Formulation and characterization of polyester-lignite composite coated slow-release fertilizers

Two polyester-lignite composite coated urea slow-release fertilizers (SRFs; Poly3 and Poly5) were developed and their physicochemical properties were studied. Both these SRFs significantly (p < 0.05) extended the urea release compared to uncoated urea; Poly3 and Poly5 by 117 and 172 h, respectively. The urea release characteristics of Poly5 were further enhanced by linseed oil application (Poly5-linseed). The SEM images demonstrated the coatings were in contact with the urea and encase urea particles completely with the average coating thickness of 167.2 ± 15 µm. The new interactions between polyester and lignite in the composite coating were confirmed by the FTIR analysis. Polyester-calcium carbonate (Polyester-CaCO 3 ) coated SRFs (Calc3 and Calc5) were developed using CaCO 3 as a filler in place of lignite and the urea dissolution rate was compared with Poly3 and Poly5. The urea release times for the polyester-CaCO 3 formulations, 48 and 72 h, were significantly ( P < 0.05) lower than the polyester-lignite formulation, showing that lignite imparted greater control over release time than CaCO 3 . Findings from this work showed that polyester-lignite composites can be used as a coating material for SRFs. Graphical abstract