Cellulose, regenerated preparation

Dialysis is a simple clean-up or purification process to remove unwanted low-molecular-weight compounds from solutions. The dialysis membrane consists of regenerated cellulose prepared from cotton linters by the viscose process. In addition to water, the membrane also contains glycerol and small amounts of sulfur compounds, which are removed during preparation of the tubing prior to use. 

Gilligan and Reese (19) have shown that chromatographically separated cellulolytic components of Trichoderma viride showed as high as twofold differences in rate of hydrolysis of regenerated cellulose preparations of DP 500 and DP 50, respectively. They suggested that cellulolytic enzymes may vary in affinity for chains of different DP, but their results... 

Viscose Generic name for fibers from regenerated cellulose (prepared by the xanthate method) —... 

Viscose vis- k6s [obs. viscose, adj, viscous] (1896) n. (1) A solution of xanthated cellulose in dilute sodium hydroxide from which rayon fibers and cellophane films are formed. The xanthated cellulose is produced by reacting alkali cellulose, i.e., wood fibers or cotton linters treated with sodium hydroxide, with oxygen and carbon disulfide. Rayon produced by this method is known as viscose rayon. (2) Generic name for fibers from regenerated cellulose (prepared by the xanthate method). Tortora PG (ed) (1997) Fairchild s dictionary of textiles. Fairchild Books, New York. 

Several cellulose esters (qv) are prepared commercially. Cellulose xanthate [9032-37-5] is made by reaction of cellulose swollen in 8.5—12% sodium hydroxide solution (alkaU cellulose [9081-58-7J) with carbon disulfide and is soluble in the alkaline solution in which it is made. When such a solution, termed viscose, is introduced into an acid bath, the cellulose xanthate decomposes to regenerate cellulose as rayon fibers or cellophane sheets (see Fibers, REGENERATED CELLULOSICS). 

Production of cellulose esters from aromatic acids has not been commercialized because of unfavorable economics. These esters are usually prepared from highly reactive regenerated cellulose, and their physical properties do not differ markedly from cellulose esters prepared from the more readily available aHphatic acids. Benzoate esters have been prepared from regenerated cellulose with benzoyl chloride in pyridine—nitrobenzene (27) or benzene (28). These benzoate esters are soluble in common organic solvents such as acetone or chloroform. Benzoate esters, as well as the nitrochloro-, and methoxy-substituted benzoates, have been prepared from cellulose with the appropriate aromatic acid and chloroacetic anhydride as the impelling agent and magnesium perchlorate as the catalyst (29). 

Fig. 5. Scanning electron micrographs of hoUow fiber dialysis membranes. Membranes in left panels are prepared from regenerated cellulose (Cuprophan) and those on the right from a copolymer of polyacrylonitrile. The ceUulosic materials are hydrogels and the synthetic thermoplastic forms a microreticulated open cell foam with a tight skin on the inner wall. Pictures at top are membrane cross sections those below are of the wall region. Dimensions as indicated.

The membrane is critically important in osomometry. Selection of a membrane involves reconciliation of high permeability toward the solvent with virtual impermeability to the smallest polymer molecules present in the sample. Membranes of cellulose are most widely used. Commercially Regenerated cellulose film is a common source. The undried gel cellophane film is often preferred, but the dry film may be swollen in water (or in aqueous solutions of caustic or zinc chloride ) to satisfactory porosity. Useful cellulose membranes may also be prepared by denitration of nitrocellulose films/ and special advantages have been claimed for bacterial cellulose films. The water in the swollen membrane in any case may be replaced by a succession of miscible organic solvents ending with the one in which osmotic measurements are to be made. Membranes of varying porosity may be... 

Investigators of cellulosic liquid crystals have two main motivations to study mesophase formation primarily from a scientific viewpoint or a technolomcsd vie oint. The main focus of the latter has been on the potential of preparing high strength/high modulus regenerated cellulose fibers. Another potentim use of cellulosic liquid crystal derivatives is as chiroptical filters (S,lfi). 

Landells, G., and C. S. Whewell Preparation and properties of regenerated cellulose containing vinyl polymers. I. Internal deposition of polymers. J. Soc. Dyers Colourists 67, 338 (1951). II. Staining, swelling, and stiffness characteristics. J. Soc. Dyers Colorists 71, 171 (195S). III. Moisture relations. J. Soc. Dyers Colorists 73, 496 (1957). 

Pikler, A., S. Suta, and A. Alfoldi Preparation of graft copolymers from regenerated cellulose. Sb. Prac. Chem. Fak. SVST (Sloven. Vysokej Skoly Tech.) 1962 (2), 123 C. A. 59, 12 965 (1963). 

