To produce sodium alginate beads coated with chitosan, following procedure was undertaken:
Sodium alginate was dissolved in distilled water at a concentration of 4% (...) The gelation medium was prepared by dissolving chitosan (1% w/v) in one percent acetic acid, followed by addition of CaCl2 at the concentration of 4% (w/v). The sodium alginate solution was added dropwise into gelation medium [and cured] *
Why do you have to add CaCl2 to the solution that makes the gelation medium?
As far as I know the CaCl2 will dissociate into $\ce{Ca^2+}$ and $\ce{Cl}$ ions. How does this aid in getting the chitosan molecules to the sodium alginate bead?
- Source: S.K. Bajpai, R. Tankhiwale / Reactive & Functional Polymers 66(2006) 645–65