Researches on Cellulose Part 5

GROUP 1. The early history of the Chardonnet process is discussed and some incidental causes of the earlier failures are dealt with. The process having been described in detail in so many publications the reader is referred to these for details. [See Bibliography, (1) and (2), (3) and (4).] The denitrating treatment was introduced in the period 1888-90 and of course altogether changed the prospects of the industry; not only does it remove the high inflammability, but adds considerably to softness, l.u.s.tre, and general textile quality. In Table I will be found some important constants for the nitrocellulose fibre; also the fibre after denitration and the comparative constants for natural silk.

TABLE 1.

_______________________________________________________________________ Tenacity Elasticity (grammes) (% elongation) __________________________________________ ___________ ________________ Nitrocellulose according to Chardonnet German Patent No. 81,599 150 23 The same after denitration 110 8 Denitrated fibre moistened with water 25 -- Nitrocellulose: Bronnert's German Patent No. 93,009 125 28 The same after denitration (dry) 115 13 The same after denitration (wetted) 32 -- Natural silk 300 18 __________________________________________ ___________ ________________

1. Tenacity is the weight in grammes required to break the thread.

2. Elasticity is the elongation per cent. at breaking.

The numbers are taken for thread of 100 deniers (450 metres of 0.05 grammes = 1 denier). It must be noted that according to the concentration of the solution and variations in the process of denitration the constants for the yarn are subject to very considerable variation.

In regard to the manufacture a number of very serious difficulties have been surmounted. First, instead of drying the nitrated cellulose, which often led to fires, &c., it was found better to take it moist from the centrifugal machine, in which condition it is dissolved (5). It was next found that with the concentrated collodion the thread could be spun direct into the air, and the use of water as a precipitant was thus avoided.

With regard to denitration which is both a delicate and disagreeable operation: none of the agents recommended to subst.i.tute the sulphydrates have proved available. Of these the author mentions ferrous chloride (6), ferrous chloride in alcohol (7), formaldehyde (8), sulphocarbonates. The different sulphydrates (9) have very different effects. The calcium compound tends to harden and weaken the thread. The ammonia compound requires great care and is costly. The magnesium compound works rapidly and gives the strongest thread. Investigations have established the following point. In practice it is not necessary to combine the saponification of cellulose ester with complete reduction of the nitric acid split off. The latter requires eight molecules of hydrogen sulphide per one molecule tetranitrocellulose, but with precautions four molecules suffice. It is well known that the denitration is nearly complete, traces only of nitric groups surviving.

Their reactions with diphenylamine allow a certain identification of artificial silks of this cla.s.s. Various other inventors, e.g. Du Vivier (10), Cadoret (11), Lehner (12), have attempted the addition of other substances to modify the thread. These have all failed. Lehner, who persisted in his investigations, and with success, only attained this success, however, by leaving out all such extraneous matters. Lehner works with 10 p.ct. solutions; Chardonnet has continually aimed at higher concentration up to 20 p.ct. Lehner has been able very much to reduce his pressures of ejection in consequence; Chardonnet has had to increase up to pressures of 60 k. per cm. and higher. The latter involves very costly distributing apparatus. Lehner made next considerable advance by the discovery of the fact that the addition of sulphuric acid to the collodion caused increase of fluidity (13), which Lehner attributes to molecular change. Chardonnet found similar results from the addition of aldehyde and other reagents (14), but not such as to be employed for the more concentrated collodions. The author next refers to his discoveries (15) that alcoholic solutions of a number of substances, organic and inorganic, freely dissolve the lower cellulose nitrates. The most satisfactory of these substances is chloride of calcium (16). It is noted that acetate of ammonia causes rapid changes in the solution, which appear to be due to a species of hydrolysis. The result is sufficiently remarkable to call for further investigation. The chloride of calcium, it is thought possible, produces a direct combination of the alcohol with a reactive group of the nitrocellulose.

