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Polyampholytes offer considerable promise as dry-strength additives, but the molecular mechanism involved in their adsorption needs to be better understood. Amphoteric terpolymers of acrylamide, itaconic acid, and N-[3-(NN’,N’dimethylamine)propyl]acrylamide (DMAPAA) with a constant ratio of basic to acidic groups (5:4) were prepared by random polymerization. The basic groups ranged from 2.5 to 20 mole percent in the terpolymers. Analysis by H and 13C nuclear magnetic resonance revealed near-quantitative agreement with the make up stoichiometry. Streaming potential tests showed significant effects of polyampholyte adsorption, depending on the charge density of the polyampholyte, its level of addition, the pH, and the background electrolyte. Polyampholytes having higher density of ionizable groups yielded more positive streaming potential at low pH values and more negative streaming potentials at high pH values, compared to polyampholytes of lower charge density. At the extremes of pH, e.g. pH=3 and pH=11, the effects of a polyampholyte on streaming potential were similar to those of single-charged polyelectrolytes having a matched degree of substitution of charged monomeric groups. Except for the sample having the lowest density of charges, all of the polyampholyte samples showed a broad maximum in adsorbed amount vs. pH within the range of about pH=5 to pH=9, which is intermediate between the pKa values of the respective charged groups.

Aspects of retention and formation: The role of polyampholyte charge density on its interactions with cellulose