Abstract

Foam formation and air entrapment pose significant challenges in pesticide formulations. This review examines their underlying mechanisms and explores advanced control strategies, including vacuum deaeration, optimized processing techniques, specialized packaging design, and formulation design modifications to minimize foam generation and air inclusion.

CONTENTS

1. Introduction
2. Liquid foam and physical mechanisms of foaming
3. Antifoaming agents
4. Defoamers
5. Strategies for high foaming formulations
6. Air entrapment in liquid pesticide formulations: challenges and solutions
7. Selecting the right pump types to prevent air entrapment
8. Mechanical deaeration
9. Common filling achine Designs to Prevent Air Inclusion

1. INTRODUCTION

Foaming and air entrapment are common challenges in the development and production of pesticide formulations. These phenomena can significantly affect the stability, performance, and usability of formulations. Foaming, resulting from air bubble inclusion and stabilization, along with air entrapment in the formulation matrix, is more than a mere process nuisance—it can cause instability, dosing inaccuracies, and reduced application efficiency.

Understanding the mechanisms behind foaming and air entrapment is crucial for developing effective strategies to control these issues. Factors such as surfactant selection, formulation viscosity, particle wetting characteristics, and process conditions all contribute to the extent and persistence of air-related problems in formulations. In turn, these factors necessitate an integrated approach combining formulation design, mechanical solutions, and advanced equipment to mitigate their impact.

Beyond formulation composition, process optimization and advanced equipment design play vital roles in mitigating these problems. Mechanical deaeration techniques, such as inline vacuum degassers or in-tank systems, are essential for removing entrapped air during processing. Similarly, selecting the right pump types can prevent the introduction of air during transfer, ensuring consistent product quality. Finally, the design of filling equipment, including anti-foam nozzles, their precise placement, and controlled filling rates, helps minimize turbulence and air inclusion during packaging.

This review explores the mechanisms driving foaming and air entrapment, their implications for formulation stability and performance, and practical strategies, including equipment-focused solutions—to control them. Insights into equipment design, process optimization, and product-specific considerations are provided, offering a comprehensive guide for tackling these challenges. By addressing these critical aspects, this review aims to support the development of robust liquid pesticide formulations, ensuring consistency, efficacy, and reliability across applications.

2. LIQUID FOAM AND PHYSICAL MECHANISM OF FOAMING.

Foaming Dynamics. Foaming is a dynamic process in which gas (air) bubbles are stabilized within a liquid. This process typically occurs under conditions such as mixing, agitation, or aeration, where gas (air) is introduced into a liquid. Surfactants stabilize the gas-liquid interface by reducing surface tension and forming elastic films around bubbles.

Definition of Foams. Liquid Foams are colloidal systems comprising a dispersed gas phase within a continuous liquid phase. The unique properties of foams arise from the presence of gas bubbles, setting them apart from other colloidal systems.

Foam Structure and Geometry. Foam consists of gas bubbles dispersed within a liquid phase. The structure is supported by Thin Liquid Films, or Lamellae, that separate adjacent bubbles. At the junctions of three or more bubbles, Plateau Borders form, redistributing liquid from the Thin Films. Most liquid resides in Lamellae or Plateau Borders, while the gas occupies the bubbles. Surfactants accumulate at the gas-liquid interface, reducing surface tension and stabilizing the foam. Surfactants in agrochemical formulations, including large polymeric molecules, enhance foam stability by reinforcing the thin films and interfaces, preventing structural collapse.

Physical Properties of Foams.

Density and Porosity: Foam density is determined by the volume fraction of the gas phase and the density of the continuous phase. Porosity represents the fraction of void space in the foam and correlates directly with density.

Mechanical Properties: Foams display viscoelastic behavior, combining elastic and viscous responses to deformation. Their stiffness, strength, and toughness depend on the properties of the continuous phase and foam microstructure.

Rheology: Foam rheology is complex due to the interplay between gas and liquid phases. Foams exhibit non-Newtonian behavior, often showing shear-thinning, where apparent viscosity decreases with an increasing shear rate. Bubble size distribution, the gas volume fraction, and the continuous phase’s properties influence viscoelasticity.

Foam Stability Mechanisms.

Thin Liquid Films: Foam stability depends on lamellae, stabilized by surfactants forming elastic monolayers that resist rupture.

Gibbs-Marangoni Effect: Surfactant redistribution at stretched bubble surfaces restores equilibrium, stabilizing the foam. Surface tension gradients oppose liquid drainage and stabilize films. Reduced surface tension at the gas-liquid interface minimizes bubble coalescence and maintains foam structure. Surfactant type and concentration are key to determining surface tension and foam stability.

Capillary Pressure: Film curvature exerts pressure that resists bubble collapse.

Steric Stabilization: Physical barriers from adsorbed surfactant molecules prevent coalescence.

Electrostatic Stabilization: Repulsive forces between similarly charged bubble surfaces enhance stability.

Viscous Liquids: High-viscosity liquids slow drainage and resist coalescence by reinforcing thin films. Examples include glycerol and high molecular weight polymers like xanthan gum.

Disjoining Pressure: Disjoining pressure arises from forces (Van Der Waals, electrostatic, and steric) between thin film interfaces. A positive disjoining pressure stabilizes foam by preventing film thinning and rupture. Surface chemistry, ionic strength, and absorbed molecules influence this pressure.

Destabilizing Factors: Foam DRAINAGE and COARSENING.

Foam stability is affected by two primary processes: Drainage and Coarsening which are two key phenomena in the foaming process that significantly impact foam stability and lifespan. These natural processes destabilize foams, driven by thermodynamic and physical forces. Understanding these mechanisms is essential for developing effective strategies to destabilize foams, particularly in applications such as agrochemical formulations.

COARSENING (Ostwald Ripening and Coalescence). Coarsening is driven by the thermodynamic instability of foam, as the system seeks to minimize its total surface energy. It results in changes to bubble size distribution, with larger bubbles growing at the expense of smaller ones. This leads to a reduction in the overall number of bubbles and an increase in average bubble size.

Mechanisms of Coarsening:

Ostwald Ripening. Small bubbles have a higher Laplace pressure due to their curvature, making gas molecules diffuse from smaller bubbles to larger ones. Over time, smaller bubbles shrink and eventually disappear, while larger bubbles grow. This process is diffusion-driven and occurs even in foams stabilized by surfactants or polymers.

