GENERAL PRINCIPLES FOR THE MANUFACTURE OF RAYONThe basic raw material of rayon is cellulose. Cellulose is the solid part or cell wall of plant life. Wood is composed almost entirely of cellulose. A special form in which it also occurs is the down or soft fibre around the seeds of certain plants. The latter form of cellulose is the purest known, and the processes that use this form obtain it from cotton seeds. As cotton fibre, is, in itself, an important textile, it is too valuable to be used for rayon, so its place is taken by what is known as cotton linters. The linters consist of short hairs which, after the removal of the longer cotton filaments, still remain on the seeds. Actually the linters are of the same substances as the cotton filaments; but they are too short for spinning into cotton yarn. At one time, these linters were left on the cotton seeds, as they could not be used for any other purpose; and a few of the Rayon Companies who produce the higher grade yarn have taken advantage of this form of cellulose, which, although cheap because it was a waste product, is the purest form of cellulose known.
The linters are removed from the cotton seed by a process called “ginning”. The Cotton filaments are pressed into bales and shipped in that form from their country of origin—usually from the U.S.A. Pine wood from Canada and Scandinavia is used to obtain the other form of cellulose used by the rayon industry. The logs are cut into six foot lengths and the bark removed. They are then cut into one inch wheels and broken up into small chips. Forty of those chips are then put into a “digester”—cylindrical boiler—chemicals are added and the chips boiled. They remain in the “Digester” for 24 hours. Then the chips are emptied into draining chests. From those they pass into sand traps—long narrow troughs in which they are cleansed of impurities. They are then bleached in large vessels called “Hollanders” and put on the drying machine—an endless belt of wire gauze. After being dried, they are compressed and cut into sheets. The mixture is then known as wood pulp and shipped, in cake form, to the rayon mills.
When the pulp sheets reach the mill, they are soaked in diluted caustic soda for several hours, and broken up into little