Equimolar cation exchange of polyacrylamide in smectite

Abstract

Smectite-polymer composites from cationic polyacrylamide (PAMS,τ40Cl) were prepared to investigate the adsorption behavior of the smectite after the intercalation procedure. PAMS,τ40Cl solutions with two different concentrations (γ = 5.18 g/L corresponds to 4.3 mmol/L and γ = 3 g/L corresponds to 4.3 mmol/L) were used to manufacture smectite-PAM+S,τ40 composites. The total amount of PAM+S,τ40 intercalated into the interlayer of the smectite was between 4.5 and 10%. This corresponds to coverage between 4 and 11 cmol(+)/kg, based on the cation exchange capacity (CEC) of the smectite. The smectite in the smectite-PAM+S,τ40 composites still possesses a CEC. The CEC decreased with increasing PAM+S,τ40 content. The CEC decrease was higher than the effective coverage. The amount of Na+ in the interlayer decreased compared to the initial amount with increasing PAM+S,τ40 content. PAM+S,τ40 prefers the interlayer with Na+. Smectite particles in the used raw bentonite (MX-80) are large enough for a planar covering of the basal surfaces by PAMS,τ40Cl. Furthermore, the distances between the charges at the basal surfaces of the smectite and in the oligomer are also large enough for planar covering. Evaluation of the mass spectrometer (MS) curve of m/z = 35 (Cl2) showed that PAM+S,τ40 does not saturate all charges of the smectite per unit cell. Some charges of PAM+S,τ40 are still saturated by Cl−. The exchange of PAM+S,τ40 for Na + in the interlayer of smectite takes place equimolar.