EFFECT OF POLY(ETHYLENE OXIDE) ON THE STABILITY AND FLOCCULATION OF CLAY DISPERSIONS

The stability and kinetics of flocculation of clay suspensions, used a s fillers in papermaking, were investigated in the presence of a nonio nic retention aid poly(ethylene oxide) (PEO) of molar mass 6 x 10(6), and CaCl2. The equilibrium adsorption isotherms of PEO, the kinetics o f adsorption and the thickness of the polymer adsorbed layer on the cl ay were measured. In a salt-free system, no flocculation took place ov er a measured period of time (20 min) at any dosage of PEO. In the pre sence of 0.5 mmol/L CaCl2 the flocculation was optimum at 2-3 mg of PE O per gram of clay. The observed rates of fast salt-induced flocculati on were about 4% of those predicted by Smoluchowski for diffusion-cont rolled flocculation. The adsorption efficiency of PEO on clay was foun d to be about 0.3%. At low PEO concentrations, the characteristic time of polymer adsorption is comparable to the flocculation time and, as a consequence, adsorption interferes with flocculation. The behaviour of clay dispersions in the presence of PEO can be explained by a compe tition between electrostatic repulsion, bridging flocculation and ster ic stability.