Development of 30% Tebuconazole-Thiophanate-methyl Water-based Suspension Concentrate

We optimized the formulation of a 30% Tebuconazole-Thiophanate-methyl suspension concentrate using orthogonal optimization methods.

The ideal mix includes 20% Tebuconazole, 10% Thiophanate-methyl, 4.5% D1002, 2.5% Agricultural Emulsifier 33#, 5% Ethylene Glycol, 0.25% Xanthan Gum, 0.3% Silicone Antifoaming Agent, and distilled water to reach the desired volume. The process involves using a vertical sand mill at 1,400 r/min with zirconium oxide beads (d = 1.2 mm) at a ratio (V) to the formulation mass (m) of 1.9. The optimal milling time is 1.5 hours.

The resulting suspension concentrate demonstrates excellent stability at pH 6.45 to 6.50 and after 14 days of heat storage at (54±2) ℃. It shows no signs of phase separation, water precipitation, with less than 1% decomposition. It meets pourability requirements, and all product parameters align with suspension concentrate standards.

Suspension concentrates are divided into four types: water-based, oil-based, dry, and water-dispersible granules. Water-based suspension concentrates have an opaque appearance and typically have dispersed particles ranging from 0.5 to 5 μm, with an ideal range of 1.0 to 3.0 μm. They're thermodynamically unstable multiphase dispersion systems [1-2]. Recently, water-based suspension concentrates have seen significant development, offering environmental friendliness, reduced solvent use, and becoming a major alternative to wettable powders [3].

Tebuconazole, a white solid with a melting point of 102.4-104.7 ℃, and Thiophanate-methyl, a yellow solid with a melting point of 172 ℃, are both water-stable and suitable for suspension concentrate formulation [4-5]. Combining these two active ingredients reduces solvent usage and production costs.

Materials and Methods1.1 Raw Materials and Excipients

• Tebuconazole (97.7%) and Thiophanate-methyl (95%) from Shanghai Chemical Co., Ltd.

• Agricultural Emulsifier 33#, Xanthan Gum, Ethylene Glycol, and others are commercially available.

1.2 Main Instruments

• Vertical Sand Mill, Electronic Balance, Digital Electric Vacuum Drying Oven, Refrigerator, Laser Particle Size Analyzer, High-Performance Liquid Chromatograph, among others.

1.3 Performance Parameter Determination for the Suspension Concentrate

• Thermal and cold stability, pH value, viscosity, and suspension rate were determined following established methods [6].

Results and Analysis2.1 Selection of Surfactants Initial screening of individual surfactants at 6% concentration didn't yield satisfactory results. Therefore, two surfactants were combined to achieve an optimal ratio.

2.2 Selection of Thickening Agent Xanthan Gum was selected as the thickening agent at 0.25% concentration due to its superior performance in maintaining stability.

2.3 Selection of Antifreeze Agent Ethylene Glycol, used at 5%, was chosen as the antifreeze agent for its effectiveness and stability.

2.4 Selection of Defoaming Agent CF-580 at 0.3% concentration was selected as the defoaming agent for its excellent performance.

2.5 Orthogonal Experiment Optimization Orthogonal optimization resulted in the optimal combination: D1002 4.5%, Agricultural Emulsifier 33# 2.5%, Xanthan Gum 0.25%, CF-580 0.3%.

2.6 Optimization of Suspension Concentrate Processing Optimizing the suspension concentrate processing focused on particle size distribution, considering zirconium oxide bead sizes and milling time.

2.7 Determination of Optimal Technical Parameters The optimal formulation includes 20% Tebuconazole, 10% Thiophanate-methyl, 4.5% D1002, 2.5% Agricultural Emulsifier 33#, 0.25% Xanthan Gum, 5% Ethylene Glycol, 0.3% CF-580, with distilled water.

2.8 Verification Experiment Verification experiments confirmed the rationality of the parameters.

Discussion The 30% Tebuconazole-Thiophanate-methyl suspension concentrate produced in this study demonstrates satisfactory stability, pourability, and a particle size distribution suitable for industrial production. It offers environmental benefits by reducing solvent use and production costs. Orthogonal optimization was instrumental in achieving the optimal combination.