Encapsulation of urea with alkyd resin-starch membranes for controlled N < inf> 2 release: Synthesis, characterization, morphology and optimum N < inf> 2 release

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© 2018 Institution of Chemical Engineers Nitrogen released into soils from uncoated urea granules is lost continuously due to volatilization, leaching, denitrification, nitrous emission, water eutrophication and surface run-off. Reducing the release rate can increase its efficiency of use and reduce nitrogen pollution. In this research, granular urea fertilizer was encapsulated with alkyd resin-starch bio-composites as materials of biodegradable and regenerative resources to obtain controlled release coated urea (CRCU). Different bio-composites were synthesized from each of castor seed oil and rubber seed oil based alkyd resin (modified with sorbitol, maleic and phthalic anhydride) and cassava starch. Effects of sorbitol, maleic anhydride and pthalic anhydride on the release kinetics of the CRCU were evaluated. Optimum nitrogen release characteristic of the CRCU was evaluated as a function of coating thickness, release time and pH. Structural and morphology elucidation of the raw urea and encapsulated ureas were established using FTIR and SEM instrumental analysis, respectively. Nutrient release kinetic of the different coated urea was determined using Kjeldahl method. FTIR result confirmed the esterification reaction and hydrogen bonding integrity of the alkyd resins and starch. The SEM images of the raw urea appears rough and have fine openings while that of CRCUs possess a seemingly decrease in membrane porosity and ordered uniform layer. 31.66 and 48.61% cumulative nitrogen release were obtained with coating thickness of 6.4(mm), time of 24 days, pH of 8 and 2.2(mm), time of 24 days, pH of 8 for RSO-St-S and CSO-St-S encapsulated urea, respectively. The encapsulated ureas perfectly satisfy the requirements of European Standard EN 13,266 for CRFs. It can be concluded that the synthesized CRCU efficiently retard nitrogen release.

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Process Safety and Environmental Protection