Alkali-cellulose

Strong alkali solutions acting on cellulose (at room temperatures) produce alkali cellulose. The studies on the structure of alkali cellulose [43] obtained with 20-40% NaOH solutions indicated that the substance is not a true alcoholate but an addition complex, RceiiOH NaOH. A true alcoholate can be obtained, for example, from dry cellulose and Na in liquid ammonia. Alkali cellulose has a large range of applications as an intermediate product in the preparation of cellulose ethers, and xanthate (dithiocarbonate), as well as in cellulose mercerization. 

Pyrolysis of alkali cellulose generates qualitatively the same decomposition products as cellulose, but the decomposition starts at lower temperatures. Also, the amount of each compound in the pyrolysate is modified, the amount of levoglucosan being lower than in pure cellulose (see Section 7.2) because of a higher tendency to form dehydrated cellulose as a first step in pyrolysis. 

Cellulose xanthate is another modified cellulose obtained from alkali cellulose RceiiOH NaOH + CSj RceiiO-C(S)SNa + HjO Xanthates undergo a pyrolytic reaction with elimination, similar to other esters  

Cellulose ethers are also common modified celluloses with many practical applications. The ethers can be classified in several groups alkyl, carboxyalkyl, hydroxyalkyl, arylalkyl ethers, etc. The idealized structure of some of these ethers is 

Most ethers are obtained from alkali cellulose in reactions with an appropriate compound  

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Hydroxyethyl cellulose (HEC), a nonionic thickening agent, is prepared from alkali cellulose and ethylene oxide in the presence of isopropyl alcohol (46). HEC is used in drilling muds, but more commonly in completion fluids where its acid-degradable nature is advantageous. Magnesium oxide stabilizes the viscosity-building action of HEC in salt brines up to 135°C (47). HEC concentrations are ca 0.6—6 kg/m (0.2—21b/bbl). 

Manufacture. MethylceUulose is manufactured by the reaction of alkali cellulose with methyl chloride (76). 

Of somewhat greater technical interest are the addition compounds and the cellulose esters and ethers. Of the apparent addition compounds the most important is alkali cellulose produced by steeping cellulose in caustic soda and considered to be of general form (CgHioOs), (NaOH) ) rather than a sodium alcoholate compound. Alkali cellulose is a particularly important starting point in the manufacture of cellulose ethers. The ability of aqueous cuprammonium hydroxide solutions to dissolve cellulose appears to be dependent on addition compound formation. 

With each of these materials the first step is the manufacture of alkali cellulose (soda eellulose). This is made by treating eellulose (either bleaehed wood pulp or eotton Enters) with concentrated aqueous sodium hydroxide in a niekel vessel at elevated temperature. After reaetion excess alkali is pressed out, and the resultant eake is then broken up and vacuum dried until the moisture content is in the range 10-25%. The moisture and eombined alkali contents must be carefully eontrolled as variations in them will lead to variations in the properties of the resultant ethers. 

The molecular weight may be regulated by controlled degradation of the alkali cellulose in the presence of air. This can be done either before or during etherification. The molecular weight of commercial grades is usually expressed indirectly as viscosity of a 5% solution in an 80 20 toluene-ethanol mixture. 

Hydroxyethyl cellulose, produced by reacting alkali cellulose with ethylene oxide, is employed for similar purposes. 

Reaction of alkali cellulose with carbon disulphide to produce a cellulose xanthate which forms a lyophilic sol with caustic soda. This may be extruded into a coagulating bath containing sulphate ions which hydrolyses the xanthate back to cellulose. This process is known as the viscose process and is that used in the manufacture of rayon. 

The first step in the manufacture of the foil involves the production of alkali cellulose. This is then shredded and allowed to age in order that oxidation will degrade the polymer to the desired extent. The alkali cellulose is then treated with carbon disulphide in xanthating chums at 20-28°C for about three hours. 

Alkali-zelle,/. (Elec.) alkaline cell alkali-metal (photo)cell. -zellstoff, m. alkali cellulose. Alkalizitat, /. alkalinity. 

Steps to Maintain High Alkali Cellulose Ratio.287... 

Cotton linters or wood pulp, usually in the form of sheets, is steeped in strong alkali (18-50%). The swollen sheets are then pressed to force out most of the excess alkali solution. This alkali cellulose is then shredded, and aged if low viscosity is desired. The aging process is the one followed in the viscose industry and is fully explained in any discussion of that process. More alkali may be introduced during the shredding, either as a concentrated solution or as solid alkali.18 The alkali... 

