Xiaoning Shi

Synthesis, characterization, and swelling behaviors of a pH-responsive CMC-g-poly(AA-co-AMPS) superabsorbent hydrogel

New superabsorbent hydrogels were synthesized through free radical graft copolymerization of partially neutralized acrylic acid (AA) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) onto carboxymethyl cellulose (CMC) backbones. The structure and morphology of the synthesized superabsorbent hydrogels were characterized by Fourier transform infrared spectroscopy and scanning electron microscope. The effect of the molar ratio of AMPS to AA, the APS concentration, and the CMC content on swelling ratio was optimized. The swelling properties in various pH solutions and saline solutions as well as the swelling kinetics were also evaluated. Results showed that the introduction of AMPS enhanced the swelling capacity, swelling rate, and salt-resistance of the superabsorbent hydrogels. Moreover, the hydrogels exhibited smart swelling behavior in multivalent salt solutions and better reversible pH sensitivity in the pH 2.0 and 7.0 solutions, which makes the hydrogels available as a candidate for drug delivery systems.

Synthesis, characterization and swelling behaviors of guar gum-g-poly(sodium acrylate-co-styrene)/vermiculite superabsorbent composites

A series of novel superabsorbent composites guar gum-g-poly(sodium acrylate-co-styrene)/vermiculite (GG-g-poly(NaA-co-St)/VMT) were prepared by the simultaneous graft copolymerization of guar gum (GG), partially neutralized acrylic acid (NaA), styrene (St) and vermiculite (VMT) using ammonium persulfate (APS) as the initiator and N,N′-methylene-bis-acrylamide (MBA) as the crosslinker. Fourier transform–infrared (FT-IR) and ultraviolet-visible (UV-vis) spectroscopy revealed that NaA and St had been grafted onto GG main-chain, and VMT participated in polymerization reaction. The simultaneous incorporation of St and VMT improved the surface pore structure, and VMT led to a better dispersion in the polymer matrix as shown by field emission scanning electron microscope (FESEM). Swelling results indicated that the inclusion of proper amount of St and VMT in the superabsorbents induced enhanced swelling capability, rate, and salt-resistant performance. Moreover, the composites showed good pH-stability in the solution of various pHs, and exhibited smart swelling–shrinking on–off swelling characteristic in physiological solution, which can be used as promising candidate for its applications in various fields.

Enhanced swelling and responsive properties of an alginate-based superabsorbent hydrogel by sodium p-styrenesulfonate and attapulgite nanorods

In this work, a series of sodium alginate-g-poly(sodium acrylate-co-sodium p-styrenesulfonate)/attapulgite (NaAlg-g-poly(NaA-co-NaSS)/APT) superabsorbent composites were prepared by graft copolymerization using N,N’-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate as an initiator. Fourier transform infrared spectroscopy revealed that NaA and NaSS had been grafted onto NaAlg, and APT participated in polymerization reaction through reactive –OH groups. The introduction of proper amount of NaSS and APT induced the improved surface morphology, swelling capacity, and swelling rate. Moreover, the swelling behaviors of the superabsorbent composites were remarkably influenced by various salt medium, pH buffer solutions and organic solvents, and especially an intriguing swelling–deswelling behavior was observed with altering water/organic solvent ratio.

Utilization of hollow kapok fiber for the fabrication of a pH-sensitive superabsorbent composite with improved gel strength and swelling properties

A pretreated kapok fiber (PKF) with a hollow tube structure was introduced into a poly(sodium acrylate) network by a simultaneous free-radical graft copolymerization and crosslinking reaction to fabricate a novel kapok fiber-g-poly(sodium acrylate) (PNaA/PKF) superabsorbent composite. The network characteristics and surface morphologies of the PNaA/PKF superabsorbent composite were investigated by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), as well as by determination of mechanical properties, swelling and stimuli responses to salts, and pH. The results showed that the incorporation of a specific amount of PKF not only improved the water absorption, but also the gel content and gel strength. The composite with 10 wt% PKF showed the best water absorption, gel content and gel strength. The swelling kinetics of the composite followed Schotts pseudo-second-order kinetics model, and the swelling rate constant was enhanced 2.63 fold after adding 10 wt% PKF. The swelling and deswelling behaviors in various saline and pH solutions revealed the stimuli-sensitivity of the PNaA/PKF composite to salt concentration, ionic charge and external pH, and a remarkable time-dependent swelling process with an overshooting characteristic was observed in pH 2 solutions.

Swelling Behavior of Guar Gum-g-Poly(Sodium Acrylate -co-Styrene)/Attapulgite Superabsorbent Composites

A series of superabsorbent composites, guar gum-g-poly(sodium acrylate-co- styrene)/attapulgite [GG-g-P(NaA-co-St)/APT], were prepared by simultaneous grafting partially neutralized acrylic acid and hydrophobic styrene (St) onto guar gum in the presence of attapulgite as an inorganic component. Equilibrium swelling capacity strongly depended on the concentration of St, drastically increasing with increasing St concentration to 24.3 mmol/L and then decreasing. The influence of St concentration on the swelling kinetics of the superabsorbent was studied by means of a Schotts second-order model. The proper amount of St is of benefit for the improvement of the initial swelling rate in either distilled water or saline solution. The influence of St concentration on the swelling behaviors in various external media (the aqueous solutions of various salts, pHs, hydrophilic organic solvent/water mixture and surfactants) was also investigated systematically. Results showed that the concentration of St is the key factor influencing equilibrium swelling capacity of the superabsorbent composites in each swelling media, and moderate amounts of St could enhance the responsiveness of the corresponding superabsorbent composite to external stimulation.