Acetylation hydrolyzed cellulose acetate

The first organic ester of cellulose was cellulose acetate, prepared by Schutzenberger in 1865 by heating cotton and acetic anhydride to about 180 °C in a sealed tube until the cotton dissolved (J ). In 1879, Franchimont acetylated cotton at lower temperatures with the aid of a sulfuric acid catalyst (2). Miles, in 1903, described the preparation of partially hydrolyzed cellulose acetate, which was easily distinguished from the fully acetylated... 

Partial hydrolysis is accomplished by adding to the methylene chloride solution aqueous acetic acid (50%). The solution is then allowed to stand in order to reach the desired degree of hydrolysis. This usually takes about 72 hours at room temperature. Sulfuric acid, still present from acetylation, is then neutralized by addition of sodium acetate and most of the methylene chloride is distilled off. The partially hydrolyzed cellulose acetate is then precipitated by addition of water and washed thoroughly. The washing also includes a two-hour wash with very dilute sulfunc acid to remove hydrogen sulfate esters that cause polymer instability. 

Secondary cellulose acetate (D.S. 2.4) is prepared by interrupting the acetylation reaction leading to CTA by adding water in the form of aqueous acetic acid of 50-75% concentration (as noted above). This also decreases the level of combined sulfuric acid which improves the stabihty of the cellulose acetate. Magnesium ions are added to produce insoluble sulfeles further improving the stability of the product. The hydrolysis rate is controlled by temperature, catalyst concentration and to a smaller extent by the water content. The amount of water influences the ratio of primary to secondary hydror l groups in the hydrolyzed cellulose acetate. 

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%... 

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. 

High temperature acetylation of cellulose above 50°C produces cellulose acetate from low purity wood pulp cellulose in shorter reaction times. In a high temperature method recently disclosed (102), cellulose reacts with 200—400% acetic anhydride in the presence of <5% acid catalyst at 68—85°C for 3—20 min. After the acid catalyst is neutralized with magnesium acetate, the cellulose acetate is hydrolyzed at 120°C for two hours (103). Several modified catalyst systems have been developed for acetylation of cellulose above 90°C (89,90). 

Figure 10 shows the IR spectrum of a normal cellulose acetate membrane. Figure 11 shows the spectrum of the hydrolyzed membrane. The decrease of absorption around 1,720 cm, and the increase of absorption around 3,200 to 3,500 cm are shown. The first peak correspond to the C = 0 double bond, and the second to the 0 - H single bond. These spectra show the decrease of the acetyl content in the membrane. 

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 38-40% acetyl. The propionate and butyrate esters are made by substituting propionic acid and its anhydride (or butyric acid and its anhydride) for some of the acetic acid and acetic anhydride. Plastic grades of cellulose-acetate-propionate resin contain 39-47% propionyl and 2-9% acetyl cellulose-acetate-butyrate resins contain 26-39% butyryl and 12-15% acetyl. 

The solubility restrictions that apply to the manufacture of the mixed esters are the same as those for the cellulose acetate, in that no soluble products are obtained by partial esterification. Hydrolysis of the esters in acid solution, however, yields uniform products showing gradually changing physical properties with increasing free hydroxyl content. The exact ratio of hydrolysis of acetyl to hydrolysis of propionyl or butyryl groups depends upon the composition of the hydrolysis solution. Thus, a cellulose acetate propionate hydrolyzed in acetic acid solution will retain a higher proportion of acetyl groups than would the same cellulose ester hydrolyzed in propionic acid. 

Derivation Reacting cellulose (wood pulp or cotton linters) with acetic acid or acetic anhydride, with H2S04 catalyst. The cellulose is fully acetylated (three acetate groups per glucose unit), and at the same time the sulfuric acid causes appreciable degradation of the cellulose polymer so that the product contains only 200-300 glucose units per polymer chain. At this point in the process the cellulose acetate ordinarily is partially hydrolyzed by the addition... 

