Physical Strength of Microcapsules

Ohtsubo et al. have described a method to identify those parameters which determine the physical strength of PU microcapsules containing liquid insecticide (viz., fenitrothion) [45]. These microcapsules have been found to be effective in con-troUing household pests such as cockroaches. As expected, the strength of the microcapsule depends mainly on the microcapsule mass mean diameter (D), the thickness of the membrane wall (T), and particle size distribution expressed as polydispersity (e.g., D /DJ. The coefficient of variation of the particle size distribution (CV) is first determined using any suitable instrument (particle size analyzer) and method. Wall thickness T is calculated from the following equation  

The weight (W) per milligram of fenitrothion apphed to the plate has been used as a parameter of the weight loaded onto the sample. Following the theory of destruction of an empty sphere with a thin wall, when introduced to the breaking of rrricro-capsules, the pressure (P) required to break a microcapsule is calculated as follows  

---