Synthesis and characterisation of chemically crosslinked chitosan citrate gels

Chitosan was modified using citric anhydride to produce film membranes via solvent evaporation. The films dissolved in acidic media which showed that crosslinking was not achieved, but it showed an appreciable amount of swelling (896%) as a result of the modification with maximum % swelling obtained by 1.0 g citric acid (CA):0.5g chitosan at pH 11 as compared with chitosan films with maximum swelling % of 314% at the same pH. N-protected chitosan was chemically crosslinked with a non-toxic crosslinker citric anhydride to obtain citrate esters and incorporate the carboxylic group onto chitosan. Products obtained did not dissolve in acidic media which confirms crosslinking and there was also a high % of swelling observed with the maximum %swelling of 875% by 1.0 g CA: 0.5g at pH 4. Characterisation was done using FTIR and C-13 NMR. Free amine content was determined by titration and the kinetic study revealed that both modified and citrate crosslinked chitosan samples obeyed pseudo 2nd order. The effect of time on crosslinking showed that as time increases crosslinking also increased. In this study, we were able to develop a pH sensitive gel that could find a wide range of applications. Keywords: Chemical Crosslinking, Citrate ester, Crosslinking Density