Polymer nanocomposites from modified clays: Recent advances and challenges

Superabsorbent polymers are hydrophilic networks that can absorb and retain huge amounts of water or aqueous solutions. They are currently used in many areas including hygienic and bio-related uses (particularly in disposable diapers), agricultural uses (e.g., water reserving in soil, soil conditioning, and controlled release of agrochemicals), pharmaceutical dosage forms, separation technology, fibers/textiles, water-swelling rubbers, soft actuators/valves, electrical, construction, packaging, artificial snow, sludge/coal dewatering, fire-extinguishing gels, etc. Addition of clays and organo-modified clays into superabsorbent formulation has funded new generations of these hydrogels, i.e., superabsorbent hydrogel composites (SHCs) and superabsorbent hydrogel nanocomposites (SHNCs). New superabsorbent hydrogels are cheaper in price, and possess superior mechanical properties than non-composite counterparts. This review introduces the SHC and SHNC polymers with the focus on different minerals and humic additives, synthetic methods, the hydrogel characteristics and their applications. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers

Superabsorbent hydrogel composites and nanocomposites: A review

Eco-friendly polyvinyl alcohol/carboxymethyl cellulose hydrogels reinforced with graphene oxide and bentonite for enhanced adsorption of methylene blue.

Nanocomposite hydrogels are polymeric networks that possess a unique property of hydration. The presence of alcohols, carboxylic acids and amides as hydrophilic moieties in structure of nanocomposite hydrogels enhances their stiffness and water-absorbing capacity. Addition of cross-linker in the synthesis of hydrogels increases their stability under extreme conditions of temperature, pH and pressure. Natural polymer-based nanocomposite hydrogels are biodegradable, highly hydrophilic and possess good mechanical strength. Gelatin, chitin, cellulose, pectin, carrageenan, starch and alginate are natural polymers commonly used to fabricate nanocomposite hydrogels. Nanocomposite hydrogels have special characteristics such as high swelling rate, selectivity and stimuli-sensitive nature. Here we review nanocomposite hydrogels for environmental protection and biomedical engineering. Applications in biomedical engineering include drug delivery agents, wound dressing, tissue engineering and antibacterials. Applications in environmental protection include ion exchangers, adsorption, photocatalysis and soil conditioning. Many nanocomposite hydrogels show excellent adsorption selectivity for heavy metal ions: Cu2+ up to 30.35 mg/g, Pb2+ up to 35.94 mg/g, and Zn2+ and Fe3+ up to 94.34 mg/g. Xanthan gum-based nanocomposite hydrogel has removed 96% dye from industrial effluent as reported. In addition, most of the nanocomposite hydrogels showed better adsorption capacity for pollutants in the pH range from 5 to 7. The nanocomposite hydrogels could also be regenerated and successfully utilized for several times. Nanocomposite hydrogels are therefore good bio-absorbent materials for environmental detoxification.

Applications of nanocomposite hydrogels for biomedical engineering and environmental protection

Acrylamide (AAm)-2-acrylamide-2-methylpropanesulfonic acid sodium salt (AMPSNa) hydrogel and AAm-AMPSNa/clay hydrogel nanocomposite having 10 w% clay was prepared by in situ copolymerization in aqueous solution in the presence of a crosslinking agent (N,N′-methylenebisacrylamide (NMBA)). Swelling properties and kinetics of the hydrogel samples were investigated in water and aqueous solutions of the Safranine-T (ST) and Brilliant Cresyl Blue (BCB) dyes. The swelling and diffusion parameters were also calculated in water and dye solutions. It was observed that the AAm-AMPSNa/clay hydrogel nanocomposite exhibits improved swelling capacity compared with the AAm-AMPSNa hydrogel. It was also found that the diffusion mechanisms show non-Fickian character. Adsorption properties of the hydrogel samples in the aqueous solution of ST and BCB dyes were also investigated. Clay incorporation into the hydrogel structure increased not only the adsorption capacity but also the adsorption rate. Adsorption capacity values of the hydrogel nanocomposite were found to be 484.2 and 494.2 mg g−1 for the ST and BCB dyes, respectively. It was seen that the adsorption of dyes by the hydrogel nanocomposite completed in 10 min while the AAm-AMPSNa hydrogel adsorbed dyes approximately in 90 min. Adsorption data of the samples were modelled by the pseudo-first-order and pseudo-second-order kinetic equations in order to investigate dye adsorption mechanism. It was found that the adsorption kinetics of hydrogel nanocomposite followed a pseudo-second-order model. Equilibrium isotherms were analyzed using the Langmuir and Freundlich isotherms. It was seen that the Langmuir model fits the adsorption data better than the Freundlich model. Copyright © 2008 John Wiley & Sons, Ltd.

