Effect of different alginate salts on the rheological and tensile properties of waterborne paints

Alginate is a seaweed derivative used as thickener in the food and biomedical industries. It is mainly known for its gelling ability with divalent cations and can exist as salt of the alginic acid with different monovalent cations. In this study, a multifunctional approach was used to evaluate the influence of different types of alginate salts on the microstructural properties of a water-based architectural coating. A basic formulation containing cellulose as thickener was considered as benchmark; three different salts of alginic acid, specifically sodium, potassium and ammonium, were investigated as alternative thickeners. The performance of alginate and the role of the counterion were evaluated through rheological, application and tensile tests. Strain sweep test was used to evaluate the paints viscoelastic nature; in particular, it is useful to investigate the storage stability. The evaluation of viscosity curves and Three Interval Thixotropy Test, 3ITT, predicted the application phase and the possible occurrence of surface defects. In addition, the coatings behavior was practically verified through the analysis of the brush application process on gypsum boards. Tensile properties of dried films were measured as well to evaluate the counterion effect in the solid state. The results showed that alginate counterions slightly influence the properties of the formulations during the storage. On the other hand, a greater influence is evidenced from 3ITT results, which foresee their application. Finally, the dried samples showed different tensile properties mainly depending on the concentration of the alginates rather than their type.