Coalescence. Occurs when the thin liquid films (lamellae) separating adjacent bubbles rupture. Bubble coalescence is initiated by local thinning of the lamellae, often due to gravity-driven drainage, surface-active impurities, or mechanical disturbances. Once ruptured, bubbles merge into larger bubbles, accelerating the foam's collapse.

Factors Influencing Coarsening:

Surfactants. Effective surfactants can create elastic and robust films to resist rupture and reduce gas diffusion.

Viscosity. High-viscosity liquids slow down coalescence by reinforcing thin films.

DRAINAGE. Drainage is the flow of liquid through the foam structure, driven by forces such as gravity and capillarity. This liquid movement leads to thinning of the lamellae and redistribution of the liquid phase, impacting foam stability.

Mechanisms of Drainage:

Gravity-Driven Drainage. Liquid flows downward through the Plateau borders and lamellae due to the density difference between the gas and liquid phases. This process is influenced by the foam's height, liquid viscosity, and bubble size.

Capillary Drainage. Driven by pressure differences between bubbles of varying sizes. Liquid moves from areas of smaller bubbles (higher capillary pressure) to larger bubbles (lower capillary pressure).

Plateau Border Suction. Liquid is drawn from thin films (lamellae) into the thicker Plateau borders due to pressure gradients. This suction effect contributes to the thinning and eventual rupture of the lamellae.

Node-Dominated Drainage. In foams with high liquid fractions and small bubbles, nodes (where multiple Plateau borders meet) become the bottleneck for liquid flow. These constricted nodes create significant pressure drops, further slowing liquid redistribution.

Interplay Between COARSENING and DRAINAGE.

Coarsening and drainage are interconnected processes that collectively govern foam stability: Drainage reduces the liquid content in lamellae, weakening the thin films and accelerating coarsening through coalescence. Coarsening alters the bubble size distribution, influencing drainage pathways and liquid redistribution.

3. ANTIFOAMING AGENTS

Antifoaming agents are crucial additives in agricultural formulations, designed to destabilize foam and prevent its formation during production or application. Foam in such formulations can impair efficient mixing, dosing accuracy, and application performance. These agents are typically low-viscosity liquids or dispersible solids with low surface tension, effectively interfering with the stabilization mechanisms of foam films.

Common Types of Antifoaming Agents.

Silicone-Based Compounds:

Polydimethylsiloxanes (PDMS): The backbone of these compounds is a silicone chain (Si-O-Si) with attached methyl groups, making them highly hydrophobic. The low surface tension and spreading ability of PDMS enable them to effectively displace surfactants from foam films, promoting destabilization.

Hydrophobic Silica Particles: When combined with PDMS, these particles enhance foam-breaking efficiency by disrupting the elasticity of foam films, facilitating faster drainage and collapse of the foam structure.

Non-Silicone Oils:

Mineral Oils and Vegetable Oils: With long hydrophobic hydrocarbon chains, these oils spread over foam films, weakening their stability. Examples include paraffinic hydrocarbons and oleic acid esters.

Waxes and Fatty Acid Esters:

Hydrophobic Waxes and Fatty Acid Esters or Alcohols: These materials introduce insoluble particles that disrupt foam films physically, while their hydrophobicity prevents re-stabilization. An example is stearyl alcohol, commonly used in aqueous formulations.

Anti-foaming Agents Mechanisms of Action.

Antifoaming agents prevent foam stabilization by targeting key foam stability factors like coarsening (bubble growth due to gas diffusion) and drainage (liquid film thinning due to gravity). They are also termed foam inhibitors and defoamers. Antifoaming agents are used in a process to avoid foaming, whereas defoamers are utilized to remove the existing foam. Alcohols like octanol work well as a defoamers but not as antifoams. It is challenging to explain the antifoaming and foam-breaking effect obtained by the addition of these compounds since foam drainage and stability of liquid films are still incompletely understood. There are different types of foam inhibitors; the first one is chemical inhibitors, which aid drainage while reducing the bulk viscosity of the liquid and may result in less stable foam. The second type is a solubilized chemical that aids antifoaming action.

Their primary mechanisms include:

Reduction in Surface Tension Gradients: By disrupting the surfactant monolayer at the air-liquid interface, antifoaming agents inhibit the Marangoni effect, which would otherwise stabilize foam films. Increased drainage accelerates foam destabilization.

Promoting Coalescence: Hydrophobic patches formed by antifoams weaken foam lamellae (the thin liquid films between bubbles), causing bubbles to merge and collapse.

Spreading Mechanism: Insoluble oils or hydrophobic particles spread rapidly on foam films, displacing surfactants and disrupting the stability of the bubble structure.

Bridging-Dewetting Mechanism: Particles bridge across the thin films, creating weak points as liquid recedes from their surfaces. These weak points initiate rupture and collapse of the foam structure.

Entering-Spreading-Bridging Mechanism: A combined mechanism where the antifoaming agent enters the foam lamella, spreads, and creates a bridge that destabilizes the foam.

Also, there are two different modes of action of antifoaming: brief fast, and slow. Fast antifoams can rupture foam films in the initial phases of film thinning; hence, in a conventional foam-stability experiment, fast antifoams entirely degrade the foaming in less than one minute. Further microscopic investigations demonstrated that such fast antifoaming agents collapse the thin layer among the bubbles by a “bridging” mechanism that involves the building of an oil bridge within the two phases of the foam. Hence, such fast antifoams are desired when the foam needs to be entirely abolished. In the case of slow antifoams, they do not break up the foam until the antifoam globules have been caught and crushed via thinning walls of the Plateau borders and nodes during the foam drainage practices. Under the influence of slow anti-foaming agents, various contrasting phases can be noticed during the evolution of the foam. These phases may last for minutes or hours.

Film rupture can also happen via undissolved oil droplets accumulating on the film surface. These oil droplets either enter the air-solvent interface or spread over the film which causes displacement of the original film, and lead to rupturing of the film.

Figure below explains the mechanistic approach of oil droplets destroying the foam by the bridging-stretching mechanism and bridging-dewetting mechanism. In either of these mechanisms, initially, the oil droplet comes into contact with two film surfaces, i.e. it forms a bridge among them (Fig. A, B). In the bridging-stretching mechanism (Fig. C, D), the oil bridge collapses. For the bridging-dewetting mechanism (Fig. E, F), the bridge cannot deform because the surfaces of the foam layer wet the oil drop surface, which causes film destabilization at the oil bridge’s circumference. The third option is when foamed film forms a stable oil bridge without rupturing the film (Fig. G, H).

