Cellulose acetate, commercial preparation

The predominant cellulose ester fiber is cellulose acetate, a partially acetylated cellulose, also called acetate or secondary acetate. It is widely used in textiles because of its attractive economics, bright color, styling versatiUty, and other favorable aesthetic properties. However, its largest commercial appHcation is as the fibrous material in cigarette filters, where its smoke removal properties and contribution to taste make it the standard for the cigarette industry. Cellulose triacetate fiber, also known as primary cellulose acetate, is an almost completely acetylated cellulose. Although it has fiber properties that are different, and in many ways better than cellulose acetate, it is of lower commercial significance primarily because of environmental considerations in fiber preparation. 

Cellulose triacetate is obtained by the esterification of cellulose (qv) with acetic anhydride (see Cellulose esters). Commercial triacetate is not quite the precise chemical entity depicted as (1) because acetylation does not quite reach the maximum 3.0 acetyl groups per glucose unit. Secondary cellulose acetate is obtained by hydrolysis of the triacetate to an average degree of substitution (DS) of 2.4 acetyl groups per glucose unit. There is no satisfactory commercial means to acetylate direcdy to the 2.4 acetyl level and obtain a secondary acetate that has the desired solubiUty needed for fiber preparation. 

Cellulose acetate [9004-35-7] is the most important organic ester because of its broad appHcation in fibers and plastics it is prepared in multi-ton quantities with degrees of substitution (DS) ranging from that of hydrolyzed, water-soluble monoacetates to those of fully substituted triacetate (Table 1). Soluble cellulose acetate was first prepared in 1865 by heating cotton and acetic anhydride at 180°C (1). Using sulfuric acid as a catalyst permitted preparation at lower temperatures (2), and later, partial hydrolysis of the triacetate gave an acetone-soluble cellulose acetate (3). The solubiUty of partially hydrolyzed (secondary) cellulose acetate in less expensive and less toxic solvents such as acetone aided substantially in its subsequent commercial development. 

Cellulose esters of aromatic acids, aUphatic acids containing more than four carbon atoms and aUphatic diacids are difficult and expensive to prepare because of the poor reactivity of the corresponding anhydrides with cellulose Httle commercial interest has been shown in these esters. Of notable exception, however, is the recent interest in the mixed esters of cellulose succinates, prepared by the sodium acetate catalyzed reaction of cellulose with succinic anhydride. The additional expense incurred in manufacturing succinate esters is compensated by the improved film properties observed in waterborne coatings (5). 

Mixed cellulose esters containing the dicarboxylate moiety, eg, cellulose acetate phthalate, have commercially useful properties such as alkaline solubihty and excellent film-forming characteristics. These esters can be prepared by the reaction of hydrolyzed cellulose acetate with a dicarboxyhc anhydride in a pyridine or, preferably, an acetic acid solvent with sodium acetate catalyst. Cellulose acetate phthalate [9004-38-0] for pharmaceutical and photographic uses is produced commercially via the acetic acid—sodium acetate method. 

Starting cellulose, prepared by deacetylation of commercial, medium viscosity cellulose acetate (40.4% acetyl content). 

Cellulose chloroacetates (30) and aminoacetates (30,31), acetate sorbates (32), and acetate maleates (33) have been prepared but are not commercially important. These esters are made from hydrolyzed cellulose acetate with the appropriate anhydride or acid chloride in pyridine. 

Cellulose acetate and triacetate fibres are brightened with disperse-type FBAs, including derivatives of 1,3-diphenylpyrazoline (11.19). These form a commercially important group of FBAs. If suitably substituted they can be applied to substrates other than acetate and triacetate. The commercially more important products of this type are used to brighten nylon and acrylic fibres. Their preparation and other aspects of pyrazoline chemistry are discussed in section 11.8. Examples of pyrazolines used to brighten acetate and triacetate... 

Fig. 1 Chemical structures of the polymers commonly used for preparation of beads poly (styrene-co-maleic acid) (=PS-MA) poly(methyl methacrylate-co-methacrylic acid) (=PMMA-MA) poly(acrylonitrile-co-acrylic acid) (=PAN-AA) polyvinylchloride (=PVC) polysulfone (=PSulf) ethylcellulose (=EC) cellulose acetate (=CAc) polyacrylamide (=PAAm) poly(sty-rene-Wocfc-vinylpyrrolidone) (=PS-PVP) and Organically modified silica (=Ormosil). PS-MA is commercially available as an anhydride and negative charges on the bead surface are generated during preparation of the beads...

Cellulose acetate membrane was studied because of its past use in concentrate preparation and the need to better define its performance for specific organic recovery. Cellulose acetate continues to be widely used for a variety of industrial and commercial water purification applications. Cellulose acetate was not expected to perform at the level of the more highly cross-linked and inert thin-film composite membrane. 

Adhesion of Coatings. Except for K-l polycarbonate [4,4 -(2-nor-bornylidene)diphenol polycarbonate] (4), an experimental polymer (inherent viscosity 0.85), all the coatings were prepared with commercial products EAB-381-0.5 and EAB-381-20 cellulose acetate butyrates from Eastman Chemical Products, Inc. VYHH vinyl chloride (87%)/vinyl acetate (13%) copolymer from Union Carbide Corp. Butvar B76 poly-(vinyl butyral) from Shawinigan Resins Corp. Plexiglas V poly (methyl methacrylate) from Rohm and Haas Co. Dylene P3I polystyrene from... 

