Superabsorbent fibers

Although regular rayon, with water retention as much as 100% of its weight, is the most absorbent of the human-made fibers, variants have been produced that far exceed this capacity [291]. The demand for superabsorbent fibers arises from the growing use of rayon in surgical and medical supplies, sanitary napkins, disposable diapers, and other nonwovens [292]. The rayon industry has responded with several versions of modified fibers. 

In aircraft, nonwovens are used as reinforcement media in composites and lightweight insulation. In electronic components, nonwovens are used as battery separators, and in cable insulation— nonwovens of superabsorbent fiber have been... 

Superabsorbent fibers are widely used in healthcare and hygiene products. These fibers can absorb up to 50 times their mass in water, whereas conventional wood-pulp and cotton Unter absorbents absorb approximately six times their mass in water. These superabsorbent fibers are also advantageous compared to superabsorbent powders in that, due to their small diameter (=30 pm) and high surface areas, they typically absorb 95% of the ultimate capacity within 15 s. 

Similar to the chemical modifications applied to alginate, chitosan can be treated with chloro-acetic acid, ethylene oxide, and propylene oxide to obtain sodium car-boxymethyl chitosan, hydroxyethyl chitosan, and hydroxypropyl chitosan, respectively. These derivatives are highly absorbent and can be used for the production of superabsorbent fibers for medical applications. In addition to enhanced absorption properties, it is known that carboxymethyl chitosan possesses unique wound-healing properties whereby the application of foams, hydrogels, or nonwoven dressings can effectively promote the healing of chronic ulcerative wounds. 

An acrylate-based superabsorbent fiber is being developed jointly by Allied Colloids and Courtaulds Fibres [58]. The price on a cost/performance basis Is projected to be... 

Alloy Rayons. It is possible to produce a wide variety of different effects by adding materials to the viscose dope. The resulting fibers become mixtures or aUoys of ceUulose and the other material. The two most important types of aUoy arise when superabsorbent or flame retardant fibers are made. 

Acrylic acid is almost exclusively used directly, or after conversion to an ester, as a monomer. Acrylate esters are produced by normal esterification processes. However, in dealing with acrylic acid, acrolein, or acrylates, unusual care must be taken to minimize losses due to polymerization and other side reactions such as additions of water, acids, or alcohols across the reactive double bond. Polyacrylic acids find use in superabsorbers, dispersants, and water treatment. The polyesters are used in surface coatings, textile fibers, adhesives, and various other applications. 

Alceru [Alternative cellulose Rudolstadt] A process for making cellulosic filaments and staple fibers. The cellulose is first dissolved in an aqueous solution of N-methyl morpholine N-oxide (NMMNO) and then spun. Developed by the Thiiringische Institut fur Textil- and Kunstoff-Forschung e.V. Rudolstadt, Germany, and Zimmer (Frankfurt) from 1987. A pilot plant was built in April, 1998 and a commercial plant was planned for installation in Baoding, China in 2005. A superabsorbent version of the fiber has been developed by Stockhausen. The fiber is now made commercially by Sea Cell GmbH, a subsidiary of Zimmer. See also Lyocell. 

Woven cloth, cotton wadding, cellulose fiber batt, papers, and foamed polyurethane have been used as traditional absorbent materials for water. These materials can absorb 1-20 g of water per gram material and the water absorbed is easily removed from the materials by applying low pressure. In recent years, superabsorbent polymers, which can absorb up to 1000 g of water per gram of polymer and up to about 100 g of dilute salt solution per gram of polymer and the water absorbed can hardly be removed from the polymers even by applying high pressure, have been prepared and commercially used in many applications. 

Superabsorbents are commercialized in many shapes of products. Most superabsorbents are amorphous powders. Film and fiber types of superabsorbents are also used. 

In the work from Liu [105], an eco-friendly superabsorbent based on flax yarn waste for sanitary napkin applications has been successfully prepared. Till now, most of the waste cellulose materials from textile industry, such as cotton linter, cotton yarn waste and flax yarn waste, are still burned or land filled, causing both resource waste and environmental pollution [105, 106]. Reutlllzatlon of these waste materials could not only reduce the consumption of cotton or flax cellulose but also decrease the treatment of industrial waste. The major component [70%] of flax yarn waste is cellulose, which has been introduced as a basic skeleton of superabsorbent in previous studies [105, 106-109]. Fluff pulp, as a good absorbent material, is a kind of special pulp with villiform fibers. Nowadays, it is widely used as raw material for the production of sanitary napkin and paper diaper [105]. 

In the period 1965-1980 a wide variety of new, stronger, and more durable rayon fibers were developed. Rayon variants are now produced which utilize the comfort and aesthetic qualities of cellulose to compliment synthetic fibers in many textile applications. Considerable emphasis has been placed on the economics and ways to meet environmental and safety standards. Special effects, such as crimp or hollow filaments, may be obtained by appropriate viscose formulations, point-of-stretch applications, spin-bath compositions, and modifiers. Flame-retardant (FR), acid-dyeable, and superabsorbent rayons are typical of the properties that can be attained by incorporating various materials in the fiber structure. Rayon is unique in the respect that the fiber can be permanently modified for a wide variety of end uses simply by adding the appropriate material to viscose. 