By utilizing the proper hydrophobic solid elements, oil drops, or oil-solid complexes, one can achieve effective control over particular foaming compounds (like surfactants, proteins, or soluble polymers). All these antifoams are referred to as “heterogeneous” antifoams because the antifoam entities are spread like distinct phases in the foaming solutions. Such heterogeneous antifoams are often referred to as “hydrophobic” antifoams; practical knowledge and theoretical study of experimental findings indicate that the surface of the dispersed units (drops) ought to be suitably hydrophobic for efficient antifoam activity. To regulate foaminess and foam stability, oils and mixes of oils containing hydrophobic components are frequently utilized in a variety of techniques. In particular cases, molecularly dispersed species (surfactants or polymeric compounds) might potentially function like foam inhibitors; they are known as "homogeneous," "molecular," or "amphiphilic" antifoams. Generally, these constituents are less effective than heterogeneous antifoams, but they possess other significant benefits such as less cost, no persistent stains on the finished product, food compatibility, etc.

4. DEFOAMERS

Defoamers are specifically formulated to collapse existing foam in agricultural formulations, a task distinct from preventing foam formation. They share some functional overlap with antifoaming agents but are more focused on rapid destabilization of foam films.

Defoamers Mechanisms of Action.

Defoamers act by disrupting foam stability through: Spreading Across Foam Lamellae. Hydrophobic materials displace surfactants and thin foam films, leading to rupture.

Promoting Coalescence of Bubbles: By forming gas bridges (capillary structures) or directly rupturing films, they collapse bubbles.

Enhancing Drainage: Defoamers facilitate liquid drainage from foam, destabilizing the film structure.

Common Defoamer Types

Silicone Oils: Highly effective in small quantities for aqueous and solvent-based systems.

Polyether-Modified Silicones: These enhance hydrophilicity and ensure efficient spreading in aqueous formulations while retaining foam-destabilizing properties. Example: Modified siloxanes with polyether groups (-CH₂CH₂OCH₃).

Hydrophobic Particles: Hydrophobically modified waxes or polymers that create gas bridges or directly rupture foam films. Example: Hydrophobically modified polyethylene wax.

Surfactant-Based Defoamers: Fatty alcohols and polyalcohols, along with alkoxylates, are effective in disrupting foam films through their amphiphilic nature and spreading ability.

Summary of Properties.

A chemical additive known as a defoamer is also an antifoaming agent and lowers and prevents the production of foam in industrial processes. Antifoams are hence referred to as potent foam suppressors. They are crucial both from a theoretical and practical standpoint of view. Thus, defoaming and antifoaming agents are often used interchangeably. Some of the basic characteristics and requirements needed for antifoams are given in the table below. The following table highlights the key differences between antifoaming agents and defoamers, summarizing their roles and characteristics:

 

Property	Antifoaming Agents	Defoamers
SPREADING ABILITY	Low surface tension (silicones, oils)	Enhanced spreading via modified silicones
HYDROPHOBICITY	High hydrophobicity to disrupt film formation	Balanced hydrophobicity for entering foam films
FOAM FILM INTERACTION	Disrupt formation by weakening surfactant adsorption	Thin and rupture foam films by spreading locally
SOLUBILITY	Insoluble in medium, prevents re-stabilization	Partially soluble for controlled spreading

5. STRATEGIES FOR HIGH FOAMING FORMULATIONS

Foam formation can present significant challenges in pesticide formulations, affecting not only the manufacturing and packaging processes but also the efficiency and precision of field applications. This chapter outlines practical strategies, supported by detailed data, to effectively manage and mitigate foam in both liquid and solid pesticide formulations.

IDENTIFYING THE PROBLEM: ROOT CAUSE ANALYSIS

The first step in addressing high foaming formulations is to identify the underlying causes. Foam generation is often influenced by formulation’s components and process conditions. Two critical factors to evaluate are:

Foam Sources: Foam formation is often triggered by formulation components like surfactants, dispersants, or wetting agents and process conditions like agitation, aeration, and other processing factors further exacerbate this issue.

Foaming Propensity Testing: Conducting controlled laboratory tests can help measure a formulation's foaming tendencies under specific conditions. Parameters such as shear rates, temperature variations, and water hardness can significantly impact foam behavior and should be considered during the testing phase.

This analytical groundwork enables formulators to design solutions tailored to the specific causes of foam in their formulations.

MITIGATING FOAM IN SUSPENSION CONCENTRATE (SC) FORMULATIONS.

Suspension Concentrates are a common pesticide formulation prone to foaming due to their high surfactant content. The following strategies can help minimize foam:

Use LOW-FOAMING WETTING AND DISPERSING AGENTS

Replacing high-foaming surfactants with low-foaming alternatives is a proven method for reducing foam. Below are examples of effective low foaming wetting and dispersing agents:

Material Name	Manufacturer	Chemical Nature	Application Purpose	Recommended concentration in SC formulations	Aggregate State	Water Solubility	Temperature Stability	Shear Stress Stability
Atlox™ 4916	Croda	Polymeric surfactant	Dispersant	1-3%	Liquid	Soluble	70°C	Moderate
Dynol™ 360	Air Products	Nonionic surfactant	Wetting agent	0.1-0.5%	Liquid	Soluble	65°C	Moderate
Dehypon® LT 104	BASF	Fatty alcohol ethoxylate	Wetting agent	0.2-1%	Liquid	Soluble	70°C	High
Silwet™ L-77	Momentive	Trisiloxane ethoxylate	Super spreader, air release	0.05-0.15%	Liquid	Dispersible	60°C	Low
Pluronic® RPE 1740	BASF	EO/PO Block copolymer	Low-foaming dispersant	0.5-2%	Liquid / Solid	Soluble	70°C	Moderate

These agents not only suppress foam but also maintain excellent wetting and dispersing properties, ensuring the formulation's performance is not compromised.

