Preparation and properties of starch-based polyurethane/montmorillonite composite coatings for controlled-release fertilizer

摘要

In order to enhance the controlled-release property of starch-based polyurethane (SPU) coating, polyurethane/montmorillonite (SPU/MMT) composite coatings for controlled-release urea were prepared by in-situ polymerization with a rotating drum. The effect of MMT on morphology, structure, physico-chemical properties, especially controlled-release property of the as-prepared composite coatings were studied in detail. The results showed that MMT particles dispersed well in SPU matrix, and the obtained SPU/MMT composite coatings possessed more tough and compact morphology with less-visible holes compared with SPU coating. With the content of MMT rising to 3%, the time needed for 75% nitrogen release increased to 49 days, much longer than 14 days of SPU coating. Further, the nitrogen release mechanism underlying the structure and properties of SPU/MMT composite coatings were discussed and elucidated. According to the analysis, the superior controlled-release property of SPU/MMT coatings originated from the impermeablity to water molecules of layered MMT acting as mechanical barriers to increase the diffusion path and resistance, the enhanced crosslinking density and hydrophobicity of composite system due to the introduction of MMT, as well as the improved mechanical properties hindering the formation of cracks and enlargement of the holes on the surface of composite coatings.