Toxicology Irritant TSCA listed Uses Flocculating aid paper sizes ion exchange resins antistatic finishing hydrophilic glass fibers superabsorbents toner polymers thickeners cement additives anticorrosives adhesives cosmetics prod, of acrylamide copolymers Manuf./Distrib. Aldrich http //www.sigma-aldrich.com... 

The basic component of tiie erqimimental system applied to this study was an absorbent material normally used in personal hygiene articles. In principle tiiis would be loose or bonded cellulose flufi possibly blen with cross-linked sodium polyacrylate granules (known as superabsorbent polymer, SAP) for enhanced liquid capacity. Cellulose fibers or whole composites served as carriers of known and potmitial urease inhibitors. These substances were physically attached to the absoibent core by exhaustion fiom their solutions and subsequent drying of the substrates. A few examples of materials treated this... 

Superabsorbent materials are frequently used in disposable absorbent articles to help improve the absorbent properties of such articles. Superabsorbent materials are generally polymer-based and are available in many forms, such as powders, granules, microparticles, films and fibers. Upon contact with fluids, superabsorbent materials swell by absorbing fluid into their structure. The superabsorbent materials quickly absorb fluids insulted into the articles and retain such fluids to prevent leakage and provide a dry feel even after fluid insult (3). 

The elastic modulus of the swollen superabsorbent polymer is important for several reasons. The powdered polymer is typically used in a physical blend with fibers such as cellulose and thermoplastic binder fibers. The resulting structure is called the absorbent core. The absorbent core relies on pore spaces between the fibers and polymer particles to provide liquid transport volume for the overall structure. When the swollen superabsorbent particles have low modulus, they are easily deformed by body pressures and can fill in the interfiber and interparticle pores. This prevents liquid flow and wicking of liquid into the drier portions of the core. Higher modulus limits the deformation of the particles and helps maintain the pore space. 

In a diaper, the poljmier is mixed with 0.5-10 times its mass of cellulose pulp fluff (processed wood fiber) to make up the core (46-48). Cores containing superabsorbents are thinner because a smaller volume of dry superabsorbent pol5mier can absorb the same volume of aqueous liquid as a larger volume of fluff. 

Initially, the amount of superabsorbent pol3mers used per diaper was minimal. Its use was only supplemental to the role of pulp fibers as the water absorbing material. 

Many new materials have been developed for transporting water effectively and separately [6-9], including crosslinked cellulose called curly fibers, thermally fused PE/PP fibers, and a special nonwoven rayon cloth. These new materials absorb a liquid quickly and distribute it to the superabsorbent polymer. In addition, these new materials show good integrity to moisture. In particular, there is no corruption of the structure even after wetting, allowing the maintenance of chaimels through which the liquid ean be transferred. 

Finally, with regard to revolutionary design, many systems adopt an acquisition layer or a combination of an acquisition layer and transport layers between the absorption core (Fig. 2) and the top sheet [9]. For the acquisition layer or the transport layer, either a crosslinked cellulose with a density of 0.04-0.1 g/cm, thermally fused PE/PP fibers, or a nonwoven cloth is used. The absorption core consists of surface-crosslinked superabsorbent polymer and pulp. In general, the concentration of the superabsorbent polymer is 40 to 60 wt %, and the weight of the polymer used per diaper is approximately 10 to 12 g [9,10]. 

Fibrous superabsorbent polymers have larger surface areas than particulate ones. Furthermore, they have excellent diffusion and permeation of liquid by capillary effect and thus high absorbencies are expected. These fibers can be manufactured with ordinary structural fibers such as cellulose fibers or synthetic fibers by the airlaid technique, and the potential for further development is high. 

Representative fibrous superabsorbent polymers are Fibersorb and Fiberdri fibers manufactured by Camelot Superabsorbent of Canada, Ltd., Oasis fiber by Allied Colloid Ltd. (USA), and Lansdale F fiber by Toyobo... 

A nonwoven cloth made of a superabsorbent polymer and a synthetic fiber has been shown to have an excellent absorbency towards blood [21]. 

Quasifibrous superabsorbent polymers are a composite of ordinary fibers and superabsorbent polymer powder that is adhered to the fiber by a binder. Various quasifibrous superabsorbent polymers are being investigated. For example, a composite made of a cellulose fiber and a superabsorbent polymer has already been developed [22]. Polycarboxylic acids, polyamines or polydiols can be used as a binder. The interaction between the cellulose fiber and the binder or the superabsorbent polymer and the binder is hydrogen bonding or covalent bonding. Quasifibrous superabsorbent polymers do not exhibit gel blocking and a capillary effect caused by the fiber networks, thus providing favorable conditions for blood absorption. 

Another example is to adhere films in sections which contain a superabsorbent polymer. Plaeed on the top surface is a water-permeable sheet but the backing sheet is made of a nonwater-permeable sheet. Between these sheets is a three-dimensional (3D) net made of an adhesive polymer. The woven points of the net are adhered to the top and backing sheets. Hence, the volume for swelling is sufficient. In addition, the strength as well as the shape is well maintained. If a metallic core fiber is ineluded in the 3D net, box-like or L-shaped absorption sheets can be manufactured. 

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