Surface Modification of Bentonites. II. Modification of Montmorillonite with Cationic Poly(ethylene oxides)

Surface modification of clay minerals has become increasingly important for optimizing the practical application of bentonites, kaolins, and clays. We describe the reaction of montmorillonite, an important mineral in bentonites, with cationic poly(ethylene oxides). Poly(ethylene oxides), PEOs, with molecular masses between 1550 and 35000, were modified by substituting the OH end groups by bromine, then replacing Br by trimethylammonium (TMA) groups. Mono-endcapped PEOs were prepared from poly(ethylene oxide)monomethyl ethers. These cationic PEOs were strongly adsorbed by montmorillonite and bound by cation exchange. The cationic end groups of the PEOs displaced external and internal exchangeable cations. The macrocations did not flocculate sodium montmorillonite dispersions but stabilized them by forming lyospheres around the particles (steric stabilization). They impeded settling of dispersed calcium montmorillonite particles, even at a 1 percent solid content, and a gel was formed that stiffened within a certain period. This is caused by a certain degree of delamination of the calcium montmorillonite particles that are split at some given break points. The initial stages of gel formation were studied with low shear viscosimetry. An interesting aspect is the temperature dependence of the flow values. The viscosity of calcium montmorillonite dispersed in solutions of di-endcapped PEOs decreased above 40–50 °C but the yield value rose sharply