Introduction to Surfactants of Dispersants

Lignosulfonates (such as sodium lignosulfonate, calcium lignosulfonate and ammonium lignosulfonate) are a type of anionic surfactants, widely used in oil fields, cement, water treatment, organic dyes and pesticides, serving as water reducers, flocculants and dispersants. In the newly developed pesticide formulations (safe and environmentally friendly suspension agents, water-dispersible granules and microcapsule suspension agents) of today, lignosulfonates also play an effective dispersing role.

The relative molecular mass of lignosulfonate is large, which not only provides electrostatic repulsion but also offers spatial steric hindrance, preventing the dispersed particles from aggregating or the suspended particles from coagulating. This provides excellent dispersibility and suspension ability. For different pesticide active ingredients, different sulfonation degrees of lignosulfonate can be selected. For pesticides with hydrophilic groups or strong hydrophilicity, a low sulfonation degree lignosulfonate can be chosen; conversely, a high sulfonation degree lignosulfonate product is preferable. Lignosulfonate dissolves quickly in water, which is conducive to particle adsorption. However, its shortcomings lie in poor reduction of surface tension, wetting ability and penetration force, poor dispersion persistence, and often having color. Generally, it is recommended to use it together with the formaldehyde condensation product of naphthalenesulfonate to achieve better dispersion and stability effects.

In order to obtain various types of lignosulfonates with specific properties, and to selectively enhance certain properties, or for the needs of certain special applications, the phenolic structure in lignin can be modified through various chemical processes; it can also be modified by forming hydrogen bonds or by substituting the α- and β-hydroxyl groups on the side chains of the phenylpropyl monomers; and the degree of sulfonation of lignin and the relative molecular mass of lignosulfonates can be further adjusted, thereby developing a series of specialized chemical products with different properties.

Sodium Naphthalene sulfonate formaldehyde condensate is a type of excellent anionic surfactant, which is widely used in the areas of water reducer, dyes and agrochemicals. Naphthalene sulfonate formaldehyde condensate is an anionic dispersant composed of many naphthalene groups providing adsorption chains and sodium sulfonate providing hydrophilic chains. Its structural formula is as follows:

The dispersibility of the sodium naphthalene sulfonic acid salt formaldehyde condensate is related to its degree of polymerization (and the number of naphthalene nuclei) and the position of the sulfonic acid group. The higher the degree of polymerization, the better the dispersibility. Only when there are more than 5 naphthalene nuclei (with a relative molecular mass of over 1000) does it have a certain dispersing effect; when the number of naphthalene nuclei increases to 9 (with a relative molecular mass of 2300), its dispersibility increases. 

Compared with other dispersants, the sodium naphthalene sulfonic acid formaldehyde condensate has stronger dispersibility, longer dispersion persistence, and no color. The drawback is that when the product gets damp during storage, its dispersibility will decrease. It is often used in combination with lignosulfonic acid salts. Common naphthalene sulfonic acid formaldehyde condensates include dispersant NNO and dispersant MF.

Polymeric carboxylate dispersants are a new type of efficient and multi-functional dispersants that have been developed in recent years. They can dissolve in water and have the functions of protecting, dispersing and stabilizing the active ingredients of pesticides and other added components in the dispersion system medium. They have been widely used in emulsifiable concentrates.

Compared with traditional dispersants, they have significant advantages, specifically as follows:

① Polymeric carboxylate dispersants contain multiple anchoring sites, which are adsorbed and dispersed on the surface of the particles through multiple sites. The adsorption capacity is large, and the water-soluble segments that are easily soluble in water fully extend in water and form a sufficient thick protective layer on the surface of the pesticide solid particles, achieving effective stabilization and dispersion of the particles in the medium through spatial steric hindrance.

② Traditional polymer dispersants have irregular distribution of anchoring groups and the existence of planar adsorption, which causes the same dispersant to often adsorb on several solid particles. This not only fails to achieve the stabilizing dispersion effect but also leads to flocculation between particles due to "bridging" effects. Polymeric carboxylate dispersants are generally comb-type copolymers, with the anchoring groups at the same end of the molecule and closely connected, without sufficient distance between each other. Therefore, different anchoring groups of the same dispersant cannot be adsorbed on different particles, thus avoiding "bridging" flocculation.

③ Polymeric carboxylate dispersants can significantly reduce the viscosity of the dispersion system, increase the content of the active ingredients of pesticides, and have good fluidity. They can be used to prepare high-content suspension systems.