Science in the Service of Man — Clothes Made of Wood

Some readers, and especially the ladies, may be surprised when they learn that many garments, particularly summer ones, have been woven from threads made of wood and cotton. That is because wood and cotton are the two raw materials for the manufacture of what we call 'artificial silk' or 'vegetable silk.'

The threads of vegetable silk (or what is known in the market by the name 'rayon' — 'Rayon') are placed in the class of semi-artificial threads, to distinguish them from purely artificial threads, such as nylon threads, and from purely natural threads, such as wool, silk, and linen. Artificial silk, then, is the result of the combined efforts of nature and man. Nature provides the raw materials, and man, with his knowledge, gathers them together to make of them a new triumph in the world of science and industry.

As regards chemical composition, the threads of vegetable silk closely resemble cotton threads, for they are all composed of the substance 'cellulose.' Clean cotton contains more than 95 percent cellulose, while wood contains about 40 percent of this substance.

Turning Wood into Silk

To manufacture vegetable silk, the wood is cut into small pieces and mixed with a large quantity of water containing certain sulfur compounds; the cellulose then separates from the other materials, because cellulose does not dissolve in this sulfurous solution, whereas the other foreign materials do dissolve in it. When the cellulose has separated from these foreign materials, it is dried and then placed in a solution of qatrun (that is, caustic soda) (Soude Caustique) for a period not exceeding sixty minutes, at a temperature of 18 degrees centigrade. The cellulose absorbs the caustic-soda solution and swells, or 'fluffs up,' as cotton, for example, 'fluffs up' when it absorbs water. The soda solution is then removed by filtering, and the cellulose is transferred to large vessels, where it is left for two days to 'ripen.'

After this period has elapsed, the cellulose is mixed with a liquid called carbon sulfur, or carbon sulfide (Sulfure de Carbon), a liquid made from carbon and sulfur by mixing these two elements in special vessels under the effect of high heat, whereupon the atoms of carbon unite with the atoms of sulfur to form the liquid referred to.

When the cellulose is mixed with the carbon sulfide, a chemical reaction takes place between these two substances, resulting in a yellow substance resembling damp straw in appearance. It is taken to special vessels, where a solution of caustic soda is added to it, and the whole is mixed well; this yellow cellulose substance then dissolves in the solution, which now becomes a thick, blended liquid, left for several days before it becomes fit for use in the next stage of its manufacture.

The cellulose, then, has now dissolved; and if we wish to extract it from the dissolved state, we have only to mix this thick liquid with another liquid, or liquids, in which cellulose does not dissolve. To reach this end, the thick liquid is forced through a tube ending in fine holes. The end of this tube is placed in a vessel containing a solution containing sulfuric acid (acide Sulfurique) and sodium sulfate (Sulfate de Soude). When the liquid is forced through these fine holes, it comes out as viscous threads which find themselves in a medium in which cellulose does not dissolve; it is thus precipitated as fine threads, which are wound on reels prepared expressly for this purpose.

When the winding on the reels is finished, the threads are dried well and then placed in special cabinets, where a current of hot air passes over them. These threads are then transferred from their old reels to new ones of conical shape (forme conique), for use in knitting stockings and underclothing, or they are made up into skeins or hanks for use in weaving cloth. In their passage from the old reels to the new ones they are stretched, gaining in strength and luster and becoming as soft as silk.

The threads are graded according to the fineness of the thread, and for this purpose what is called the denier scale is used. The denier is an agreed unit signifying the weight in grams of a thread nine thousand meters in length. When it is said, for example, that nylon or silk stockings are made of '40' or '51' denier thread, this means that if we took a thread nine kilometers long and weighed it, we should find that it weighs 40 or 51 grams. Hence the smaller the number, the finer the thread. In the manufacture of the various kinds of cloth, threads of various gauges, from 40 to 450 denier, are used.

The manufacture of vegetable silk from cotton follows many of the stages through which the manufacture of silk from wood passes, except that the solution in which the cotton is dissolved differs from the solution in which the wood is dissolved. While wood is dissolved in a solution of caustic soda, cotton requires a solution of ammonia containing copper oxide; this too yields a thick, viscous liquid, which is forced through the perforated tube into a vessel consisting of water alone. The threads are then stretched and taken to a second vessel containing sulfuric acid. From here the same operations described above are followed.

This artificial silk is often used together with genuine silk in the weaving of textiles, producing fabrics as strong as genuine silk but cheaper in price than fabrics of pure silk. And nothing shows more clearly how widespread the use of this new kind of silk has become than the statistics which showed that the factories of America alone produce more than 150,000 tons a year of this new industrial material.