Toshiro Ohtsubo

A study of the physical strength of fenitrothion microcapsules

Fenitrothion, a widely used organophosphorous insecticide, was microencapsulated with polyurethane via an interfacial polymerization method, and the relationship between the formulation factors, such as mass median diameter (D) and wall thickness (T), and the physical strength of the microcapsules was studied. It was found that the larger the ratio DT, the smaller the pressure per capsule required to break 50% of microcapsules (P50). This result agreed with the theory of the destruction of an empty sphere with a thin wall. Moreover, the result obtained by the physical breaking test coincided with that obtained by the breaking test of microcapsules by cockroaches.

Permeation of urea through various polyurethane membranes.

BACKGROUND Controlled-release systems using polymer membranes are very important in agriculture for labour-saving and effective delivery of pesticides and other agents. Polymer-coated granules are one of the most useful formulations, and a study of the factors for polymer design is necessary to achieve various release patterns. A permeation study using plain membranes was carried out in order to clarify parameters, and the results were compared with the release from polymer-coated granules. RESULTS The permeation coefficient of urea through a plain polyurethane membrane decreased significantly as the urethane and alkyl side chain content increased. The glass transition temperature and crosslink density of the polyurethanes hardly influenced its permeability. The release rate from polyurethane-coated granules was also reduced by alkyl side chains. However, it was faster than that through a plain membrane because of capsule expansion by continuous water penetration and structural changes in the membrane. CONCLUSION The release rate of urea through a polyurethane plain membrane and from polyurethane-coated granules can be controlled by changing the chemical properties of the membrane. In addition, physical properties such as the glass transition temperature T(g) or crosslink density should be considered to assess the release profile from polyurethane-coated granules.

Sustained-release microsphere formulation containing an agrochemical by polyurethane polymerization during an agitation granulation process.

In this report, a new solventless microencapsulation method by synthesizing polyurethane (PU) from polyol and isocyanate during an agglomeration process in a high-speed mixing apparatus was developed. Clothianidin (CTD), which is a neonicotinoid insecticide and highly effective against a wide variety of insect pests, was used as the model compound. The microencapsulated samples covered with PU (CTD microspheres) had a median diameter of <75μm and sustained-release properties. The CTD microspheres were analyzed by synchrotron X-ray computed tomography measurements. Multiple cores of CTD and other solid excipient were dispersed in PU. Although voids appeared in the CTD microspheres after CTD release, the spherical shape of the microspheres remained stable and no change in its framework was observed. The experimental release data were highly consistent with the Baker-Lonsdale model derived from drug release of spherical monolithic dispersions and consistent with the computed tomography measurements.

Effect of binder composition on physicochemical properties of water dispersible granules obtained through direct granulation of agrochemical suspension using fluidized bed

A water dispersible granule (WDG) was prepared through direct granulation of an agrochemical suspension composed of a mixture of sodium lignosulphonate and polyvinyl alcohol (PVA) as a binder using a fluidized bed granulator. The evaluation of various physicochemical properties showed that the mass median diameter (MMD) and disintegration time of the WDG increased with an increase in the PVA content. It was also revealed that the MMD was positively correlated with the viscosity of the agrochemical suspension and that the disintegration time decreased with an increase in solubility of the binder mixture.

Evaluation of the Thermosensitive Release Properties of Microspheres Containing an Agrochemical Compound

The purpose of this study was to develop a deeper understanding of the key physicochemical parameters involved in the release profiles of microsphere-encapsulated agrochemicals at different temperatures. Microspheres consisting of different polyurethanes (PUs) were prepared using our previously reported solventless microencapsulation technique. Notably, these microspheres exhibited considerable differences in their thermodynamic characteristics, including their glass transition temperature (Tg), extrapolated onset temperature (To) and extrapolated end temperature (Te). At test temperatures below the To of the PU, only 5-10% of the agrochemical was rapidly released from the microspheres within 1 d, and none was released thereafter. However, at test temperatures above the To of the PU, the rate of agrochemical release gradually increased with increasing temperatures, and the rate of release from the microspheres was dependent on the composition of the PU. Taken together, these results show that the release profiles of the microspheres were dependent on their thermodynamic characteristics and changes in their PU composition.