Materials used to develop the preparation method for microencapsulating the uycalyptus oil containing the fine water droplets are as follows:

The first core material was Uycalyptus oil (UO) (Wako Junyaku Co., Ltd.). Span 80 (Wako Junyaku Co., Ltd.) and Soybean Lecithin (Wako Junyaku Co., Ltd.) were used as the oil soluble surfactant. Hydroxy propyl methyl cellulose (HPMC) (50SH-50: Shinetsu Chemical Ind Co., Ltd.) and Tannic acid (TA) were used as the reactants to form the microcapsule shell. These chemical species were used as received.

In order to investigate whether the microcapsules can be prepared by the microencapsulation mechanism pre- sented in this study or not, the pre-microencapsulation experiment was tried as follows.

Figure 1 shows the schematic diagram of pre-microencapsulation procedure. Namely, the HPMC aqueous solution and the UO were poured into the beaker as shown in Figure 1. The UO and the HPMC aqueous solu- tion were separated to form the upper oil phase and the lower aqueous phase, respectively. Then, the TA aque- ous solution was dropped into the oil phase through the nozzle by the syringe pump. If TA could transfer through the oil phase and react with HPMC on the interface between the oil phase and the HPMC aqueous solu- tion, the gelated HPMC film should be formed on the interface. As a result, the TA aqueous droplet may be maintained on the formed film for a while.

According to this microcapsule shell formation mechanism, the pre-microencapsulation experiment was per- formed by changing the concentrations of HPMC and TA.

Figure 2 shows the schematic diagram of experimental apparatus used to prepare the microcapsules. The reactor was the separable flask with the effective volume of 500 cm³. Four baffles made of aluminium plate were set on the wall of reactor. The six bladed disc turbine impeller with the diameter of 5 cm was used to stir the reaction mixture. The reactor was set in the thermos tatted water bath to keep temperature of reaction mixture constant. Figure 3 shows the flow chart for microencapsulating the UO containing the fine water droplets by using the interfacial condensation reaction between HPMC and TA. The aqueous solution dissolving TA as a gelation agent was dispersed into the UO dissolving Soybean Lecithin (SL) of an oil soluble surfactant to form the (W/O) emulsion.

Then, the (W/O) emulsion was dispersed into the continuous water phase dissolving HPMC to form the (W/O)/W emulsion. The operation stated above was performed at room temperature.

After formation of the (W/O)/W emulsion, temperature of the (W/O)/W emulsion was raised to 30˚C to per- form the condensation reaction between TA and HPMC. When the reaction was continued for 1h, it was inves- tigated whether the microcapsules of UO containing the fine water droplets could be prepared or not.

The formation of microcapsules was confirmed by observing the stability of the (W/O)/W emulsion after the microencapsulation process and by optical microscope. If the microcapsules were prepared well, the photo- graphs of them were taken. Contrary to this, if the microcapsules were not prepared well, the emulsion should be broken rapidly.

In the fundamental experiment stated above, the concentrations of HPMC and TA were mainly changed. The experimental conditions in this experiment were shown in Table 1.

Figure 4 shows the photographs of the TA aqueous droplet and the interface on which the gelated HPMC film was formed according to the concentrations of HPMC and TA. When the concentrations of HPMC and TA were low (C_HPMC = 0.05 wt%, C_TA = 0.01 mol), the TA aqueous droplet was kept on the interface as shown in Figure 4(a), but dissolved into the HPMC aqueous solution in a few min. The short life of TA aqueous droplet on the interface may be due to the formation of thinner film. On the other hand, when the concentrations of HPMC and TA were higher (C_HPMC = 0.2 wt%, C_TA = 0.06 mol), the TA aqueous droplet was kept on the interface for ca. 10 min as shown in Figure 4(b) due to the thicker film formation.