The hydroxyl groups of the cellulose appear to be somewhat acidic. While studies of the composition of alkali cellulose and adsorption of sodium hydroxide have not clearly proved the presence of any sodium compound in alkali cellulose, the reactions of alkali cellulose with carbon disulfide and with etherifying agents would seem to justify the assumption that such an intermediate exists or that the hydroxyl hydrogen at least ionizes. This view is strengthened by the fact that the rate of etherification is proportional to a high power of the concentration of alkali.19... 

Ethylcellulose is made commercially by the action of ethyl chloride on an alkali cellulose prepared by steeping cotton linters or wood pulp... 

Treatment of alkali cellulose with sodium chloroacetate results in an ether with a free carboxyl group. This ether, in the form of its sodium salt, is water-soluble even when the degree of substitution is relatively low. Since the alkali-soluble modification of this substance is of much greater industrial importance it will be discussed in detail under that heading. 

The low-substituted hydroxyethylcellulose which, like methyl- and ethylcellulose, is soluble in alkali, particularly when cooled, has much to recommend it from an industrial point of view. It can be formed by the action of only small quantities (0.25 to 0.5 moles) of ethylene oxide on alkali cellulose.47 The reaction product need not be isolated since there are no salts formed, but may be diluted with water or weak alkali to give a spinning solution. The product should therefore be quite cheap. Preparation and properties of hydroxyethylcellulose have been discussed by Schorger and Shoemaker.47... 

By the action of relatively small quantities of sodium chloroacetate on alkali cellulose, carboxymethyl ethers are obtained which give smooth solution in dilute alkali but which can be regenerated to give threads or films of high tensile strength. These products are relatively hygroscopic. The substances are soluble in the form of their sodium salts and form insoluble salts with many metals.8... 

Viscose Also known as the Cross-Bevan-Beadle process. A process for making regenerated cellulose fibers. The product has been known by the generic name rayon since 1924. Cellulose, from cotton or wood, is first reacted with sodium hydroxide ( mercerization), yielding alkali cellulose. This is dissolved in carbon disulfide, yielding cellulose xanthate, which is dissolved in sodium hydroxide solution. Injection of this solution (known as viscose... 

Alkali cellulose, 4 716 Alkali earth metal nitrides, 17 206-207 Alkali flame-ionization detector (AFID), gas chromatography, 6 381 Alkali-gravity-viscosity (AGV) charts, for silicate glasses, 22 462, 463 Alkali halide disk method, 14 229 Alkali-immobile compounds, dye release from, 19 288... 

Cotton linters (DP ca. 1000) Cotton linters alkali cellulose after shred- 98.5 5.3... 

Cellulose is sometimes used in its original or native form as fibers for textile and paper, but is often modified through dissolving and reprecipitation or through chemical reaction. The xanthate viscose process, which is used for the production of rayon and cellophane, is the most widely used regeneration process. The cellulose obtained by the removal of lignin from wood pulp is converted to alkali cellulose. The addition of carbon disulfide to the latter produces cellulose xanthate. 

This is an Sn2 reaction, which is proportional to the concentration of the epoxide and alkali cellulose, but since the base is regenerated, it is first order in epoxide. 

Cellulose (VIII) is spun into fiber or cast into film by using a chemical reaction to convert it into a soluble xanthate derivative (Turbak, 1988). This is achieved by treating cellulose with 18-20% aqueous sodium hydroxide solution at 25-30°C for about 0.5-1 h. Much of the sodium hydroxide is physically absorbed into the swollen polymer some of it may be in the form of cellulose alkoxides. The excess alkali is pressed out of the cellulose pulp and the mass aged to allow oxidative degradation of the polymer chains to the desired molecular weight. The alkali cellulose is then treated with carbon disulfide at about 30° C and the resulting mass dissolved in dilute sodium hydroxide to form the sodium... 

While reactions of low-molecular-weight compounds can sometimes be carried out in the gas phase, this technique is not applicable to macromolecular substances since they are not volatile. However, it is indeed possible to let low-molecular reagents act upon solid or dissolved polymers in gaseous form. This is done, for example, in the commercial preparation of methylcellulose by conversion of alkali cellulose with gaseous methyl chloride. 

Ion exchangers can also be made from cellulose, especially for scientific applications. They are prepared from alkali cellulose by reaction, for example, with chloroacetic acid (for preparation of sodium carboxymethylcellulose, see Example 5-6). By conversion with 2-chloroethyldiethylamine one obtains so-called DEAE-cellulose, an anion exchanger carrying 2-diethylaminoethyl groups, -C2H4N(C2H5)2. 

From the variation of the dm spacing in alkali-celluloses I, II, and V, the number of water molecules has been calculated to be 3, 1, and 5, respectively. A value of c/,0i = 1.51 nm, which is the largest reported so far for alkali-celluloses, was obtained by mercerization of sulfite cellulose with 11% sodium hydroxide solution for one hour at 20°. Between six and eight water molecules are included in this structure. 

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