These additives, which are based on naphthalene sulfonate, disperse cement into the water by creating an electrostatic repulsion mechanism between the cement particles, thus increasing the slump. Poly naphthalene sulfonate (PNS) is one of the first materials to be used as a water reducer agent since the 1970s with extensive performance in additive compounds. Originally used as a synthetic rubber additive in the 1930s, it entered the concrete additive market in Japan in the 1970s and was used as a strong or superplasticizer water reducer.

The first stage of PNS production is the sulfonation of naphthalene with sulfuric acid, as shown in Figure 1. In the second stage, the condensation reaction (condensation) of naphthalene sulfonic acid with formaldehyde is performed and leads to the production of poly methylene naphthalene sulfonic. The neutralization process is then performed with sodium hydroxide to remove excess alkali in the system.

Due to the symmetry in naphthalene molecules, the substitution of hydrogen by sulfonate can occur in both α and β positions. The α position occurs at temperatures below 100 ° C and the β position occurs at temperatures above 150 ° C, which is much more stable. As a result, only PNSs with β-type substitution have dispersing properties. The α and β junction positions are shown in the figure below. Negative charges on the sulfonate group cause the additive to be adsorbed on the cement particles and disperse these particles through the electrostatic repulsion force.

The average molecular weight of these polymers is between 25,000 and 50,000 g / mol, and the properties created will usually get better as the molecular weight increases.