Cellulose esterifying

Cellulose butyrate contains the bulkier butyryl group these esters are more compatible and soluble than acetates, but are too soft for most coating applications. Cellulose esterified with blends of alkyl groups can provide many intermediate properties needed in coatings. Selection of the appropriate cellulose acetate butyrate [9004-36-8] (CAB) and cellulose acetate propionate [9004-39-f] (CAP) content must be based on specific application requirements. 

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. 

Urea—Phosphate Type. Phosphoric acid imparts flame resistance to ceUulose (16,17), but acid degradation accompanies this process. This degradation can be minimized by iacorporation of urea [57-13-6]. Ph osph oryl a ting agents for ceUulose iaclude ammonium phosphate [7783-28-0] urea—phosphoric acid, phosphoms trichloride [7719-12-2] and oxychloride [10025-87-3] monophenyl phosphate [701-64-4] phosphoms pentoxide [1314-56-3] and the chlorides of partiaUy esterified phosphoric acids (see Cellulose esters, inorganic). 

In many appHcations succinic acid and anhydride are esterified with polyhydric compounds, ie, polyols (57—59), cellulose (60), or starch (61—64). 

Ca.ta.lysts for Acetylation. Sulfuric acid is the preferred catalyst for esterifying cellulose and is the only known catalyst used commercially for this function. The role of sulfuric acid during acetylation has been discussed (77,78). In the presence of acetic anhydride, sulfuric acid rapidly and almost quantitatively forms the cellulose sulfate acid ester (77). Even in the absence of anhydride, the sulfuric acid is physically or mechanically retained (sorbed) on the cellulose. The degree of absorption is a measure of the reactivity or accessibiUty of different celluloses. 

Stabilization and Digestion. Following the initial washing steps, the stabilization of CN occurs. This involves removal of any remaining sulfuric acid since it would catalyze the decomposition of CN. The sulfuric acid present is both physically entrained in the product and chemically bonded to the cellulose chain. CN can contain 0.2—3% esterified H2SO4, depending on the DS of nitration. The sulfonate ester can be easily removed by... 

Acetic acid is a versatile reagent. It is an important esterifying agent for the manufacture of cellulose acetate (for acetate fibers and lacquers), vinyl acetate monomer, and ethyl and butyl acetates. Acetic acid is used to produce pharmaceuticals, insecticides, and dyes. It is also a precursor for chloroacetic acid and acetic anhydride. The 1994 U.S. production of acetic acid was approximately 4 billion pounds. 

As previously discussed, solvents that dissolve cellulose by derivatization may be employed for further functionahzation, e.g., esterification. Thus, cellulose has been dissolved in paraformaldehyde/DMSO and esterified, e.g., by acetic, butyric, and phthalic anhydride, as well as by unsaturated methacrylic and maleic anhydride, in the presence of pyridine, or an acetate catalyst. DS values from 0.2 to 2.0 were obtained, being higher, 2.5 for cellulose acetate. H and NMR spectroscopy have indicated that the hydroxyl group of the methy-lol chains are preferably esterified with the anhydrides. Treatment of celliflose with this solvent system, at 90 °C, with methylene diacetate or ethylene diacetate, in the presence of potassium acetate, led to cellulose acetate with a DS of 1.5. Interestingly, the reaction with acetyl chloride or activated acid is less convenient DMAc or DMF can be substituted for DMSO [215-219]. In another set of experiments, polymer with high o -celliflose content was esterified with trimethylacetic anhydride, 1,2,4-benzenetricarboylic anhydride, trimellitic anhydride, phthalic anhydride, and a pyridine catalyst. The esters were isolated after 8h of reaction at 80-100°C, or Ih at room temperature (trimellitic anhydride). These are versatile compounds with interesting elastomeric and thermoplastic properties, and can be cast as films and membranes [220]. 

Pectins occur naturally in both soluble and insoluble forms. Soluble pectin occurs in plant juices and is particularly abundant in those juices which form jellies, such as black-currant and gooseberry. Insoluble pectins tend to occur in the green parts of plants, in fruit and in root crops.1 This insolubility is apparently due either to the presence of the pectin as its insoluble calcium or magnesium salt or because it is combined (esterified ) with cellulose or some other insoluble polysac-... 