Apply ANTIFOAMING AND DEFOAMING AGENTS

Antifoaming and defoaming agents are essential tools in foam management. While both categories reduce foam, they act at different stages:

• Antifoaming agents prevent foam formation by reducing the surface tension of the medium.
• Defoaming agents disrupt existing foam by penetrating the foam lamellae and collapsing the bubbles
• Key Differences Between Antifoaming and Defoaming Agents

Feature	Antifoaming Agents	Defoaming Agents
Primary Function	Prevent foam formation	Eliminate existing foam
Mechanism of Action	Reduce surface tension before foam forms	Disrupt foam lamellae and spread over liquid-gas interface
Application Timing	Added proactively during formulation or processing stages	Added reactively to address existing foam
Key Property	Low solubility in the medium	High surface activity and spreading ability

Below are examples of antifoaming and defoaming agents applied in SC formulations:

Material Name	Manufacturer	Chemical Nature	Application Purpose	Recommended concentration in SC formulations	Aggregate State	Water Solubility	Temperature Stability	Shear Stress Stability
Silcolapse® 5020	Elkem	Silicone compound, PDMS	Defoaming agent for immediate foam suppression	0.1-0.4%	Liquid	Dispersible	85°C	High
Xiameter® AFE-1510	Dow Corning	Silicone emulsion	Antifoam for immediate foam suppression	0.1-0.3%	Liquid	Dispersible	80°C	Moderate
Tego® Antifoam 1488	Evonik	Modified polyether siloxane	Antifoaming agent for long-lasting effect	0.1-0.5%	Liquid	Dispersible	70°C	Moderate
Agnique® AF 100, 400	BASF	Fatty alcohol-based	Antifoam for long-lasting effect	0.1-0.3%	Liquid	Dispersible	70°C	Moderate
Foam Ban TK 150	Munzing	Mineral based defoamer	Defoaming agent	0.1-0.5%	Liquid	Insoluble	85°C	High
Foam Ban TK 4990	Munzing	Premium grade silicon compound	Defoaming agent	0.1-0.4%	Liquid	Dispersible	110°C	Extremely High

Key Considerations:

Defoamer

Anti-foaming Agent

Always check for defoamer with high surface activity, i.e., a stronger reduction of surface tension than the surfactant that causes the foam. In WG/WP formulations, ensure compatibility with the binder so that it helps to prevent the formation of surface irregularities (crater defects). The selected defoamer must be able to enter foam lamellae and spread effectively on the liquid/gas interface. Your selected chemistry should be effectively insoluble in the foaming medium.

The surface tension of the anti-foaming agent must be lower than that of the foaming solutions. The solubility of the anti-foaming agent in the foaming solution must be low & must not react with the foaming solution. It should have a high spreading co-efficient. Always ensure there is no odor or residue left in the formulation that is detrimental to the product.

MANAGING FOAM IN WETTABLE GRANULE (WG) AND WETTABLE POWDER (WP) FORMULATIONS

Solid formulations such as WG and WP can exhibit crucial foam-related challenges during production and application. These strategies are particularly effective:

Use LOW-FOAMING POWDERED WETTING AND DISPERSING AGENTS, e.g.:

Material Name	Manufacturer	Chemical Nature	Application Purpose	Recommended concentration for WP/WG formulations	Aggregate State	Water Solubility	Temperature Stability	Shear Stress Stability
Vanisperse® A	Borregard	Lignosulfonate, Sodium salt	Low-foaming dispersant	2-5%	Powder	Soluble	85°C	High
Morwet™ D425	Nouryon	Naphthalene Sulfonate Formaldehyde condensate NSF	Low-foaming dispersant	2-4%	Powder	Soluble	90°C	Good
Geropon® T/36	Solvay	Sodium salt of polycarboxylic acid	Low-foaming dispersant	1-4%	Powder	Soluble	70°C	Good
Tamol® DN	BASF	Phenol sulfonic acid-formaldehyde condensate	Low-foaming dispersant	1-3%	Powder	Soluble	80°C	Good
Stepsperse DF 500	Stepan	Spray dried blend of liquid anionic surfactants and modified lignosulfonates	Low-foaming dispersant	1-3%	Powder	Soluble	85°C	Good
Stepwet DF200	Stepan	Sodium salt NSF	Low-foaming wetting agent	0.5-2.0%	Free-flowing granules	Soluble	80°C	Moderate

Key Considerations:

Powdered low-foaming wetting and dispersing agents used in WG formulations should demonstrate strong stability under the high temperatures and shear stress encountered during processing.

Use LIQUID LOW-FOAMING WETTING AND DISPERSING AGENTS FOR WG FORMULATIONS.

In addition to powdered low-foaming dispersants, liquid low-foaming dispersants can be utilized when necessary for the efficient dispersion of WG (Water-Dispersible Granules) formulations in the spray tank. Refer to dispersants indicated for SC (Suspension Concentrate) formulations, while keeping in mind that the recommended concentrations for SC and WG formulations may differ:

Material Name	Manufacturer	Chemical Nature	Application Purpose	Recommended concentration for WG formulations	Aggregate State	Water Solubility	Temperature Stability	Shear Stress Stability
Atlox™ 4916	Croda	Polymeric surfactant	Dispersant	1-4%	Liquid	Soluble	70°C	Moderate
Dynol™ 360	Air Products	Nonionic surfactant	Wetting agent	0.2-0.8%	Liquid	Soluble	65°C	Moderate
Dehypon® LT 104	BASF	Fatty alcohol ethoxylate	Wetting agent	0.3-1.5%	Liquid	Soluble	70°C	High
Silwet™ L-77	Momentive	Trisiloxane ethoxylate	Super spreader, air release	0.1-0.3%	Liquid	Dispersible	60°C	Low
Pluronic® RPE 1740	BASF	EO/PO Block copolymer	Low-foaming dispersant	0.8-2.5%	Liquid / Solid	Soluble	70°C	Moderate

Key Considerations:

For WG formulations, liquid low-foaming dispersants are applied in the wetting solution for extrusion granulation or added to the formulation premix before spray drying. It is crucial that the liquid low-foaming dispersing and wetting agents exhibit stability under high temperature and shear stress, as this is a vital factor for their application in WG formulations.

Incorporate SILICA-SUPPORTED PRE-ADSORBED ANTIFOAMING AGENTS, e.g.:

Pre-adsorbed agents simplify foam control in WG and WP formulations. These ready-to-use materials can be added directly to the premix.

