Oxiteno: Studies of the application of SURFOM^® SC 8895 in pesticide suspension formulations

ABSTRACT : Development comprises the production and subsequent assessment of the performance of suspension concentrates (SC) and suspo-emulsions (SE) with regard to physicochemical stability in the following cases:, Atrazine 600 g/L (SC), Atrazine 500 g/L + Mesotrione 50 g/L (SC), Azoxystrobin 200 g/L + Cyproconazole 80 g/L, and the case of suspo-emulsion (SE) Azoxystrobin 125 g/L + Propiconazole 75 g/L.

The assessment consists of physical-chemical stability tests of the formulations, which are crucial to understanding the product's performance. These assessments are related to the quality of SURFOM^® SC 8895 as a dispersant and wetting agent package for pesticide suspension systems.

SURFOM^® SC 8895 proved to be a valuable agent in terms of dispersion and wetting of suspension pesticide formulations assessed in these physicochemical tests, and compared to market standards, demonstrating that SURFOM^® SC 8895 is robust and applicable in various scenarios.

SURFOM^® SC 8895 is EPA approved on the inert list and all the components listed on the IESC China. In terms of REACH, it needs to be assessed according to the region. Please contact us for information on its regulatory status in the region required.

INTRODUCTION

The Suspension Concentrate formulation markets accounts for 27% of the total Crop Protection market by value, and 15% of the volume applied, which illustrates the relevance of the price of these products when compared with different types of formulations. In the last ten years, the value has increased by more than 10%, according to Phillips McDougall.

SCs offer important benefits over other formulations, as they are water-based, safe, do not produce the dust that powdered formulations do, and are non-flammable. The active ingredient(s) can be dispersed over a wide range of concentrations, from low to high loads, the latter being challenging systems that require good dispersion system performance. The role of the dispersant is to reduce viscosity, keeping solid particles dispersed and stable, preventing further aggregation or flocculation, and stabilizing suspended systems with increasing complexity, such as different active ingredients in the same formulation, or higher loads, is highly demanding (T. Adros, 2017).

SURFOM^® SC 8895 is a product in Oxiteno's portfolio which presents in its compound surfactants with wetting and dispersing properties to assist in the grinding process and maintain the physicochemical properties of the formulation during its stability. The study of these formulations is important in assessing their importance in the agribusiness scenario. According to Mark Moore, this assessment is about the Atrazine and its mixes are one of the many options to be used by farmers. Atrazine is an initial pre- and post-emergence herbicide, recommended for the control of annual weeds in corn, sugarcane and sorghum crops, according to the Atrazine Suspension 500SC label. Atrazine’s metabolism can cause a decrease in biological activity due to changes in steric structure, although the changes in solubility prevent the inhibitor from penetrating chloroplasts, as suggests Harley R. Swanson.

Azoxystrobin and its combinations have a significant market share (Global Azoxystrobin Consumption Market Report), driven by its performance in the field. This fungicide is systemic and inhibits spore germination, mycelial growth and fungal spore production (Francis P. Wong). The combination of fungicides resulted in better control in the field, involving the use of Azoxystrobin combinations with triazoles, according to M. Jakelinny, for several diseases in soybean and wheat.

The pesticides studied can be formulated to make them manageable. SURFOM^® SC 8895 is assessed in the production of these formulations with stability data studies to establish the wetting and dispersion properties of suspended systems.

METHODS

 ● Suspension concentrate  (SC) or Phase B for the Suspoemulsion process

Procedure: In a stainless steel bowl equipped with a Cowles blade stirrer, add glycol, water, SURFOM^® SC 8895 and defoamer, and mix until homogenous (approximately 15 minutes). Add the active ingredient while stirring at 900 RPM for 15 minutes, or until a homogeneous large particle paste is obtained. Transfer the formulation to a ball crusher equipped with a cooling system to dissipate the energy introduced into the grinding process at 5°C, grinding the formulation. A Netzsch-Feinmahltechnik MINIZETA circulating grinding system was used at approximately 2000 RPM to achieve the D50 particle size distribution in the range of 2 – 5 microns and D90 <10 microns. Transfer the formulation to a beaker and use a low speed mechanical stirrer to reduce the amount of air incorporated during grinding. Add xanthan gum previously solubilized at 2% in water to achieve the desired viscosity range.

 ● Phase A in suspo-emulsion

To prepare the formulation, heat SURFOM^® CE 8434 to 40°C. Add technical Propiconazole while stirring at approximately 500 RPM until it completely dissolves. Add the emulsification pack while stirring until completely homogenized.

 ● Suspo-emulsion (SE) mixing procedure

Mix phase B with phase A and the rest of the compounds in Suspoemulsion (SE) at 400 RPM and make further additions to adjust viscosity.

