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

Tensile strength.—The greatest internal force per unit of cross section which a material develops before failure under tension.[30]

Thermoplastic.—The property of softening under heat. All molding materials are thermoplastic at the initial application of heat. One class (the so-called thermoplastics) remains soft permanently under heat; the other (thermosetting), after first softening, sets or cures more or less quickly to a more solid form. A practical distinction is that with the first class the mold must be cooled before the molded article is removed, but not with the second. A thermoplastic substance is adequately rigid at normal temperatures and under ordinary conditions of stress but is capable of deformation under heat and pressure.

Thermosetting.—The property of undergoing a chemical change when heated whereby a hardened product is obtained. Property most pronounced in phenol and urea formaldehyde resins and less so with alkyds. A thermosetting substance possesses initially the properties of a thermoplastic but under the influence of heat undergoes chemical change so that it is no longer thermoplastic but becomes permanently infusible.

Viscosity.—Internal friction or resistance to change of form of a liquid. The constant ratio of shearing stress to rate of shear.

Water-absorption.—Amount of water taken up when exposed to humid conditions or when immersed. Both rate of absorption and total absorption are important, also change in dimensions. A certain amount of absorbed water may improve mechanical properties but usually weakens electrical characteristics.

FOOTNOTES

[1] A glossary of technical terms is included in [appendix F.] p. [160] of this report. There are, however, certain fundamental terms which it would be advisable to have clearly in mind at this point.

[2] Shellac is a substance secreted by lac insects feeding on certain types of hardwood trees.

[3] Journal of the Society of Chemical industry, 1901. Vol. 20, p. 1075.

[4] Current sales prices in the United States average between 7 and 10 cents per pound and any imports would be dutiable under the provisions of par. 28 of the Tariff Act of 1930 at 45 percent ad valorem based on American selling price plus 7 cents per pound. Based on an American selling price of 7 cents per pound, the import duty would be slightly more than 10 cents per pound, while on an American selling price of 10 cents per pound the duty would be 11.5 cents per pound.