Interaction of sodium alginate thickener with components of architectural water-based coatings

Non-ionic polysaccharides, mainly cellulose ethers, have been extensively studied as thickeners in paint formulation. Their mechanism of interaction with the surrounding system is well known and, due to their easy dissolution properties and availability on the market, they are the most used thickening agents. On the other hand, ionic polysaccharides, having possible interaction with the components of the formulation, are less used. In this work, the role of an anionic polysaccharide, sodium alginate (SA), as a thickener, was investigated in a typical wall paint formulation by evaluating its interaction with the principal components of the formulation: water, binder, pigment and extender. Rheology and FTIR spectroscopy were used to evaluate the occurrence of chemical bonds between the polysaccharide chains and the surrounding system. Contemplating the results, so- dium alginate, depending on its molecular weight, Mw, and concentration, turns out to be a suitable thickener for wall paint formulations. In particular, the possibility of building-up a network due to the presence of entan- glements, and the interaction with water molecules and extender, demonstrated that the formulation prepared with 0.2 wt. % of a medium Mw alginate was the most promising one. On the other hand, low Mw alginate exhibited a weaker gel structure and only if present at 0.4 wt. % was appropriate concentration for a ready-to-use product.