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.

The spraying of coatings previously formed by the inversion phase technique – wet method made them denser. Porosity and thickness of double sprayed coatings were decreased by about 20% in comparison with the reference coating. It was also observed that neither of these parameters was dependent on PSF concentration in the spraying solution. The applied method of preparaing coatings resulted in a decrease of the N, P, and K release [1] K.L. Smith, B. Holmes and F. Matthew, Asymmetric microporous beads for controlled release, EP 0466986, 1990. [2] A. Ombodi and M. Saigusa, Broadest application versus band application of polyolefin-coated fertilizer on green peppers grown, J. Plant Nutr., 23(10) (2000) 1485–1493. [3] N. Cosuge and K. Tobataku, Coated granular fertilizers, EP 030331, 1989. [4] O.A. Salman, Polyethylene-coated urea. 1 Improved storage and handling properties, Ind. Eng. Chem. Res., 28 (1989) 630–632. [5] T. Posey and R.D. Hestar, Developing a biodegradable film for controlled release of fertilizer, Plastics Eng., 1 (1994) 19–21. [6] W.P. Moore, Reinforced-resin coated fertilizer granules, US 6045810, 2000. [7] G. Pipko, Method for manufacture of slow-release fertilizers, EP 0276179, 1988. [8] A.J. Rajsekharan and V.N. Pillai, Membraneencapsulated controlled-release urea fertilizers based on acrylamide copolymers, Appl. Polym. Sci, 60 (1996) 2347–2351. [9] B. Gordonov, A. Shoviv and E. Zlotnikow, Manufacture of fan encapsulated slow-release particulate fertilizer, US 5560768, 1996. [10] J. Wolstenholme, D.G. Pauly, M. Nyborg and E. Solberg, High efficiency controlled release phosphate-based fertilizer, EP 0731067, 1996. [11] M.C. Garcia, A. Vallejlo, L. Garcia and M.C. Cartagena, Manufacture and evaluation of coated triple superphosphate fertilizers, Ind. Eng. Chem. Res., 36 (1997) 869–873.