Polymeric Dispersants and Wetting Agents for High-Performance Solid Agrochemical Formulations

Shrikant Aherkar, Lead Scientist, Stepan Agricultural Solutions  Asia Pacific

Solid agrochemical formulations such as dust (D), granules (GR) and wettable powders (WP) have been in the market for many years. However, in the 1980s, a growing popularity was seen with the introduction of water dispersible granules (WDG) and wettable granules (WG). ¹ In the North American markets, WG are also referred to as dry flowables (DF). 

WG formulations are preferred especially for water-sensitive actives and combinations. These formulations are water-free and allow for manufacturing at a significant scale with very high active loading up to 93% actives. This makes them not only commercially attractive but also positions them as a safer alternative to WP and suspension concentrate (SC) formulations. To create these granules, several processes are employed, including pan granulation, extrusion, spray drying, fluid bed processing and high-speed granulation. The choice of process depends on factors such as the nature of the active ingredient, the loading, production volume, market needs and application. Extrusion is the preferred process for smaller volume formulations due to its ease in switching between different formulations. On the other hand, spray drying is more favoured for higher volume formulations with dedicated set up such as Mancozeb 75 WG and Sulphur 80 WG.

The market is witnessing a higher demand in the introduction of high active loading and combination formulations as regulatory pressure and Global Environment, Social and Governance (ESG) initiatives increase. ² To meet these challenging performance requirements, formulators prefer to use effective dispersing agents at lower dosage and polymeric dispersants have been proven to be one of the best chemistries to address this. Conversely, conventional lignosulfonate or naphthalene sulfonate-based dispersants require a higher dosage of 5–10% by weight to achieve desired performance. This makes it challenging to formulate WGs that are greater than 90% active with these dispersants. Moreover, these dispersants are mostly brown colored and due to their dark color, not preferred by some customers.

Stepan Agricultural Solutions offers a range of polymeric dispersants tailored for liquid formulations. Building on the success of these recently introduced dispersants suitable for liquid formulations, ³ Stepan has developed solid variants of polymeric dispersants, such as STEPSPERSE^® 3000. 

STEPSPERSE 3000 is an anionic polymethyl methacrylate-polyethylene glycol graft copolymers. It is a colourless, free-flowing powder that provides excellent dispersion at very low dosages in solid formulations. With its liquid variant, STEP-FLOW^® 3000, is an effective dispersant and crystal growth inhibitor in water-based dispersions. 

Typical Properties of STEPSPERSE 3000:

Figure 1. Stepan Company’s STEPSPERSE 3000, Polymethyl Methacrylate-PEG Graft Copolymer

This polymeric dispersant is commonly used in combination with wetting agents and Stepan offers a

range of wetting agents for formulators. 

Table 1. Stepan Company’s Wetting Agents

The following are some of the more challenging formulations that were developed using a combination of polymeric dispersants and wetting agents, along with their results. 

Atrazine 93% DF

Atrazine is a selective systemic herbicide for maize, sugarcane and pineapple. It can be formulated in WP, SC and OD formulations. WG is the preferred formulation for high active loading up to 93% actives. In the case of Atrazine 93% DF, an extruded WG formulation was developed, utilizing STEPWET DF-90 and STEPSPERSE 3000, resulting in excellent suspensibility and stability even after exposure to heat at 54°C for 14 days.

Table 2. Atrazine 93% DF Formulation

Table 3. Test Results for Atrazine 93% DF using STEPWET DF-90 and STEPSPERSE 3000

The application shows high loading WG and DF formulations can be created using the low dosage of approximately 3% of Stepan’s polymeric dispersant, while the suspensibility and dispersibility of the formulation is >90%. No significant drop in performance was observed even after the exposure to elevated temperatures of 54°C for 14 days. 

Beyond these newly developed polymeric dispersants, Stepan Agricultural Solutions continues to offer our legacy naturally derived lignosulfonate-based dispersants as the STEPSPERSE DF Series. Notable products in this series include STEPSPERSE DF-200 and STEPSPERSE DF-500, which are spray-dried blends of liquid anionic surfactants and modified lignosulfonates. These products provide good performance in formulations that require high silica levels and also act as binders, eliminating the need for an additional binder, in most cases.

STEPSPERSE DF-600 is another product in the series, offering improved dispersion of low-melting actives and is effective in hard water while reducing viscosity in SC formulations. 

These versatile dispersants can be used in a variety of applications, including WG, DF, SC, capsule suspension (CS) and mixed combinations (ZC) formulations.

Stepan’s solid polymeric dispersants presented in colourless, free-flowing powder forms, offer several advantages over conventional dispersants based on naphthalene formaldehyde condensates and lignosulfonates. They provide suspensibility boost at lower dosage levels as well as binding properties, eliminating the need for external binders in WG formulations. 

As the market continues to evolve, Stepan Agricultural Solutions remains committed to cultivating innovation. To learn more about our full range of products and advance formulation services, visit www.stepan.com/agriculture.

References:

¹AgroPages, February 10, 2023

²ADAMA ESG Report, 2022

³AgroPages, May 2020 and Nov 2022

⁴REACH = Registration, Evaluation, Authorisation and Restriction of Chemicals

⁵U.S. EPA FIFRA = United States Environmental Protection Agency, Federal Insecticide, Fungicide, and Rodencide Act

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