Part 2 (1/2)
A. FRAENKEL and P. FRIEDLAENDER (Mitt. k.-k. Techn. Gew. Mus., Wien, 1898, 326).
The authors, after investigation, are inclined to attribute the l.u.s.tre of mercerised cotton to the absence of the cuticle, which is destroyed and removed in the process, partly by the chemical action of the alkali, and partly by the stretching at one or other stage of the process. The authors have investigated the action of alcoholic solutions of soda also. The l.u.s.tre effects are not obtained unless the action of water is a.s.sociated.
In conclusion, the authors give the following particulars of breaking strains and elasticity:--
-------------------------------------------------------------------------- Treatment
Experiments
Breaking strain
Elasticity --------------------------------------------------------------------------
Elongation
Grammes
in mm.
Cotton unmercerised.
1
360
20
2
356
20
3
360
22
Mercerised with
Soda 35B.
1
530
44
2
570
40
3
559
35
Alcoholic soda 10 p.ct.
1
645
24 cold
2
600
27
3
610
33
Alcoholic soda 10 p.ct.
5
740
33 hot
2
730
38
3
690
30 --------------------------------------------------------------------------
FOOTNOTES:
[2] This and other similar references are to the matter of the original volume (1895).
SECTION II. SYNTHETICAL DERIVATIVES--SULPHOCARBONATES AND ESTERS
(p. 25) ~Cellulose sulphocarbonate.~--Further investigations of the reaction of formation as well as the various reactions of decomposition of the compound, have not contributed any essential modification or development of the subject as originally described in the author's first communications. A large amount of experimental matter has been acc.u.mulated in view of the ultimate contribution of the results to the general theory of colloidal solutions. But viscose is a complex product and essentially variable, through its p.r.o.nounced tendency to progressive decomposition with reversion of the cellulose to its insoluble and uncombined condition. The solution for this reason does not lend itself to exact measurement of its physical constants such as might elucidate in some measure the progressive molecular aggregation of the cellulose in a.s.suming spontaneously the solid (hydrate) form. Reserving the discussion of these points, therefore, we confine ourselves to recording results which further elucidate special points.
_Normal and other celluloses._--We may certainly use the sulphocarbonate reaction as a means of defining a normal cellulose. As already pointed out, cotton cellulose pa.s.ses quant.i.tatively through the cycle of treatments involved in solution as sulphocarbonate and decomposition of the solution with regeneration as structureless or amorphous cellulose (hydrate).
a.n.a.lysis of this cellulose shows a fall of carbon percentage from 44.4 to 43.3, corresponding with a change in composition from C_{6}H_{10}O_{5} to 4C_{6}H_{10}O_{5}.H_{2}O. The partial hydrolysis affects the whole molecule, and is limited to this effect, whereas, in the case of celluloses of other types, there is a fractionation of the ma.s.s, a portion undergoing a further hydrolysis to compounds of lower molecular weight and permanently soluble. Thus in the case of the wood celluloses the percentage recovered from solution as viscose is from 93 to 95 p.ct. It is evident that these celluloses are not h.o.m.ogeneous. A similar conclusion results from the presence of furfural-yielding compounds with the observation that the hydrolysis to soluble derivatives mainly affects these derivatives. In the empirical characterisation of a normal cellulose, therefore, we may include the property of quant.i.tative regeneration or recovery from its solution as sulphocarbonate.
In the use of the word 'normal' as applied to a 'bleached' cotton, we have further to show in what respects the sulphocarbonate reaction differentiates the bleached or purified cotton cellulose from the raw product. The following experiments may be cited: Specimens of American and Egyptian cottons in the raw state, freed from mechanical, i.e.
non-fibrous, impurities, were treated with a mercerising alkali, and the alkali-cotton subsequently exposed to carbon disulphide. The product of reaction was further treated as in the preparation of the ordinary solution; but in place of the usual solution, structureless and h.o.m.ogeneous, it was observed to retain a fibrous character, and the fibres, though enormously swollen, were not broken down by continued vigorous stirring. After large dilution the solutions were filtered, and the fibres then formed a gelatinous ma.s.s on the filters. After purification, the residue was dried and weighed. The American cotton yielded 90.0 p.ct., and the Egyptian 92.0 p.ct. of its substance in the form of this peculiar modification. The experiment was repeated, allowing an interval of 24 hours to elapse between the conversion into alkali-cotton and exposure of this to the carbon disulphide. The quant.i.tative results were identical.
There are many observations incidental to chemical treatments of cotton fabrics which tend to show that the bleaching process produces other effects than the mere removal of mechanical impurities. In the sulphocarbonate reaction the raw cotton, in fact, behaves exactly as a compound cellulose. Whether the const.i.tutional difference between raw and bleached cotton, thus emphasised, is due to the group of components of the raw cotton, which are removed in the bleaching process, or to internal const.i.tutional changes determined by the bleaching treatments, is a question which future investigation must decide.
_The normal sulphocarbonate (viscose)._--In the industrial applications of viscose it is important to maintain a certain standard of composition as of the essential physical properties of the solution, notably viscosity. It may be noted first that, with the above-mentioned exception, the various fibrous celluloses show but slight differences in regard to all the essential features of the reactions involved. In the mercerising reaction, or alkali-cellulose stage, it is true the differences are considerable. With celluloses of the wood and straw cla.s.ses there is a considerable conversion into soluble alkali-celluloses. If treated with water these are dissolved, and on weighing back the cellulose, after thorough was.h.i.+ng, treatment with acid, and finally was.h.i.+ng and drying, it will be found to have lost from 15 to 20 p.ct. in weight. The lower grade of celluloses thus dissolved are only in part precipitated in acidifying the alkaline solution. On the other hand, after conversion into viscose, the cellulose when regenerated re-aggregates a large proportion of these lower grade celluloses, and the final loss is as stated above, from 5 to 7 p.ct.
only.
Secondly, it is found that all the conditions obtaining in the alkali-cellulose stage affect the subsequent viscose reaction and the properties of the final solution. The most important are obviously the proportion of alkali to cellulose and the length of time they are in contact before being treated with carbon disulphide. An excess of alkali beyond the 'normal' proportion--viz. 2NaOH per 1 mol.
C_{6}H_{10}O_{5}--has little influence upon the viscose reaction, but lowers the viscosity of the solution of the sulphocarbonate prepared from it. But this effect equally follows from addition of alkali to the viscose itself. The alkali-cellulose changes with age; there is a gradual alteration of the molecular structure of the cellulose, of which the properties of the viscose when prepared are the best indication.
There is a progressive loss of viscosity of the solution, and a corresponding deterioration in the structural properties of the cellulose when regenerated from it--especially marked in the film form.