The fluidity of this solution using one mol. CaCl_{2} per 1 mol.

tetranitrate (17) reaches a maximum in half an hour's heating at 60-70C. The fluidity is increased by starting from a cotton which has been previously mercerised. After nitration there is no objection to a chlorine bleach. Chardonnet has found on the other hand that in bleaching before nitration there is a loss of spinning quality in the collodion. The author considers that the new collodion can be used entirely in place of the ordinary ether-alcohol collodion. With regard to the properties of the denitrated products they fix all basic colours without mordant and may be regarded as oxycellulose therefore. The density of the thread is from 1.5 to 1.55. The thread of 100 deniers shows a mean breaking strain of 120 grammes with an elasticity of 8-12 p.ct. The cardinal defect of these fibres is their property of combination with water. Many attempts have been made to confer water-resistance (18), but without success. Strehlenert has proposed the addition of formaldehyde (19), but this is without result (20). In reference to these effects of hydration, the author has made observations on cotton thread, of which the following table represents the numerical results:

Breaking Strain Mean of 20 experiments

Skein of bleached cotton without treatment 825 Skein of bleached cotton without treatment, but wetted 942 Ditto after conversion into hexanitrate, dry 884 The above, wetted 828 The cotton denitrated from above, dry 529 The cotton denitrated as above and wetted 206

The author considers that other patents which have been taken for spinning nitrocellulose are of little practical account (21) and (22).

The same conclusion also applies to the process of _Langhans_, who proposes to spin solutions of cellulose in sulphuric acid (23) (24) and mixtures of sulphuric acid and phosphoric acid.

GROUP 2. _l.u.s.tra-cellulose._--Thread prepared by spinning solutions of cellulose in cuprammonium.

This product is made by the Vereinigte Glanzstoff-Fabriken, Aachen, according to a series of patents under the names of H. Pauly, M. Fremery and Urban, Consortium mulhousien pour la fabrication de fils brillants, E. Bronnert, and E. Bronnert and Fremery and Urban (1). The first patent in this direction was taken by Despeissis in 1890 (2). It appears this inventor died shortly after taking the patent (3) The matter was later developed by Pauly (4) especially in overcoming the difficulty of preparing a solution of sufficient concentration. (It is to be noted that Pauly's patents rest upon a very slender foundation, being antic.i.p.ated in every essential detail by the previous patent of Despeissis.) For this very great care is required, especially, first, the condition of low temperature, and, secondly, a regulated proportion of copper and ammonia to cellulose. The solution takes place more rapidly if the cellulose has been previously oxidised. Such cellulose gives an 8 p.ct. solution, and the thread obtained has the character of an oxycellulose, specially seen in its dyeing properties. The best results are obtained, it appears, by the preliminary mercerising treatment and placing the alkali cellulose in contact with copper and ammonia. (All reagents employed in molecular proportions.) The author notes that the so-called hydrocellulose (Girard) (5) is almost insoluble in cuprammonium, as is starch. It is rendered soluble by alkali treatment.

GROUP 3. _l.u.s.tra-cellulose_ prepared by spinning a solution of cellulose in concentrated chloride of zinc.

This solution has been known for a long time and used for making filaments for incandescent lamps. The cellulose threads, however, have very little tenacity. This is no doubt due to the conditions necessary for forming the solution, the prolonged digestion causing powerful hydrolysis (1). Neither the process of Wynne and Powell (2) nor that of Dreaper and Tompkins (3), who have endeavoured to bring the matter to a practical issue, are calculated to produce a thread taking a place as a textile. The author has described in his American patent (4) a method of effecting the solution in the cold, viz. again by first mercerising the cellulose and was.h.i.+ng away the caustic soda. This product dissolves in the cold and the solution remains unaltered if kept at low temperature.

Experiments are being continued with these modifications of the process, and the author antic.i.p.ates successful results. The modifications having the effect of maintaining the high molecular weight of the cellulose, it would appear that these investigations confirm the theory of Cross and Bevan that the tenacity of a film or thread of structureless regenerated cellulose is directly proportional to the molecular weight of the cellulose, i.e. to its degree of molecular aggregation (5).

