Ingevity Solutions for Challenging Water Dispersible Granular Formulations

Introduction on Water Dispersible Granules (WDGs)

Water dispersible granules (WDGs) also known as dry flowable in North America, have been available since the 1980s. However, since the 1990s they have been developed on a significant scale as safer and commercially attractive alternatives to wettable powder and suspension concentrates globally. Water dispersible granules are non-dusty, free-flowing granules, which should disperse or dissolve quickly when added to water in the spray tank. As there are no spillage hazards, and with safer disposal of packaging, they are regarded as more attractive, convenient, and environmentally friendly products than EC (Emulsifiable Concentrate), S (Solutions), Dusts, Pellets, and WP (Wettable Powders) formulations.

Dispersible granules are obtained by blending and agglomerating a ground solid active ingredient together with surfactants/binders and other formulation ingredients. After granulation, drying step is necessary to reduce moisture to the acceptable and required limit. The shape, size and performance of the granules vary according to the manufacturing process used to produce them.

Extruded WDG is one of the rapidly growing formulation types that provides quicker dissolution while maintaining pallet integrity. These formulations have a high loading of active ingredients, which reduces transportation costs.

However, with the need of extra-high loading active and multi-active loading WDG, there are plenty of challenges that formulators are facing currently.

• Suspensibility and disintegration
  

• Long shelf life
  

• Formulating a granule that will extrude well and disperse well
  

• Cold water breakup
  

Among those mentioned above, the most frequently occurring problem in achieving desired performance is the high-suspension stability, so called suspensibility, with rapid granular disintegration. As most active ingredients are hydrophobic compounds, they often require low solubility dispersants to provide high suspensibility; while high water solubility dispersant is desired to provide quick disintegration. These two properties are diametrically opposed, making the selection of a dispersant difficult.

Importance of dispersant

Dispersing agents, so called dispersants, change the potential of interactions by adsorption on the surface of the active ingredient particle, avoiding re-agglomeration or flocculation through steric and/or electrostatic stabilization. The lipophilic part of a dispersant is adsorbed onto the organic particles and the hydrophilic part provides good affinity to the aqueous medium. (See Figure 1). For a successful formulation, with good coverage of dispersants on particle surfaces, particles would not agglomerate or fuse during storage. Thus, upon dilution, the granules can break up quickly and the particles can suspend in the liquid easily without agglomerating or flocculation, resulting in quick breakup and good suspensibility.

Figure 1. Schemes of (a) the electrostatic repulsion and steric stabilization mechanism; (b) dispersant covering on particle surface.

Ingevity’s Kraft lignosulfonate dispersants

Lignosulfonates are a class of dispersant that is bioderived and inherently biodegradable. Ingevity’s long-lasting research legacy in lignin process chemistry and robust engineering control provides us with a wide range of high-quality lignosulfonate products satisfying your diverse formulation needs. In contrast to sulfite lignin products where the sulfonation chemistry is done by the paper mill, Ingevity's main objective is focused on lignin chemistry. Our lignin is derived from the kraft process which isolates unsulfonated lignin. This gives us the ability to control the chemical architecture in our production facility resulting in lignosulfonate products that have consistent quality, a wide array of physical properties and high performance in various formulations.

The kraft lignin process

Figure 2. Kraft lignosulfonate production process vs sulfite lignosulfonate production process

Kraft Lignosulfonates Benefits

• Better coverage & efficient with lower use rates
  

• Low, medium, and high sulfonation levels
  

• Several MW levels
  

• Different sites of sulfonation – aliphatic, aromatic, and hybrid
  

• High milling efficiency
  

• Long shelf life
  

• Stronger binders and more hydrophobic dispersants (i.e., Polyfon H and O) than are offered by competitive products.
  

• High ionic strength and broad pH compatibility
  

• Premium performer in WP/WDG formulations
  

• Preferred choice for more challenging, multi-active, high active loading, and hard to formulate actives
  

Performance is the key
 
In the past, many dispersants did not address the main properties of WDGs—disintegration rate, suspensibility stability in spray tanks, and attrition resistance. The properties of Kraft lignin impacting performance are degree of sulfonation and molecular weight. Generally, a high degree of sulfonation products provide better dispersibility; higher Mw products give better suspensibility.

Table 1. Ingevity product degree of sulfonation, Mw properties relationship with dispersibility and suspensibility in WDG formulations.

Dissolution rate follows degree of sulfonation trend

The below figure shows the rate of dissolution for compacted Kraft lignosulfonate dispersants. Samples were immersed in water for two-minute intervals and weight loss was measured upon drying. As degree of sulfonation increases, a faster dissolution rate can be achieved.

