Preparation, assessment and swelling study of amphiphilic Acrylic acid/chitosan based semi-interpenetrating hydrogels

In the last few decades, acrylic acid-chitosan amphiphilic superabsorbent hydrogels have received great research interest because these hydrogels can uptake a large amount of water and have antibacterial activities [1,2].Due to their excellent properties, chitosan-acrylic acid hydrogels play a key role in wastewater treatment [3,4].Chitosan has been known as a renewable biopolymer with considerable biocompatibility, biodegradability, antimicrobial activity, etc.Its properties can be altered under mild conditions due to its reactive amino and hydroxyl group [5].However, the swelling ratio of chitosan is high just at a low pH value.Introducing poly(acrylic acid) is a potential role to amend the swelling degree of chitosan in a variety of pH values [6].Ge et al. [7] synthesized the superabsorbent polymer based on chitosan-acrylic acid using the thermal reaction.Shim and coworkers [8] prepared Gamma irradiated poly(acrylic acid)-chitosan hydrogels for the purpose of increasing the drug release aptitude.They reported that release behavior of the drug, 5-fluorouacil from the hydrogel was different based on the pH value of the medium, monomer percentage, and the radiation dose.Zheng et al. [9] investigated the recovery of a valuable metal Ni 2+ using aqueous dispersion polymerized chitosan-acrylic acid hydrogel.They observed that the prepared absorbent had a good affinity to Ni 2+ .Also, it is observed that chelation interaction among the carboxylated group, and Ni 2+ is the main mechanism of absorption.Today, numerous kinds of hydrogels have been formed.Among them, amphiphilic semi-interpenetrating networks (semi-IPN) have been extensively favored because of their excellent properties [10][11][12].Marjub et al. [13] used Acrylic acid-chitosan semi-IPN hydrogel for copper (II) and lead (II) ions adsorption from waste water.Torrado and coworkers [14] investigated the drug release behavior of PAAc-chitosan hydrogels.In semi-IPN hydrogels, each polymer network retains its individual characteristics like its homopolymer as well as, when one portion shrinks or swells, another portion could be created for supporting via repulsive and attractive interaction of the whole network.It is noteworthy that when an amphiphilic semi-IPN hydrogel swells, the network can constitute hydrophobic interaction, suggesting the reduction of the swelling degree of the hydrophilic network [15][16][17].The aim of this study was to synthesize amphiphilic semi-IPN hydrogels based on acrylic acid and chitosan and characterize their swelling behavior.For this purpose, free radical polymerization was performed using AIBN as a free Abstract: The aim of this study was to synthesize amphiphilic semi-IPN hydrogels based on acrylic acid (AA) and chitosan (CS) using AIBN as an initiator and N,N'methylene bis acrylamide as a crosslinking agent.The swelling behavior of the hydrogels was evaluated at a variety of pH values, temperature, the salinity of media and time, and the swelling mechanism was investigated using Fickian diffusion and Schott's 2nd-order-kinetics models.FTIR spectroscopy was used to confirm the synthesis of AA/CS hydrogel.The swelling results showed that, in the acidic media, as the CS content increase the hydrogel swelling ratio reduces.It was found that the maximum swelling ratio (8550%) is attained for the sample HAC2 with an AA/CS ratio of 1:0.001 in the alkaline Ph value.It also revealed that the absorption capacity is directly dependent on the temperature and inversely related to the salt concentration.Besides, the absorption capacity of the synthesized hydrogels in the saline solution of Na 2 SO 4 was higher than NaCl.