Use of Regenerated Cellulose

For the packaging of sensitive foods, PP films are coated with polyvinylidene chloride, polyvinyl acetate, EVAcopolymers, polyacrylates, styrene-butadiene copolymers, LDPE, poly-l-butene or random copolymers of propene with ethylene and 1-butene. By using these various coatings PP has recently sharply reduced the use of regenerated cellulose (cellophane), the previous market leader in this area. 

Originally, the word rayon was appHed to any ceUulose-based man-made fiber, and therefore included the cellulose acetate fibers. However, the definition of rayon was clarified in 1951 and includes textiles fibers and filaments composed of regenerated cellulose and excludes acetate. In Europe the fibers are now generally known as viscose the term viscose rayon is used whenever confusion between the fiber and the cellulose xanthate solution (also called viscose) is possible. 

Cellulose may be solubilised by treatment with sodium hydroxide and carbon disulfide. It can be regenerated by acidification of the solution. This is the basis of the production of regenerated cellulose fibre, so-called viscose rayon , which is a major textile fibre. The technique is also used for the production of continuous cellulose-derived film, so-called cellophane (from cellulose and diaphane , the latter being French for transparent). 

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... 

Bipolar plates, MCFC, 12 223 Bipolar transistors, silicon based semiconductors in, 22 246-249 Bipolymers, 20 533, 534 Bipropellants, 10 727 Bipyridines, uses for, 21 127 Bipyridinium herbicides, 13 315 Bipyridium, 24 51 Bipyridyl trimers, 24 50 Biquinolines, 21 200 Birefringence, 14 675, 680 19 745 in ferroelectric crystals, 11 94 polycarbonate, 19 822 of regenerated cellulose fibers,... 

The hollow-fiber bioreactor is a stenle renal dialysis cartridge, and may be obtained from distributors or hospital supplies departments There are various sizes, but we find the most useful to have an internal volume of 50 or 150 mL. Not all dialysis cartridges are suitable for growing cells The fibers should be of regenerated cellulose, about 10,000 in number, and approx 200-jum diameter and 8-10-pm wall thickness. 

Like the triacetate, secondary cellulose acetate (CA) is used in solution processes to produce fibers and films. CA fibers were originally called "rayon." the name that was already in use for regenerated cellulose fibers. In 1951. however, the regulatory authorities formally acknowledged the chemical distinction between CA and cellulose, and the term rayon was reserved for libers of regenerated cellulose. CA fibers are officially called acetate. and they are used in a wide variety of fabrics. They also are used for cigarette filters. However, the majority of CA produced is used for manufacture of plastics. 

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. 

They concluded that the surface charge of HS controlled their recovery, and any carrier component decreasing the effective surface charge of HS led to a sorption increase. Furthermore, the cross-flow rate influenced recovery dramatically, which supports the idea that either sorption to membrane or permeation through it is responsible for losses. Finally, other channel components play a minor role. The authors recommendations were to use 0.005 M TRIS-buffer (pH 9.1) as a carrier solution (recovery of about 85-90%) and use a regenerated cellulose membrane with a 5-kDa cutoff as the accumulation wall. 

A possible way to lower the costs of fibers and films of regenerated cellulose would be to run cellulose through a twin-screw ultrasonic extruder with a minimum of solvent and pass the extrudate through a stream of hot air to recover the solvent for reuse. This stronger cellophane could be used in place of many plastic films used today. A great number of derivates of cellulose have been made. Methyl, ethyl, carboxymethyl, hydroxyethyl, and hydroxypropyl ethers are made commercially today. These are used as water-soluble polymers, except for ethylcellulose, which is a tough plastic used in screwdriver handles and such. 

While legislating on a broad scale, i.e. in relation to various sectors of production, the Commission has also been obliged to lay down rules for individual substances which have been the cause of considerable public concern. This applies to the vinyl-chloride monomer used in PVC and the mono (MEG) and diethylene glycol (DEG) used in regenerated cellulose film. 

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. 

Cellulose is a polymer that meets these requirements as an adhesive. However, due to its semicrystalline structure, highly hydrogen-bonded cellulose cannot be dissolved easily in conventional solvents, and it cannot be melted before it burns. This is because the attractive forces and stability of crystal structures are greater than those that result from interaction between polymer and solvent. Hence, cellulose itself is not suitable for use as an adhesive. The same can be said of regenerated cellulose. In order to make cellulose soluble or meltable, the hydrogen bonds must be broken (i.e., cellulose molecules must be more flexible and possess high entropy, so that they can be separated easily). 

The KAURIT types are either free or etherified N-methylol compounds of urea or of melamine. They are used mainly for the resin finishing of regenerated cellulose fibres, alone and in blends with synthetics. The term "self-crosslinking agents" characterizes their mode of reaction. 

CONDENSOL A Is a catalyst which contains ammonium nitrate as active substance and Is used mainly for the resin finishing of regenerated cellulose. It is liable to change the shade of coloured goods, and it may also impair the light fastness of optical brighteners. 

Heteropolysaccharides are, in general, highly desirable components of paper-grade pulps while they are not tolerated in dissolving-grade pulps used for the production of regenerated cellulose products and cellulose derivatives. A vast body of literature exists on the effects of hemicellu-loses on the papermaking process. 

Covers sponges made of regenerated cellulose or synthetic plastic and used for general cleaning operations. 

---