Material Name	Manufacturer	Chemical Nature	Recommended concentration for WG/WP formulations	Aggregate State	Water Solubility	Temperature Stability	Shear Stress Stability
Dow Corning® 200 Powder	Dow Corning	Silica-supported PDMS	0.2–0.8%	Powder	Insoluble	200°C	Good
SPI-SILICONES SP-30	SPI-SILICONES	Modified silicone polymer	0.3–1%	Powder	Dispersible	190°C	Moderate
Geropon AF 78	Solvay	Defoaming agent adsorbed on inert carrier	0.5-2%	Powder	Insoluble	75°C	Good

Key Considerations:

The key parameters for pre-adsorbed antifoaming agents are their stability under high temperatures and shear stress. If they lack stability under these conditions, their effectiveness will diminish after processes such as extruder granulation, spray drying, and fluid bed drying.

Incorporate LIQUID ANTIFOAMING AGENTS AND DEFOAMERS instead of powdered agents.

When ready-to-use powdered antifoaming agents are insufficiently effective in WG formulations, liquid antifoaming agents and defoamers can be used as alternatives or in combination with powdered agents. Refer to those recommended for SC formulations. They can be applied in one of three ways: into the wetting solution when preparing slurry for extrusion granulation, into the formulation slurry before spray drying, or after granule drying by spraying onto the dried granules. In the first two cases, their stability under high temperatures and shear stress is crucial to ensure consistent performance. It is important to note that the concentrations of liquid antifoaming agents in WG formulations differ from those used in SC formulations:

Material Name	Manufacturer	Chemical Nature	Application Purpose	Recommended concentration for WG formulations	Aggregate State	Water Solubility	Temperature Stability	Shear Stress Stability
Silcolapse® 5020	Elkem	Silicone compound, PDMS	Defoaming agent for immediate foam suppression	0.2-0.8%	Liquid	Dispersible	85°C	High
Xiameter® AFE-1510	Dow Corning	Silicone emulsion	Antifoam for immediate foam suppression	0.2-0.6%	Liquid	Dispersible	80°C	Moderate
Tego® Antifoam 1488	Evonik	Modified polyether siloxane	Antifoaming agent for long-lasting effect	0.2-1.0%	Liquid	Dispersible	70°C	Moderate
Agnique® AF 100, 400	BASF	Fatty alcohol-based	Antifoam for long-lasting effect	0.2-0.5%	Liquid	Dispersible	70°C	Moderate
Foam Ban TK 150	Munzing	Mineral based defoamer	Defoaming agent	0.2-1.0%	Liquid	Insoluble	85°C	High
Foam Ban TK 320, 340, 360	Munzing	Organo-modified siloxane	Defoaming agent	0.2-0.8%	Liquid	Dispersible	90°-100°C	Very High
Foam Ban TK 4990	Munzing	Premium grade silicon compound	Defoaming agent	0.2-0.7%	Liquid	Dispersible	110°C	Extremely High

APPLICATION MASTERY: FROM FORMULATION TO FIELD

Effective foam control extends beyond the manufacturing process and into the field. Field applications present their own challenges, such as variability in water quality, spray tank agitation, and environmental conditions. To ensure formulations perform effectively in the field, it is crucial to integrate user-friendly defoamers, optimize their selection and usage, and address the specific requirements of the formulation's actual use, including field application concentrations and separate antifoam application in spray tank mixes.

USER-FRIENDLY (DILUTION-ACTIVATED) DEFOAMERS

User-friendly defoamers are designed to activate upon dilution in water, making them ideal for the field application concentrations and direct inclusion in spray tank mixes. These defoamers suppress foam without negatively affecting the pesticide’s performance or application characteristics. They are particularly valuable in field settings, where farmers require straightforward and effective solutions.

Examples of User-Friendly Defoamers include:

Silicone-Based Defoamers: Silcolapse® 5020 (Elkem): A highly concentrated silicone-based defoamer that activates upon dilution, providing instant foam suppression in both soft and hard water; Xiameter® AFE-1510 (Dow Corning): A silicone emulsion defoamer, effective in rapidly collapsing foam during spray operations.

Polyether-Based Defoamers: Foamaster® MO 2133, 2190, 2193 (BASF): A non-silicone, polyether-based anti-foaming agent that activates under spray tank conditions, particularly in high-agitation environments; Pluronic® RPE 1740 (BASF): EO/PO block copolymer low foaming dispersant that works well in water-based systems and activates upon dilution, reducing foam during spraying operations.

Organomodified Silicone Defoamers: Break-Thru® AF 9903 (Evonik): An organomodified silicone-based defoamer designed for compatibility with diverse agrochemical formulations; Silwet® DF 134 (Momentive): a highly effective silicone polyester defoamer activated by dilution in spray tanks, offering excellent foam control and compatibility with pesticide formulations.

Selection and Usage Tips:

Selecting the appropriate defoamer or antifoaming agent for a specific formulation requires careful consideration of the following factors:

Compatibility: Ensure the defoamer is chemically compatible with pesticide formulation and does not destabilize active ingredients or formulation components.

Surface Activity: Choose a defoamer with high surface activity, capable of penetrating foam lamellae and spreading effectively at the liquid-gas interface.

Environmental Conditions: Consider temperature stability and performance under shear stress, especially in formulations subjected to high agitation or extreme temperatures.

Residual Effects: Select defoamers that do not leave undesirable residues, odors, or visible deposits on treated surfaces or spray equipment.

Field Testing: Always conduct field trials under realistic spray tank conditions to evaluate the defoamer’s performance with various water qualities (e.g., soft, hard, alkaline).

By incorporating the dilution-activated defoamers, you can effectively manage foam during field applications without compromising the performance of the pesticide. The concentration of antifoaming agents depends on the type of formulation (SC, WG, WP, etc.). The table below contains recommended concentration ranges, along with data on their manufacturers, chemistry, and stability under high temperature and shear stress.

