210 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1940 



ingredients were mixed together, and the product sheeted on a calen- 

 der, vulcanized, and then cut mechanically to form threads of rec- 

 tangular cross section. In the latex process the operation is con- 

 tinuous, the latex compound being introduced at one end of the 

 machine and the dried and vulcanized product being delivered from 

 the other. 



Latex provides a highly satisfactory medium for the introduction 

 of rubber in varying amounts into other materials or products. It 

 is now used in the manufacture of paper. In one process the latex 

 is introduced in the beater. In another process a specially prepared 

 paper is passed through a bath of latex. Latex is also used for the 

 manufacture of pile fabrics and a number of other products where 

 it is desirable to utilize a rubber dispersion of high concentration 

 and low viscosity, and where a rubber which is tough and of high 

 quality is required. 



The shipment of rubber in the form of latex has grown rapidly. 

 In 1923, 2,300 tons were shipped; in 1938, 22,950 tons. Although 

 this is small compared with the total, it is equal to the world's 

 production of rubber in 1890. 



SYNTHETIC RUBBERLIKE PLASTICS 



By the middle of the nineteenth century, owing to the develop- 

 ment of organic chemistry, there was great activity in synthesizing 

 from simpler materials those organic compounds which occur in 

 nature. As would be expected, rubber with its unique properties 

 excited the interest of a number of organic chemists, and a great 

 deal of work has been done in an endeavor to develop a practical 

 synthesis. In the strict sense of the term, no one has made synthetic 

 rubber; that is, no one has prepared a product identical in physical 

 and chemical properties with the natural product. However, a num- 

 ber of new products have been produced which are sufRcientl}'^ similar 

 to rubber to permit their use in place of rubber in certain products, 

 and wliich are sufficiently superior in certain respects to make such 

 use practical in spite of higher cost. These materials may conven- 

 iently be classified into two groups : Butadienoid polymers — that is, 

 those made by the polymerization of butadiene and similar com- 

 pounds ; and nonbutadienoid polymers. 



Butadienoid Polymers: These resemble rubber in that they are 

 unsaturated and vulcanizable. They are probably fairly close to 

 natural rubber in structure. 



Isoprene. — Bouchardat first polymerized isoprene. Tilden is com- 

 monly regarded as the first to show a method of synthesis because 

 he discovered that isoprene could be obtained from turpentine, an 

 independent source of raw material. This method is of no com- 



