Superabsorbents
“Superabsorbent refers to a water-swellable, water-insoluble, organic or inorganic material capable of absorbing at least about 10 times its weight and up to about 30 times its weight in an aqueous solution containing 0.9 weight percent sodium chloride solution in water. A superabsorbent polymer is a crosslinked polymer that is capable of absorbing large amounts of aqueous liquids and body fluids, such as urine or blood, with swelling and the formation of hydrogels, and of retaining them under a certain pressure in accordance with the general definition of superabsorbent.”
“Gel blocking is a well-known problem that may be associated with the use of superabsorbent polymers in absorbent articles such as diapers. Gel blocking occurs when rapid expansion of the superabsorbent polymer particles around the point of entry of body fluid into an absorbent article causes a closing of the interstitial spaces and pores in the SAP-fluff matrix. Since the transport of liquid by diffusion through swollen hydrogel is much slower than transport through the interstitial spaces, a sealing effect occurs in the area of fluid entry. This effect is referred to as gel blocking.”
Smith et al, US Patent 7,795,345, 9/14/2010
Wikipedia, Superabsorbents, 11/20/2010
Superabsorbents 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 and fire-extinguishing gels. (Kabri et al, Polym. Comp., 32, #2, 277-289 (2011))
Acrylamide /Acrylic Acid Superabsorbents
Agriculture Superabsorbents
Acrylic Superabsorbents
Hydroxyethyl Cellulose-g-Polyacrylic Acid Superabsorbents
Petroleum Technology
Protein Superabsorbents
Superabsorbent Hydrogels
Recent US Patents
11/1/2011
8,048,942
Process for the production of a superabsorbent polymer
Fricker et al of Evonik Stockhausen , Germany,produced a superabsorbent polymer by polymerizing an aqueous monomer mixture of monomers an making a basic aqueous medium comprising carbonate and/or hydrogen carbonate gel. (RDC 11/4/2011)
9/13/2011
8,017,553
Superabsorbent polymers in agricultural applications
Doane, Doane and Savich of Absorbent Technologies, Orgeon, developed superabsorbent polymer (SAP) products for use in agricultural applications based on a mixture of monomers, selected from acrylic acid, acrylamide, acrylonitrile, methacrylamide, 2-acryloamido-2-methyl-propanesulfonic acid, methacrylic acid, vinyl sulfonic acid, ethyl acrylate and potassium acrylate that are graft polymerized onto a starch. (RDC 9/15/2011)
8,017,549
Superabsorbents having superior permeability and conveying properties
Herfert et al of BASF, Germany, developed a superabsorbent having superior permeability and conveying properties comprises a permeability enhancing agent and a cohesion control agent and has a free swell gel bed permeability of at least 15 Darcies and a Hausner ratio in the range of 1.18 to 1.34. (RDC 9/15/2011)
1/18/2011
7,871,640
Surface cross-linked superabsorbent polymer particles and methods of making them
Flor and Lindner, of Procter & Gamble, Ohio, developed superabsorbent polymer particles with improved surface cross-linking and their use in absorbent articles. (RDC 8.5/2011)
9/14/2010
7,795,345
Superabsorbent polymer with high permeability
Smith et al of Evonik Stockhausen have developed superabsorbent, crosslinked polymers—based on partly neutralized, monoethylenically unsaturated monomers carrying acid groups—with improved capacity, a high gel bed permeability, and high centrifuge retention capacity. (RDC 12/2/2010)
9/7/2010
7,790,823
Acidic superabsorbent hydrogels
Funk et al of BASF, Germany produced acidic superabsorbent hydrogels based on polyacrylic acid whose degree of neutralization of 20 to 30 mol % resulting in sood super absorbent properties as well as improved odor control. (RDC 12/3/2010)
Recent Journal Articles
Preparation of superabsorbent hydrogels from poly(aspartic acid) by chemical crosslinking
(1285-1292) Polymer Bulletin 67 #7 (2011)
Umeda, Nakade and Kakuchi, Japan, synthesized modified poly(aspartic acid)s containing pendant allyl groups by the reaction of poly(succinimide) with an allyl amine in dimethylformamide. Hydrogels were prepared using modified poly(aspartic acid) by chemical crosslinking using redox radical initiators including ammonium persulfate and potassium peroxodisulfate. These results suggested that allyl group-modified poly(aspartic acid)s are useful in providing biodegradable hydrogels. (RDC 10/6/2011)
Stimuli-Responsive Elastic Polyurethane-Based Superabsorber Nanomat Composites
(517–523)Macromolecular Materials and Engineering 296 #6 (2011)
Chen, Greiner and Agarwal of Philipps-University Marburg, Germany, used photoresponsive superabsorber particles containing a crosslinked hydrophilic core and a hydrophobic azobenzene-containing shell to prepare photoresponsive polymeric nanomats, thus combining photoresponsivity with high porosity, toughness, and hydrophilicity. The properties of the nanomat composites were highly dependent upon the amount of the superabsorber photochromic particles added. Stable, highly elastic composite nanomats with very high loading (up to ≈50 wt.-%), good water absorption capacity (4 000%) and relatively good tensile strength (3 MPa) were obtained. (RDC 6/21/2011).
Preparation and swelling characteristics of a superabsorbent nanocomposite based on natural guar gum and cation-modified vermiculite
( 3675–3686)Journal of Applied Polymer Science 119 #6 (2010)
Wang, Zhai and Wang of the Graduate University of the Chinese Academy of Sciences produced a series of superabsorbent nanocomposites by the solution radical polymerization of natural guar gum , partially neutralized acrylic acid [sodium acrylate], and cation-exchanged vermiculite with ammonium persulfate as the initiator in the presence of the crosslinking agent N,N′-methylene-bis-acrylamide. The vermiculate was exfoliated during polymerization to form a nanocomposite. The nanocomposite exhibited intriguing overshooting swelling characteristics in a multivalent saline solution and acidic pH solution and showed switching pH-responsive behaviors in buffer solutions between pH 2 and pH 7.2. (RDC 12/9/2010)
Review Articles
1/28/2011
Review
Superabsorbent hydrogel composites and nanocomposites: A review
(277–289)Polymer Composites 32 #2 (2011)
Kabiri et al of the , Iran Polymer and Petrochemical Institute, Iran and Nova Southeastern University, Canada reviews superabsorbent polymers which are hydrophilic networks that can absorb and retain huge amounts of water or aqueous solutions.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. (RDC 2/28/2011)