Cellulose acetates

Cellular Cellulose Acetate A number of solvents can be used by themselves in cementing cellulose acetate. The following formulations involve mixtures of several solvents, including bodying resins (dope-type cements) (5). 

3 Bleaching of cellulose acetate with peracetic acid 

Peracetic acid is very suitable for bleaching of cellulose acetate fibres. The liquor should be made-up in the following manner  

The solution is adjusted to pH 5-6 by the addition of well diluted sodium hydroxide and bleaching is carried out in 1 h at 66°C. It is desirable that pH should be checked at intervals. The bleached goods is then rinsed in hot and then in cold water. 

There are two types of cellulose acetate fibers. When all three hydroxyl groups per cellulose unit (see Section 17.5.3.1) are acetalized, cellulose triacetate is obtained. Cellulose triacetate is spun from dichloromethane (DCM) plus 5-15% methanol 

Cellulose acetate contains approximately 2.5 acetate groups per cellulose unit, and is actually produced by partially hydrolyzing the triacetate. The polymer is spun from a solution in acetone/water (approximately 95 5). With a large excess of drying air it is possible to remain below explosion limits. Nevertheless, all operations are carried out in closed equipment. 

Most acrylic fibers are wet-spun, but dry spinning is also applied. The most common solvent is dimethylformamide, DMF. The polymerization of acrylics can also be carried out in DMF and the polymerization solution can then be directly spun. The boiling point of DMF is 153°C, making complete removal of solvent in the spinning column almost impossible. Most dry-spun acrylic production is staple fiber, and the remaining solvent is then removed during tow processing. 

Further information on acrylic fibers is given in Section 17.5.3.2. 

Large body of information is available on the plasticization of cellulose acetate beearrse of the long history of the polymers and the wide spread applications for plasticized eellrrlose acetate. The following plasticizers and plasticizing compounds are frequently rrsed  

The following are the most typical ranges of plasticizer concentrations in different products  

In this composition of solvents, MeOH has a much greater plasticizing effect than MTBE. Experimental data show that when methanol concentration in its feed is low, the permeation of MTBE is veiy low but it drastically increases when 

Cellulose acetate plasticized by 10 wt% of diethyl phthalate had the same biodegradation rate, measured by conversion of carbon to CO2, as uiqrlasticized polymer. At the same time, the plasticizer decomposed very rapidly to harmless degradation products. After 10 weeks more than 80% plasticizer was converted compared to about 20% polymer conversion. 

In the middle of the 20 century some museum quality documents have been displayed by laminating them between sheets of cellulose acetate. The Declaration of Independence written by Thomas Jefferson in 1776 is one such document. In 1947, this document was laminated between two 

Today the principal outlets are knife handles, table-tennis balls and spectacle frames. The continued use in knife handles is due to the pleasant appearance and the ability of the material to after-shrink around the extension of the blade. Table-tennis balls continue to be made from celluloid since it has been difficult to match the bounce and handle of the celluloid ball, the type originally used, with balls fabricated from newer polymers. Even here celluloid is now meeting the challenge of synthetic polymers. Spectacle frames are still of interest because of the attractive colour. There are, however, restrictions to their use for this application in certain countries and cellulose acetate is often preferred. 

The earliest preparation of cellulose acetate is credited to Schiitzenberger in 1865. The method used was to heat the cotton with acetic anhydride in sealed tubes at 130-140°C. The severe reaction conditions led to a white amorphous polymer but the product would have been severely degraded and the process difficult to control. Subsequent studies made by Liebermann, Francimont, Miles, the Bayer Company and by other workers led to techniques for controlled acetylation under less severe conditions. 

The methods available today may be considered under two headings, homogeneous acetylation, in which the acetylated cellulose dissolves into a solvent as it is formed, and the heterogeneous technique, in which the fibre structure is retained. 

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. 

The preparation of the acetate by homogeneous acetylation may be considered in three stages  

---

Diacetin is chiefly the 1 3-diacelate CH3OOCCH3.CHOH.CH2OOCCH3. Used as plasticizer for cellulose acetate lacquers and as a solvent for basic dyes. 

C4H8O, CH3COCH2CH3. Colourless liquid with a pleasant odour, b.p. 80°C. It occurs with propanone in the products of the destructive distillation of wood. Manufactured by the liquid or vapour phase dehydrogenation of 2-butanol over a catalyst. Used as a solvent, particularly for vinyl and acrylic resins, and for nitrocellulose and cellulose acetate, also for the dewaxing of lubricating oils. U.S. production 1978 300 000 tonnes. 

CH2CI2. A colourless liquid with a chloroform-like odour b.p. 4I°C. Prepared by heating chloroform with zinc, alcohol and hydrochloric acid manufactured by the direct chlorination of methane. Decomposed by water at 200°C to give methanoic and hydrochloric acids. Largely used as a solvent for polar and non-polar substances, particularly for paint removal (30%), dissolving cellulose acetate and degreasing (10%). It is more stable than carbon tetrachloride or chloroform especially towards moisture or alkali. It is somewhat toxic. U.S. production 1981 280000 tonnes. 

CH3COCH2CH1COCH3. Colourless liquid which becomes yellow on standing b.p. I9PC. Obtained by boiling 2,5-dimethylfuran with dilute sulphuric acid. It readily condenses with a variety of substances to give derivatives of furan, thiophen and pyrrole, and is a solvent for cellulose acetate. 

McjC = CHCOCH3. Colourless liquid b.p. 129"C, with a strong peppermint-like odour. Prepared by distilling diacetone alcohol in the presence of a trace of iodine. Converted to phorone by heating in propanone with dehydrating agents such as sulphuric acid. It is a solvent For cellulose acetate and ethyl-cellulose and other polymers. 

Highly colored, they have been used to dye cellulose acetate (552) and acrylic fibers (553). Cationic dyes prepared from 2-azothiazoles by simple alkylation on the ring nitrogen (552) have been used increasingly with the introduction of polyacrylonitrile fibers with basic sites that can be colored with such dyes (554). 

Dyes for dyeing and printing polyester and cellulose acetate fibers fast blue and red shades... 

Dyes for polyesters or cellulose acetate fiber-, deep blue to greenish blue shades... 

IS placed at the center of a sheet of cellulose acetate The sheet is soaked with an aqueous solution buffered at a pH of 6 0 At this pH aspartic acid C ) exists as its — 1 ion alanine as its zwittenon and lysine as its +1 ion... 

Cellulose-acetate-propionate resin Aromatic nylons... 

Cellulose-acetate-butyrate resin Poly(amide-imide)... 

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%... 

Polycarbonate acrylonitrile-butadiene-styrene alloy Allyl-diglycol- carbonate polymer Diallyl phthalate molding Cellulose acetate Cellulose-acetate-butyrate resin... 

The hydrogen peroxide then diffuses through the innermost membrane of cellulose acetate, where it is oxidized at a Pt anode. 

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. 

---