Influences of polyacrylic acid adsorption and temperature on the alumina suspension stability

The temperature influence on the alumina (Al(2)O(3)) suspension stability in the absence and presence of polyacrylic acid (PAA) was studied. The investigated temperature range was 15-35 degrees C. Stability measurements were carried out by the use of Turbiscan Lab(Expert) with a thermostatic system. Additionally, at 25 degrees C the suspension stability was determined from the spectrophotometric data. The obtained data and calculated values of Turbiscan Stability Indexes (TSI) suggest that for the alumina suspensions without polymer, the values of TSI and the rates of solid particles settling as well as the thickness of sediment were the lowest at all investigated temperatures. Moreover the PAA adsorption causes pronounced decrease of system stability at 15 and 35 degrees C while at 25 degrees C polyacrylic acid adsorption slightly improves the alumina stability. The conformational changes of adsorbed polymer macromolecules are responsible for such behaviour of the investigated systems. At all investigated temperatures the solid suspension is not stable in the presence of PAA. In the case of PAA 2 000 the coagulation by charge neutralization takes place, whereas in the case of PAA 240 000 the bridging flocculation is the most probable process. The destabilization of systems by the adsorbed polymer occurs with the lowest effectiveness at 25 degrees C. (C) 2009 Elsevier B.V. All rights reserved.