Croda: Designing new and novel aqueous dispersants – Atlox™ 4917

Atlox 4917 is a new and novel dispersant that Croda recently launched into the market. James Flavell, Technology Specialist at Croda delves into why dispersants are necessary, how Atlox 4917 was developed and showcases a snapshot of the extensive data set that supports this product.

For more in-depth information about this product or to speak directly to James himself, join Croda’s free, live webinar hosted on 21st April. Click here to register for the event.

What are dispersants?

Dispersants play a vital role in agrochemical formulations, maintaining stability both in the concentrated system and upon dilution. This ensures the active ingredient remains homogenously suspended throughout the formulation and is delivered effectively whilst minimising wastage of the active ingredient. With the development of new active ingredients with varying chemical structures and the requirement to combine multiple active ingredients within one system, new dispersant technology is needed to effectively stabilise these increasingly complex formulations.

Croda specialise in polymeric dispersants underpinned by a strong understanding of how structure function relationships impact product performance. We were therefore, in an ideal position to design and develop a new dispersant to fit the ever-changing needs of the market. Polymeric dispersants can be separated into several structural types, including block copolymers (such as AB, ABA, BAB), random copolymers and graft copolymers (such as comb, dendrimer, hyperbranched). Each of these configurations has their own pros and cons making them suited to meet different formulation needs. Common to all these categories, there are two fundamental building blocks for a dispersant: an anchoring (or adsorbing group) and a stabilisation group.

1. Anchoring to the surface

The anchoring group adsorbs to the solid particle surface, effectively covering the particle surface and adhering strongly to prevent displacement by other formulation components, such as wetting agents or adjuvants. To account for this, several anchoring mechanisms are available with different affinities for various surfaces (surface charge, crystallinity, size, and size distribution, shape, and density). This takes account of the various types of surfaces that need to be stabilised such as hydrophobic active ingredients and more polar materials such as micronutrients.

Once the dispersant is anchored in place it is very important it remains in position. This is specifically true for agrochemical formulations which are often complex and contain free molecules such as surfactants and adjuvants which can compete at the particle surface interface. Designed to be large molecules with high molecular weights, polymeric dispersants have multiple large anchoring groups which gives them an important advantage over their smaller monomeric counterparts. As a polymeric dispersant has multiple large anchoring groups, for each group which desorbs, several others are still adsorbed enabling them to remain anchored to the particle surface, even in the face of challenging conditions. Polymeric dispersants are thus highly preferable for stabilising dispersed systems.

2. Stabilisation

Equally important to anchoring is the stabilisation mechanism. There are two principal mechanisms for stabilising the dispersed particles: steric and electrostatic. Steric stabilisation uses large, high molecular weight chains to prevent flocculation by blocking/screening the dispersed particles from each other. Electrostatic stabilisation utilises ionic groups contained within the polymer structure to create an electric double layer around the dispersed particle. This is then repelled by the electric double layers of other approaching particles, preventing flocculation.

Introducing Atlox 4917

Atlox 4917 was designed to combine both stabilisation mechanisms as illustrated in Figure 1. This enables Atlox 4917 as a dispersant to exploit the positive effects of both stabilisation mechanisms, whilst offsetting the negatives associated with each one alone. This results in Atlox 4917 having several unique benefits.

Figure 1: Structure of Atlox 4917

Key benefits of Atlox 4917

• Compatible with a wide array of active ingredients (initially tested on over seven different active ingredients)
• Electrolyte tolerant (including both hard water and glyphosate)
• Effective at low use rate
• Crystal growth control
• Performs a dual function in suspoemulsion (SE) formulations
• Maintains performance in the presence of adjuvants 

There is a vast dataset to support the claims and benefits of Atlox 4917 but here I will focus on two key areas, performance at low use rate (including adjuvant compatibility) and electrolyte tolerance.  

Low use rate and compatibility with adjuvants

The benefits of a low dispersant use rate extend further than just a cost-in-use advantage. If the use rate is low it frees up more formulation space, allowing the formulator to target high loading, multiple active ingredients, and adjuvant incorporation. Atlox 4917 particularly excels at low use rates due to its highly efficient adsorption and packing at the solid/liquid interface. Adjuvant molecules, particularly those based on small dynamic materials, are likely to compete at the interface with a dispersant. The highly efficient packing of Atlox 4917 at the interface enables adjuvants to be incorporated with minimum effect on overall stability.

Diflufenican was chosen as the active ingredient for further investigation as it is a challenging material to disperse into an aqueous system due to properties such as high LogP, low water solubility and its strong electronegativity from high levels of fluorination. Thus, creating a highly challenging formulation. 

Table 1: Generalised recipe of a low dispersant use rate suspension concentrate (SC) formulation containing an adjuvant.

