(722m) Preparation and Evaluation of Thermosensitive Microcapsules Using Double Tube Nozzle

Thermo-responsive microcapsule consisted of N-isopropyl acrylamide (NIPAAm) and alginate was prepared using double tube nozzle. In this method, NIPAAm and alginate were used as thermo-responsive polymer and support structure polymer, respectively. In the experiment, the solution which contained NIPAAm monomer, cross-linking agent and sodium alginate was pumped out from outer tube, and cocoa suspension as marker was pumped out from inner tube of the double tube nozzles to form droplets of double layered structure. The formed droplets were then dropped into consolidation solution which contained polymerization initiator, promoter and CaCl₂. In the solution, at first gellation and consolidation of the alginate in the outer layer of the droplet occurred due to the calcium cation cross-linking of the alginate molecules and it formed support structure of the capsule. Then, NIPAAm monomers were polymerized within the alginate gell layer, and thermo-responsive microcapsules were obtained.

In the experiment, the effect of the flow rate of the solution from the outer tube (Fout) and that from the inner tube (Fin) on the size and shell thickness of the capsules was examined. The result showed that the size of the capsule increased and the shell thickness decreased with the increase of the flow rate ratio (Fin / Fout) and they are not dependent on the absolute value of the flow rates in the range used in this study (15-60 mL/h). However, when the flow rate ratio (Fin / Fout) exceeded 0.45, formation of the capsule became difficult. Temperature-responsive volume change of the capsules was also measured. The result showed that the capsule started to shrink when the temperature increased, and it swollen when the temperature decreased. The temperature responsive volume change was reversible and the swelling ratio changed from 15-40 % depending on the conditions that if the NIPAAm polymer in the capsules or beads were crosslinked or not.