Gelation of photocrosslinkable carboxymethyl chitosan and its application in controlled release of pesticide

The gelation of a photocrosslinkable carboxymethyl chitosan (Az-CMCS), which was synthesized by mixing azidobenzaldehyde (Az) and an aqueous solution of carboxymethyl chitosan (CMCS), has been studied. The photocross-linking reaction kinetics were rapid, and the time required for completely converting into the insoluble hydrogels was less than 60 s for 10% aqueous solution of Az-CMCS samples upon exposure to 273.5 nm irradiation of UV lamp (4 W or 20 W). A relatively high photoirradiation intensity and Az content incorporated in AZ-CMCS could obviously shorten the time. The obtained hydrogels showed good pH sensitivity and the lysozymatic degradability. Diuron-loaded hydrogel membranes could also be formed rapidly by solar-simulated UV irradiation of a mixed aqueous solution of AZ-CMCS and diuron. Release profiles of diuron from the diuron-loaded hydrogel membranes in a buffer of pH 6.0 were shown to be diffusion controlled. The formation of a porous structure in the hydrogels on swelling was assumed to be the reason for this diffusion behavior.