Material Name	Manufacturer	Chemical Nature	Application Purpose	Recommended concentration in SC formulations	Recommended Concentration in WG formulation	Aggregate State	Water Solubility	Temperature Stability	Shear Stress Stability
Pluronic RPE 1740	BASF	EO/PO Block copolymer	Low foaming Wetting / dispersing agent	0.5-2.0%	0.8-2.5%	Liquid / Solid	Soluble	70°C	Moderate
Silcolapse 5020	Elkem	Silicone compound PDMS	Defoaming agent	0.1-0.4%	0.2-0.8%	Liquid	Dispersible	85°C	High
Xiameter AFE-1510	Dow Corning	Silicone emulsion	Antifoam	0.1-0.3%	0.2-0.6%	Liquid	Dispersible	80°C	Moderate
Foamaster MO2133 (formerly Foamaster SA-3), 2190, 2193	BASF	Mineral oil based	Defoaming agents	0.2-0.6%	0.3-1.0%	Liquid	Insoluble	90°C	High
Silwet DF134	Momentive	Silicone polyether	Defoaming agent	0.1-0.4%	0.2-0.8%	Liquid	Dispersible	75°C	Moderate
Break-Thru AF9903	Evonik	Organo-modified siloxane	Defoaming agent	0.1-0.5%	0.2-1.0%	Liquid	Dispersible	75°C	High

SPECIFICS OF TANK MIX APPLICATIONS

Tank Mix applications present unique challenges, as foam can form rapidly due to agitation during mixing and spraying. Addressing foam in this context requires strategic addition of antifoaming or defoaming agents. Key recommendations include:

Typical Concentrations for Tank Mix applications:

Silicone-Based Defoamers: 10–50 ppm (0.01–0.05 g/L).

Polyether-Based Defoamers: 20–100 ppm (0.02–0.1 g/L).

Organomodified Silicone Defoamers: 10–30 ppm (0.01–0.03 g/L).

These low dosages ensure that foam is effectively controlled without introducing excess material that could impact spray performance or leave residue.

Pre-Dilution:

Highly concentrated defoamers may need to be pre-diluted in water to ensure even dispersion in the spray tank. This step prevents localized overdosing and enhances the effectiveness of the agent.

Addition Order:

Add the defoamer to the spray tank first, before introducing other components of the pesticide formulation. This allows the defoamer to establish a barrier against foam formation during the subsequent mixing process.

Agitation Control:

Minimize excessive agitation during the mixing process. While agitation is necessary for uniform distribution, overly vigorous mixing can exacerbate foam generation.

Adjusting Dosage:

The concentration of the defoamer should be adjusted based on specific conditions, such as water hardness, temperature, and the inherent foaming tendency of the pesticide formulation. For example, hard water may require slightly higher dosages to counteract foam-promoting interactions.

Monitoring Spray Quality:

Excessive defoamer usage can impact spray droplet formation and deposition. It is critical to use the minimum effective concentration to maintain spray quality and avoid compromising pesticide efficacy.

On-Site Adjustments:

Farmers and applicators should be trained to assess foam levels during tank preparation and make real-time adjustments to defoamer dosages as needed.
By integrating these practices, spray tank mixing operations can be optimized to ensure uniform application, reduced equipment downtime, and improved overall performance in the field.

Summary.

Antifoaming agents and defoamers play complementary roles in managing foam in agricultural formulations. While antifoams prevent foam formation by enhancing drainage and destabilizing foam films, defoamers act on existing foam to accelerate its collapse. Both approaches ensure efficient processing, accurate dosing, and effective application of agrochemicals, contributing significantly to agricultural productivity. Their mechanisms and effectiveness depend on careful selection of materials and consideration of formulation conditions, such as temperature, pH, and compatibility with other ingredients.

6. AIR ENTRAPMENT IN LIQUID PESTICIDE FORMULATIONS: CHALLENGES AND SOLUTIONS

Air entrapment is a common yet critical issue in liquid pesticide formulations, such as Emulsifiable Concentrates (EC), Emulsions in Water (EW, oil in water), Dispersible Concentrates (DC), and Suspension Concentrates (SC). Unlike foaming, which involves stable dispersion of air bubbles due to surfactants, air entrapment results from physical entrapment of air bubbles during formulation, packaging, or application processes. This phenomenon has distinct mechanisms and impacts, necessitating focused strategies for mitigation.

MECHANISMS OF AIR ENTRAPMENT

Air entrapment occurs through various processes that introduce and trap air within liquid formulations. Key mechanisms include:

Vortex Formation: High-speed stirring during formulation creates vortices that pull air into the liquid.

Cavitation: Equipment like pumps can generate air bubbles through rapid pressure changes or loose fittings.

Turbulent Flow: Sudden changes in flow direction or velocity in pipes and conveyor systems can lead to air pocket formation.

Splashing During Filling: High-speed filling operations often cause turbulence, which entraps air in the liquid.

Emulsification and Dispersion: During the emulsification process in EW formulations or active ingredient dispersion in DCs, EC and SCs, air can become trapped.

Temperature Variations: Rapid heating or cooling during production may expand or contract air, leading to entrapment.

Particle Suspension: In SCs, air bubbles may adhere to or become trapped among suspended particles.

Equipment-Related Air Entrapment Sources

Critical equipment components contributing to air entrapment include:

Mixing tanks: Vortex formation and Improper impeller design

Pumps: Cavitation and Loose fittings

Conveyor systems: Flow direction changes and Air pocket creation

Filling machines: High-speed filling and Splashing

Impacts of Air Entrapment

Air entrapment can negatively affect both the stability of pesticide formulations and their performance. Common issues include:

Reduced Shelf Life: Trapped air accelerates oxidation and degradation of active ingredients, reducing product longevity.

Inconsistent Active Ingredient Distribution: Air bubbles can create uneven concentration, leading to improper dosing and reduced efficacy.

Altered Physical Properties: The presence of air affects viscosity and flow characteristics, complicating application processes.

Increased Volatilization: Air pockets may enhance volatilization, particularly in formulations with higher vapor pressures.

Phase Separation: In emulsion-based formulations, trapped air can destabilize the system, causing phase separation.

Equipment Malfunction: Air bubbles interfere with pumps and sprayers, leading to inconsistent application rates.

Comparison with Foaming

While foaming and air entrapment may seem related, their mechanisms and consequences differ significantly. Foaming involves the stabilization of small gas bubbles by surfactants, creating a semi-stable structure, whereas air entrapment results from larger air bubbles entrapped through physical processes. Foam bubbles are typically 3–10 μm in size, while trapped air bubbles range from 1.5 to 2.6 mm. These differences make foaming more of a surfactant-related issue and air entrapment a process engineering challenge.

MITIGATION STRATEGIES

Effective management of air entrapment requires a combination of equipment optimization, process control, and design improvements:

Degassing Equipment: Using degassing units during production or before packaging effectively removes entrapped air.

Slow-Fill Techniques: Reducing the filling rate minimizes turbulence, lowering the likelihood of air entrapment.

