encapsulation process is a method by which sensitive materials (core) are covered with polymeric materials (wall). As most encapsulation techniques need complicated equipments, long laboratory works and are expensive, therefore, in this study a new technique is utilized for producing microcapsules at a very short time and low cost. This technique is based on the difference between dielectric constants of core and wall materials as well as electromagnetic energy. Edible citric acid crystals (core) were combined with some coating materials such as salab, gum tragacanth, refined starch, sucrose, guar gum, agarose, gelatin, fibrosis carboxymethylcellulose (CMC), inulin, low and high methoxyl pectin (LMP & HMP), casein, and sorbitol at ratios about 1:2 up to 1:100 (core:wall). Each mixture was treated up to 600 seconds (depending on the type of wall materials) at various microwave power intensities (10-100%). Afterwards, the prepared microcapsules were separated by distinct (with defined mesh No.) sieves, and their apparent structure and quality were evaluated using binocular and their photographs were taken by a microscope equipped with digital camera. Our findings revealed that amongst the materials were examined only inulin, casein, LMP (9.5%), fibrosis CMC, and sorbitol were able to produce high quality as well as highly efficient microcapsules, respectively. In addition, the highest coating efficiency was seen at 100% microwave power intensity (1200W) at 1:10 mixing ratio. Moreover, the optimum microwave treating time for casein, inulin, fibrosis CMC, LMP (9.5%), and sorbitol was 400, 75, 400, 100, and 100 seconds, respectively.

Polyurea microcapsules containing pesticide (Dursban trade name for O,O-3,5,6-trichloro-2-pyridyl phosphorothioate, C9H11C13NO3PS) as an active agent were prepared by reaction of polyisocyanate (such as toluene diisocyanate) and polyamine (such as diethylene triamine) as the monomers. The first step gives rise to the formation of oil-in-water emulsion, this is followed by initiation of polymerization process to produce polyurea capsule wall. It has been found that the microcapsule formation depends on temperature, type and amount of emulsifier, co-emulsifier, matrix forming agent, stirring speed, organic phase, etc. This paper is devoted to the studies of above factors that optimize the formation of microcapsules wall. Formation of polyurea was confirmed by F-I-IR technique and the thermal behaviour of polyurea microcapsules was investigated by differential scanning calorimetery method. The morphology of microcapsules was studied by scanning electron microscope.