Superabsorbent cellulosic fibers

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. 

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... 

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. 

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. 

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. 

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. 

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. 

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]. 

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