Anionic Polyacrylamide Polymers Effect on Rheological Behavior of Sodium‐Montmorillonite Suspensions

Abstract

Polyacrylamide (PAM) is a long‐chain synthetic polymer that acts as a strengthening agent, binding clay particles together. The interaction between anionic PAM and clay particles is not well understood yet. This interaction was evaluated by rheological measurements for Na‐montmorillonite suspensions. Three anionic PAMs of three molecular weights (MWs) (3.5 × 103, 2 × 105, and 8 × 106 g mol −1) at similar hydrolysis levels (>85%) and three anionic PAMs at various degrees of hydorlysis (DH) (15, 33, and 92%) of similar MW were studied. In an electrolyte‐free clay suspension at DH >85%, only the polymers with high MWs (2 × 105, and 8 × 106) could form a three‐dimensional structure of clay platelets. The smallest polymer molecule size (3.5 × 103) was too short for bonding two adjacent platelets. At similar MW, the effect of the polymers increased with DH. At NaCl concentration of 10 mmolc L−1, at which the attractive forces between clay platelets were weak, the polymers had a significant impact on flow behavior. The effectiveness of the polymers increased with increasing MW and DH. At NaCl concentration of 100 mmolc L−1, the three polymers of DH > 85% stabilized flocs that already existed in the clay suspension. The effectiveness of the polymers in bridging adjacent clay flocs increased as their DH decreased. The polymer conformation factor has a greater impact on clay structure stabilization in suspension than the electrostatic repulsion effect. The clay structure stability was increased with increasing polymer electrostatic negative charge for similar molecular weights.