Octaphenyl polyoxyethylene regulates the flexibility of pyraclostrobin-loaded soft microcapsules by interfacial polymerization for better foliar adhesion and pesticide utilization

In the preparation of microcapsules (MCs) by interfacial polymerization, octaphenyl polyoxyethylene (OP) is utilized as an emulsifier to control the particle size distribution of MCs. In the preparation system with polyisocyanate as the oil phase monomer, OP has a single hydroxyl (–OH) group that can react with the isocyanic group (–CNO) to prevent polymerization, and the aggregation of OP at the oil–water interface affects the polymer configuration. By the “steric hindrance” and “polymer chain end sealing” of OP, the compactness of the shells was reduced significantly to produce soft MCs. As OP-10 was added and used to increase in pyraclostrobin-loaded MCs preparation, the deformation, adhesion and release of pyraclostrobin-loaded MCs were improved. Therefore, the water scouring resistance of MCs on peanut leaves increased significantly as the MCs became soft. Unfortunately, the safety of zebrafish (Danio rerio) declined at the same time. By foliar spraying to control peanut leaf spot in the rainy season, MCs-2% OP-10, with the strongest resistance to rainfall, had the best effect on disease control. In conclusion, an effective strategy is to balance the foliar application efficiency and ecotoxicity of pesticide-loaded MCs by regulating the compactness and components of shells to control their deformation, adhesion and pesticide release.