Cellulose hydrates

Cellulose hydrates, 5 379 Cellulose laurate, moisture properties, 5 416t... 

Cellulose hydrate is used with sweets and as artificial skin for sausages. 

Single crystals of the D-glucan from Acetobacter xijlinum were prepared in water-methanol solutions at room temperature. Using electron and X-ray diffraction, a hexagonal unit-cell, with a = h = 0.518 nm and c = 2.0 nm, was derived. It was concluded that the chain axes lie parallel to the surface of the lamellar crystals, that there are 2.5 water molecules per /3-D-Glcp residue, and that the structure is similar to that of cellulose hydrate II (Ref. 42). 

In addition to the above, there are emulsion and suspension stabilizers that act as protective colloids and in some cases as thickeners gums (such as acacia and traga canth), alginates, starch and starch derivatives, casein, glue, egg albumin, methyl cellulose, hydrated Mg and Al silicates, etc Refs Same as in previous item... 

Compounds of this type are unstable, and hydrolyse in water, hence sodium hydroxide can be completely removed by water washing. In effect swollen cellulose is produced. Formerly, in view of the difficulty of removing the water contained in such cellulose by drying, it was called hydrated cellulose, the idea that it represented a water-cellulose compound, a cellulose hydrate , being current at that time. 

Cellulose hydrate is more hygroscopic than cellulose and demonstrates increased reactivity, e.g. esterification. Cellulose hydrate can also be produced by the action of dilute nitric acid. 

In his introduction to the Lehrbuch, Heuser states objectively Even the methods of treatment adopted by Schwalbe and by Heuser seem to be fundamentally unprofitable, because they do not lead to definite results. These authors have divided the subject along the lines of the various derivatives of cellulose, such as cellulose hydrate, hydrocellulose, oxycellulose, etc. Such discussions are of little value because the substances to which the above names have been applied are not homogeneous chemical individuals, but are mixtures of the most varied degradation products of cellulose and may react very differently under apparently similar conditions. Cross and Bevan have also made the same unfruitful and dangerous mistake of trying to build a system of cellulose chemistry on the basis of such mixtures.. . ... 

Besides the cellulose structures I-IV and their subclasses, cellulose forms a variety of crystalline complexes. Soda celluloses were mentioned above, and there is an extensive array of complexes with amines [236]. Soda cellulose IV [237] is actually a hydrate of cellulose and contains no sodium (historically, cellulose hydrate meant cellulose II, which is now known to contain no water ). Many cellulose derivatives such as the nitrate (see above) and the triacetate [238] also give diffraction patterns. The most recent analysis of triacetate I shows a single-chain unit cell [239]. 

When cellulose is treated with carbon disulphide and sodium hydroxide, a cellulose xanthate is formed. This salt when stirred with a small amount of water forms a thick solution, called viscose, which is converted into cellulose hydrate by heat or certain salts. By squirting viscose through capillary tubes into a solution which brings about this decomposition, threads of cellulose are obtained having a silky luster. From these artificial silk is made. Viscose is also used for paper-sizing, in textile printing, and as a cement. 

Cellulose does not swell very greatly in water it hydrates. For example, cellulose pulp hydrates in paper beaters. The question depends upon what one means by swelling. By hydration one generally means that a hydrophylic molecule becomes associated with an atmosphere of water molecules that are held in a semifixed state and that interpolysaccharide secondary bonds become fewer as a consequence. In other words, th polysaccharide secondary forces are taken up mainly by water molecules. To this extent guar gum and cellulose hydrate in the same way. Guar gum hydrates much more extensively than cellulose consequently its molecules may become separated so as to form a suspension. 

Cellulose acetate is the most well known plastic with a cellulose base. Others are cellulose acetobutyrate and cellulose propionate. Cellulose hydrate may be used as a vulcanized fiber. Cellulose may be identified fairly simply. Dissolve or suspend a sample in acetone, react it with 2-3 drops of a 2 % solution of a-naphthol in ethanol, and carefully introduce a layer of concentrated sulfuric acid under this. At the phase boundary, a red to red-brown ring forms. In the presence of cellulose nitrate, a green ring forms. Sugars and lignin produce interference. For differentiation between cellulose acetate and cellulose acetobutyrate, it is usually sufficient to examine the vapors produced by dry heating of the sample. The acetate smells like acetic acid the acetobutyrate smells of both acetic acid and butyric acid (like rancid butter). 

Figure 9-3. The time dependence of the hydrostatic heads Ap, of solutions of poly(ethylene glycol) (c = 2 X lO " g/cm (A/n)=4000, (M v)= 4300 g/mol molecule) in formamide, methanol, or water on cellophane 600 membranes (cellulose hydrate) at 25°C. The theoretically expected osmotic pressure in an ideal solution at this concentration is Ilid = 127 Pa (according to H.-G. Elias).

In regenerated cellulose, sometimes called cellulose hydrate, the unit cell is an allotropic modification of cellulose I, designated cellulose II. This form is general for all rayons, cellophanes, and mercerized cellulose. Other allotropic modifications are known. Proposed dimensions for cellulose I, II, III, and IV are listed in Table 10.8. 

To prepare cell glass (cellulose hydrate films), it is necessary to use higher concentrations of cellulose, otherwise the freshly produced film would contain too much solvent and therefore would tear too readily. But one must proceed from a basic copper sulfate or copper hydroxide solution to achieve high cellulose concentrations, since the use of copper sulfate would produce too much sodium sulfate which would reduce the cellulose solubilizing power of the Cuoxam solution. 

In many cases, two films are also bonded or welded to each other. Cellulose hydrate (cell glass) films, for example are backed with poly(ethylene)... 

Unsized paper from linters or soda wood pulp is likewise made up into vulcanized fiber. The paper roll tracks are welded together by a parch-mentization process involving treatment with 70% ZnCl2 solution at 50-70 C, forming a sandwichlike material. Thick parchment paper and thin vulcan fiber are almost identical. A cellulose hydrate is considered to be formed in the parchmentization process ... 

Cellophan Cellulose hydrate from pulp KaUe... 

The plant cell walls of bast fibers consist mainly of cellulose, hemicellulose, and lignin. The uptake of water by a hygroscopic material as cellulose or hemicellulose is a hydration process involving accessible hydroxyl groups, or in this case -CH2OH groups of the host material. Water molecules absorbed by dry cellulose form a true cellulose hydrate, and the reaction is exothermic, which provides the driving force (Pizzi 1987). 

---