Cellulose triacetate is often known as primary cellulose acetate, and partially hydrolyzed material is called secondary cellulose acetate. Many physical and chemical properties of cellulose acetylation products are strongly dependent on the degree of esterification, which is measured by the acetyl content (i.e., the weight of acetyl radical (CH3CO-) in the material) or acetic acid yield (i.e., the weight of acetic acid produced by complete hydrolysis of the ester). 

Acetyl tri butyl citrate Acetyl triethyl citrate Acetyl trimethyl citrate Cellulose acetate butyrate Cellulose acetate propionate Ditrimethylolpropane tetraacrylate Ethylene/acrylic acid/vinyl acetate copolymer PVM/MA copolymer, isopropyl ester Trihexyl citrate Trimethyl citrate film-former, colored cosmetics Diisostearoyl trimethylolpropane siloxy silicate film-former, conditioners Hydrolyzed wheat protein Polyquaternium-6 film-former, conditioning shampoo Polyquaternium-2 film-former, cosmetic emulsions Acrylates/C10-30 alkyl acrylate crosspolymer film-former, cosmetic topicals PEG-8/SMDI copolymer PPG-51/SMDI copolymer... 

As mentioned earlier, cellulose acetates of increasing degree of acetylation have lower water absorption. Thus cellulose triacetate is preferred for X-ray and cine-film where dimensional stability is required. It may be noted that cellulose triacetate has displaced celluloid (which also has low water absorption) in these applications, mainly because cellulose triacetate does not have the great inflammability of celluloid. All types of cellulose acetate are readily hydrolyzed by aqueous acids and alkalis cellulose triacetate is initially more resistant to hydrolysis since it is less easily wetted. 

Steam explosion increases the accessibility of cellulose but also rendering the production of compoimds that may inhibit the activity of catalysts such as H SO, SO2, and NaOH (Zheng et al., 2014). Hemicelluloses will be hydrolyzed into acetic acid due to the presence of acetyl group which could be further processed for the production of ethanol and syngas (Hendriks and Zeeman, 2009a). 

Amyloid.—When treated with concentrated sulphuric acid cellulose dissolves and undergoes hydrolysis. If the solution is diluted with water a gelatinous product is obtained which gives the blue color with iodine characteristic of starch. This product is known as amyloid. When boiled in the dilute acid the amyloid is hydrolyzed and dextrin and finally glucose are obtained. Concentrated hydrofluoric acid and phosphoric acid also dissolve cellulose. With glacial acetic acid in the presence of acetic anhydride and sulphuric acid cellulose yields acetyl derivatives indicating its alcoholic character. From the products of this reaction the acetate of a di-saccharose is obtained. 

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. 

In the manufacture of cellulose triacetate using sulfuric acid catalyst in the batch process, there is a stabilization step following the acetylation. The residual sulfate groups are hydrolyzed (called desulfation) at an elevated temperature by slow addition of dilute aqueous acetic acid solution containing magnesium or sodium acetate or other suitable base to neutralize the liberated sulfuric acid [26,27]. 

The acetylation reaction of cellulose is often prepared by forming a solution in a mixture of acetic anhydride and sulfuric acid. This results in the formation of a triacetate. When a lower degree of esterification is desired, the triacetate is partially hydrolyzed. A two-step procedure is needed, because it is not possible to control the degree of esterification in the reaction with acetic anhydride and sulfuric acid. In a typical process, dry cellulose is pretreated with 300 parts acetic anhydride, one part sulfuric acid, and 400 parts methylene chloride. The reaction mixture is agitated while the temperature is maintained at 25-35 for 5-8 eight hours. By the end of that period all the cellulose... 

As known, polarizing film mainly consists of CTA and PVA (the structures of CTA and PVA are shown in Figures 17.9 and 17.10). That is to say, in the hydrothermal process, the production of acetic add primarily comes from CTA or PVA. In the chemical structure of CTA, all cellulose hydroxyl groups are replaced by acetyl groups. And the physical characteristics of PVA are dependent on its method of preparation from the hydrolysis, or partial hydrolysis, of polyvinyl acetate. PVA is generally classified into two groups, partially hydrolyzed and fully hydrolyzed. 

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