Kinetic study of chitosan-tripolyphosphate complex reaction and acid-resistive properties of the chitosan-tripolyphosphate gel beads prepared by in-liquid curing method

Chitosan gel beads were prepared using am in-liquid curing method by the io notropic crosslinking with sodium tripolyphosphate. Crosslinking characteri stics of the chitosan-TPP beads were improved by the modification of in-liq uid curing mechanism of the beads in TPP solution. Chitosan gel beads cured in pH value lower than 6 were really ionic-crosslinking controlled, wherea s chitosan gel beads cured in pH values higher than 7 were coacervation-pha se :inversion controlled accompanied with slightly ionic-crosslinking depen dence. According to the result, significantly increasing the ionic-crosslin king density of chitosan beads could be achieved by transferring the pH val ue of the curing agent, TPP, from basic to acidic. The swelling behavior of various chitosan beads in acid appeared to depend on the ionic-crosslinkin g density of the chitosan-TPP beads that were deeply affected by the curing mechanism of the beads. The mechanism of chitosan-TPP beads swollen in wea k acid was chain-relaxation controlled, while the mechanism of chitosan-TPP beads swollen in strong acid seem to be not only chain-relaxation but also chain-scission controlled. Chitosan-TPP beads prepared in acidic TPP solut ion decreased the chain-scission ability due to the increase of ionic cross linking density of the beads. By the transition of curing mechanism, the sw elling degree of chitosan-TPP beads was depressed, and the disintegration o f chitosan-TPP beads would not occur in strong acid. The mechanism of ionic -crosslinking reaction of chitosan beads could be investigated by an unreac ted core model, and the curing mechanism of the chitosan beads is mainly di ffusion controlled when higher than 5% of chitosan was employed. (C) 1999 J ohn Wiley & Sons, Inc.