Formulation and Characterisation of Polyester-Lignite Composite Coated Controlled-Release Fertilisers

Two polyester-lignite composite coated urea controlled-release fertilisers (CRFs; Poly3 and Poly5) were developed and their physicochemical properties were studied. Both these CRFs significantly (p < 0.05) extended the urea release compared to uncoated urea; Poly3 and Poly5 by 117 and 172 hours, 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 CRFs (Calc3 & 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, 48h and 72h, 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 CRFs.