Because of their anti-polyelectrolyte behavior, the solubility of amphoteric polymers in aqueous solution can increase with the presence of low molecular weigh electrolytes. In this case, the electrostatic interaction between positive and negative groups is reduced. This leads to a change in the polymer conformation in the bulk. Upon adsorption on charge surfaces (silica and cellulose) amphoteric polymers show a distinctive water-holding ability.

In fact, fiber wall swelling capacity is essential in the development of paper dry-strength. Therefore, it is expected that related formulations could be effective in improving this functional property. It has been hypothesized that this effect is closely related to the conformability and the ability of the fibers to form strong joints during the drying process.The objective of this study is to verify the polyampholyte behavior as enhancer of dry strength under different conditions of ionic strength. To this end we monitored the viscoelastic properties of adsorbed polyampholytes by using the QCM-D technique. Comparison of water holding ability for actual fibers will be presented.