YOUcan not make a silk purse out of a sows I ear is a familiar quotation. Its use, however, will probably be discontinued by the next generation, as silk is now made artificially by mechanical means out of material which, if not a product of the pork packers slaughter house, is about as low down in the aesthetic scale. Wood pulp made from spruce trees, or in fact from any variety of wood—is dissolved in various chemicals and the solution is spun into a beautiful lustrous yarn, the sheen and gloss of which outrivals the most costly cocoon silk. An industry of enormous proportions has been built up with the development of this new product, factories in Austria, France, Germany, and more recently in England turning out many thousands of pounds of the yarn every day. And at the present time an enormous plant is just starting to manufacture in this country (near Chester, Pa.) , making the same product. In certain textile lines, notably the braids and trimmings for women's dresses and hats and in knitted neckties, the artificial silk or wood silk as it is sometimes called has practically replaced the real article. Probably ninety per cent of the braids and passementerie now manufactured are wood silk, though the retail consumer seldom realizes this fact. The yarn is also used largely in tapestries and curtains and dress os, ile rios ris tr fbrics sl an almost limitless field which is being invaded by this latest triumph of man's ingenuity. True synthetic silk has been made by chemists, it is claimed, the product of the cocoon ei s ltel licte i every respect, chemical and physical, but this achievement, successful as it was as a scientific laboratory experiment, had no commercial value on account of the enormous cost of production. A Frenchman, Hilaire de Chardonnet by name, was the first to make wood silk on a commercial basis; and although he is now very wealthy, it is said that he went into bankruptcy several times before he was finally successful. Chardonnet used a solution of ni-tro-cellulose in which sulphuric ether is the solvent, and several of the largest of the European mills are still using his process or modifications of it. The second process to be developed commercially was based on the use of what is known as the cupram-monium solution of cellulose in which copper salts and ammonia are the solvents. A third cellulose solution was discovered about twenty years ago by the English chemists, Cross and Bevan, and “viscose,” as it is called, is now rated as the best of them all for making the artificial filaments. The nitro-cellulose process depends on the use of the same solution that is used for making celluloid and guncot-ton and the first yarn made from it was highly explosive and dangerous to handle being therefore impracticable as a commercial article. After numerous failures, however, the French inventor discovered a way of denitrating the finished yarn and thus made it no more explosive or inflammable than so much cotton or paper. A German chemist by the name of Lehner made further improvements in the Chardonnet process and now there are great factories at Besangon in France; at Frankfort, Germany, and Zurich, Switzerland, where thousands of pounds of Chardonnet silk are manufactured daily. The nitro cellulose solution, made by dissolving the wood pulp in ether, is squirted through exceedingly fine jets or capillary tubes of glass. As it emerges either into a water bath or into the air the cellulose originally held in solution partially solidifies and a gummy filament is the result. A number of these filaments, 12 to 20, are gathered together and twisted into a yarn in the same way that cocoon silk threads are spun or thrown together. The artificial silk threads, while still soft and gummy are then stretched on drums or reels and dried, during which process they take on the beautiful luster so eagerly sought for by silk manufacturers. The process of making viscose silk starts from an alkaline solution of cellulose. The wood or cotton pulp is treated with caustic soda until a merceriza-tion somewhat similar to the chemical reaction in mercerizing cotton yarn has taken place. But the decomposition is carried much farther in making viscose. Bisulphide of carbon is then added to the partially decomposed pulp and the fibrous nature of the material disappears, altogether leaving a gummy mass which passes into a perfect solution when weak caustic liquor is added. For spinning the viscose solution somewhat different apparatus has been developed from that used for the earlier processes. All mechanical impurities, etc., are removed from the viscose solution by filtering the same through cotton wadding and cheese cloth. The clear solution then passes to a small platinum cap in which are drilled 15 or 18 holes approximately 4/1000 inch in diameter. The cap is immersed in an acid bath and the alkali in the viscose as it emerges from the spinneret is neutralized by the acid, the particles of cellulose coming together into 15 or 18 filaments according to the number of holes in the cap. Instead of being wound upon a reel at this point these delicate threads are dropped over a bobbin or pulley wheel into a small hole in the top of a rapidly revolving spinning box. This box turns at some 1,500 revolutions per minute, and the centrifugal force throws the filaments away from the center and winds them up in a cake, also putting a slight twist into the resultant yarn. The yarn is then reeled into bundles or skeins on a regular silk winder, being drawn from the inside of the cake. The advantage of this method of spinning the soluble cellulose, as compared with former methods in which the filaments were reeled into skeins as soon as spun, is the delicacy of the apparatus. The filaments, until they have been stretched and dried, are exceedingly frail and the less they are handled, the more perfect the yarn produced. All of the artificial silks take the same dyestuffs as cotton and are readily dyed, the luster being brilliantly accentrated especially by certain shades. Care has to be taken, however, while the skeins are wet as the filaments loose much of their strength while in this condition. The cellulose is very hygroscopic and after absorbing a large percentage of water, swells up and its physical structure is much weakened. But as soon as the yarn dries again it is as strong as ever, and the luster returns with all of its original brilliancy. The appended table, prepared by Haller, a French expert, shows some interesting figures obtained as the result of strength tests with various samples. All the forms of soluble cellulose are progressive solutions, the chemical reaction being continuous, and great care has to be taken to spin the mixtures at exactly the right moment to get the best results. In consequence, a fixed temperature is necessary for all rooms in which the solutions are mixed and aged. The artificial silk filaments when dry are of almost incredible fineness, one pound of yarn of some sizes containing as many as six hundred miles of individual filaments. The bulk of the yarn spun contains about 33,000 yards to the pound, 18 filaments being twisted together to form the yarn. A conservative estimate of the total length of the filaments produced daily at the present time by the world's factories is considerably over 3,000,000 miles every 24 hours. Cotton pulp is used instead of wood pulp in some of the foreign artificial silk factories and has been experimented with extensively in the United States, but wood pulp seems to be considered more suitable. At the present time about 20 per cent of the world's consumption of silk yarn is the artificial product. Many millions in money have been expended in Europe and America in the perfection of the various processes for spinning artificial silk, and as is usual in the development of a new industry, the inventors and original pioneers as a rule have reaped but a small share of the profits. The first American group to exploit viscose expended over $1,000,000 in experimenting, without obtaining any return whatever. Absolute Strength in Kilogrammes per Millimeter of Diameter Dry Wet Thread. Thread Cotton, ordinary thread................ 11.5 18.6 Cocoon or Real Silk raw (in the gum) .. 50.4 40.9 “' boiled off (gum removed) ......... 25.5 13.6 dyed black and weighted to 111 per cent ......... 12.0 8.0 Artificial Silk, French-Nitrocellulose- Chardonnet ..... 14.7 1.7 German - Nitrocellu- lose-Lehner ,..... 17.1 4.3 French - (Jupra - am- monium-Pauly . . 19.1 3.2. English-Viscose-Stearn 21.5 3.5 In another generation, however, the manufacture of artificial silk will probably be standardized, and as well understood as the wool and cotton industry of to-day.
This article was originally published with the title "Artificial Silk-A Textile Marvel" in Scientific American 105, 26, 576-577 (December 1911)