Preparation of Microcapsules Containing Water and Effect of Water Content on Expansion Behavior

Microcapsules can contain as the core materials the various substances such as solid, liquid and gas and release optionally them. Also, microcapsules containing water among these core materials have been applied in a lot of fields such as pharmacy, adhesives, agriculture, cosmetics, and so on. The research work was conducted in order to establish the optimum conditions for preparing the expanded polystyrene beads without harmful substances and was aimed at the preparation of the microcapsules containing water and investigation of the effect of the water content on the expansion behavior of microcapsules.

In the experiment, microcapsules were prepared with the suspension polymerization method and the suspension polymerization in parallel with interfacial polycondensation method using the multiple emulsion (W/O)/W and adding a few additives.

The results demonstrated that with increasing the crosslinking agent concentration in the suspension polymerization method, the water content increased from R = 5.8 wt% (C_T = 0) to R = 8.2 wt% (C_T = 4 wt%) and then decreased to R = 7.5 wt% (C_T = 9.0 wt%), while the expansion ratio increased from E = 1.01 (C_T = 0) to E = 2.20 (C_T = 4 wt%) and then decreased to E = 1.01 (C_T = 7.0 wt%). With increasing the added amount of wax in the suspension polymerization method, the water content gradually increased from R = 2.5 wt% to R = 8.0 wt%, while the expansion ratio increased from E = 1.01 to E = 1.5 and then decreased. The water content and the expansion ratio could be increased by conducting suspension polymerization in parallel with interfacial polycondensation reaction from R = 5.0 wt % to R = 8.0 wt % and from E = 1.01 to E = 1.3, respectively. The maximum expansion ratio of E = 2.58 in this work was obtained under the conditions of crosslinking agent concentration of C_T = 4 wt %, the added amount of wax of 3.0 g, addition of Agarose and the expansion temperature of T = 150°C.

In conclusion, the water content and the expansion ratio could be increased by adding the crosslinking agent, wax and hydrophilic additives. The water content could be increased by forming the polyurethane shell on the surface of the inner water droplets; as a result, the expansion ratio could be increased. However, there were the optimum concentration of crosslinking agent and the added amount of wax required to increase the expansion ratio. In the near future, the effect of the physical properties of matrix polymer of microcapsules such as modules of elasticity and melting point should be discussed.

Article by Yoshinari Taguchi, et al, from Niigata University, Niigata-shi, Japan.

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