Challenges and Solutions in Developing Stable, Effective, and high-quality Suspo-Emulsion (SE) Formulations

Dr. Kamlesh Fondekar, Head – R&D, Godrej Agrovet Limited

Introduction 

In the agrochemical industry, formulation science plays a critical role in ensuring that crop protection products are effective, stable, and safe for use. One of such advanced formulation types that have come into the prominence is the Suspo-Emulsion (SE). Suspo-emulsion (SE) formulations are used to combine two active ingredients with very different physical properties into one formulation. They are a combination of suspension concentrate (SC) and concentrated aqueous emulsion (EW) technologies, which are both water-based. Sometimes This biphasic system combines the properties of suspension concentrates (SC) and emulsifiable concentrates (EC), enabling the simultaneous delivery of solid and liquid active ingredients (Or solid active ingredient dissolved in solvent) in a single formulation.  The advantages are that it is possible to formulate multiple active ingredients of different nature together, broadening the spectrum of activity and eliminating the disadvantage of tank-mix incompatibility. Although this biphasic system has its own advantages, in terms of development, there is a complicated complex set of problems. This article discusses the primary challenges in developing stable and of high-quality SE formulations and presents practical solutions.

Understanding Suspo-Emulsions

Suspo-Emulsions are multi-phase systems composed of fine solid particles suspended in water and oil droplets emulsified within the same continuous aqueous phase. The unique combination allows formulators to incorporate both hydrophilic and lipophilic active ingredients, thereby broadening the scope of pest control and improving application convenience. 

Key Challenges in SE Formulation Development

Physical Instability: Sedimentation and Creaming

Sedimentation is a process where dispersed particles within a formulation settle down under the influence of gravity. This phenomenon is commonly observed in formulations like suspension concentrate (SC) and Suspo-emulsion (SE), where the density difference between the dispersed phase and the continuous phase is significant. Sedimentation can lead to a non-uniform distribution of particles, resulting in a clear layer at the top and a dense particle-rich layer at the bottom. Creaming, on the other hand, is akin to sedimentation but occurs in the opposite direction. It is observed in emulsions where the dispersed droplets, being less dense, migrate upwards, forming a concentrated layer at the top. Creaming is particularly problematic in emulsifiable concentrates (EC) and Suspo-emulsion (SE) formulations, where it can lead to phase separation, affecting the texture, appearance, and efficiency of the product. This separation not only affects the visual homogeneity of the product but can also compromise its efficacy and user experience. In Agrochemical suspensions, for instance, sedimentation may lead to uneven distribution of active ingredients, impacting the efficacy and inconsistency during field application. 

Control of Particle Size Distribution

The particle size of both suspended solids and emulsified droplets plays a crucial role in formulation stability. Ideally, solid particles D10-D90 should be within the range of 1-5 microns, while emulsified droplets should be as small and uniform as possible. If the solid particles are too large, they tend to settle quickly (sedimentation). If the emulsion droplets are too big, they tend to rise or cream due to density differences. If the particle size is not controlled precisely, flocculation, agglomeration and coalescence may destabilize the formulation, resulting in sedimentation and/or creaming.

Complex Surfactants and Emulsifiers system

The selection of surfactants and emulsifiers in SE pesticide formulations requires a balanced, science-driven approach. A well-chosen surfactant system ensures physical stability, ease of application, and consistent efficacy of the final product. Leveraging the right combination of emulsifiers, dispersants, and wetting agents is essential to the success of any SE formulation. The surfactants and emulsifiers chosen must work synergistically to stabilize both phases without causing incompatibility, precipitation, or phase separation. Finding the right combination of Emulsifiers (for oil phase), Dispersants and Wetting Agents (for solid phase) that is effective for both phases without causing adverse interactions or precipitation is a complex and sensitive process. 

Viscosity Management

Viscosity is another critical parameter that significantly impacts formulation performance. A formulation with excessive viscosity becomes difficult to pump, handle, and spray, particularly through conventional agricultural spraying equipment. On the other hand, a formulation with low viscosity is prone to phase separation and inadequate suspension stability. Striking the right viscosity balance is essential to ensure both processability and stability.

Chemical Stability of Active Ingredients

Agrochemical active ingredients are often prone to chemical degradation, especially in aqueous environments. hydrolysis is major pathway through which actives can degrade over time. Ensuring the chemical stability of each active component in a multi-phase system is particularly challenging and requires the use of stabilizers and pH regulators.

