Challenges and Solutions in Suspension Agent Processing

Processing suspension agent products often presents issues such as stratification, clumping, gelling, crystallization, ambient thickening, heat solidification, and post-storage heteroparticle coagulation. Moreover, excessive fine foam during processing, which cannot be promptly defoamed, severely impacts packaging and application. Other processing challenges are primarily related to the solid material's structure and properties (including impurities, high melting points, solubility, crystalline forms) and the high solid content of the SC product. The choice of wetting agents, dispersants, antifreeze agents, thickeners, or defoaming agents is also crucial.

6.1 High Solubility Active IngredientsProcessing active ingredients with high solubility for SC products can lead to Ostwald ripening. For example, processing 30% thiacloprid SC products, with thiacloprid having a melting point of 139.1°C (a high melting point) and a water solubility of 4.1g/L (eight times that of imidacloprid), is challenging due to its large water solubility. Thiacloprid's molecular structure includes thiazole and imidazoline groups, both of which are Lewis bases capable of undergoing Lewis acid addition reactions. This polarity results in poor adhesion of typical dispersants' hydrophobic chains to the active ingredient particles, leading to Ostwald ripening. To overcome this, selecting appropriate and high-molecular-weight polymer dispersants like sulfonates, carboxylates, or emulsifying agents is essential to ensure secure adhesion of the hydrophobic chains to the active ingredient particles. The right combination can prevent Ostwald ripening, resulting in stable thiacloprid suspension agent products.

Additionally, in cases of thiacloprid SC, the choice of high-molecular-weight polymer dispersants is essential, as these dispersants contain anionic groups that form a double electric layer in the aqueous phase. This layer ensures stable particle protection, preventing aggregation or precipitation.

2 Formation of Water ClustersRepresentative active ingredients like acetamiprid have low solubility, but they can easily form water clusters due to their specific molecular structure. In original grinding, they can reversibly absorb water, exhibiting viscoelasticity or gelling and leading to poor pourability and inadequate dispersibility. Using wet acetamiprid materials with higher water content (usually around 70%) can resolve this issue and produce stable suspension agents. For instance, acetamiprid with 15% to 25% water content has been used to create successful 25% acetamiprid SC products. Proper formulation includes acetamiprid content at 25%, wetting and dispersing agents at 6%, polydimethylsiloxane defoaming agent at 0.3%, isothiazolinone preservative at 0.4%, propylene glycol antifreeze agent at 5%, xanthan gum thickener at 0.3%, and water to adjust the total volume. The performance of this 25% acetamiprid SC meets all suspension agent requirements.

In these cases, choosing high-molecular-weight polymer dispersants is essential. These dispersants contain anionic groups that form a double electric layer in the aqueous phase, ensuring stable particle protection.

3 Influence of Unknown Impurities in Raw Materials3.1 Imidacloprid's structure contains pyridine and imidazoline groups. Selecting dispersants with higher molecular weight and viscosity-reducing properties can produce stable suspension agents. However, a challenge arises when processing 600g/L imidacloprid suspension agents. Changing to another supplier's high-purity imidacloprid raw material, even with a 97% purity, can lead to unstable products due to different production processes and the presence of unknown impurities. These impurities neutralize the charge of the previously chosen dispersants, disrupting or altering the protective layer of particles. Adjusting the dispersant system is necessary to achieve stability.

3.2 In the formulation of 25% pyrazole ether antibiotic SC, the importance of pyrazole ether antibiotic raw material impurity content is emphasized. Typically, 97% purity is targeted, as lower purity may introduce multiple crystal forms during processing, leading to complex interactions between particles and decreased formulation stability. Excessive impurities can also impact the toxicity of agricultural products and the toxicity of raw materials. Therefore, using pyrazole ether antibiotic raw materials with a purity of 97.5% and strict control of water content and pH is crucial to ensure stability in the final formulation.

4 Contaminants in Large QuantitiesProcessing 10% thiamethoxam SC is challenging because thiamethoxam raw material has a high content of 72% and impurities of 28%. Processing 10% thiamethoxam SC can result in undesirable characteristics.