Cellulose Esters, solubility

The structure of cellulose has only relatively recently been tackled through the examination of its trinitrate, that is. nitrocellulose of ca, 14% N. Trinitrate of cellulose was chosen as a readily available cellulose ester, soluble in polar solvents, of an almost unique unbranched polymer chain structure having a broad range of molecular weights manifested by the degree of polymerization 250-9000. 

Two important classes are cellulose esters (qv) and cellulose ethers (qv). Cellulose esters are not water soluble and are not discussed here cellulose ethers are an important segment of water-soluble polymers. 

Cellulosics. CeUulosic adhesives are obtained by modification of cellulose [9004-34-6] (qv) which comes from cotton linters and wood pulp. Cellulose can be nitrated to provide cellulose nitrate [9004-70-0] which is soluble in organic solvents. When cellulose nitrate is dissolved in amyl acetate [628-63-7] for example, a general purpose solvent-based adhesive which is both waterproof and flexible is formed. Cellulose esterification leads to materials such as cellulose acetate [9004-35-7], which has been used as a pressure-sensitive adhesive tape backing. Cellulose can also be ethoxylated, providing hydroxyethylceUulose which is useful as a thickening agent for poly(vinyl acetate) emulsion adhesives. Etherification leads to materials such as methylceUulose [9004-67-5] which are soluble in water and can be modified with glyceral [56-81-5] to produce adhesives used as wallpaper paste (see Cellulose esters Cellulose ethers). 

Several cellulose esters (qv) are prepared commercially. Cellulose xanthate [9032-37-5] is made by reaction of cellulose swollen in 8.5—12% sodium hydroxide solution (alkaU cellulose [9081-58-7J) with carbon disulfide and is soluble in the alkaline solution in which it is made. When such a solution, termed viscose, is introduced into an acid bath, the cellulose xanthate decomposes to regenerate cellulose as rayon fibers or cellophane sheets (see Fibers, REGENERATED CELLULOSICS). 

Cellulose Deriva.tives, Cellulose can be derivatized to make both water-soluble gums and hydrophobic polymers. The preparation of the hydrophobic cellulose esters (qv), cellulose acetates and cellulose nitrates, has already been mentioned. The water-soluble cellulose derivatives are cellulose ethers (qv). 

Production of cellulose esters from aromatic acids has not been commercialized because of unfavorable economics. These esters are usually prepared from highly reactive regenerated cellulose, and their physical properties do not differ markedly from cellulose esters prepared from the more readily available aHphatic acids. Benzoate esters have been prepared from regenerated cellulose with benzoyl chloride in pyridine—nitrobenzene (27) or benzene (28). These benzoate esters are soluble in common organic solvents such as acetone or chloroform. Benzoate esters, as well as the nitrochloro-, and methoxy-substituted benzoates, have been prepared from cellulose with the appropriate aromatic acid and chloroacetic anhydride as the impelling agent and magnesium perchlorate as the catalyst (29). 

Hydroxypropylcellulose (HPC) is a thermoplastic nonionic cellulose ester that is soluble in both water and a number of organic liquids. It is synthesized through reaction of the basic cellulose slurried with propylene oxide. 

The nature of solubility and the strength of solvent. According to present views the dissolution of cellulose esters consists in the separation of the chain-molecules under the specific influence of the solvent until all bonds between the chains disappear. The macromolecules of polymer can slide apart even at the swelling stage. Because of their elasticity, it is possible that the chains can be pushed aside in certain places or along the entire molecules. Further, a shortening of chains occurs, but being a secondary effect it proceeds slowly. 

Finally Papkov [52] observed that the surface tension of the solvent is a further factor influencing the solubility of cellulose esters. This worker established that the best solvents from a series of liquids resembling each other chemically, e.g. in a homologous range, were characterized by a moderate, optimum surface tension. Liquids having higher or lower surface tensions than this optimum value are worse solvents. The rule is also valid for mixtures. Thus a 50 50 acetone-water solution with a surface tension a = 30.4 dyne/cm caused only a weak swelling of... 

According to Hess, Trogus and Tomonari [8] mixed sulphuric and nitric esters of cellulose are soluble in methyl alcohol. Hence by boiling nitrocellulose in methyl alcohol it is possible to remove these substances up to a quantity corresponding to some 1% of the nitrocellulose mass. The extracted product contains three N02 and two S03H groups for every two C6H10O5 units. 

This group (sometimes called water-soluble resins) includes such chemically treated natural polymers as carboxymcthylcclluosc, mcthylccllulosc, and other cellulose esters, as well as various kinds of modified starches (esters and acetates). 