The temperature of the water used to precipitate the casting solution is important this temperature is controlled in commercial membrane plants. Generally low-temperature precipitation produces lower flux, more retentive membranes. For this reason chilled water is frequently used to prepare cellulose acetate reverse osmosis membranes. 

The first commercial brackish water RO(BWRO) was on line at the Raintree facility in Coalinga, California. Tubular cellulose acetate membranes developed and prepared at UCLA were used in the facility. Additionally, the hardware for the system was fabricated at UCLA and transported piecemeal to the facility.9... 

Cellulose acetate has replaced cellulose nitrate in many products, for example, in safety-type photographic films. When a solution of cellulose acetate in acetone is passed through the fine holes of a spinneret and the solvent evaporates, solid filaments are produced. Acetate rayon is prepared from threads of these filaments. Some applications and solvents of commercial cellulose acetate grades are summarized in Table 9-5. 

The preparation of the first starch acetate, as well as the first cellulose acetate, was announced by SchUtzenberger in 1865. These acetates were prepared by heating the carbohydrates in acetic anhydride to about 140-160 . Further examination of this reaction has been made by Traquair who found that on heating starch to 90° with acetic anhydride a derivative of low acetyl content (1-4%) is obtained which is capable of forming clear, somewhat elastic films. This starch acetate, termed Feculose, was produced commercially for a time, being sold for use as a thickening agent and as a size for textiles and paper. 

Cellulose can be esterifled with almost any organic acid [81,82,84], Whereas this is possible in principle with both alkyl chlorides and carboxylic anhydrides, commercial practice has focused on the anhydride option. Although many esters have been described in the literature, industrially manufactured organic esters are prepared only with aliphatic fatty acids with between 2 and 4 carbon atoms in length (i. e., acetates to butyrates, CA to CB). Exceptions are some mixed esters with phthalic acid, which are used for enteric coatings in pharmaceutical applications and a novel carboxymethyl cellulose acetate butyrate (CMCAB), which is used in water-borne coatings applications [81,84],... 

ITP can be carried out preparatively using such supports as polyacrylamide or Sephadex. This method will be discussed further in Sections 2.4.4 and 2.4,5. On a microscale, both commercially available instruments can operate in a semipreparative mode. The LKB instrument, the Tachofrac, uses a cellulose acetate strip to collect the separated sample (A15, A16, MIO), while the Shimadzu equipment relies on the manual removal of the zone of interest by means of a microsyringe. The use of the available equipment is described in Section 2.4. A detailed discussion of equipment and instrument design is to be found in the book on ITP by Everaerts and co-workers (E7). 

Cellulose derivative fibers are commercially available and extensively used for the preparation of dialysis modules. Cellulose acetate fibers functionalized with metal alkoxides for the immobilization of enzymes was described by Kurokawa and Hanaya [60], In this example, the presence of metal alkoxides induced the gelifica-tion of cellulose acetate due to the coordination of the polyvalent metal on the hydroxyl groups on pyranose rings. The strength of the fiber strongly depends on alkoxide content. 

Ultraflltraiion membranes are commonly asymmetric (skinned) polymeric membranes prepared by the phase inversion process. Materials commercially made into membranes include cellulose nitrate, cellulose acetate, polysulfone. aramids, polyvinylidene fluoride, and nctylonitrile polymers and copolymers. Inorganic meni-braues of hydrous zirconium oxide deposited on a tubular carbon backing are also commercially available. 

Because of unfavorable sorption effects on paper that cause tailing, materials with lower adsorptivity were sought. Thus, cellulose acetate [35] and nitrocellulose [36,37] membranes were introduced. Cellulose acetate can be either prepared in the laboratory by treating cellulose with acetic anhydride, or it may be purchased from commercial sources. Cellulose acetate membranes are readily soluble in phenol, glacial acetic acid, dichloromethane and acetone. In part they can be solubilized in several solvent mixtures e.g., chloroform/ethanol (9 1 v/v). For detection (optical scanning) the foil can be made translucent by immersion in cottonseed oil, decalin, liquid paraffin or Whitemore oil 120. 

The cellulose acetate used commercially for acetate yam has an acetyl content of about 39.5 per cent and has a degree of polymerization of about 400. Material of this composition is soluble in acetone, and spinning dopes of about 25 per cent solids concentration can easily be prepared. Materials having a 39-41 per cent acetyl content can be made into plastics by compounding the cellulose acetate with plasticizers such as diethyl phthalate. Cellulose triacetate (43.0-44.8 per cent acetyl content) is finding increased commercial use. By coating from appropriate solvents, a film base of greatly improved phj ical properties has been produced. Triacetate yams are now in commercial production. 

Acetic anhydride is made on the industrial scale for use in the preparation of cellulose acetate and for other purposes. It is manufactured by heating sodium acetate with sulphur chloride, S2CI2, at about 80°. It is probable that a part of the salt is first converted into acetyl chloride which then reacts as indicated above. The chloride is ordinarily prepared from glacial acetic acid and phosphorus trichloride. The replacement of these relatively expensive materials by those used in the commercial preparation, which can be obtained at a low price, made it possible to lower the cost of the anhydride and thus extend its use. 

---