Practical Solutions and Technological Approaches

Despite these challenges, numerous strategies and technological advancements can help formulators develop robust and stable SE formulations:

Advanced Milling and Homogenization

Controlling the particle size of suspended solids is typically achieved using high-energy milling techniques, such as bead milling or high-pressure homogenization. Similarly, for the emulsion phase, high-shear mixers can be employed to produce fine and stable oil droplets. One of the best methods to obtain good Suspo-emulsions is to separately prepare a suspension concentrate with the solid active and a concentrate emulsion with the liquid or low melting point active (EW/EC). These two formulations are then mixed together under agitation. In this way the characteristics of the formulation are controlled very well. It is also important to avoid a wet-milling of the mixture that include solid and liquid active together for these main reasons: The liquid active could act as a lubricant and could disturb the milling process. The solid active content is usually too low for a good wet-milling. It is better to mill the solid alone at the highest possible concentration for the efficient particle size reduction. The emulsifiers ratio and the grade of obtained emulsifiability could be disturbed (wider particle size distribution etc.) by the components used for the SC. These methods help in reducing the solid particles to the desired micron sizes, ensuring better suspension stability and minimizing the chances of agglomeration. 

Rational Selection of Surfactants and Dispersants

Surfactants (emulsifier, dispersing and wetting agents) should be chosen based on their Hydrophilic-Lipophilic Balance (HLB) values and compatibility with both active ingredients and each other. Often, a blend of non-ionic and anionic surfactants is used to achieve the desired balance. Compatibility testing and phase behavior analysis can aid in selecting the optimal combination of Surfactants. Emulsifiers, dispersing and wetting agents provide wetting and dispersion of the solid particles of the active ingredient into the water continuous phase by reduction of the oil/water interfacial tension and steric and/or electrostatic stabilization of the micronised droplets to avoid flocculation, aggregation or coalescence. Surfactants also serve to avoid flocculation or aggregation between solid dispersed particles and liquid active droplets. They can have the double role of dispersing agent and emulsifier.

Viscosity Modifiers and Rheology Control

Viscosity can be fine-tuned using rheology modifiers, such as cellulose derivatives, xanthan gum, or synthetic polymers. These additives improve the suspension stability without making the formulation overly viscous. Importantly, thixotropy behaviour or shear-thinning behavior is preferred, where the formulation thins or become flowable under shear (during spraying) and recovers its viscosity at rest to prevent sedimentation. Rheological characterization should be part of the formulation development process to ensure the product remains stable during storage and is easily applied in the field.

Enhancing Chemical Stability

To protect the active ingredients from degradation, formulators can incorporate Antioxidants pH buffers to maintain an optimal pH that slows hydrolysis. Chelating agents to neutralize metal ions that catalyze degradation. Microencapsulation or protective colloids that isolate the active ingredient from the aqueous environment. Proper packaging, such as air-tight containers with minimal headspace sometimes Nitrogen purging required, also contributes to chemical stability.

Stability Testing and Quality Control

A comprehensive stability testing protocol is essential before commercially producing an SE formulation. Tests should include: AHS (Accelerated stability studies) at elevated temperatures. Freeze-thaw cycles to assess resilience to temperature variations. Centrifugation to simulate long-term sedimentation/creaming. Viscosity and particle size monitoring over time. In addition, field testing under real-use conditions helps verify that the formulation performs consistently during application.

Future Trends and Innovations

With the rising demand for sustainable and efficient crop protection products, SE formulations will most likely experience further innovation. Emerging trends include: Green surfactants and biopolymers with environmental impact reduction potential. Nano- emulsion and nano-suspension methods for enhanced absorption and bioavailability. Smart tools of formulation using AI and machine learning for predictive modelling. When combined with a greater appreciation of the colloidal and interfacial science, these developments will also contribute to the development of next generation SE formulations. 

Conclusion

Developing a stable and efficient Suspo-Emulsion of high quality is a multi-faceted challenge which calls for knowledge of both physical and chemical understandings. In managing phase separation, in controlling particle size, in maximizing surfactants, and in the chemical stability of the formulation, it is necessary that every step of the formulation process be engineered carefully. However, providing the right tools, techniques, and testing protocols, one can manage to overcome these constraints and produce SE Formulations, having high performance and responding to the growing needs of modern agriculture. Utilizing scientific improvements and adopting innovation, the formulators can unlock the full potential of SE technology and help develop more efficient, sustainable, and easy-to-use agrochemical products.

This article was published in the magazine of 2025 Formulation & Adjuvant Technology. Follow this magazine to read more articles/stories.

If you'd like to share your company story/solution or have any promotion demands/advertise in this magazine and AgroPages, please contact Grace Yuan: grace@agropages.com