Synthetic resins and their raw materials / A survey of the types and uses of synthetic resins, the organization of the industry, and the trade in resins and raw materials, with particular references to factors essential to tariff consideration. Under the general provisions of section 332, title III, part II, Tariff act of 1930.

by United States Tariff Commission

5. UREA RESINS

One of the most important series of thermosetting resins is the group made by condensing urea and formaldehyde. As early as 1897 it was discovered that an amorphous condensation product was obtained from the reaction of urea and formaldehyde. The clear glass-like mass obtained led to considerable research work toward the development of a substitute for glass. It was found, however, that the resin obtained absorbed moisture, resulting in a dimming of its luster, and that on standing for a time, the condensation continued producing cracks, fissures, and disfigurements in the molded article. In 1926 a successful commercial product was developed in England by the use of thiourea. Cost of production, however, was high. The addition of thiourea gave the product greater strength and water resistance than that obtained with urea alone but retarded the rate of cure. Also the sulphur present attacked steel molds, which necessitated the use of expensive chromium plated or stainless steel molds.

About 1929 the first successful straight urea product was perfected in the United States. It was found that a filler, such as highly refined alpha cellulose, minimized the stresses. The filler (as much as 30 to 40 percent is usually incorporated), destroys the transparency but permits the manufacture of translucent articles in a wide range of color. Many of the colors possible with the urea resins, particularly the light shades, cannot at present be obtained in molded tar-acid resins.

An interesting fact concerning these resins is that they are produced indirectly from four gases: Ammonia, carbon dioxide, hydrogen, and carbon monoxide. Ammonia and carbon dioxide react to form urea, and hydrogen and carbon monoxide yield methyl alcohol which is converted to formaldehyde.