Chapter 3

The author critically discusses the grounds of the now celebrated patent controversy, arising out of the conflict of the claims of German patent 85,564/1895 of the former, and English patent 4452/1890 of the latter. The author concludes that Lowe's specification undoubtedly describes the lustreing effect of mercerising in much more definite terms than that of Thomas and Prevost. These inventors, on the other hand, realised the effect industrially, which Lowe certainly failed to do, as evidenced by his allowing the patent to lapse. As an explanation of his failure, the author suggests that Lowe did not sufficiently extend his observations to goods made from Egyptian and other long-stapled cottons, in which class only are the full effects of the added lustre obtained.

Following these original patents are the specifications of a number of inventions which, however, are of insignificant moment so far as introducing any essential variation of the mercerising treatment.

The third section of the work describes in detail the various mechanical devices which have been patented for carrying out the treatment on yarn and cloth.

The fourth section deals with the fundamental facts underlying the process and effects summed up in the term 'mercerisation.' These are as follows:--

(a) Although all forms of fibrous celluloses are similarly affected by strong alkaline solutions, it is only the Egyptian and other long-stapled cottons--i.e. the goods made from them--which under the treatment acquire the special high lustre which ranks as 'silky.' Goods made from American cottons acquire a certain 'finish' and lustre, but the effects are not such as to have an industrial value--i.e. a value proportional to the cost of treatment.

(b) The lustre is determined by exposing the goods to strong tension, either when under the action of the alkali, or subsequently, but only when the cellulose is in the special condition of hydration which is the main chemical effect of the mercerising treatment.

(c) The degree of tension required is approximately that which opposes the shrinkage in dimensions, otherwise determined by the action of the alkali. The following table exhibits the variations of shrinkage of Egyptian when mercerised without tension, under varying conditions as regards the essential factors of the treatment--viz. (1) concentration of the alkaline lye, (2) temperature, and (3) duration of action (the latter being of subordinate moment):--

_______________________________________________________________________ | | | | | | | Concentration | | | | | | of lye (NaOH) | 5°B. | 10°B. | 15°B | 25°B | | | | | | | | | | | | | | Duration of | | | | | | | | | | | | action in | 1 | 10 | 30 | 1 | 10 | 30 | 1 | 10 | 30 | | | minutes | | | | | | | | | | | | | | | | | | | | | | | | Temperatures | Percentage shrinkages (Egyptian yarns) as under:-- | | as under:-- | | | | | | | | | | | | 2° | 0 | 0 | 0 | 1 | 1 | 1 | 12.2 | 15.2 | 15.8 | 19.2 | | 18° | 0 | 0 | 0 | 0 | 0 | 0 | 8.0 | 8.8 | 11.8 | 19.8 | | 30° | 0 | 0 | 0 | 0 | 0 | 0 | 4.6 | 4.6 | 6.0 | 19.0 | | 80° | 0 | 0 | 0 | 0 | 0 | 0 | 3.5 | 3.5 | 9.8 | 13.4 | |_______________|___|____|____|___|____|____|______|______|______|______| _______________________________________________________________________ | | | | | | Concentration | | | | | of lye (NaOH) | 25°B | 30°B | 35°B | | | | | | | | | | | | Duration of | | | | | | | | | | action in | 10 | 30 | 1 | 10 | 30 | 1 | 10 | 30 | | minutes | | | | | | | | | | | | | | | | | | | | Temperatures | Percentage shrinkages (Egyptian yarns) as under:-- | | as under:-- | | | | | | | | | | 2° | 19.8 | 21.5 | 22.7 | 22.7 | 22.7 | 24.2 | 24.5 | 24.7 | | 18° | 20.1 | 21.0 | 21.2 | 22.0 | 22.3 | 23.5 | 23.8 | 24.7 | | 30° | 19.5 | 19.0 | 18.5 | 19.5 | 19.8 | 20.7 | 21.0 | 21.1 | | 80° | 13.7 | 14.2 | 15.0 | 15.1 | 15.5 | 15.0 | 15.2 | 15.4 | |_______________|______|______|______|______|______|______|______|______|

The more important general indications of the above results are--(1) The mercerisation action commences with a lye of 10°B., and increases with increased strength of the lye up to a maximum at 35°B. There is, however, a relatively slight increase of action with the increase of caustic soda from 30-40°B. (2) For optimum action the temperature should not exceed 15-20°C. (3) The duration of action is of proportionately less influence as the concentration of the lye increases. As the maximum effect is attained the action becomes practically instantaneous, the only condition affecting it being that of penetration--i.e. actual contact of cellulose and alkali.

