Thermal, Swelling and Stability Kinetics of Chitosan Based Semi-Interpenetrating Network Hydrogels

The present study is focused on studying the swelling kinetics, thermal and aqueous stabilities, and determination of various forms of water in the chitosan (CS) and polyacrylonitrile (PAN) blend and semi-interpenetrating polymer network (sIPN). CS/PAN blend hydrogel films were prepared by solution casting technique. The blend film with optimum swelling properties was selected for the synthesis of sIPN. CS in the blend was crosslinked with the vapors of Glutaraldehyde (GTA) to prepare sIPN. The fabricated CS/PAN blend and sIPN hydrogels films were characterized with Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA) and field emission scanning electron microscope (FESEM). The kinetics of swelling, bound and unbound waters and aqueous stability were determined experimentally. FESEM showed good miscibility between CS and PAN, FTIR showed no chemical interaction between CS and PAN; however, it did show a doublet for the sIPN, TGA showed improved thermal stability and swelling kinetic followed second order kinetics. The degree of swelling of the sIPN hydrogels samples at room temperature varied from similar to 2200 % (with a fair degree of stability (similar to 30 %)) to similar to 1000 % (with high degree of aqueous stability (43 %)) with increase in the crosslinking time. The calculated unbound water (W-UB) max., for the blend was 52.3 % whereas for the bound (W-B) the max., was 41.9 %. However, for sIPN hydrogel films, the W-UB water decreased (max. 21.0 %) where as the W-B increased (max. 52.0 %). The decrease in W-UB and increase in the W-B is attributed to the formation of a compact structure and increase in the contact area between the water and polymers in sIPN hydrogels due to the induction of new water contacting point in these hydrogel films, respectively.