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DIVISION S-1 - SOIL PHYSICS

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

Institute of Soil, Water and Environmental Sciences, The Volcani Center, Agriculture Research Organization (ARO), P.O. Box 6, Bet Dagan 50250, Israel

* Corresponding author (rkeren{at}agri.gov.il)

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 x 10³, 2 x 10⁵, and 8 x 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 x 10⁵, and 8 x 10⁶) could form a three-dimensional structure of clay platelets. The smallest polymer molecule size (3.5 x 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 mmol_c 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 mmol_c 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.

Abbreviations: DDL, diffuse double layer • DH, degree of hydrolysis • MW, molecular weight in units gram per mole • PAM, polyacrylamide • PVA, polyvinyl alcohol • SDS, sodium dodecylsulfate (SDS)

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				A. I. Mamedov, S. Beckmann, C. Huang, and G. J. Levy Aggregate Stability as Affected by Polyacrylamide Molecular Weight, Soil Texture, and Water Quality Soil Sci. Soc. Am. J., October 29, 2007; 71(6): 1909 - 1918. [Abstract] [Full Text] [PDF]

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