The world’s continuously growing population, along with a decreasing amount of arable land and scarce water resources, are driving regulators to impose more stringent environmental mandates1. As a result, formulators must also continue to innovate and develop high-performing pesticide products that lessen overall impact on the environment. This increasingly challenging landscape requires chemical suppliers to provide sustainable solutions to formulators that support their demanding formulation needs.
Oil-based suspension formulations, known as oil dispersions (ODs), are commonly used for water-sensitive active ingredients and require specific products with unique properties that aim to ensure long-term stability for pesticide applications. An OD formulation consists of active ingredient particles suspended in an oil medium with the aid of a dispersant and rheology modifier. The built-in emulsifier is used to emulsify the oil into emulsion droplets once the formulation is diluted in water.
To solve the obstacles OD formulations present, such as formulation instability, pine-based chemistry provider Ingevity developed AltaOil™, a portfolio of oil products that provide enhanced long-term stability and built-in adjuvancy. Compared to alternative commonly used oils such as vegetable oil and methylated vegetable oil, Ingevity’s AltaOil products provide excellent formulation stability, hard water stability and built-in rainfastness. AltaOil has strong compatibility with a range of solvents and surfactants, offering greater flexibility for different formulation needs.
Enhancing formulation stability with AltaOil
Although achieving OD formulation stability can be challenging, selecting the appropriate oil medium is vital since it is the heaviest component in the formulation. Additionally, choosing proper dispersants and rheology modifiers will contribute to overall long-term stability. Compared to commonly used oils derived from soybean and methylate, AltaOil provides better formulation stability due to its unique product composition and chemistry (see Table 1).
Table 1. Basic properties of Ingevity’s AltaOil product line compared to commonly used oils.
Both AltaOil grades have similar viscosity and density compared to alternative oils, making them easier to handle in strenuous formulations. AltaOil has a lower pour point than soybean oil and methylated soybean oil, which is advantageous for use in colder environments. The high flash point of AltaOil also makes it safe to handle during transportation and production. AltaOil’s relatively high acid number comes from the product’s inherent pine chemistry composition. Although a high flash point can be challenging with certain actives, AltaOil showed no major issues with AI degradation when combined with nicosulfuron, with which formulation is notoriously difficult.
Ingevity’s AltaOil product grades are designed for different formulations based on their performance properties. For example, AltaOil 1105 is ideal for use in biological OD formulations due to its low toxicity, and both AltaOil 1105 and AltaOil 1120 can excel in conventional OD formulations.
Compatibility with various surfactants
AltaOil has great compatibility with various surfactants of different chemistries, offering flexibility for formulations, shown in Table 2. Compared to all four tested surfactants, AltaOil is compatible with all, while soybean oil is only miscible with one.
Table 2. Surfactant compatibility of AltaOil and soybean oil
The use of AltaOil in mancozeb and nicosulfuron OD
Mancozeb OD is formulated using AltaOil 1120 (Formulation 1) or vegetable oil (Formulation 2). The detailed recipe is shown in Table 3.
Table 3. Mancozeb OD (10%) formulation recipe with AltaOil (Formulation 1) or soybean oil (Formulation 2)
*Oil: AltaOil 1120 (Formulation 1) or vegetable oil (Formulation 2)
Figure 1. Mancozeb OD (10%) formulations with AltaOil 1120 (Formulation 1) and vegetable oil (Formulation 2), after being stored at room temperature (RT) or 54 C (HT) for 2 weeks.
Both mancozeb OD Formulation 1 and Formulation 2 were subjected to room temperature (20℃) and 54℃storage test for two weeks. Following storage, Formulation 2 including vegetable oil had a much greater oil syneresis layer than Formulation 1, indicating formulation instability.
Nicosulfuron is another active ingredient commonly formulated into OD. A 7.5% nicosulfuron OD was successfully prepared using AltaOil 1120 with detailed recipe shown in Table 4.
Table 4. Nicosulfuron OD (7.5%) formulation recipe
The above formulation is highly stable under various storage conditions and blooms well in water. Nicosulfuron is known to hydrolyze easily when exposed in a medium with an active proton. AltaOil has acid functionality, which could cause significant degradation for nicosulfuron (>5%). The above formulation was subjected to freeze-thaw and 54 ℃ for two weeks of storage, and the degradation was 1.6% and 3.6%, which is well within the acceptable level of nearly 5%. Once diluted into 1% using deionized (DI) water, the resulting emulsion/suspension had an emulsion droplet/particle size of 3.7um at D50, resulting in a very stable and homogeneous diluted emulsion/suspension.
The use of AltaOil in Bacillus spp. OD
AltaOil 1105 is safe with various spore forming microorganisms, including bacteria and fungi. When AltaOil 1105 was used in Bacillus spp. OD, we compared it to soybean oil, shown below in Table 5.
Table 5. Bacillus spp. OD formulation recipe with AltaOil 1105 or soybean oil
After formulation preparation, the above samples were subjected to 45 ℃ storage for two weeks. Upon completion, the three formulations all developed oil syneresis layers, seen in Figure 2 (left). However, the formulation including soybean oil (Formulation C) had the largest oil layer separation, indicating formulation instability. When the formulations were reverted by 180 degrees, the formulations with AltaOil (Formulation A and B) flow to the other side of the vial with no issues. In contrast, Formulation C including soybean oil did not flow well.
Figure 2. Bacillus spp. OD formulations appearance after being stored at 45 ℃ for two weeks.
When the above three formulations were diluted into 1% emulsion with DI water, both Formulation A and Formulation B had a emulsion/particle size ~5um at D50 and ~20um at D90, while the Formulation C had an emulsion/particle size ~9um at D50 and ~50um at D90. With smaller emulsion/particle size for diluted Formulation A and B, AltaOil proved to have much higher formulation stability than soybean oil.
Achieve additional rainfastness adjuvancy with AltaOil
Besides providing excellent formulation stability, OD formulations containing AltaOil offer additional rainfastness benefits. For two Bacillus spp. OD formulations using AltaOil or soybean oil as the only oil medium, 1% emulsion was prepared by diluting the OD formulations using DI water. After depositing a 200ul diluted formulation onto parafilm and 24 hours air drying, the dry film covered area was marked using a black marker (shown in Figure 7). Both formulations yielded similar coverage area. After simulated rain (dipping into water for 10 times), the covered area for soybean oil-based OD formulation shrunk to the center (as in the green marked area) while the AltaOil-based OD formulation didn’t show significant decrease in coverage area. This experiment highlights AltaOil’s additional rainfastness and adjuvancy properties in stable OD formulations.
Figure 3. Bacillus spp. OD pesticide film formation on parafilm substrate before simulated rain (black mark) and after simulated rain (green mark) for both AltaOil- and soybean oil-based formulations
Achieve high-performing formulations with Ingevity’s sustainable oil technology
Ingevity’s newest product, AltaOil, offers increased flexibility to formulators for oil-based formulations. With plant-based origins, AltaOil has 100% bio-derived green content and is fully biodegradable. AltaOil can replace synthetic oils, vegetable oil or methylated vegetable oil with increased performance while helping formulators simultaneously achieve sustainability goals. AltaOil is also fully approved for agricultural uses in North America, South America, Europe and Asia Pacific countries with tolerance exemption.
1. Phillips McDougall. (2018). Evolution of the Crop Protection Industry since 1960. https://croplife.org/wp-content/uploads/2018/11/Phillips-McDougall-Evolution-of-the-Crop-Protection-Industry-since-1960-FINAL.pdf.
This article will be published in AgroPages '2021 Formulation & Adjuvant Technology' magazine to be published this May.
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