Oxidized regenerated cellulose fibers

Research on the weathering and mechanism of photo-degradation of cellulose is reviewed. It is pointed out that many factors such as dyes and delustrants, in the case of regenerated cellulose fibers, as well as the ambient atmosphere and the wavelength of the irradiation may affect the rate of degradation. Recent work on the photodegradation of oxidized cellulose is described. 

Advances of the past three decades, however, have produced alternatives to the heavy metal-based cellulose solvents. Prominent among them are dimethylacetamide/LiCl (DMAc/LiCl) N,MMN-0 hydrate (NMMO) tetrabutylammonium fluoride/DMSO (TBAF/DMSO) and potassium thiocyanate/DMSO [48]. While many of these solvents have gained significant popularity among laboratory chemists, only the amine oxide solvent, N,MMNO, has achieved industrial practicality. This will be discussed in the section on regenerated cellulose fibers. Several other important physical properties of cellulose are given in O Table 4. 

Regenerated cellulose fibers are uniform in diameter. This permits a tmiform oxidation and imparts uniform chemical and physical characteristics to the pharmaceutical material. In the early 1960 s, Johnson Johnson entered the market with an oxidized knitted rayon fabric, SURGICEL Absorbable Hemostat. Since then, Johnson Johnson has dev eloped a few other oxidized knitted rayon products. A list of currently av ailable bioabsorbable oxidized cellulose and oxidized regenerated cellulose products, and the respecthe manufacturer is contained in TkdUe 1. A list of relevant patents for oxidized cellulose technology is contained in IkUe 2. 

Within the range of 16-24% carboxylic acid content, oxidized cellulose has a pH of approximately 3.1. The material is biocompatible, bioabsorbable, and hemostatic. Based on these unique properties, Johnson Johnson pioneered an industrial-scale oxidation process by using nitrogen dioxide to convert regenerated cellulosic fibers into oxidized regenerated cellulose (ORC) fibers. When knitted into a flexible fabric, ORC can be used as an absorbable hemostat in various surgical operations where blood loss should be controlled. 

An alternate procedure used in a few specialty applications is the cuprammonium process. This involves stabilization of cellulose in an ammonia solution of cupric oxide. Solubilization occurs by complex formation of cupric ion with ammonia and the hydroxyl groups of cellulose. Regeneration of cellulose, after formation of the desired products, is accomplished by treatment with acid. The main application of the cuprammonium process is for the synthesis of films and hollow fibers for use in artificial kidney dialysis machines. The cuprammonium process yields products with superior permeability and biocompatibility properties compared to the xanthation process. Less than 1% of all regenerated cellulose is produced by the cuprammonium process. 

Amine oxides - [AMINE OXIDES] (Vol 2) - [AMNES - FATTY AMINES] (Vol 2) - [FIBERS - REGENERATED CELLULOSICS] (Vol 10) -use m cosmetics [COSMETICS] (Vol 7)... 

An important process is the manufacture of regenerated cellulose applied to make fibers (e.g., rayon) and films (e.g., Cellophane). Solvents used classically in cellulose regeneration are a mixture of carbon disulfide and sodium hydroxide or ammoniacal copper solutions. More recent solvents include N-methylmorpholine-N-oxide and phosphoric acid [4]. The cellulose solution is extruded through nozzles into an acidic precipitation bath and is spun into fibers. Recently, the partly toxic and strongsmelling solvents have been replaced by ionic liquids which are even able to improve the solubility of the slightly soluble cellulose [10]. For example, 1 1 of l-butyl-3-methylimidazolium chloride dissolves lOOg of cellulose at 100°C [11],... 

Cellulosic fibers are characterized by favorable properties such as renewability, biodegradability, environment friendly, excellent affinity for chemical functionalization as well as potential applicability [149]. Cellulosic fibers may be natural, such as cotton, flax, and jute, or regenerated fibers such as lyocell, using NMMO [N-methyl, morpholine-N-oxide] as a solvent for cellulose pulp, viscose, via, more environment-friendly viscose process, as well as bamhoo viscose fibers [24,142,149]. 

Newer technology, based on the use of N-methylmorpholine-N-oxide as a cellulose solvent (40), has been developed with the aim of reducing hazardous by-products and producing a more environmentally friendly process. The viscose technology, however, still dominates (see Cellulose Fibers, Regenerated). 

There are already encouraging alternatives. Processes with N-methyl morpholine oxide/water as a solvent for cellulose (- cellulose fibers) are now in commercial use. These fibers have been given the generic name Lyocell . Under these circumstances, the importance of regenerated or modified cellulose fibers may increase once again. 

Among the best-known nonderivatizing solvent systems is a combination between copper, alkali, and ammonia termed Schweizer s reagent. Solutions of cuprammonium hydroxide have been used for both analytical and industrial cellulose dissolution. Regenerated fibers with silk-like appearance and dialysis membrane have been (and partially continue to be) industrial products on the basis of cellulose dissolution in cuprammonium hydroxide. The success of this solvent is based on the ability of copper and ammonia to complex with the glycol functionality of cellulose as shown inO Fig. 11. Because of the potential side reactions (oxidation and crosslinking, Norman compound formation), alternatives to both ammonia as well as copper have been developed. Cuen and cadoxen are related formulations based on the use of ethylene diamine and cadmium, respectively. The various combinations of alkali, ammonia. 

TEMPO-mediated oxidation. With regenerated and mercerized celluloses, the oxidation leads to water-soluble p-l,4-linked poly glucuronic acid sodium salt (cellouronic acid, CUA) quantitatively [16]. In contrast, with native celluloses having the cellulose I crystal structure, the cellulose slurries maintain the slurry states even after TEMPO-mediated oxidation. These modified celluloses form water-insoluble fibers [17]. This has enabled modification of the surface of cellu-losic fibers. 

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