Ethyl cellulose polymer microspheres for controlled release of norfluazon

The pesticide norfluazon has been microencapsulated using ethyl cellulose t o develop controlled-release formulations that decrease its mobility throug h the soil and protect it from photodegradation. Ethyl cellulose microspher es loaded with norfluazon were prepared by the solvent-evaporation method. To obtain the microspheres, certain conditions (pesticide/polymer ratio, pe rcentage of emulsifying agent and solvent) were varied. The shape and size of the microspheres obtained were studied by scanning electron microscopy. Other parameters, such as solids recovery, encapsulation efficiency and pes ticide loading, were also studied. The release rate of norfluazon from the different microspheres was slower than that of pure norfluazon. In particul ar, microspheres obtained with o-xylene, which provided the largest diamete r, retarded the initial release of the pesticide relative to microspheres o btained with chloroform, or to pure norfluazon. Moreover, the studies showe d that the pesticide/polymer ratio controlled the release of norfluazon, wh ich was slower when this ratio was low. Release rates conformed to a genera lised kinetic equation for a diffusion-controlled release mechanism, and th e time taken for 50% of the active ingredient to be released into water, t( 50) was calculated. (C) 2001 Society of Chemical Industry.