The principal raw materials entering into the manufacture of urea resins are urea and formaldehyde. Formaldehyde has already been discussed (see pp. 133-135) and urea and thiourea are discussed below.

UREA

Urea is a white crystalline material, made by condensing carbon dioxide and ammonia under heat and pressure. It is an excellent fertilizer because of its high nitrogen content (46.6 percent) but this use is limited by its relatively high cost. Urea is an important synthetic resin material, being a constituent of urea-formaldehyde resins, known commercially under the trade names Beetleware and Plaskon.

Production of urea in the United States was started in 1916, when the German supply was cut off. In 1920 the domestic output was estimated at more than 200,000 pounds of fertilizer grade. Production ceased in 1922. Urea in ammonia solution for use in the manufacture of mixed fertilizer was first produced in 1933.

Crystal urea production in the United States was begun in 1935 and was largely made possible by the larger volume of urea in ammonia solution manufactured for fertilizer use. Prior to that time our requirements of crystal urea were imported, principally from Germany. Consumers of resin grade urea report that the domestic product is as good or better than the imported from Europe. The domestic output of crystal urea in 1936 showed an appreciable increase over that in 1935.

Statistics of imports of urea are given in table 88, showing imports of all grades combined. Up to 1931, and again in 1936, the imports were probably all for fertilizer use. From 1931 through 1935 some portion of the imports went into the manufacture of resins, but even in this period most of the imports were probably used in fertilizer.

Table 88.—Urea: United States imports for consumption, 1919-20 and 1923-37

Table 89 shows the sources of imports of urea in recent years. Germany has supplied from 90 to 100 percent of the total quantity, and Canada and the Netherlands the greater part of the remainder. There have been occasional shipments from Belgium, France, and Japan.

Table 89.—Urea: United States imports for consumption by countries, 1931 and 1933-37

Imports of urea enter the United States free of duty under paragraph 1793 of the Tariff Act of 1930. In spite of that fact a substantial production in the United States has been achieved. This is due, at least to a considerable extent, to the production of crude urea in ammonia solution, which is used in ammoniating superphosphates for fertilizer use. It is shipped by tank car but would be difficult to transport by ship. The volume market for this form of the product has aided in the production of crystal urea for both resin and fertilizer use.

THIOUREA

Thiourea (thiocarbamide) is a white crystalline solid, melting at 180° C. It is made commercially by treating a solution of calcium cyanamide with sulphur and ammonium sulphide or with hydrogen sulphide and ammonia. The principal uses of thiourea are in making intermediates and pharmaceuticals, as a photographic developer, as an insecticide, and in medicine. Because of the water resistance it imparts it was for some time widely used in urea resins. During the past few years, however, its use in resins has declined sharply owing to its deleterious action on ordinary molds and its slow rate of cure. In molding compounds, thiourea requires about 10 minutes curing time as compared with 3 minutes or less for urea resins and tar-acid resins. Since ways have been found to fabricate water-resistant urea resins without using thiourea, the consumption of thiourea in this use has declined.

There is no known commercial domestic production of thiourea.

Imports through the New York Customs District, according to invoice analyses made by the Tariff Commission, are shown in table 90. Thiourea is dutiable at 25 percent under paragraph 5 of the act of 1930.

Table 90.—Thiourea: United States imports through the New York Customs District, 1931-37