Figure 3. Dissolution rate of different Kraft lignosulfonate products with different degree of sulfonation.

WDG Examples with recipe using Ingevity Dispersants

Saflufenacil 70% WDG

We formulated saflufenacil 70% WDG with Kraft lignosulfonate Reax 825E at low use rate 4% and compared it to a sulfite lignosulfonate (LS). At the same time, a commercial product was purchased as a benchmark product. The formulation and properties before and after storage were tested and the results are shown below.

Table 2. Formulation of 70% saflufenacil WDG.

Figure 4. Disintegration and suspensibility of the saflufenacil WDG before and after storage with different dispersants and the commercial product.

It’s important to note that although the commercial WDG showed very good suspensibility, it was not able to disintegrate no matter how many times the formulation was inverted. On the other hand, formulation with sulfite LS shows acceptable inversion numbers, but much lower suspensibility and storage stability. As we discussed above, achieving both high suspensibility and high disintegration at the same time is a major problem for challenging WDG formulations and in our studies only kraft LS provided that benefit. After reviewing the results of the accelerated storage test, it was apparent that the low use rate of Reax 825E can provide good suspensibility and great disintegration at the same time even in post stability test.

Atrazine 90% WDG

Combination of low and high degree of sulfonation dispersant balance dispersibility and suspensibility in WDG.

For this high loading atrazine 90% WDG, as we discussed above, to achieve rapid disintegration, hydrophilic dispersants with low molecular weights are good choices; however, often highly hydrophilic dispersants give poor suspension stability. Combining a hydrophilic with a hydrophobic dispersant can often be the best option. Reax 88B, a hydrophilic low molecular weight kraft lignosulfonate, can be used with a small amount of a hydrophobic high molecular weight dispersant, such as Ingevity’s Reax 907, to balance the suspension stability and disintegration of extruded WDGs.

Table 3. Formulation of atrazine 90% WDG

Figure 5. Suspension test samples of atrazine 90% WDG with different dispersant systems after 54 °C storage for 2 weeks.

Table 4. Testing results of 90% Atrazine WDG formulations of the initial samples and after the accelerated storage test at 54 °C for two weeks.

Beuveria bassiana WDG

Biological formulations, especially with hydrophobic biological microorganisms, are challenging when formulating into WDG formulations. Beauveria bassiana is a fungus that naturally exists in soil and can act as a parasite on various arthropod species, causing white muscardien disease; thus, it can be used as a biological insecticide to control several pests. However, Beauveria bassiana is very hydrophobic and hard to wet and suspend. We tested its WDG formulation, with 5% active loading and 4% dispersant use rate, and compared our new generation of AltaBio with polyacrylic based dispersant, naphthalene sulfonate formaldehyde condensate (NSF) based dispersant and sulfite lignosulfonate at the same dispersant use rate.

The study determined AltaBio 200 gives the best and most consistent suspensibility and disintegration after accelerated storage conditions in benefit of its low hydrophilicity and high molecular weight (see figure 6). Interestingly, although the initial disintegration of all four formulations is in the acceptable range, a dramatic increase in numbers of inversion was observed with the other three formulations, except with AltaBio 200. In conclusion, AltaBio 200 provides the best disintegration and stable formulation among all the dispersants tested.

Table 5. Formulation of Beuveria bassiana 5% WDG.

* Formulation contains a minimum of 6x10¹⁰ conidia/gram

Table 6. Suspensibility of Beuveria bassiana 5% WDG with different dispersants.

Figure 6. Disintegration of Beuveria bassiana 5% WDG with different dispersants.

Lower dilution rate in less water

Lower dilution test with the AltaBio formulation shows consistent particle size, high suspensibility and fast disintegration, indicating high dispersant performance.

Table 7. Formulation performance at different dilution rates.

Lower use rate of dispersants of 1%

We further lowered the dispersant use rate to 1 % and the formulation still shows great performance. This indicates that with AltaBio 200, we can use very low use rate and still achieve high performance for challenging formulations.

Table 8. Performance test of Beauveria bassiana WDG with 1% AltaBio 200.

Summary and Conclusion

As pesticide formulations continue to become more complex with higher performance demands, high performing dispersants are in great need to solve the challenges. By combining dispersants with different properties, formulators can enhance properties of pesticide products and technologies. WDGs made with Ingevity’s dispersants perform well across formulations with lower use rate, formulation stability, fast disintegration and suspensibility, giving growers the desired product that really performs.