Effect of Polymeric Binder and Dispersant on the Stability of Colloidal Alumina Suspensions

Polymeric additives include dispersants and binders which play a key role in processing of colloidal ceramic suspensions. In this work, the dispersion behaviour of colloidal Al2O3 suspensions in the presence of polymeric binder (polyethylene glycol) and dispersant (ammonium salt of polyacrylic acid) was investigated by sedimentation technique, viscosity measurement and FTIR method. The effects of polymeric binder molecular weight and concentration and its interaction with polymeric dispersant were investigated. The results showed that PEG 6000 can be used as a suitable polymeric binder in colloidal processing of alumina suspensions. The optimum concentration of polymeric binder which results in optimum stability conditions was obtained 5 wt% PEG 6000 based on the dry powder weight. Further increasing of binder concentration causes instability of the alumina suspensions via depletion mechanism. In the optimum range of the dispersant concentration (0.2-0.3 mL/100 g powder), suspensions with optimum binder concentration have lower stability compared to those with only dispersant as a polymeric additive. This behaviour is confirmed by FTIR spectra analysis of the polymeric species remained in supernatant liquid. The stability behaviour of the colloidal alumina suspensions with different contents of polymeric binder and dispersant was also evidenced by scanning electron microscopy imaging of the sediment layers after 3 weeks.