A high mechanical strength hydrogel from polyacrylamide/polyacrylamide with interpenetrating network structure by two-steps synthesis method

A simple two-steps polymerization method was used to prepare a polyacrylamide hydrogel with a full interpenetrating network structure based on the sorption and porous properties of polyacrylamide superabsorbent. In conditions of 10 g acrylamide monomer, 0.04 g crosslinker for the first polymerization and the second polymerization, respectively, and the swelling ratio of 9, the hydrogel possessed a tensile strength of 1.22 MPa and elongation at break of 900 %. Introduction Superabsorbent polymer has stronger hydrophilic groups and lightly crosslinked network structure. Not only it is able to absorb a large amount of water, but also the absorbed water is hardly removed under some pressure [1]. The superabsorbent polymer can form a stable hydrogel with three-dimensional (3-D) polymer networks that swell, but do not dissolve in water. Owing to the hydrogel’s unique properties such as stimulus-responsive property, osmotic property, elasticity, sorption, it has been used in separation membranes, biosensors, artificial muscles, chemical valves [2, 3], superabsorbents [4], drug delivery devices [5, 6] etc. However, the applications of the hydrogels are always restricted due to their poor mechanical properties. In the past decades, to improve the properties of hydrogels, many efforts such as introduction of dangly comb-chains [7, 8], addition of polymer particles in gel network [9], cold treatment [10] or freeze-drying [11] swollen hydrogel, incorporating clay with polymer [12-15], formation of interpenetrating network structure [16-19] have been made. The formation of a full interpenetrating network structure is believed to be an effective method for enhancing the mechanical strength of hydrogel [16, 17], but the method is moderately complicated. In this paper, to prepare a polyacrylamide hydrogel with high mechanical strength, based on the sorption and porous properties of polyacrylamide superabsorbent, a full interpenetrating network structure was introduced in the hydrogel and a simple twosteps synthesis method [20] was used. The synthesis course is shown below. prepolymerization int roducing AM polymerization AM PAM PAM AM PAM PAM ⎯⎯⎯⎯⎯⎯→ ⎯⎯⎯⎯⎯→ + ⎯⎯⎯⎯⎯→ − Polyacrylamide with 3-D network was formed in the prepolymerization reaction (step I), then, acrylamide monomers were introduced in the polyacrylamide network by immersing polyacrylamide in acrylamide monomer solution, an accessional polyacrylamide network was produced in the polymerization reaction (step II). Once