Semi-Interpenetrating Polymer Networks Based on Chitosan and Poly(Acrylic Acid)

The interpenetrating polymer networks (IPNs) provide a convenient route for modification of properties to meet specific needs [1]. A semi-IPNs, which consist of both linear and crosslinked polymers that are polymerized simultaneously are sequentially, have been used to improved the properties of polymer blends and composits. In recent years, interest in natural-based superabsorbent hydrogel has increased, mainly due to high hydrophilicity, biocompatibility, and biodegradability of biopolymers. These materials are defined as crosslinked macromolecular networks that can absorb water or physical fluids up to many times of their own weight in a short time [2]. Chitosan, a natural poly(aminosaccharide), is non-toxic and easily bioadsorbable [3]. This biopolymer is a weak base with an intrinsic pKa of 6.5 and with gel forming ability at low pH. In acidic solutions, the amine groups of a crosslinked chitosan are protonated and form a cationic hydrogel and result in swelling of the hydrogel network. A semi-interpenetrating polymer network (semi-IPN) hydrogel composed of crosslinked chitosan and poly(acrylic acid) (PAA) was prepared in the presence of formaldehyde as a crosslinker (Scheme 1). The swelling capacity of hydrogel was shown to be affected by the crosslinker and the PAA/chitosan ratio. The PAA/chitosan semi-IPN hydrogels are swelled at low pHs that attributed to repulsion of –NH3+ groups on chitosan backbones.