PPGs were prepared by free-radical polymerization of monomers at room temperature (27 °C) in distilled water, using N,N-methylenebis (acrylamide) (MBA) as cross-linking agent and Sodium persulphate as initiator. Some additive such as ammonium chloride, N,N,N’,N’ tetramethylethylenediamine, and the nano-clay montmorillonite Na+ was used as a swelling, catalyst and mechanical properties modifier. All the syntheses were performed in distilled water at different mass percentage of acrylamide (AM), N,N-dimethyl acrylamide (DA), 2-acrylamido-2-methylpropane sulphonic sodium salt (AMPSNa) and N-vinylpyrrolidone (NVP). The manufacturing process is as follows:
Nano-clay montmorillonite Na+ was added to the required amount of distilled water followed by placing the mixer in an ultrasonic bath for 4 hours under continuous irradiation. Then specific amounts of AM and NVP monomers were weighed, and sprinkled gently to the dispersed clay solution while stirring the solution followed by adding DA and AMPSNa monomer and specific temperature stability agent. Stirring was continued for one hour until all the monomers were completely dispersed. The weighed MBA were poured into the solution following by adding ammonium chloride while strong stirring and nitrogen purging were used. After stirring for 40 minutes, specific amounts of Sodium persulphate and the N,N,N’,N’-tetramethylethylenediamine catalyst were added and then nitrogen purging was stopped. The exothermic polymerization reaction began almost immediately, and hydrogel formation was observed within 20 minutes. Two types of PPGs were obtained, one by cutting resulting gel into small pieces and then dried in an oven at 55 °C under vacuum condition for 24 hours and the other one by pouring the gelant into molds (with dimensions of 0.08 cm×1 cm×1 cm) to form completely polymerized films. The films were then dried in an oven at 55 °C under vacuum for 24 hours.
