Cellulose cellophane production

Cellulosics. Rayon and other cellulose products such as cellophane and cellulose ethers (qv) consume 1.9% of U.S. caustic soda demand. Because of competitive products, however, this market has been decreasing since 1965 and forecasted average annual growth through 1992 is less than 0.4% (6) (see Cotton). 

Plastics and Other Synthetic Products. Sulfur is used in the production of a wide range of synthetics, including cellulose acetate, cellophane, rayon, viscose products, fibers, and textiles. These uses may account for 2% of sulfur demand in developed countries. Sulfur intermediates for these manufacturing processes are equally divided between carbon disulfide and sulfuric acid. 

The principal chemical iadustry based on wood is pulp and paper. In 1995, 114.5 x 10 metric tons of wood were converted iato - 60 x 10 metric tons of fiber products ranging from newsptint to pure cellulose ia the United States (1,76). Pure cellulose is the raw material for a number of products, eg, rayon, cellulose acetate film base, cellulose nitrate explosives, cellophane, celluloid, carboxymethylceUulose, and chemically modified ceUulosic material. 

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). 

Cellulose is sometimes used in its original or native form as fibers for textile and paper, but is often modified through dissolving and reprecipitation or through chemical reaction. The xanthate viscose process, which is used for the production of rayon and cellophane, is the most widely used regeneration process. The cellulose obtained by the removal of lignin from wood pulp is converted to alkali cellulose. The addition of carbon disulfide to the latter produces cellulose xanthate. 

According to the 1981-83 National Occupational Exposure Survey, as many as 15 600 workers in the United States were potentially exposed to di(2-ethylhexyl) adipate (NOES, 1999). Occupational exposure may occur through inhalation, mainly as an aerosol, during its manufacture and its use, particularly as a plasticizer of PVC films and in other materials used in food packaging such as adhesives, cellophane and hydroxy ethyl cellulose films. Exposure may also occur during the manufacture of rubber products, nonferrous wire, cosmetics, lubricants and hydraulic fluids (Opresko, 1984). No measurements of di(2-ethylhexyl) adipate exposure in manufacturing and processing industries are available. 

Cellulosic raw materials. Linters or wood pulp cellulose are in use as raw material for manufacturing lacquer nitrocellulose. It is essential to use very well purified and bleached raw material. Wood cellulose should contain mainly a-cellulose. The admissible pentosan content is limited to traces only, because these compounds are a source of products insoluble in organic solvents. Cellophane can also be utilized for nitration. 

Cotton treated in this way is almost pure cellulose, and su Is in greal demand by those industries using cellulose. The pure cellulose of the fiber may be dissolved and then precipitated in sheets, giving the familiar thin transparent cellophane. Or the dissolved cellulose may be pressed through fine holes and solidified, giving rayon. If treated wilh concentrated causlic soda, cotton fibers lake on a high degree of luslcr. The product of this process is called mercerized collon, after John Mercer, its discoverer. 

The term film is also applied to sheets of cellophane, polyethylene, polyvinylidene chloride, etc., used for wrapping and packaging of food products, meats, and poultry (especially shrink films that are stretched before application). These function as a moisture vapor harrier. Plaslic lilms are also used as slip surfaces in concrete structures such as airstrips, ice rinks, and highways. Photographic film is made from cellulose acetate. 

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. 

With the exception of the blue copper phthalocyanine derivatives, these products are azo dyes that are soluble in polar solvents such as alcohols, glycols, esters, glycol ethers, and ketones. Dyes soluble in alcohols and esters are used in protective lacquers for the transparent coating of metal (aluminum) foils and other materials, such as wood (greening lacquers) in flexographic inks for the printing of metal foils, cellophane, and paper as well as for the coloration of cellulose esters, celluloid, and poly(vinyl acetates), and, in the office supplies sector, for... 

The group of plastics known as regenerated celluloses forms a transition from the natural polymers to the completely synthetically produced plastics. As a converted natural product, regenerated cellulose foil (Cellophane) has formed the basis for the first transparent, flexible packaging for food and tobacco which contributed significantly to the development of the self service shops since the beginning of the 1920s. 

Later still, methods were discovered by which cellulose could be dissolved unchanged, and then reprecipitated as fiber or film by subsequent chemical treatment. This process yields viscose rayon fiber and cellophane film from the reconstituted cellulose and is still in use. These are much more useful products than were available from the early acetate rayon. 

Although the majority of vacuum coating installations now in use are batch-type units, a few have been made for semicontinuous coating of paper and plastic films such as cellophane, cellulose acetate, and Mylar. Mylar exhibits unusual adhesion characteristics for the vacuum-deposited aluminum film, and is potentially the source of a host of decorative and functional products. 

Viscose is a solution of cellulose xanthate in caustic soda. This solution can be processed into rayon or cellophane. The production of viscose consists of two steps. First, certain forms of cellulose, mainly from sulfite pulp and cotton linters, are reacted with pure caustic soda. This reaction converts the -OH groups on the cellulose unit to -ONa. The caustic soda must be pure and is obtained from mercury cells. Caustic soda from diaphragm cells contains sodium chloride which makes it unusable without purification. This solution must be aged for 2-3 days. Aging reduces the length of the cellulose chain which makes it easier to dissolve into caustic soda. The second step involves the reaction of the alkali cellulose and carbon disulfide in excess caustic soda. The net reaction of viscose is ... 

Carbon disulfide s most important industrial use, however, has been in the manufacture of regenerated cellulose rayon by the viscose process (viscose rayon) and of cellophane (Davidson and Feinleib 1972 EPA 1978a NIOSH 1977 Timmerman 1978 WHO 1981). In 1974, over 80% of the carbon disulfide manufactured was used to make viscose rayon and cellophane (Austin 1974). This proportion fell to 50% in 1984, but the rayon and cellophane uses still accounted for the greatest fraction of carbon disulfide production (Mannsville Chemical Products Corp. 1985). Since 1989, the consumption of carbon disulfide in the production of carbon tetrachloride has increased to 38%, while the rayon industry s consumption has dropped to 34% (HSDB 1995). 

In 1989, the estimated distribution of carbon disulfide utilization was as follows 34% of production went to manufacture viscose rayon, 6% to produce cellophane, 38% to produce carbon tetrachloride, 7% to produce rubber chemicals, and 15% to produce pesticides and to solubilize waxes and oils (HSDB 1995). Future use patterns remain uncertain, although it is expected that less may be used to produce viscose rayon, cellulose, and carbon tetrachloride, products for which the demand has declined and for which alternate production processes may be found (HSDB 1995 Mannsville Chemical Products Corp. 1985 Timmerman 1978). Unless substitutes for carbon disulfide are found, its use levels may depend largely on relative import and export levels of textiles and apparel (Mannsville Chemical Products Corp. 1985). Carbon disulfide use for many other specialty industrial purposes is expected to continue (HSDB 1995 Timmerman 1978). 

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