Effects of PEG molecular weights on rheological behavior of alumina injection molding feedstocks

The rheological behaviors of alumina injection molding feedstocks containing polyethylene glycol (PEG) binders having different molecular weights were analyzed using capillary viscometer. The results indicate that the feedstock containing larger molecular weight PEG shows a higher yield stress and shear stress. The relative viscosity of feedstocks with PEG binder system is small, which show a good fluidity, and the viscosity decreases with increasing both temperature and shear rate. However, when temperature is above 90 degreesC, the fluidity of feedstocks with PEG I K and PEG 1.5K is too high to catch powder, which may induce dissociation occurring between the binder and the powder particles. Based on the results, feedstock D containing PEG20K as the binder has the lowest fluidity, however, it possesses viscosities smaller than 10(3) Pa s for all working temperatures. The feedstocks all show pseudoplastic behavior with n value in the range 0.41-0.66, which would be accepted for injection molding. In addition, feedstock D with PEG20K shows a lower temperature dependence of viscosity in the temperature range just below the nozzle temperature. It has the best rheological properties and is most suitable for injection molding. (C) 2002 Elsevier Science B.V. All rights reserved.