GROUP 4. 'Viscose' silks obtained by spinning solutions of xanthate of cellulose.

In 1892, Cross and Bevan patented the preparation of a new and curious compound of cellulose, the thiocarbonate (1) (2) (3). Great hopes were based upon this product at the time of its discovery. It was expected to yield a considerable industrial and financial profit and also to contribute to the scientific study of cellulose. The later patents of C.

H. Stearn (4) describe the application of viscose to the spinning of artificial silk. The viscose is projected into solutions of chloride of ammonium and washed in a succession of saline solutions to remove the residual sulphur impurities. The author remarks that though it has a certain interest to have succeeded in making a thread from this compound and thus adding another to the processes existing for this purpose, he is not of opinion that it shows any advance on the l.u.s.tra-cellulose (2) and (3). He also considers that the bisulphide of carbon, which must be regarded as a noxious compound, is a serious bar to the industrial use of the process, and for economic work he considers that the regeneration of ammonia from the precipitating liquors is necessary and would be as objectionable as the denitration baths in the collodion process. The final product not being on the market he does not p.r.o.nounce a finally unfavourable opinion.

The author and the Vereinigte Glanzstoff-Fabriken after long investigation have decided to make nothing but the l.u.s.tra-cellulose (2) and (3). A new factory at Niedermorschweiler, near Mulhouse, is projected for this last production.

BIBLIOGRAPHY

_Introduction_

(1) Bull. de la Soc. industr. de Mulhouse, 1900.

(2) Reaumur, Memoire pour servir a l'histoire des insectes, 1874, 1, p.

154.

(3) English Pat. No. 283, Feb. 6, 1855.

(4) Swinburne, Electrician, 18, 28, 1887, p. 256.

(5) Weston (Swinburne), Electrician, 18, 1887, p. 287. Eng. Pat. No.

22866, Sept. 12, 1882.

(6) German Pat. No. 3029. English Pat. No. 161780, April 28, 1884 (Swan).

(7) Wynne-Powell, English Pat. No. 16805, Dec. 22, 1884.

_Group I_

(1) German Pat No. 38368, Dec. 20, 1885. German Pat. No. 46125, March 4, 1888. German Pat. No. 56331, Feb. 6, 1890. German Pat. No. 81599, Oct.

11, 1893. German Pat. No. 56655, April 23, 1890. French Pat. No. 231230, June 30, 1893.

(2) Industrie textile, 1899, 1892. Wyss-Noef, Zeitschrift fur angewandte Chemie, 1899, 30, 33. La Nature, Jan. 1, 1898, No. 1283. Revue generale des sciences, June 30, 1898.

(3) German Pat. No. 46125, March 4, 1888. German Pat. No. 56655, April 23, 1890.

(4) Swan, English Pat. 161780, June 28, 1884. See also Bechamp, Dict. de Chimie de Wurtz.

(5) German Pat. No. 81599, Oct 11, 1893.

(6) Bechamp, art. Cellulose, Dict. de Chimie de Wurtz, p. 781.

(7) Chardonnet, addit. March 3, 1897, to the French Pat. 231230, May 30, 1893.

(8) Knofler, French Pat. 247855, June 1, 1895. German Pat. 88556, March 28, 1894.

(9) Bechamp, art. Cellulose, Dict. de Chimie de Wurtz. Blondeau, Ann.

Chim. et Phys. (3), 1863, 68, p. 462.

(10) Revue industrielle, 1890, p. 194. German Pat. 52977, March 7, 1889.

(11) French Pat. 256854, June 2, 1896.

(12) German Pat. 55949, Nov. 9, 1889. German Pat. 58508, Sept. 16, 1890.

German Pat. 82555, Nov. 15, 1894.

(13) German Pat. 58508, Sept. 16, 1900.

(14) French Pat. 231230, June 30, 1893.

(15) German Pat. 93009, Nov. 19, 1895. French Pat. 254703, March 12, 1896. English Pat. 6858, March 28, 1896.