Paraformaldehyde -in water rinse removers [PAINT - PAINT AND FINISH REMOVERS] (Vol 17) - [FIBERS - REGENERATED CELLULOSICS] (Vol 10) -phenolic resin preparation [PITENOLIC RESINS] (Vol 18)... 

The use of membranes for separating particles of colloidal dimensions is termed dialysis. The most commonly used membranes are prepared from regenerated cellulose products such as collodion (a partially evaporated solution of cellulose nitrate in alcohol plus ether), Cellophane and Visking. Membranes with various, approximately known, pore sizes can be obtained commercially (usually in the form of sausage skins or thimbles ). However, particle size and pore size cannot be properly correlated, since the permeability of a membrane is also affected by factors such as electrical repulsion when. the membrane and particles are of like charge, and particle adsorption on the filter which can lead to a blocking of the pores. 

Regenerated cellulose Stable in most organic solvents (typically prepared from cellulose acetate as precursor) High crystalline content 4-9... 

Cellophane film Is prepared from regenerated cellulose and Is similar to rayon fiber In that It has a lower molecular weight than cotton and contains a small amount of hemlcellulose, as does linen. Cellophane film, therefore, although not a duplicate of any natural fiber, Is similar enough In chemical structure and morphology to make It useful as a model system. Moreover, Its transparency and the precision of Its manufacture make It quite useful for this type of study. 

In hemodialysis, blood from the patient flows on one side of a membrane and a specially prepared dialysis solution is fed to the other side. Waste material in the blood such as urea, excess acids, and electrolytes diffuse into the dialysate the blood is then returned to the patient, as shown in Fig. 48. A patient typically undergoes dialysis three times per week in sessions lasting several hours each. Modern dialysis systems combine sophisticated monitoring and control functions to ensure safe operation. Regenerated cellulose was the first material used in hemodialysis membranes because of its biocompatibility and low cost it remains the most popular choice. Subsequently, high-permeability dialysis membranes derived from cellulose esters, modified polysulfone, or polyacrylonitrile copolymers have also gained wide acceptance because of the shorter sessions they make possible. 

Microcrystalline cellulose (MCC) is obtained by a controlled acid treatment intended to destroy the molecular bonding in the amorphous zones of cellulose. Usually HC1 or H2SO4 are used at 110°C for 15 min over native cellulose or regenerated cellulose. Colloidal gels are thus obtained showing thixotropy. MCC is used in the preparation of pharmaceutical compressed tablets due to its binding and disintegration properties. 

Although it was known in the years following the discovery by Cross and Bevan that a viscose type of solution could be used in the preparation of regenerated cellulose, the conversion of this solution into useful fibers was not possible until the discovery that the solution required aging until ripe. Ripening is the first part of the actual chemical decomposition of cellulose xanthate, which, if allowed to proceed unhampered, would result in gelation of the viscose solution. 

One of the most special aspects of cellulose polymorphy is the transformation from I to II. The conversion of the parallel-packed cellulose I structures to an antiparallel cellulose II structure is interesting because it can occur without loss of the fibrous form. This transformation is widely thought to be irreversible, although there are several reports [231-233] of regenerated cellulose I. The observation that there are two different forms of cellulose III and of IV is also remarkable. The two subforms of each allomorph have essentially identical lattice dimensions and at least similar equatorial intensities. Other intensities are different, particularly the meridional intensities, depending on whether the structures were prepared initially from cellulose I or II. The formation of the III and IV structures is reversible and the preceding polymorph (I or II) results. 

The amorphous or disordered component plays an enormous role in the physicochemical properties of cellulose. Its nature is still poorly defined [66-69] and like crystallites is influenced by physical and chemical treatments as reflected in solubility and reactivity characteristics [14-17]. The alkali solubility of cotton cellulose cannot be correlated entirely with its apparent amorphous content [16]. A regenerated sample prepared from a cuprammonium solution having a 94% amorphous content was totally soluble in 10% NaOH while a powdered cellulose obtained by ball milling to a similar amorphous content (92%) had an alkali solubility of only 58%. 

Cellulose-based monoliths prepared from cross-linked sponge-like regenerated cellulose with a continuous, interconnected, open pore stmcture (50-300 p.m) are commercialized by Sepragen under the trade name Seprasorb and are available for ion-exchange chromatography. 

Gilbert, R.D. Hu, X. Fornes, R.E. Preparation of high-strength/high-modulus regenerated cellulose fibers from lyotropic mesophases. J. Appl. Polym. Sci. 1995, 58 (8), 1365-1370. 

Figure 9. Electron mlcrophotograph of the dry regenerated cellulose membrane prepared through micro-phase separation method primary particles are observed In a secondary particle with a diameter of ca. 300 nm.

The pore size distribution N(r), experimentally determined for the regenerated cellulose membrane prepared through the micro-phase separation method, is compared with the theoretical N(r) in Figure... 

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