(d) The question as to whether the process of 'mercerisation' involves chemical as well as physical effects is briefly discussed. The author is of opinion that, as the degree of lustre obtained varies with the different varieties of cotton, the differentiation is occasioned by differences in chemical constitution of these various cottons. The influence of the chemical factors is also emphasised by the increased dyeing capacity of the mercerised goods, which effect, moreover, is independent of those conditions of strain or tension under mercerisation which determine lustre. It is found in effect that with a varied range of dye stuffs a given shade is produced with from 10 to 30 p.ct. less colouring matter than is required for the ordinary, i.e. unmercerised, goods.

In reference to the constants of strength and elasticity, Buntrock gives the following results of observations upon a 40^{5} twofold yarn, five threads of 50 cm. length being taken for each test(Prometheus, 1897, p. 690): (a) the original yarn broke under a load of 1440 grms.; (b) after mercerisation without tension the load required was 2420 grms.; (c) after mercerisation under strain, 1950 grms. Mercerisation, therefore, increases the strength of the yarn from 30 to 66 p.ct., the increase being lessened proportionately to the strain accompanying mercerisation. _Elasticity_, as measured by the extension under the breaking load, remains about the same in yarns mercerised under strain, but when allowed to shrink under mercerisation there is an increase of 30-40 p.ct. over the original.

The _change of form_ sustained by the individual fibres has been studied by H. Lange [Farberzeitung, 1898, 197-198], whose microphotographs of the cotton fibres, both in length and cross-section, are reproduced. In general terms, the change is from the flattened riband of the original fibre to a cylindrical tube with much diminished and rounded central canal. The effect of strain under mercerisation is chiefly seen in the contour of the surface, which is smooth, and the obliteration at intervals of the canal. Hence the increased transparency and more complete reflection of the light from the surface, and the consequent approximation to the optical properties of the silk fibre.

The work concludes with a section devoted to a description of the various practical systems of mercerisation of yarns in general practice in Germany, and an account of the methods adopted in dyeing the mercerised yarns.

RESEARCHES ON MERCERISED COTTON.

A. FRAENKEL and P. FRIEDLAENDER (Mitt. k.-k. Techn. Gew. Mus., Wien, 1898, 326).

The authors, after investigation, are inclined to attribute the lustre 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 lustre effects are not obtained unless the action of water is associated.

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 35°B. | 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 accumulated 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 pronounced 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 assuming 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 passes quantitatively through the cycle of treatments involved in solution as sulphocarbonate and decomposition of the solution with regeneration as structureless or amorphous cellulose (hydrate).

Analysis 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 mass, 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 homogeneous. 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 quantitative 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 homogeneous, 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 mass 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 quantitative 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 constitutional 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 constitutional 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 classes there is a considerable conversion into soluble alkali-celluloses. If treated with water these are dissolved, and on weighing back the cellulose, after thorough washing, treatment with acid, and finally washing 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. In regard to viscosity the following observations are typical:--

(a) A viscose of 1.8 p.ct. cellulose prepared from an alkali-cellulose (cotton) fourteen days old.

(b) Viscose of 1.8 p.ct. cellulose from an alkali-cellulose (cotton) three days old.

(c) Glycerin diluted with 1/3 vol. water.

a b b c Diluted with equal vol. water Times of flow of equal volumes from 112 321 103 170 narrow orifice in seconds

Similarly the cellulose in reverting to the solid form from these 'degraded' solutions presents a proportionate loss of cohesion and aggregating power expressed by the inferior strength and elasticity of the products. Hence, in the practical applications of the product where the latter properties are of first importance, it is necessary to adopt normal standards, such as above indicated, and to carefully regulate all the conditions of treatment in each of the two main stages of reaction, so that a product of any desired character may be invariably obtained.

Incidentally to these investigations a number of observations have been made on the alkali-cellulose (cotton) after prolonged storage in closed vessels. It is well known that starch undergoes hydrolysis in contact with aqueous alkalis of a similar character to that determined by acids [Béchamp, Annalen, 100, 365]. The recent researches of Lobry de Bruyn [Rec. Trav. Chim. 14, 156] upon the action of alkaline hydrates in aqueous solution on the hexoses have established the important fact of the resulting mobility of the CO group, and the interchangeable relationships of typical aldoses and ketoses. It was, therefore, not improbable that profound hydrolytic changes should occur in the cellulose molecule when kept for prolonged periods as alkali-cellulose.

