Four kinds of polymer coated urea(PCU)were put in distilled water at 30℃ to determine the variation of coating penetrability and give a precise description of the urea release kinetics. The urea release from PCU coul...Four kinds of polymer coated urea(PCU)were put in distilled water at 30℃ to determine the variation of coating penetrability and give a precise description of the urea release kinetics. The urea release from PCU could be divided into four stages: lag stage, swell stage, steady stage and decay stage. The release rate coefficient K, a measure of coating penetrability, was linearly increased at swell stage, but almost not variable at steady stage. At decay stage, the relation of X to time t could be described by the equation K= mtn-1where m and n are the coefficients). When n>1, the coating penetrability was gradually increased, and the urea release from PCU was accelerated; when n=1, the coating penetrability was steady, and the urea release from PCU obeyed the first-order kinetics; and when n<1.the coating penetrability was gradually decreased, and the urea release from PCU was delayed, resulting in a significant 'tailing effect'.展开更多
基金supported by the National 863 Program,Ministry of Science and Technology of China(2001AA246021)the Knowledge Innovation Engineering of the Chinese Academy of Sciences(KZCX2-402).
文摘Four kinds of polymer coated urea(PCU)were put in distilled water at 30℃ to determine the variation of coating penetrability and give a precise description of the urea release kinetics. The urea release from PCU could be divided into four stages: lag stage, swell stage, steady stage and decay stage. The release rate coefficient K, a measure of coating penetrability, was linearly increased at swell stage, but almost not variable at steady stage. At decay stage, the relation of X to time t could be described by the equation K= mtn-1where m and n are the coefficients). When n>1, the coating penetrability was gradually increased, and the urea release from PCU was accelerated; when n=1, the coating penetrability was steady, and the urea release from PCU obeyed the first-order kinetics; and when n<1.the coating penetrability was gradually decreased, and the urea release from PCU was delayed, resulting in a significant 'tailing effect'.