Equipment Design: Incorporating venting mechanisms in tanks, pipes, and filling machines allows air to escape during critical stages.

Nozzle Improvements: Nozzles designed to reduce splashing during filling help prevent air incorporation.

Closed Transfer Systems: These systems ensure air-tight transfer of formulations, reducing air introduction during handling.

Container Design: Containers with smooth internal surfaces, shapes facilitating complete emptying and venting features reduce air entrapment during storage and usage.

Pressure Equalization: Incorporating features to equalize pressure during filling and sealing minimizes turbulence.

Automated packaging systems: Utilize fully automated packaging systems that can maintain consistent filling speeds and minimize human error.

Conclusion

Air entrapment is a significant concern in liquid pesticide formulations, affecting stability, efficacy, and application consistency. Unlike foaming, which is chemically driven, air entrapment is primarily a physical process influenced by equipment and handling techniques. By understanding the mechanisms of air entrapment and implementing targeted mitigation strategies, manufacturers can enhance product reliability, ensuring better performance and user satisfaction.

7. SELECTING THE RIGHT PUMP TYPES TO PREVENT AIR ENTRAPMENT

Using the right type of pump can significantly reduce the risk of air entrapment, ensuring a more efficient and effective pesticide application process. To prevent air entrapment when pumping liquid pesticide formulations, peristaltic pumps and diaphragm pumps are generally recommended.

RECOMMENDED PUMPS:

PERISTALTIC PUMPS: These pumps use a flexible tube that is compressed by rollers to move the liquid. The design ensures that there is no contact between the liquid and the pump mechanism, which minimizes the risk of air being drawn into the liquid. The tube is completely enclosed, preventing air from entering the system.

DIAPHRAGM PUMPS: These pumps use a flexible diaphragm that moves back and forth to create a vacuum and push the liquid through the pump. The diaphragm acts as a barrier between the liquid and the pump's internal components, reducing the chance of air entrapment. The diaphragm provides a seal that keeps air out of the liquid.

Not Recommended Pumps:

Centrifugal Pumps: These pumps use a rotating impeller to move the liquid. While they are efficient for many applications, they can introduce air into the liquid if not properly primed or if there are leaks in the system. The rotating impeller can create a vortex that draws air into the liquid.

Gear Pumps: These pumps use gears to move the liquid. The common design can sometimes allow air to be drawn into the pump, especially if there are gaps or wear in the gears. Gaps or wear in the gears can allow air to be drawn into the pump.

HIGH-CAPACITY PERISTALTIC PUMPS FOR TRANSFERRING LARGE VOLUMES

High-capacity peristaltic pumps are required for transferring large volumes of liquid formulations. For instance:

FLUIMAC HELIOS ASP HIGH-PRESSURE PERISTALTIC DOSING PUMPS

Helios ASP peristaltic pumps, with a head of up to 10 bar and a maximum flow rate of 25,000 l/h. They are effective solutions for liquids with viscosity u to 60,000 cps and achievable suction up to 8 meters. Pump Variants: ASP FX: Fixed flow rate, ASP VX: Adjustable flow rate with mechanical variator, ASP IX: Adjustable flow rate with motor-inverter.

NETZSCH PERIPRO® PERISTALTIC PUMPS

The PERIPRO® peristaltic pumps are highly efficient and heavy-duty machines, Ideal for handling sensitive liquids without introducing air. The hose compression system offers the highest accuracy, effectiveness and durability. The absence of valves and mechanical seals means that the PERIPRO® is completely leak-free. In addition, the PERIPRO® peristaltic pump withstands dry running completely undamaged, even over a longer period of time. The chemical version of the PERIPRO® pump is a fully protected unit with a TEFZEL® coating, that is resistant to the attack of highly corrosive acids and all kinds of difficult chemicals. High quality hose with unique manufacturing process: extruded inner layer with high-density textile reinforcement and precisely machined outer layer. Thanks to controlled tolerances, the hose ensures optimal compression and fast installation. Due to the large diameter of the rollers, the hose is squeezed optimally and gently. The roller principle reduces the load (friction) on the hose, compared to the sliding shoe, considerably. Flow rates from 0.05 to 230 gpm/11 to 52,000 l/h, using a double-head pump, it can be expanded to up to 460 gpm/104,000 l/h. For pressures up to 145 psi /10 bar.

HIGH-CAPACITY DIAPHRAGM PUMPS FOR TRANSFERRING LARGE VOLUMES

Here are a couple of examples of high-capacity diaphragm pumps suitable for preventing air entrapment:

YAMADA® NDP-80 SERIES DOUBLE DIAPHRAGM PUMP

Yamada® NDP-80 series Aodd pumps provide a maximum flow rate of 215 gallons per minute (48,830 l/h). Pumps are available in aluminum, stainless steel (316), Kynar® (PVDF), groundable acetal, and polypropylene construction.

IWAKI AIR HIGH PRESSURE 3″ TC-X801 SERIES DIAPHRAGM PUMP

The TC-X801 Series pumps offer excellent flow rates and an updated heavy duty body design. The pumps can operate with variable air pressures and are suited for both start/stop and fully continuous duty pumping applications. They can easily handle high pressure and long discharge piping. Maximum Flow Rate: 251 gpm (950 LPM – 57,000 l/h). Available in Stainless Steel, Aluminium, Cast Iron, Polypropylene.

NETZSCH TORNADO ROTARY LOBE PUMPS

Although Netzsch rotary lobe pumps are technically gear pumps, which are generally not recommended for air-preventing systems, they offer an effective solution for transferring liquid formulations without introducing air. These pumps are specifically designed for low-pulsation gentle and continuous conveyance, featuring a unique physical separation between the pump housing and gearbox to maintain the integrity of deaerated liquids. The conveying capacity is achieved through the contra-rotation of two rotors within the pump housing, which displaces the fluid from the suction side to the discharge side. They accommodate flow rates ranging from 6 to 4,000 gpm (1 to 900 m³/h) and pressures up to 145 psi (10 bar).

The innovative NETZSCH GSS technology (Gearbox Security System) of Netzsch Tornado T1 Rotary Lobe Pumps ensures the pump chamber and gearbox remain physically separated. Additionally, the NETZSCH PRS technology (Pulsation Reduction System) delivers near-pulsation-free operation, enhancing process efficiency and reliability.

