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%
(CT = 0) to R = 8.2 wt% (CT = 4 wt%) and then
decreased to R = 7.5 wt% (CT = 9.0 wt%), while the expansion
ratio increased from E = 1.01 (CT = 0) to E = 2.20 (CT =
4 wt%) and then decreased to E = 1.01 (CT = 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 CT =
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.
Full access: http://mrw.so/2jS4JE
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