Figure 5 shows the measured results of the time elapsing from arrival of a TA aqueous droplet at the interface to disappearance. From these results, it is found that the film was not formed at C_TA = 0 in spite of elapsing of ca. 30 s and the gelated film was formed above the concentrations of C_HPMC = 0.05 wt% and C_TA = 0.01 mol. Here, ca. 8 min at C_HPMC = 0.05 wt%, and ca. 10 min at C_HPMC > 0.1 wt% don’t mean that the TA aqueous droplet dis- appeared at these elapsing times, but mean that the measurement of elapsing time was finished at these times.

From these results, as the gelated HPMC film was found to be formed on the interface between the UO and the HPMC aqueous solution above C_HPMC = 0.05 wt% and C_TA = 0.01 mol. Taking these results into considera- tion, the formation mechanism of film may be stated as shown in figure 6. TA should transfer from the TA aqueous droplet to the interface through the UO and react with HPMC on the interface to form the gelated HPMC film. If the concentrations of HPMC and TA are lower, the thinner shell film should be formed. Contrary to this, if the concentrations of HPMC and TA are higher, the thicker and stronger shell film should be formed.

Furthermore, it was investigated whether the microcapsules could be prepared or not by the preparation me- thod presented in this study. Namely, the stability of the (W/O)/W emulsion was observed with and without the microencapsulation process.

Figure 7 shows the photographs of the (W/O)/W emulsion just after the microencapsulation process (a) and after 10 min (b). The (W/O)/W emulsion without the microencapsulation process was separated rapidly into the oil phase and the water phase, but the observation result is not shown. Contrary to this, the (W/O)/W emulsion with the microencapsulation process, namely the (W/O) droplets microencapsulated floated on the water phase and was kept to stably disperse as shown in Figure 7(b). From these results, the UO droplets containing the fine water droplets were estimated to be microencapsulated well by the gelated HPMC shell.

Figure 8 shows the optical microscopic photographs of microcapsules prepared by changing the concentration of HPMC at C_TA = 0.06 mol. From these photographs, the following interesting results are obtained. The micro- capsules could be prepared according to the formation mechanism presented in this study. The mean diameters of microcapsules changed from 780 µm to 1330 µm by changing the concentration of HPMC as shown in Figure 8. The fine water droplets were microencapsulated well, but become larger due to coalescence between the fine water droplets. In order to stably disperse the fine water droplets in the oil droplet and to utilize as the first core material, it must be necessary to select the optimum oil soluble surfactant species and the concentra- tions of them. The microcapsules become irregular with the concentration of HPMC. This result is considered to be due to the fact that the oil droplets containing the fine water droplets are hard to break by the stronger shell formed with the higher concentration and become irregular. These microcapsules could be stably dispersed in the continuous water phase under stirring of revolution speeds from 200 rpm to 500 rpm with the six bladed disc turbine impeller of 5 cm diameter.

From the results obtained above, the formation mechanism of microcapsules may be presented as shown in Figure 9. TA dissolved in the inner water droplets should transfer to the interface through the UO phase, react with HPMC on the interface and form the gelated HPMC film as the microcapsule shell.

In the case of the lower concentration of HPMC or TA, as the weak shell is formed, the (W/O) emulsion may be broken. As a result, the microcapsules cannot be prepared. Contrary to this, in the case of the higher concen- tration of HPMC and TA, as the stronger shell is formed, the microcapsules can be prepared well. The fine inner

water droplets may coalesce each other to form the larger water droplets. If the fine water droplets could be dis- persed stably, TA may transfer rapidly due to the larger interface area between the UO phase and the inner water phase. As a result, the shell may be formed rapidly and the microcapsules may be prepared more satisfactory. As many kinds of chemical species can be dissolved in the fine inner water droplets as the first core material and in the oil phase as the second core material at the same time, the microcapsules will be given the many kinds of functions. Namely, the microcapsules with the multiple functions can be prepared by using the microencapsula- tion method developed in this study.

However, it has to be investigated whether the microcapsules with the other oil species can be prepared by the microencapsulation mechanism presented here or not. Because, as it is necessary for TA to transfer through the

oil phase, the fundamental experiments with regard to mass transfer of TA in the other oil species have to be performed.