 ● Analysis

pH, pure product: CIPAC MT 75.3; Density at 20°C: OECD 109; Viscosity: Brookfield S34, 80RPM; Suspensibility: CIPAC MT 187; Particle size: CIPAC MT 187; Wet sieving: CIPAC MT 185; Persistent Foam: CIPAC MT 47.3; Accelerated storage (54 ± 2)°C for 14 days: CIPAC MT 46.3. Emulsion stability: CIPAC MT 180, and ABNT NBR 13425: 2016

RESULTS

Development of suspension concentrate formulation (SC) for Atrazine 600 g/L

After the production of this formula, dispersion performance can be assessed via particle size, comparing the freshly prepared situation with that after 14 days at 54°C, as shown in Figure 1. This makes it possible to study rheological behavior through a flow curve for the initial formula and after the aging process. In addition to particle size distribution, suspension rheology plays a key role in assessing dispersant robustness.

Based on Figure 2, it is possible to infer that the formula for Atrazine 600SC has low thixotropy, since the difference between the flow and return curves in the flow curve is low. This experiment consists of applying an increasing shear rate over time and evaluating the shear stress to which the formula is subjected. After this assessment, the shear rate is reduced and the return to equilibrium of the formula is assessed. If this return presents a large shear stress variation in order to provide the presence of a thixotropic behavior in the formula, in Figure 2, this behavior is absent in this formulation.

Figure 1: Superimposed particle size distribution curves for the 14-day early and post-aging situations at 54 °C for Atrazine 600 g/L.

Figure 2: Flow curves plotted for the initial situation and aged in 14 days at 54°C for Atrazine 600 g/L.

Developing suspension concentrate formulation (SC) for Atrazine 500 g/L + Mesotrione 50 g/L

Based on the robustness of the SURFOM^® SC 8895 dispersant package for Atrazine at two concentrations, it is possible to infer the concepts by evaluating the combination of herbicides as studied for Atrazine and Mesotrione.

This formulation typically provides density analysis at 20°C of (1.036 ± 0.001) g/cm3. To assess the compound in Table 1, stability analyzes are carried out comparing the initial situations of the formulation, after the aging process of 14 days at 54°C and with a sample of a commercial product with these actives. This assessment is featured in the Table 2. Based on the stability work, it is possible to maintain the concept of low surfactant concentration and good physicochemical performance.

Table 1: Compound of SC formulations.

Table 2: Physicochemical assessment of the initial formula and subsequent aging.

Developing Suspension Concentrate (SC) formulation for Azoxystrobin 200 g/L + Cyproconazole 80 g/L

To assess the performance of this compound, SURFOM^® SC 8895 was replaced at the same concentration and assessed using other products such as sulfonated alkyl naphthalene, high molecular weight EO-PO block copolymer and tristyryl phenol ethoxylate phosphate derivative. Physical and chemical properties were assessed after 14 days of aging at 54°C, as shown in Table 3.

The rheology expressed by viscosity, in this experiment, is very important to assess the stability of the suspension, since the increase in flow resistance is a property caused by the aggregation of particles, which shows the instability of the suspension. This behavior was observed in the Oxiteno solution.

The assessment of a regular product on the market such as sulfonated alkyl naphthalene, known as a good dispersant due to its molecular volume, is not effectively expressed in the dispersion of the studied system. Meanwhile, SURFOM^® SC 8895 develops with rheological and colloidal stability as shown in Table 4 with sulfonated alkyl naphthalene. It was not possible to measure the viscosity due to the significant increase in the aging process at 54°C after 14 days, going from ( 215.3 ± 0.1 ) cP for an error situation, keeping the analysis conditions such as temperature, axis and shear constant for all comparisons.

The particle size distribution, using the sulfonated alkyl naphthalene used as a dispersant in the suspension, increased by 104.3 µm, which initially was a D90 of (3.7 ± 0.2) µm. After 14 days at 54° C, particle aggregation was observed with 90% of the particles at (108.0 ± 0.2) µm, resulting on particle agglomeration in almost 30x over the initial results.

During the preparation of the formula with a compound containing SURFOM^® SC 8895, similar figures were obtained, starting at (2.6 ± 0.2) µm and after aging at 54°C at (3.3 ± 0.2) µm, resulting in a robust suspension system.

Developing suspo-emulsion (SE) formulation for Azoxystrobin 125 g/L + Propiconazole 75 g/L

The development of this type of formulation is quite challenging with regard to the stability of the suspended, rheological and emulsified oil phases.

Therefore, the stability assessment studies in this example include analyzes to demonstrate suspension robustness due to the dispersant properties of SURFOM^® SC 8895.

SURFOM^® SC 8056, which is an emulsification package, includes assessment of the quality of the emulsion corresponding to the emulsion of a sustainable oil conducting carrier, SURFOM^® CE 8434 (material available at: https://oxiteno.com/us/en/product/surfom-ce-8434/), this solvent solubilized propiconazole and this was emulsified by SURFOM^® CE 8056 (material available at https://oxiteno.com/us/en/product/surfom-ce-8056/) as an optimized compound for an ester-based solvent emulsifier system.

There is synergy between Oxiteno's products to provide the emulsion quality and suspension stability required by this type of formulation.

