178 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1934 



the cellulose was converted to cellulose nitrate which was dissolved 

 in a mixture of alcohol and ether, and this solution, after careful 

 filtration, was squirted through fine orifices into a stream of warm 

 air which caused the solvent to evaporate, leaving fine filaments of 

 cellulose nitrate. The solvents were recovered and the fibers sub- 

 jected to an alkaline saponification treatment for the purpose of 

 reducing their inflammability. This left them finally in the form 

 of regenerated cellulose. This process is now being used by only a 

 single company in the United States. 



Another process takes advantage of the solubility of cellulose in 

 cuprammonium solutions. In this case the deep blue, viscous cellu- 

 losic solution passes from the fine orifices directly into a liquid regen- 

 erating bath which may be either a dilute acid or a dilute alkali. 

 After being freed from copper, these fibers also are composed of 

 regenerated cellulose. 



The process by which at least 80 percent of the artificial silk is 

 produced today, is the viscose process. In its barest outline it con- 

 sists in treating purified cellulose with caustic soda solution, followed, 

 after a suitable aging period, by treatment with carbon bisulfide 

 which produces a cellulosic compound soluble in dilute alkali. This 

 also is ripened and then squirted into dilute sulfuric acid which 

 breaks down the soluble compound and regenerates the cellulose. 



In all of these three processes it will be noted that the finished 

 fibers are composed of a modified cellulose. In the fourth commer- 

 cial process and the one which just now is expanding at the most 

 rapid rate, the cellulose is converted into cellulose acetate and the 

 finished fibers are composed of the same material. The solvent is 

 usually acetone and the solution is ejected from the orifices into a 

 stream of air in which the acetone evaporates and from which it is 

 recovered. One of the advantages of this process is that the fibers 

 require no further chemical purification treatment before they are 

 ready for what might be called the textile operation of twisting. 



When artificial silk first appeared on the market it was rather 

 coarse and somewhat harsh in its feel. Since then, however, there 

 have been marked improvements in the strength of the fibers and, 

 also, there has been a general tendency toward reducing the size 

 of the individual filaments as well as the size of the threads. Per- 

 haps one of the most remarkable developments in the rayon industry 

 in recent years has been the marked increase in the demand for fibers 

 in which the normally high luster has been reduced. Originally 

 artificial silk achieved popularity because of its high luster, yet 

 today considerably more than half of all the rayon produced has 

 the luster more or less reduced. 