Figure 12. Surface concentration (Cs) of the hydroxyl groups half-esterified hy adipoyl chloride for cellulose and PVA films (O) Visking (A) cellophane (0)...

Shiraishi, N., Matsunaga, T. and Yokota, T. (1979). Thermal softening and melting of esterified wood prepared in an N,0,-DMF cellulose solvent medium. Journal of Amlied Polymer Science, 24(12), 2361-2368. 

Amongst the important chemical conversions of macromolecular substances are the various reactions of cellulose. The three hydroxy groups per CRU can be partially or completely esterified or etherified. The number of hydroxy groups acetylated per CRU are indicated by the names, i.e., cellulose triacetate, cellulose 2-acetate, etc. Another commercially important reaction of cellulose is its conversion to dithiocarboxylic acid derivatives (xanthates). Aqueous solutions of the sodium salt are known as viscose they are spun into baths containing mineral acid, thereby regenerating the cellulose in the form of an insoluble fiber known as viscose rayon. 

This cellulose derivative is a partial acetate ester of cellulose, which has been reacted with phthalic anhydride. One carboxyl residue of the phthalic acid is esterified with cellulose acetate. The final product contains about 20% acetate groups and about 35% phthalate groups. In the acid form, it is soluble in organic solvents and insoluble in water, whereas in the salt form it is readily soluble in water. This combination of properties makes it useful in coating of tablets because it is resistant to acids of the stomach but it is readily soluble in the more alkaline environment of the intestinal tract. 

O-Nitration is an exothermic reaction. Approximate calculations which have been made (Kagawa [70] Calvet and Dhers-Pession [71]) on the basis of esterifying methyl alcohol and cellulose indicate that the esterification of one hydroxyl group is accompanied by the development of 2 0.2 kcal of heat (see pp. 46, 147). 

Wetting and swelling. As stated above, the presence of hydroxyl groups in cellulose enables it to be esterified up to a maximum of three ester groups to every anhydroglucose unit. Further, the high content of hydroxyl groups endows cellulose with hydrophilic properties. Nevertheless, the amount of water absorbed by cellu-... 

If all or nearly all the hydroxyl groups are esterified (as in cellulose trinitrate), then the long-chain-molecules again possess a regular structure, and under the influence of forces of adhesion (van der Waals bonds) close mutual contact may be maintained (Fig. 89a). Here again the solvent may be too weak as to push aside... 

The first attempts to esterify cellulose by means of nitric acid consisted in treating cellulose with the acid without any dehydrating agents. Vieille [1] discovered in 1882 that on nitration with nitric acid alone the rate of reaction and the nitrogen Content of the nitrocellulose increased as the concentration of HN03 was increased ... 

According to Sapozhnikov, the esterification proceeds most intensively in the presence of anhydrous nitric add HN03, as in eqn. (2). In the presence of smaller amounts of sulphuric acid, nitric acid hydrates are formed in practice they are not capable of esterifying cellulose. 

Celluronic acid nitrates (carboxycelluloses nitrates). Celluronic acid obtained by treating cellulose with nitrogen dioxide may then be esterified by means of nitric acid. 

Celluronic acid produced by treating cellulose with nitrogen tetroxide may then be esterified by means of nitric acid. It has been found that even in. the presence of small number of carboxylic groups a considerable change in the properties of the nitric esters is brought about, as compared with cellulose. 

The usual diet of ruminants consists of fresh and preserved herbage and cereals. As a result of microbial activity in the rumen, esterified dietary fatty acids are hydrolyzed, short chain fatty acids are produced by fermentation of cellulose and other polysaccharides, unsaturated fatty acids are hydrogenated and/or converted to geometric (trans) and positional isomers, and microbial lipids are synthesized. These activities account in part for the enormous diversity of fatty acids in milk and the unique features short-chain and a high proportion of long chain saturated fatty acids. (Patton and Jensen, 1976 Christie, 1979B). 

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