This formulation compound includes two phases, phase A consists of the solubilization of Propiconazole in SURFOM^® CE 8434. The compound of the oil phase with Propiconazole is as follows: Propiconazole tec. 97% (680 g/L); SURFOM^® CE 8056 (100 g/L); SURFOM^® CE 8434 (QS to 1L).

The suspension in Phase B has the following compounds: Azoxystrobin tec. 98% (250 g/L); Ethylene glycol (50 g/L); SURFOM^® SC 8895 (50 g/L); Defoamer (2 g/L); Preservative (1 g/L).

After phases A and B, the SE formulation can be prepared: Phase A (11.03% w/w); Phase B (50% w/w); Propylene glycol (5% w/w); Xanthan gum, 2% preserved solution (4.62% w/w) and water (29.35% w/w).

The physicochemical data referring to this formulation is featured in Table 4, assessing the stability under different temperatures after 14 days. In Figure 3, the change in particle size distribution can be seen.

Table 3: Analysis for physicochemical properties of SC formulation for Azoxystrobin200 g/L + Cyproconazole 80 g/L.

Table 4: Analysis for physicochemical properties of the SE formulation contains Propiconazole 75 g/L and Azoxystrobin125 g/L.

Figure 3: Particle size distribution of the Suspoemulsion formulation, comparison between the initial sample at RT and 14 days of storage at 0°C, 25°C and 54°C

Based on the data in Table 3, the quality of the emulsion includes the diluted suspoemulsion under different hardness of water. Considering that the quality of the emulsion remained constant throughout the stability, the good efficiency when evaluating 1h at 30 °C, as established in the method for all the studied water hardness, is proven.

In the 24h assessment at 30 °C for the system, based on the experiment data, there is no syneresis and the dispersible cream formed after 24h allows us to infer that the kinetic stability of the system is good over a wide range of water hardness. The increase in the electrolyte content causes a destabilization of the quality of the emulsion due to the double layer electrical theory (Sinha, S).

Analyzing the stability of pure pH, it is possible to avoid hydrolysis of the pesticide in the formula, proving that SURFOM^® SC 8895 can maintain its physicochemical properties after storage.

CONCLUSION

SURFOM^® SC 8895 is a product composed of wetting and dispersing agents, capable of increasing performance through the physicochemical stability of formulations containing herbicides, fungicides and the appropriate mixtures. It is an easy-to-handle product which aids in the grinding process and has good performance in terms of suspension and suspoemulsion rheology. They are robust formulations with low surfactant dosages and high stability, meeting key formulation requirements.

When assessing formulations featuring Atrazine, SURFOM^® SC 8895 has a superior performance or similar to other options on the market. Furthermore, it requires lower concentrations and is easy to handle and less complex.

To assess the contribution of the formulations of the SURFOM^® SC 8895 fungicide, the product proved to be superior to a known reference in the sulphonated alkyl naphthalene market. This superiority is proposed through colloidal stability due to particle size distribution and sedimentation, proving that low concentrations of dispersants can keep systems suspended properly.

It is also possible to demonstrate the robustness of Oxiteno's product when evaluating a challenging formulation such as suspoemulsions, where there are several variables to be controlled and all maintained their proper physicochemical aspects, using SURFOM^® CE 8434 as a sustainable solvent carrier, all acting in synergy with SURFOM^® SC 8895, which kept the suspended system stable and aligned with the sustainable goals of easy handling and safety.

REFERENCES

1. Agrochemical Market by Formulation Type - McDougall, Phillips
2. Top 10 herbicides – Moore, Mark. Available in: https://www.farmprogress.com/herbicides/top-10-classic-herbicides Access in 17th May, 2021
3. 2019 – 2024 Global Azoxystrobin Consumption Market Report. Chapter 2. Publishing Date: 22th February of 2019
4. Comparative Physical Modes of Action of Azoxystrobin, Mancozeb, and Metalaxyl Against Plasmopara viticola (Grapevine Downy Mildew). Francis P. Wong and Wayne F. Wilcox, Department of Plant Pathology, Cornell University, New York Agricultural Experiment Station, Geneva, NY 14456
5. Atrazina metabolism, selectivity and mode of action. Richard H. Shimabukuro and Harley R. Swanson
6. Desempenho de combinações de fungicidas químicos e sua influência com aspectos fitossanitários da soja (Glycine max), Silva, M. Jakelinny
7. SURFOM^® CE 8434 promotion material available in: https://oxiteno.com/us/en/product/surfom-ce-8434/
8. SURFOM^® CE 8056 promotion material available in: https://oxiteno.com/us/en/product/surfom-ce-8056/
9. Eletric double layer effects in water separation from water-in-oil emulsions. Sinha, S. etal, Colloids and Surfaces A: Physicochemical and Engineering Aspcts, Vol. 489, 20 January 2016, Pages 216 – 222.
10. ADROS, T. F. (2017) Suspension Concentrates: Preparation, Stability and Industrial Application, p. 103-151