AkzoNobel: Novel Formulation Technology – Fertilizer Suspension Concentrate

Concentrated aqueous formulations, such as a suspension concentrate (SC), have been used to deliver agrochemicals to targeted sites for many years. However, a typical SC may contain a significant amount of non-essential ingredients for plant growth in order to maintain the stability of SC formulations.

These non-essential ingredients include dispersants, such as a naphthalene sulfonate condensate, suspension aids/stabilizers, such as an acrylate copolymer stabilizer, anti-freezing agents, such as propylene glycol, defoamers, thickeners, such as xanthan gum or modified clay, preservatives, and wetting agents. These non-essential ingredients not only increase the formulation costs, but also increase potential pollution to farm lands and potential health issues for workers.

We have developed a unique formulation technique (patent pending) using a concentrate aqueous fertilizer as a medium to suspend agrochemical powders without any additives or with only a small amount of wetting agent. We call this type of SC a Fertilizer Suspension Concentrate (FSC).

We know that solid agrochemicals are typically heavier than water. In order to stabilize the powders in water, a thickener plus a stabilizer are used to prevent the settling of the powders. In order to prevent freezing of water, an anti-freezing agent is necessary.

The technique first involves finding out the appropriate aqueous fertilizers and an appropriate concentration for the powder. If the powder is not hydrophilic enough, add a few percent wetting agents, such as a Phospholan® phosphateester. Milling may further improve the stability of the FSC.

Examples of the aqueous fertilizers are 10-34-0 (N-P-K, ~56% ammonium polyphosphate) and URAN 32 (~ 80% solid with ~45% ammonia nitrogen and ~34.8% urea in ~20% water). Many powders will float in 10-34-0 because 10-34-0 has a very high density (1.40 g/ml). On the other hand, URAN 32 has a lower density (1.32 g/ml) than 10-34-0. Therefore, combining 10-34-0 with URAN 32 or 10-34-0 with water will give you a fertilizer solution with a wide density range that sufficiently matches the density of the powders (see illustration in Fig. 1).

 
Fig 1. By changing the density of the liquid medium, imidacloprid particles can be made float or sink in the continuous medium. The graph shows separation after storage of formulations containing 20% Imidacloprid and 5% glucoside surfactant (AG™ 6202) in water (A), fertilizer 10-34-0 (C) or a mix of water and fertilizer (B). B can be used as is or diluted with water or fertilizers (such as 10-34-0, Uran 32, Uran 28, 28-40% AMS) without forming crystals or coagulations.

The FSC formulation technology directly utilizes Stoke’s law. According to Stoke’s law, the separation velocity V of a spherical particle in a liquid is given by

          

where g is a gravitational acceleration, ρp the density of the particles, ρf the density of the liquid, μ the dynamic viscosity of the liquid, and R the radius of the sphere.

There are three ways to slow down the separation speed of the particle in the liquid: (1) minimize the density difference between the particle and the liquid, ρp - ρf, which is utilized in FSC technology; (2) reduce the particle size; and (3) increase the viscosity of the liquid. In principle, if the density difference is very small, the FSC formulation will be stable.

We are able to prepare stable FSC formulations with pesticide powders, such as bifenthrin, clothianidin, and captan. Typical concentration of powders is 20 to 40 percent in FSC. We notice that the FSC technology is not suitable for “COOH” containing pesticides because carboxylate containing pesticides tend to form crystal in FSC.

One interesting application of this FSC is in seed planting with an in-furrow starter fertilizer 10-34-0 and an insecticide. The insecticide SC is first mixed into farmer’s tank containing 10-34-0 without further dilution with water. The resulting suspension in 10-34-0 is required to have at least a few hours stability. A machine carrying the seeds and the resulting suspension in 10-34-0 is then used.

The machine is able to, in one pass, plough open a furrow, drop a grain of seed (or seeds) from a seed container, apply a small dose of an aqueous 10-34-0 containing insecticide to the soil close to or on top of the seed (or seeds), and close the furrow to bury the seed (or seeds) and the fertilizer/insecticide. This application is becoming more and more popular because the starter fertilizer with insecticides can provide, not only protection to the seeds by keeping the worms away, but also provide the necessary initial boosting nutrients to the young plant, rendering the expensive and complicated seed coating/treatment process unnecessary.

Neonicotinoid insecticides are typically coated on seeds. Dusts of insecticides are prone to be airborne and kill bees. This farming practice may allow the use of neonicotinoid without the dusty problem from the coated seeds.

A typical insecticide SC cannot be mixed well with 10-34-0 because the level of non-essential ingredients is too high and these ingredients tend to separate out of 10-34-0. However, FSC formulations can be mixed well in 10-34-0 without separation for hours because FSC only contains aqueous fertilizer 10-34-0 (and maybe with other fertilizer) and powder insecticides (already dispersed in the aqueous fertilizer) and with or without a small amount of wetting agent.

FSC doesn’t need an anti-freezing agent because the high electrolyte content in FSC can lower the freezing point of water to -10 to -18°C. It doesn’t require a preservative either because the microbial is unlike to grow under the high electrolyte environment.


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