The rice husk biochar/acetate starch-urea (RHBC/AS-UR) composite films were prepared by casting method with different AS:UR:RHBC mass ratios of 8:1:1, 8:2:1, 8:4:1, respectively. The micromorphology and structure properties of the RHBC/AS-UR composite films were investigated by SEM, FTIR, XRD and TGA. The RHBC/AS-UR composite-coated UR fertilizers were prepared in a spouted fluidized bed coating equipment and its release characteristics were tested. The results show that the rice husk biochar can be uniformly dispersed in the RHBC/AS-UR composite film and has good bonding with AS-UR in a "solid bridge" structure. In the mean time, the thermal stability of RHBC/AS-UR composite films is enhanced by adding RHBC. The adding of UR can improve the ductility of RHBC/AS-UR composite film. When the mass fraction of UR is 18.2wt%, the best mechanical properties of the RHBC/AS-18.2wt%UR composite film can be reached and the elongation at break increases by 500%. Compared to the pure UR granule without and with RHBC/AS-UR coating, the UR coated with different mass ratios of RHBC/AS-UR composite films can effectively reduce the release rate of UR-N. The total release rate of RHBC/AS-18.2wt%UR coated UR is the lowest (only 81%), which exhibits better slow-release property.
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