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

Processes of resin manufacture.

The processes of and patents for the manufacture of tar-acid-formaldehyde resins are numerous. No attempt is made here to describe in detail the several processes of manufacture or the endless number of variations and modifications. In general the processes in operation may be designated (a) one stage wet, (b) two stage wet, and (c) dry.

The one-stage wet process consists in heating molecular proportions of tar acid and formaldehyde (40-percent solution) in the presence of an acid or alkaline catalyst. The formaldehyde is added all at once and the reaction proceeds with the elimination of water. The difficulty with this process is that of obtaining uniform batches because it cannot be controlled exactly.

The two-stage process is probably the one most widely used today and consists in introducing formaldehyde in two or more stages as the reaction progresses. Much better process control and more uniform results are so obtained. A soluble, fusible resin is formed from which the water is easily removed. Fillers and pigments may be added during the latter part of the operation.

The dry process is the least important and is used only where cast resins are being made. Light-colored, transparent resins are obtained and the operation is carried on to the final stage (C resin). In this process the aldehyde used is solid paraformaldehyde or hexamethylenetetramine. These materials are more costly than formaldehyde solution.

Proportions of raw materials used vary widely—Baekeland suggested 7 mols of formaldehyde and 6 mols of phenol (210 parts of 100-percent formaldehyde to 564 parts of phenol), with a yield of resin equivalent to 118 percent of the phenol. Larger proportions of formaldehyde are said to increase the yield to as much as 140 percent of the phenol.

Catalysts used to aid in the condensation of the reacting bodies may be acids or bases. Certain properties of the resins may be varied by the kind and quantity of catalyst used. Large proportions of basic or acidic catalysts may affect the filler or metal inserts. Basic catalysts used include caustic soda, caustic potash, ammonia, carbonates, and alkali sulphites. Acid catalysts are usually one of the mineral acids such as hydrochloric acid or sulphuric acid.

While formaldehyde in the form of a 40-percent solution is the principal aldehyde used with the tar acids, certain other aldehydes are used in small amounts. Among these are acetaldehyde, butyraldehyde, benzaldehyde, and others. Resins from furfural and phenol are discussed as “Furfural Resins,” page [51].