Encapsulation of mineral fertilizer by polysulfone using a spraying method

Studies on the encapsulation of the commercial granular fertilizer, NPK 6-20-30, with polysulfone (PSF) as a coating were performed. In order to improve the properties of coatings, the granules of previously coated fertilizer (wet method) were sprayed with a polymer solution or pure solvent (N,N dimethylformamide). Concentration of the polymer in solutions used for spraying was in the range of 13–17 wt%. Measurements of thickness, porosity of prepared coatings and microphotographic observation of the coatings were taken. It was observed that the porosity and thickness of additionally sprayed layers was decreased by about 30% compared with the reference coating. However, the experiments showed that the above-mentioned parameters were independent of PSF concentration in the spraying solution. The release rate of nutrients as a function of time was examined at room temperature. It was observed that the application of the method of preparation of coatings resulted in a reduction of the release rate of NPK from a coated granule. Moreover, the increase of the number of sprayed polymer layers caused a decrease in the release of each macroelement by ca. 25%. The reduction of the release rate was associated with a more compact structure and lower porosity of sprayed coating compared to the reference one.