Modified carrageenan. 6. crosslinked graft copolymer of methacrylic acid and kappa-carrageenan as a novel superabsorbent hydrogel with low salt- and high pH-sensitivity

Abstract

A novel, polysaccharide-based, superabsorbent hydrogel was synthesized through crosslinking graft copolymerization of methacrylic acid (MAA) onto kappa-carrageenan (κC), using ammonium persulfate (APS) as a free radical initiator in the presence of methylenebisacrylamide (MBA) as a crosslinker. A proposed mechanism for κC-g-polymethacrylic acid (κC-g-PMAA) formation was suggested and the hydrogel structure was confirmed using FTIR spectroscopy. The effect of grafting variables, including MBA, MAA, and APS concentration, was systematically optimized to achieve a hydrogel with the maximum possible swelling capacity. The swelling kinetics in distilled water and various salt solutions were preliminarily investigated. Absorbency in aqueous salt solutions of lithium chloride, sodium chloride, potassium chloride, calcium chloride, and aluminum chloride indicated that the swelling capacity decreased with increased ionic strength of the swelling medium. This behavior can be attributed to the charge screening effect for monovalent cations, as well as ionic crosslinking for multivalent cations. The swelling of superabsorbing hydrogels was measured in solutions with pH ranging from 1 to 13. In addition, the pH reversibility and on-off switching behavior, at pH levels of 3.0 and 8.0, give the synthesized hydrogels great potential as an excellent candidate for the controlled delivery of bioactive agents.

Synthesis and Characterization of pH and Thermo Dual-Responsive Hydrogels with a Semi-IPN Structure Based on N-Isopropylacrylamide and Itaconamic Acid

“…However, as the pH value went up from 8 to 10, the swelling ratios reduced slightly. This may be because the existence of alkaline ions in the swelling environment with high concentration caused a “charge screening effect” [ 49 ]. These positive ions function to reduce the electrostatic repulsion between the same charged –COO – groups.…”

pH-responsive carboxymethylcellulose-g-poly(sodium acrylate)/polyvinylpyrrolidone semi-IPN hydrogels with enhanced responsive and swelling properties

“…Currently, most of the superabsorbents used in practice are petroleum-based synthetic polymer with high production cost and poor environmental friendly properties, 14 and thus new types of multi-component superabsorbents derived from naturally available polysaccharides and facile synthesis methods are desired. [15][16][17][18][19] Semi-interpenetrated polymer network (semi-IPN) is a way of blending two polymers where only one is crosslinked in the presence of the another to produce an additional noncovalent interaction between the two polymers. 20 Semi-IPN is an unique "alloys'' of crosslinked polymers, which has been developed as a convenient technique of preparing multicomponent polymer materials and provided a convenient route to modify the properties of natural polymer-based hydrogels.…”

Novel Superabsorbent Hydrogel Based on Natural Hybrid Backbone: Optimized Synthesis and its Swelling Behavior

“…pH Sensitivity: The swelling behavior of the superabsorbent hydrogel was studied at room temperature at various pH values between 1 and 13 ( Figure 5a). 22 To prepare the pH media standard HCl (pH 1) and NaOH (pH 13) solutions were diluted with distilled water to reach the desired acidic and basic pHs, respectively. The swelling of the hydrogel increased with increasing pH from 1 to 5, but it is decreased in the pH range between 7 and 13.…”