Cellulose groups

As mentioned in Section 22.1 the probability of acetylation of any one cellulosic group is strongly dependent on its position in the fibre. Since they cannot be dissolved before acetylation it will be realised that some molecules will be completely acetylated whilst others may be untouched. It is thus necessary first to acetylate completely the cellulose and the resultant triacetate material, which is soluble in certain solvents, may then be back-hydrolysed in solution. Under these conditions the probabilities of hydrolysis of any acetyl groups in one molecule will be similar to the reaction probabilities of these groups in another molecule and products with a reasonably even degree of substitution less than three may be obtained. 

Moisture relations in textile polymers are concerned mostly with the hydrophilic fibers, such as the cellulose groups of cotton, flax, hemp, jute, viscose, modal, and acetates. This is not to say however that the essentially hydrophobic fibers, which fall into the synthetic polymer group (see Fig. 1) have zero moisture imbibition or are totally unaffected by moisture, although this will be true for some of the fibers in this group. 

Fiber, cellulose acetate Acetyl derivative of cellulose. Triacetate designation can be used when not less than 92% of the cellulose groups are acetylated. 

An all-cellulose group that includes cotton composites... 

Biodegradability Nonbiodegradability (Group BFl) natural fibers, wood flour, spider silk (Group BF2) rayon-based carbon, carbonized wood flour, carbonized cellulose (Group PFl) fibers made from PMl (Group PF2) chemical fibers, glass, PAN-based carbon, hydroxyl-apatite, nanoclay, and crashed shell... 

The starch-cellulose group.) Higher members insoluble lower members form colloidal solutions in water. 

SH or — NH group to give acetyl (ethanoyl) derivatives which are useful for characterization. Largely used for the production of cellulose ethanoate, also used for the manufacture of vinyl ethanoate and aspirin. U.S. production 1978 680 000 tonnes. 

Procion dyes A group of azo dyestuffs which can form covalent bonds to cellulose by reactive groups. 

Cellulose Acetate, Propionate, and Butyrate. Cellulose acetate is prepared by hydrolyzing the triester to remove some of the acetyl groups the plastic-grade resin contains 38 to 40%... 

Rayon. Viscose rayon is obtained by reacting the hydroxy groups of cellulose with carbon disulfide in the presence of alkali to give xanthates. When this solution is poured (spun) into an acid medium, the reaction is reversed and the cellulose is regenerated (coagulated). 

The cellulose molecule contains three hydroxyl groups which can react and leave the chain backbone intact. These alcohol groups can be esterified with acetic anhydride to form cellulose acetate. This polymer is spun into the fiber acetate rayon. Similarly, the alcohol groups in cellulose react with CS2 in the presence of strong base to produce cellulose xanthates. When extruded into fibers, this material is called viscose rayon, and when extruded into sheets, cellophane. In both the acetate and xanthate formation, some chain degradation also occurs, so the resulting polymer chains are shorter than those in the starting cellulose. 

Nitration of cellulose may result in the addition of from one to three nitrate groups per glucose anhydride unit. The following compounds and their nitrogen content have been postulated ... 

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, the second oldest synthetic fiber, is an important factor in the textile and tobacco industries 731,000 metric tons were produced worldwide in 1991 (Fig. 11) (74). Acetate belongs to the group of less expensive fibers triacetate is slightly more expensive. An annual listing of worldwide fiber producers, locations, and fiber types is pubHshed by the Fiber Economics Bureau, Inc. (74). 

Antimony Oxide as a Primary Flame Retardant. Antimony oxide behaves as a condensed-phase flame retardant in cellulosic materials (2). It can be appHed by impregnating a fabric with a soluble antimony salt followed by a second treatment that precipitates antimony oxide in the fibers. When the treated fabric is exposed to a flame, the oxide reacts with the hydroxyl groups of the cellulose (qv) causing them to decompose endothermically. The decomposition products, water and char, cool the flame reactions while slowing the production and volatilization of flammable decomposition products (see Flaa retardants for textiles). 

Boron also reacts with hydroxyl-containing polymers such as cellulose. When exposed to a flame the boron and hydroxyl groups form a glassy ester that coats the substrate and reduces polymer degradation. A similar type of action has been observed in the boron—alumina tfihydrate system. 

Mesylated and Tosylated Celluloses. It has been estabUshed that the flame resistance of ceUulose (qv) is improved by oxidation of —CH2OH groups to —COOH (58—60). To correct some of the shortcomings of this treatment, mesyl or tosyl ceUulose was prepared and then the mesyl (CH2SO2) or tosyl (CH2CgH4S02) group was replaced with bromine or iodine (58—60) ... 

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