To view the full formulation, visit the Formulation Finder on the Croda Crop Care website (click here).

The formulation was compared to industry benchmarks. These were assessed using several key test methods to analyse multiple physical properties. A selection of data is shown here detailing the physical observations for the formulations produced.  

Key: NS – no separation, St – Separation top
Table 2: Visual stability data of SC formulation in Table 1

Breakdown of the formulations was noted in two ways; top separation caused by sedimentation of the dispersed solids and through the formation of a clay layer at the base of the storage formulation vessel. Top separation was observed by the formation of a water/surfactant layer at the top of the formulation. The second aspect, formation of a clay layer is identified as a hard-sticky sediment layer at the bottom of the storage vessel. If present this indicates an issue with the dispersant system depleting from the particle surface. The suspended particles have flocculated, and then sedimented, resulting in the formation of a coagulated layer.

The results in Table 2 show that Atlox 4917 produced the most stable formulation resulting in 10% separation after 14 days of storage at 54 °C, compared with 24% and 33% for the benchmark dispersants. As these formulations were designed to be highly stressed, high levels of separation were expected. These results do show an immediate advantage when formulating using Atlox 4917 as it had the lowest level of separation in a highly stressed system and prevented the formation of a clay layer.

This advantage is also observed in the particle size control of the formulation. The formulations were assessed via laser diffraction using a Malvern Mastersizer 3000.

Figure 2: Particle size data for Atlox 4917 and TSP benchmark

As can be seen in the particle size data in Figure 2, the formulation prepared using TSP was experiencing agglomeration on day 1 due to poor dispersant performance whereas the formulation containing Atlox 4917 showed a single peak distribution. This difference was exacerbated over the storage testing resulting in the high levels of separation and sedimentation observed visually.

Electrolyte tolerance

Dispersant performance can be impacted by the presence of electrolytes in the system. This presents potential issues for the use of electrolytes such as active ingredients that are electrolytes themselves (e.g., glyphosate salts), fertilisers, micronutrients and ions dissolved in hard water. Electrolytes cause the electric double layer in electrostatic dispersants or the steric chains (such as PEG) to collapse, reducing the effective radius of the dispersant. This reduces the effectiveness of the dispersant molecules resulting in sedimentation in concentrated formulations and poor performance upon dilution. Atlox 4917 has been designed to incorporate electrolyte tolerant monomers into the structure. These monomers serve as electrolyte sinks allowing the other stabilising monomers to remain effective even in the presence of high levels of electrolyte.

Figure 3: Schematic of the effect of electrolytes in stabilised particles

The cloud point of a material is the temperature at which it begins to phase separate and is typically observed by the solution turning cloudy, due to a loss in solubility. If a surfactant reaches its cloud point, its effectiveness decreases leading to formulation breakdown. The presence of electrolytes can cause side chains on dispersants to collapse, a behaviour characteristic in particular to ethoxylate chains which curl into hydrophilic coils, reducing the solubility and therefore the cloud point of a dispersant. To evaluate the electrolyte tolerance of Atlox 4917 cloud point assessments have been carried out in the presence of various electrolytes.

*Tested tanked mixed with a 400 g/L IPA SL diluted 200-fold.
Table 3: Cloud point results of Atlox 4917 in various electrolytes

Atlox 4917 was able to maintain high cloud point in many of the electrolytes assessed. This high level of electrolyte tolerance allows Atlox 4917 to maintain performance in challenging formulations such as those with built in glyphosate. Utilising electrolyte tolerant dispersants such as Atlox 4917 allows for vastly improved performance both in concentrate and upon dilution.

Conclusion

Agrochemical formulations are increasingly becoming more complex, incorporating features such as multiple active ingredients, higher loading levels of active ingredients and the inclusion of adjuvants. Sophisticated dispersant technology is required in these situations to offer the formulator more choice in selecting the dispersant chemistry to best match the active ingredient structure. Atlox 4917 has been carefully designed to expand Croda’s range of aqueous dispersants building on the well-established technology, providing benefits such as:
• New innovative dispersant chemistry
• Compatible with a wide range of active ingredients
• Disperses multi-active ingredient systems
• Effective at a low use rate
• Produces highly stable formulations even in the presence of adjuvants
• Demonstrates electrolyte tolerance (including both hard water and glyphosate)
• Helps supress crystal growth in highly loaded formulation concentrates and in spray dilutions
• Has dual functionality as an aqueous dispersant and emulsion stabiliser in SEs

To view the full data set on Atlox 4917 visit the Croda Crop Care website (click here) to download the datasheet. Alternatively, sign up for the upcoming live webinar on 21st April to ask James any questions (click here to register). To order a sample please contact your local sales team or contact James ( James.Flavell@croda.com).

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