Secondary cellulose acetate fibers

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. 

Secondary Acetate Processes. There is no commercial process to directiy produce secondary cellulose acetate sufficientiy soluble in acetone to produce fiber. Hence, the cellulose is completely acetylated to the triacetate during the dissolution step and then hydrolyzed to the required acetyl value. 

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. 

It has already been implied that cellulose triacetate will not produce a thermoplastic, as its softening point cannot be reduced appreciably by plasticizers. It is used in solution processes, however, to produce films and libers. Triacetate films absorb less water than films of secondary cellulose acetate, and they arc therefore more dimensionally stable in environments where the humidity is not controlled. Triacetate fibers, with a similar resistance to water, impart to fabrics wrinkle resistance, dimensional stability, and the ability to dry rapidly. Under United Slates federal regulations, a filler must tic made from a cellulose acetate having... 

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. 

By far the greatest use of secondary cellulose acetate is as cigarette filter tow. At a D.S. of ca. 2.4 the cellulose acetate is soluble in acetone and the resulting solution in spun into fibers using solution spinning. The removal and recovery of the acetone is the most expensive aspect of the spin process. An aligned tube of these fibers is the actual "filter" on a cigarette. 

M.P. Schutzenberger produced cellulose acetate, with a degree of substitutions (DS) of about three by the reaction of acetic anhydride and cellulose in 1859. Cross and Bevan produced filaments and films from chloroform solutions of this triacetate but this was not an economical process. The commercial cellulose acetate rayon fiber process, based on acetone solutions of secondary cellulose acetate (DS=2), was developed and patented by G.W. Miles who partially saponified the triacetate in 1903 (11). 

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. 

Pulp mills. These separate the fibers of wood or other materials, such as rags, Enters, waste-paper, and straw, in order to create pulp. Mills may use chemical, semichemical, or mechanical processes, and may create coproducts such as turpentine and tall oil. Most pulp mills bleach the pulp they produce, and, when wastepaper is converted into secondary fiber, it is deinked. The output of some pulp mills is not used to make paper, but to produce cellulose acetate or to be dissolved and regenerated in the form of viscose fibers or cellophane. 

The basic cellulose unit contains three hydroxyl groups. The triester cellulose triacetate forms when cellulose is reacted with glacial acetic acid. Hydrolysis removes some of the acetate groups to form a secondary ester, which averages about 2.4 acetyl groups per unit rather than three. The secondary ester is then dissolved in acetone and the solution ejected through a spinneret to form fibers. Cellulose acetate processed in this manner is referred to as acetate rayon, but it may be more commonly known by its trade name Celanese. 

Cellulose Triacetate. Cellulose acetate having 92% or more of the hydroxyl groups acetylated is referred to as triacetate. This fiber is characteristically more resistant to alkali than the usual acetate and may be scoured, generally, in open-width, with aqueous solulions of a synthetic surfactant and soda ash. Triacetate is a hydrophobic liber, as compared to secondary acetate, and consequently does not dye rapidly. It is necessary to increase the rate of diffusion of the disperse dye into the fiber by increasing the dyeing temperature to 110— 130CC or using a dye accelerant or carrier, or both. 

Cellulose acetate is usually produced by the so-called solution process with exception of the fully acetylated end product (triacetate). In the solution process the pulp is first pretreated with acetic acid in the presence of a catalyst, usually sulfuric acid. The purpose of this activation step is to swell the fibers and increase their reactivity as well as to decrease the DP to a suitable level. Acetylation is then performed after addition of acetic anhydride and catalytic amounts of sulfuric acid in the presence of acetic acid. After full acetylation the final triacetate obtained is dissolved. This "primary" acetate is usually partially deacetylated in aqueous acetic acid solution to obtain a "secondary" acetate with a lower DS of about 2 to 2.5. 

The abrasion resistance of cellulose acetate is lower compared with that of other fibers. Abrasion resistance was measured by the wet-flex abrasion determined with the Stoll Abrasion Tester. Abrasion resistance of several fibers was rated in the following decreasing order nylon, polyester fiber, acrylic fiber, wool, cotton, viscose rayon, and acetate. It was suggested that the abrasion resistance of fabrics is related to the strength and the recovery properties of fibers. The fact that acetate is not a particularly strong fiber probably accounts in part for its inferior abrasion resistance. Heat-treated cellulose triacetate fabrics have both higher tensile strength and abrasion resistance than secondary acetate fabrics for the conditions of dry, wet, and hot wet (80°C) [53,63]. 

Hie cellulose esters triacetate and acetate (secondary acetate) are the two major fibers of this type. The production of acetate fibers resulted from an attempt to find a new outlet for cellulose acetate used as aircraft "dope" in World War 1. By 1921, the first acetate fibers were being produced. Although small quantities of cellulose triacetate fibers were produced before World War I, it was not until after 1954 that cellulose triacetate fibers were produced commercially in large quantities. 

Total consumption worldwide in 1987 760000 mt. One major outlet for cellulose acetates is textile fibers (1987 240000 mt). Much secondary acetate and less triacetate is used. 

P.R.170 is not always heat stable enough to allow application in polyolefins. In HDPE systems formulated at 1/3 SD, the pigment tolerates exposure to 220 to 240°C for one minute. Its tinctorial strength, on the other hand, is excellent. P.R.170 is also occasionally used in polypropylene and polyacrylonitrile spin dyeing in the latter medium, it satisfies the specifications of the clothing and home textiles industries. Besides, P.R.170 lends color to viscose rayon and viscose cellulose it is used for the mass coloration of semisynthetic fibers made of cellulose last but not least, it colors yarns, fibers, and films made of secondary acetate. 

Various benzimidazolone pigments are heat stable enough to be used in polypropylene spin dyeing. Several types find extensive use in the spin dyeing of other fibers, such as polyacrylonitrile, viscose reyon, and vicose cellulose, or secondary acetate. 

There is no satisfactory commercial means to directly acetylate to the 2.4 acetyl level and obtain a secondary acetate that has the necessary solubility for fiber preparation. Since cellulose is highly crystalline and its polymer chains are held tightly together in an ordered manner through extensive hydrogen bonding, it is insoluble in the reaction medium until almost complete acetylation is achieved. Thus, commercially, cellulose is fully acetylated to triacetate and then hydrolyzed back to secondary acetate of 2.4 DS. Careful hydrolysis is nearly random yielding uniform polymer. 

The most commonly used EWAs in laundry products today are shown in Table 28.2 and represent three chemistries—distyrylbiphenyl, coumarin, and stilbene. The selection of the EWA to be used in a specific type of laundry product will depend on several factors such as compatibility with the formulation, fabrics, product claims, laundry conditions, application, and manufacturing limitations. For example, compounds 60 and 62-65 are substantive to cellulosics and compound 61 is substantive to sUk, wool, nylon, secondary acetate, and triacetate fibers. Eor bleach-based products (e.g., hydrogen peroxide) compound 60 is used as distyrylbiphenyl chemistry exhibits the required stability. 

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