silicate powder, polyethylene wax (PE-wax) as binder with additions of stearic acid (SA). The ceramic powder consisted of mullite, corundum and tridymite phases. The organic binders contained 3 to 8 wt.% ethylene-vinyl acetate (EVA) and were filled with various volume fractions of ceramic powder. The yield stresses of suspensions were estimated using shear stress-shear rate data measured at 90-120 degreesC. The addition level of EVA was shown to have a considerable effect on the yield stress of suspensions. The effect of EVA on the flow parameters was also investigated over the temperature range of 90 to 120 degreesC. It was shown that the addition of 5 wt.% EVA in organic binder causes a decrease of viscosity at a temperature of 90 degreesC and the higher the volume fraction of ceramic powder, the higher the efficiency of EVA in reducing the viscosity. But at higher temperature, EVA acts as a flow modifier rather than increasing the wettability of polymer blend. In fact at this temperature the polymer-particle interaction weakens with EVA content. Moreover, it was found that the required amount of EVA depends on the degree of powder agglomeration. (C) 2002 Elsevier Science Ltd and Techna S.r.l. All rights reserved.