Biodegradable polyurethane materials from bark and starch. II. Coating material for controlled‐release fertilizer

Biodegradable polyurethane foams (PUFs) as coating materials for the controlled release of fertilizer were prepared from a four‐component system consisting of diisocyanate, polyester, Acacia mearnsi bark, and corn starch. Ammonium sulfate [(NH 4 ) 2 SO 4 ] was used as a fertilizer to evaluate the effects of the preparation conditions on the release ratio. The release ratio of (NH 4 ) 2 SO 4 decreased with an increasing amount of biomass in PUFs and increasing sizes of sample particles; the ratio increased with increasing doses of water, which was used as a foaming agent in the preparation of polyurethane, regardless of the amount of coating material. The remaining fertilizer in the polyurethane seemed to be released completely because the PUFs were degradable, to some extent, by soil microorganisms.