用聚合物乳液为包膜剂制备缓释尿素

Slow-release Urea Preparation by Film Coating with Polymer Latex

介绍了采用聚合物乳液作为包膜剂制备包膜缓释尿素,具有工艺简洁和包膜过程绿色的特点,能够根本解决现有包膜过程中毒性有机溶剂的污染和回收问题。实验考察了聚合物乳液包膜剂平板成膜时的渗透系数,表明聚合物乳液是良好的缓释包膜剂。实验采用转鼓流化床工艺制备包膜尿素,测定了包膜尿素在水中的释放特性。通过扫描电镜检测包膜尿素和膜层的形貌特征。结果表明,采用聚合物乳液直接对尿素颗粒包膜时,在颗粒表面形成的高湿性环境容易导致尿素表面溶解,水分蒸发后形成针状尿素结晶,复合在聚合物膜层中,包膜尿素进入水中时,针状尿素快速溶出,造成膜层多孔性渗漏,降低了包膜尿素的缓释性能。在聚合物乳液包膜前,先在尿素颗粒表面包覆一层硫磺阻隔层或石蜡疏水层,能有效抑制尿素在包膜时的溶出过程。

Polymer latex was used as film coating materials for producing slow release urea (particles). The film coating process is environmentally benign and simple, which can radically (eliminate) the pollution and recovery problems of the toxic organic solvent comparing with current technologies. The permeability of water vapor through a plate film made from the polymer latex was investigated. The low permeability showed that the polymer latex was suitable as film (coating) materials for slow release urea preparation. The film coating process was carried out in a drum fluidized bed in which a fluidized bed was set in a rotating drum, and the release properties of the coated urea were examined. The film surface of coated urea particles was checked by (scanning) electron microscopy (SEM). The experimental results showed that a highly moist (circumstance) formed in the vicinity of the particle surface due to the presence of polymer latex (affected) the film formation and properties significantly. When the latex drop collideds on the (particle) (surface) of urea, urea might dissolve and form needle like urea crystals after water was (evaporated), and the needle like urea crystals were compounded with the polymer film during the coating process. When the film coated urea particles were put into water, the urea in the (composite) film dissolve soon and some pores are left on the film, leading to a quick release of the urea in water. (Experiments) showed that pre coating with sulfur as a steric hindrance layer or wax as a hydrophobic film on urea surface could effectively prevent urea’s dissolving in the coating process.