We may cite an extreme case. A series of products were examined after 12-18 months' storage. They were found to contain only 3-5 p.ct. 'soluble carbohydrates'; these were precipitated by Fehling's solution but without reduction on boiling. They were, therefore, of the cellulose type. On acidifying with sulphuric acid and distilling, traces only of volatile acid were produced. It is clear, therefore, that the change of molecular weight of the cellulose, the disaggregation of the undoubtedly large molecule of the original 'normal' cellulose--which effects are immediately recognised in the viscose reactions of such products--are of such otherwise limited character that they do not affect the constitution of the unit groups. We should also conclude that the cellulose type of constitution covers a very wide range of minor variations of molecular weight or aggregation.

The resistance of the normal cellulose to the action of alkalis under these hydrolysing conditions should be mentioned in conjunction with the observations of Lange, and the results of the later investigations of Tollens, on its resistance to 'fusion' with alkaline hydrates at high temperatures (180°). The degree of resistance has been established only on the empirical basis of weighing the product recovered from such treatment. The product must be investigated by conversion into typical cellulose derivatives before we can pronounce upon the constitutional changes which certainly occur in the process. But for the purpose of this discussion it is sufficient to emphasise the extraordinary resistance of the normal cellulose to the action of alkalis, and to another of the more significant points of differentiation from starch.

_Chemical constants of cellulose sulphocarbonate (solution)._--In investigations of the solutions we make use of various analytical methods, which may be briefly described, noting any results bearing upon special points.

_Total alkali._--This constant is determined by titration in the usual way. The cellulose ratio, C_{6}H_{10}O_{5} : 2NaOH, is within the ordinary error of observation, 2 : 1 by weight. A determination of alkali therefore determines the percentage of cellulose.

_Cellulose_ may be regenerated in various ways--viz. by the action of heat, of acids, of various oxidising compounds. It is purified for weighing by boiling in neutral sulphite of soda (2 p.ct. solution) to remove sulphur, and in very dilute acids (0.33 p.ct. HCl) to decompose residues of 'organic' sulphur compounds. It may also be treated with dilute oxidants. After weighing it may be ignited to determine residual inorganic compounds.

_Sulphur._--It has been proved by Lindemann and Motten [Bull. Acad. R. Belg. (3), 23, 827] that the sulphur of sulphocarbonates (as well as of sulphocyanides) is fully oxidised (to SO_{3}) by the hypochlorites (solutions at ordinary temperatures). The method may be adapted as required for any form of the products or by-products of the viscose reaction to be analysed for _total sulphur_.

The sulphur present in the form of dithiocarbonates, including the typical cellulose xanthogenic acid, is approximately isolated and determined as CS_{2} by adding a zinc salt in excess, and distilling off the carbon disulphide from a water bath. From freshly prepared solutions a large proportion of the disulphide originally interacting with the alkali and cellulose is recovered, the result establishing the general conformity of the reaction to that typical of the alcohols. On keeping the solutions there is a progressive interaction of the bisulphide and alkali, with formation of trithiocarbonates and various sulphides. In decomposing these products by acid reagents hydrogen sulphide and free sulphur are formed, the estimation of which presents no special difficulties.

In the spontaneous decomposition of the solution a large proportion of the sulphur resumes the form of the volatile disulphide. This is approximately measured by the loss in total sulphur in the following series of determinations, in which a viscose of 8.5 p.ct. strength (cellulose) was dried down as a thin film upon glass plates, and afterwards analysed:

(a) Proportion of sulphur to cellulose (100 pts.) in original. (b) After spontaneous drying at ordinary temperature. (c) After drying at 40°C. (d) As in (c), followed, by 2 hours' heating at 98°. (e) As in (c), followed by 5 hours' heating at 98°.

a b c d e Total sulphur 40.0 25.0 31.0 23.7 10.4

The dried product in (b) and (c) was entirely resoluble in water; in (d) and (e), on the other hand, the cellulose was fully regenerated, and obtained as a transparent film.

_Iodine reaction._--Fresh solutions of the sulphocarbonate show a fairly constant reaction with normal iodine solution. At the first point, where the excess of iodine visibly persists, there is complete precipitation of the cellulose as the bixanthic sulphide; and this occurs when the proportion of iodine added reaches 3I_{2} : 4Na_{2}O, calculated to the total alkali.