Most experiments were performed with cotton or cotton linters as highly crystalline celluloses. Table I shows conditions leading to complete dissolution. A minimum amount of an acid which forms a cellulose ester (sulfuric or trifluoromethylsulfuric acid) (Entries 5 7-14) is necessary for the reaction. The dissolution is accelerated by a temperature increase (Entries 10-12 13, 14) and leads to water-soluble cellulose acetate hydrogensulfate. Whereas this primary hydrolysis can be achieved within 1-5 min, the deesterification and complete hydrolysis of the soluble cellulose derivative proved to be much more difficult. This is in contrast to the generally accepted view that the main resistance to the hydrolysis of cellulose lies in the crystalline nature or low accessibility determining the heterogeneous first step of the reaction. 

Synonyms 2-chloroethanol, 2-chloroethyl alcohol Formula C2H5OCI Stmctme Cl-CH2-CH2-OH MW 80.52 CAS [107-07-3] used as a solvent for cellulose esters and in making ethylene glycol and ethylene oxide colorless liquid with a faint ether odor boils at 129°C freezes at -67°C density 1.197 g/mL at 20°C soluble in water, alcohol, and ether highly toxic. 

MW 138.20 CAS [78-59-1] used as a solvent for vinyl resins and cellulose esters boils at 215°C solidifies at -8°C density 0.92 g/mL at 20°C slightly soluble in water readily miscible with alcohol, ether, and acetone. 

With the exception of the blue copper phthalocyanine derivatives, these products are azo dyes that are soluble in polar solvents such as alcohols, glycols, esters, glycol ethers, and ketones. Dyes soluble in alcohols and esters are used in protective lacquers for the transparent coating of metal (aluminum) foils and other materials, such as wood (greening lacquers) in flexographic inks for the printing of metal foils, cellophane, and paper as well as for the coloration of cellulose esters, celluloid, and poly(vinyl acetates), and, in the office supplies sector, for... 

In the presence of potassium hydroxide, cellulose adds to carbon disulfide (Figure 8.4). In this way potassium xanthate A is produced. It is soluble in water, but restores the water-insoluble cellulose upon addition of acid. The primary protonation product is the dithiocarbonic acid O-cellulose ester B. B reacts just like the unstable carbonic acid derivatives in Figure 8.3, namely via a zwitterion (C) and its decomposition into cellulose (a heteroatom nucleophile)... 

Cellulose esters (e.g., cellulose triacetate, cellulose diacetate, cellulose propionate, and cellulose butyrate) are prepared by initially treating cellulose with glacial acetic acid (or propionic acid and butyric acid) followed by the corresponding acid anhydride with a trace of strong acid as a catalyst in chlorinated hydrocarbon. Complete esterification reactions result in the formation of a triester, which undergoes water hydrolysis to form a diester. Cellulose acetate alone or in combination with cellulose triacetate or cellulose butyrate is used as a semipermeable membrane for osmotic pumping tablets, primarily in controlled release systems. The permeability of the membrane can be further modulated by adding water-soluble excipients to the cellulose esters. 

Chromium. Chromium is not an easily analyzed element because three distinct standards are listed by OSHA (Tables IV and V ). One standard exists for hexavalent chromium, chromic acid and chromates, another standard for soluble chromium compounds and chromous salts, and another standard for insoluble chromium compounds and chromium metal. The permissible amount of chromium in air decreases as the oxidation state increases. The analysis of chromium is further complicated by the multiplicity of NIOSH methods for chromium compounds. Hexavalent chromium shall be collected on PVC filters, although a criteria document for chromic acid (14) specifies mixed cellulose ester filters. The analytical method described in the hexavalent... 

In some cases, the rate-controlling polymeric membrane is not compact but porous. Microporous membranes can be prepared by making hydrophobic polymer membranes in the presence of water-soluble materials such as polyethylene glycol), which can be subsequently removed from the polymer matrix by dissolving in aqueous solution. Cellulose esters, loosely cross-linked hydrogels and other polymers given in Table 4.2 also give rise to porous membranes. 

The reaction product is soluble in the acetylation mixture as it is formed and dissolved, new surfaces of the cellulose are presented to the reagents. One variation of this procedure uses methylene chloride, rather than an excess of acetic acid in the reaction mixture. This chemical is used both to dissipate the heat by refluxing (boiling point, 41.2°C) and to dissolve the cellulose ester as it is formed. As the reaction proceeds, the temperature is... 

---