Effect of Molecular Weight and Chemical Composition of Polyelectrolyte on the Inhibition of Scale Deposition -Studies on the Prevention of Calcium Carbonate Scale Deposition by the Addition of Polyelectrolytes. II.-

Abstract

The function of polyelectrolytes (polymers) to inhibit CaCO₃ scale deposition explained in a previous paper was thoroughly examined using solutions with various pHs and a number of polymers with different molecular weights and chemical compositions. Polymers used were nine polyacrylates (PAA) having mole cular weight of 600-25000, five acrylate/2-hydroxy-3-allyloxy-1-propanesulfonate copolymers (AA/HAPS) with molecu lar weight of 3000, and four acrylate/3-allyloxy-1, 2-propanediol copolymers (AAJAPDO) with molecular weight of 3000.
As pointed out prev iously, the inhibiting ability of polymers increases with its chelation affinity to Ca²⁺ ion but decreases when the chelation affinity excessively increases to facilitate the gelation. The maximum inhibition was obtained in a certain intermediate range of molecular weight for PAA, and at a suitable AA mole fraction for AA/HAPS and AA/APDO copolymers. The inhibition efficiency decreases with an increase of solution pH, probably because the degree of supersaturation of CaCO₃ is higher with higher pHs. For all the polymers, a simple common relationship between the inhibiting ability of polymer for CaCO₃deposition and its chelation affinity is obtained.
For all the gels, it was found that Ca²⁺ ion is contained in the gels and the mole ratio of Ca²⁺ ion and COO^- group is always 1/2. This result indicates that the gelation results from the formation of zero-charge polymer complexes by the reaction with Ca²⁺ ion.