Dye removal by a novel hydrogel-clay nanocomposite with enhanced swelling properties

Preparation of composites and nanocomposites based on bentonite and poly(sodium acrylate). Effect of amount of bentonite on the swelling behaviour

A series of novel composites and nanocomposites xerogels based on acrylic acid, sepiolite and N,N′-methylenebisacrylamide were prepared using a solution polymerization technique at 70 °C. The quality of dispersion of the micronized sepiolite in the monomer is the crucial point for obtaining nanocomposites. A good dispersion explains the improvement of the absorbent properties of the nanocomposites with respect to the composites. This work investigates not only the influence of the mixing procedure on the swelling behaviour, but also the effect of the amount of clay on the absorbency of these hydrogels in deionized water and saline solution (0.2 wt% NaCl(aq)). A crosslinker concentration of 5 wt% sepiolite nanocomposite superabsorbent was shown to give the best results (1419 g g−1). Moreover, experimental results indicate that the absorbency in saline solution is smaller than that in deionized water. Rates of swelling for these absorbents were found to fit the Voigt expression. Finally, the model approximates Case II sorption in the early stages of the swelling process and Case I in the later stages. Copyright © 2006 Society of Chemical Industry

Synthesis and swelling behaviour of poly (sodium acrylate)/sepiolite superabsorbent composites and nanocomposites

Oxidation of 2,3-butanediol by alkaline hexacyanoferrate(III) using Ru(III) or Ru(VI) as catalyst†

Abstract Novel superabsorbent hydrogels of poly(sodium acrylate) [poly(SA)] with crude vermiculite (CVMT) and exfoliated vermiculite (EVMT) were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). Both types of hybrids are more stable materials than poly(SA) and their thermal stability increases as the clay content increases. The equilibrium water absorbency for each hybrid type varies with the clay content, showing a maximum at 15 wt% and 20 wt% for EVMT and CVMT, respectively. The equilibrium water absorbency is higher for the hybrids than for poly(SA) at clay contents close to their maxima. The swelling kinetics obey a Voigt-based equation. The water desorption kinetics showed the existence of free water and bound water within the polymeric matrix. All of the superabsorbent materials investigated retained the water absorption capacity after repeating five wet-dry cycles.

Superabsorbent hydrogels of poly(sodium acrylate) with crude and exfoliated vermiculites

The kinetics of the Ru(VI)-catalyzed oxidation of benzyl alcohol by hexacyanoferrate(III), in an alkaline medium, has been studied using a spectrophotometric technique. The initial rates method was used for the kinetic analysis. The reaction is first order in [Ru(VI)], while the order changes from one to zero for both hexacyanoferrate(III) and benzyl alcohol upon increasing their concentrations. The rate data suggest a reaction mechanism based on a catalytic cycle in which ruthenate oxidizes the substrate through formation of an intermediate complex. This complex decomposes in a reversible step to produce ruthenium(IV), which is reoxidized by hexacyanoferrate(III) in a slow step. The theoretical rate law obtained is in complete agreement with all the experimental observations. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 421–429, 2002

F. Santiago

Papers

Preparation of composites and nanocomposites based on bentonite and poly(sodium acrylate). Effect of amount of bentonite on the swelling behaviour

Synthesis and swelling behaviour of poly (sodium acrylate)/sepiolite superabsorbent composites and nanocomposites

Oxidation of 2,3-butanediol by alkaline hexacyanoferrate(III) using Ru(III) or Ru(VI) as catalyst†

Superabsorbent hydrogels of poly(sodium acrylate) with crude and exfoliated vermiculites

Kinetic study of the ruthenium(VI)‐catalyzed oxidation of benzyl alcohol by alkaline hexacyanoferrate(III)