Development of Citric Acid Cross-Linked Starch for Controlled-Release Fertilizer (CRF)

The development of controlled-release fertilizers (CRF) have minimized plant nutrient loss uncontrolled by conventional fertilizers but still contain flaws in terms of the non-biodegradability and price of the coating material. This research aims to explore more on the potential of citric acid cross-linked starch as coating for CRFs. Since films developed from pure starch have weak mechanical properties, starch can be strengthened through chemical modifications such as cross-linking to produce value-added starch. Citric acid is used as a cross-link agent and its effectiveness is being studied. Preliminary preparation of starch solutions was done using deionized water, glycerol, native tapioca starch and citric acid of varying concentrations (0-30% w/w). Films were cast in an oven and were subjected to the water uptake test and swelling/disintegration test. The cross-linked film squares immersed in water for the swelling/disintegration test appeared to be intact for up to one week whereas the non-cross-linked film square degraded early in the test. As for the water uptake test, the starch films containing a higher amount of citric acid exhibited a lower percentage water uptake as compared to starch films containing a lower amount of citric acid. This phenomenon is attributed to the extent of cross-linking within the starch molecular structure which may encourage or inhibit the entry of water molecules. Urea prills coated with the cross-linked starch solution were viewed under a scanning electron microscope. The images show that the coating process was successfully done, with the coating adhering to the surface of the urea prill, although not very homogenously.