Tuning physicomechanical properties of PEG-interpenetrated anionically modified semi-IPN cryogels functionalized with carboxylate groups

Anionically modified interpenetrated polymer network (semi-IPN) cryogels containing linear polyethylene glycol chains (PEG) were prepared via in situ synthesis and directed assembly of the negatively charged copolymer poly(acrylamide-co-sodium acrylate) (PAN) network template. The influence of reaction conditions; the concentration of linear PEG chains, and polymerization temperature on the elasticity and swelling of these IPNs was analyzed in detail. The interpenetrating structure of PEG chains and PAN host network have been confirmed by FTIR, TGA and XRD analysis. The equilibrium water content, oscillatory swelling/deswelling kinetics, and water transport mechanism were analyzed as a function of PEG content. The results showed that semi-IPN gels exhibited different swelling behavior as the reaction conditions varied. Addition of 13.9% (w/v) PEG resulted in a 25-fold increase in the swelling ratio of semi-IPN hydrogels. By performing compression tests on semi-IPN gels to determine the change of compression properties, the effective cross-linking density of semi-IPN PAN/PEG was expressed as a second-order polynomial depending on the amount of PEG. The swollen modulus of semi-IPN cryogels was much higher than that of semi-IPN hydrogels for all PEG concentrations. Semi-IPNs showed reversible on-off switching with remarkable sensitivity to external pH stimulus. Structural parameters, degree of swelling, volume fraction of cross-linked polymer in the swollen state, and diffusion coefficients due to pH-induced swelling of semi-IPN gels were determined. The presence of linear PEG chains in the structure promoted swelling by both increasing the swelling rate and significantly reducing the time required to reach the equilibrium-state. The swelling process was Fickian diffusion, and the diffusion coefficients for swelling of PEG-interpenetrated semi-IPNs increased with PEG content. The effectiveness of removing methylene blue (MB) dye from aqueous solutions by semi-IPNs was evaluated. Batch adsorption experiments were performed as a function of the gelation temperature, amount of PEG, contact time, and initial dye concentration. The adsorption isotherm and kinetics were described well by Langmuir isotherm model and pseudo-second-order model, respectively. Adsorption of MB was a multi-step process involving surface adsorption followed by intra-particle diffusion. Semi-IPN PAN/PEG cryogels prepared under cryocondition with high adsorption capacities and fast adsorption rates have been developed as new adsorbents effective in removing dyes and other toxic substances with higher mechanical strength in water and wastewater treatment.