8. MECHANICAL DEAERATION

Mechanical deaeration techniques physically remove entrapped air or foam from formulations during processing. These methods include inline deaeration, such as vacuum inline degassers, and in-tank deaeration, using specialized deaeration tanks to prevent air entrapment during continuous processing. Mechanical deaeration is especially critical for high-viscosity or concentrated formulations where chemical additives alone are insufficient.

IN-TANK DEAEARATION: HIGH-CAPACITY SPECIALIZED DEAERATION TANKS WITH IN-TANK DEAERATION SYSTEMS.

Vacuum-Assisted Degassing. These systems create a vacuum environment inside the tank, allowing air and foam to escape efficiently from the formulation. Examples of vacuum pumps for industrial-scale degassing are: VACUUBRAND VACUU·PURE® 10, De Dietrich QVF® Vacuum Systems.

Agitation with Degassing Blades. Tanks equipped with specialized agitators or blades designed to release entrapped air while maintaining uniform mixing. Industrial equipment examples are: IKA PROCESS DR 2000/3000 Series Mixers - High-shear mixers with integrated deaeration capabilities, ROSS VersaMix Multi-Shaft Mixers - Equipped with vacuum-rated tanks and degassing agitators for viscous and complex formulations.

Spray Nozzle Systems. Spray nozzles distribute the material into thin layers, increasing the surface area for air release under controlled vacuum or pressure. Industrial equipment example: GEA VARIVENT® Spray Deaerators.

Application Note:

It is important to note that the suitability of each system depends on specific processing requirements, such as formulation viscosity, sensitivity to temperature, and production scale. The integration of these systems should be tailored to the specific formulation and processing needs. For example: high-viscosity formulations: Benefit most from agitation with degassing blades or vacuum-assisted systems. Low-viscosity formulations: Spray nozzle systems are more effective.

INLINE DEAERATION. VACUUM INLINE DEGASSERS.

Among leading industry solutions, NETZSCH, a German manufacturer, leads with integrated systems that pair deaeration devices and specialized pumps for pesticide processing, proven through extensive field testing and widespread adoption.

DeAerator Type DA 602

With the NETZSCH Vacuum DeAerator Type DA 602, it is easy to continuously deaerate free-flowing products. Even micronized gas and air inclusions are removed from liquids of various viscosities or from viscous masses with this machine. The machines can be integrated into systems both in passage operation from interchangeable tanks and in inline operation. The possible throughput rates are strongly influenced by the product viscosity. Product flow rate 500-10,000 l/h. Vacuum pump 3 kW, Vacuum pump flow rate 100 m3/h.

The underlying operating principle of the NETZSCH Vacuum DeAerator is the so-called Vacuum Thin film Rotation (VTR) principle. The product is drawn in by the vacuum in the deaeration chamber (1) and directed to the center of the rotating plate. The thin layer of product on the rotating deaeration plate (2) is continuously deaerated. Centrifugal force affects the discharge of the product through an outlet pipe (3). The residence time of the product within the deaeration chamber (and thus the throughput) is influenced by non-return flaps and valves (4).

Options Explosion-proof design All stainless-steel construction Level monitoring Integration into process sequences

Designing an efficient liquid deaeration system involves strategic placement of deaeration equipment and selecting appropriate pumps to prevent re-aeration.

Placement Considerations:

Height Alignment: The deaeration equipment should be positioned at a level that allows gravity feed from the aerated liquid vessel or is equipped with a feed pump to ensure consistent flow.

Pumps: A suitable pump, such as a peristaltic or diaphragm pump, or Netzsch Rotary Lobe pumps, can be placed before the deaeration equipment to transfer the liquid without introducing additional air.

Post-Deaeration: Pumps should be installed downstream of the deaeration equipment to transfer the deaerated liquid to storage or further processing stages.

Height Consideration: The pump should be positioned at or below the level of the deaeration equipment outlet to facilitate gravity-assisted feeding and minimize suction-related air entrainment.

In summary, the strategic placement of deaeration equipment and the selection of appropriate pumps are critical to maintaining liquid quality in processing systems.

9. COMMON FILLING MACHINE DESIGNS TO PREVENT AIR INCLUSION

Air introduction during the filling of liquid pesticide formulations can indeed lead to inaccurate weighing, foaming, and inconsistencies. To address these issues, packaging machinery employs several strategies to minimize air entrapment and ensure smooth and accurate filling. Here's how the problem is commonly solved:

Special Nozzles

Anti-Foam Nozzles: Designed to reduce turbulence and foam formation, these nozzles dispense liquid in a controlled and laminar manner.

Bottom-Up Filling Nozzles: These nozzles move with the liquid level, staying submerged during filling to minimize air mixing and foam formation.

Nozzle Placement

Proper placement of the nozzle or spout is critical. Typically, the nozzle is inserted deeply into the bottle, close to the bottom, to ensure the liquid flows smoothly without splashing or introducing air. As the bottle fills, the nozzle gradually rises to stay just below the liquid surface.

Filling Speed and Flow Control:

Slower initial filling reduces turbulence and prevents splashing. The speed can then increase as the bottle fills, often in stages.

Using multi-stage or adjustable filling profiles (e.g., slow at the start and end, faster in the middle) helps maintain precision while minimizing foam.

Pressure Control:

Gravity filling is often used for low-viscosity liquids to prevent turbulence, but for more viscous formulations, pressurized filling or vacuum filling may be employed to control the flow more precisely and avoid air inclusion.

A consistent and low-pressure filling process ensures minimal disturbance.

Degassing Systems:

Some machinery incorporates degassing systems or venting to remove air from the liquid formulation before filling. This is particularly useful for highly aerated or foamy liquids.

Anti-Foaming Agents:

While this is more of a formulation-based approach, adding a small amount of anti-foaming agent to the pesticide formulation can significantly reduce foam generation during filling.

Machine Design Considerations:

Smooth and round machine parts (e.g., filling pipes and spouts) prevent turbulence.

Some machines are designed to reduce the angle or height of liquid entry into the container, ensuring a gentler flow.

Vacuum Filling Systems:

Vacuum-assisted filling machines remove air from the container before or during filling, ensuring a precise filling without introducing bubbles or foam.

Environmental Controls:

Temperature stabilization of the liquid prior to filling can reduce foaming, as some formulations tend to foam more at higher temperatures.

By combining these techniques, modern filling machinery can effectively minimize air inclusion, improve weighing accuracy, and optimize the packaging process for liquid pesticide formulations.