Self-Assembled Microplastic-Free Microcapsules Using Aromatic Bis-Ureas with Improved Strength and Tunable Barrier Properties for Encapsulating Cinmethylin

Microencapsulation technology can be used for safe handling and controlled release of agrochemicals. Commercial microencapsulated formulations typically use cross-linked polymeric microcapsules, which encapsulate agrochemicals for improved efficiency and precise application. However, these polymeric microcapsules are nonbiodegradable and add to the growing microplastic pollution challenge at the end of their life cycle. Herein, we demonstrate a simple one-pot process for the interfacial self-assembly of aromatic bis-urea molecules to synthesize microplastic-free microcapsules encapsulating cinmethylin, an effective cineolic pre-emergence herbicide commonly used against grass weeds in annual crops. The urea linkages act as hydrogen-bonding motifs forming a self-assembled supramolecular shell at the oil-water interface. The shell material's chemical composition was analyzed using infrared spectroscopy, ¹H-NMR, and mass spectrometry. Four batches of well-dispersed microcapsules (diameter, 1-10 μm) with encapsulation efficiency >99% and varying payload were synthesized. Accelerated thermal release tests proved that encapsulation reduced the cinmethylin evaporation by up to 90%, over nonencapsulated cinmethylin, and crucially, the release profiles of the bis-urea microcapsules were comparable to conventional polyurea microcapsules prepared industrially. The release rate of cinmethylin increased with payload, indicating that barrier properties of bis-urea microcapsules are tunable, making them adaptable for encapsulating a variety active ingredients. Additionally, all the four batches of bis-urea microcapsules were mechanically stronger than the polyurea microcapsules. Synthesized using a straightforward process requiring no modifications to existing industrial equipment, these bis-urea microcapsules have great potential to replace commercial nonbiodegradable microplastic microcapsules.