Preparation of urea-containing starch-castor oil superabsorbent polyurethane coated urea and investigation of controlled nitrogen release.

With the aim of improving water absorption and controlled release performance of current controlled release fertilizers, a novel composite coating method for superabsorbent-polyurethane coated urea (SAPCU) was developed. Superabsorbent-polyurethane (SAPU) composite coating material was successfully formed through an insitu reaction, where castor oil polyurethane (COP) and superabsorbent polymer (SAP) were connected through urethane bonds with an optimal reaction ratio of SAP and PAPI as 2.5:1 (w w-1). The ideal nitrogen release and water absorption characteristics of SAPCU were achieved by adjusting the amount of COP and SAPU. The SAPCU had a high total nitrogen content (40.23-42.14 %), large swelling ratios (120-160 g water/g SAPU), and long nitrogen release period (60-150 days).