Compreg

Compreg is the name given to a stable form of phenolic resin-treated compressed wood. Its dimensional stability and its resistance to wood-destroying organisms, chemicals, and flow of electricity are practically the same as that of impreg. Most of the strength properties are increased about in proportion to the compression. It is tougher than impreg but not quite so tough as the original wood.

Because of the plasticizing action of the resin-forming chemicals on wood at temperatures used in hot pressing, the treated wood can be appreciably compressed under a pressure that scarcely compresses untreated wood at all. Because of this plasticizing action of the resin-forming chemicals on wood, it is possible to make a combination of resin-treated Compressed faces on an untreated and uncompressed core in a single assembly and compression operation.

When compreg is compressed to about one-third to one-half the thickness of normal wood, it assumes a glossy finish. A marred surface can be sanded and buffed to virtually its original glossy finish without the use If applied coatings. This is a feature of compreg that would make it desirable to use in furniture and flooring. Panels with a yellow-poplar compreg face, a yellow-poplar impreg back, and a Douglas-fir plywood core have been made for a flooring service test at our laboratory.

Compreg, largely in the form of thick, highly compressed panels, was manufactured by several companies for war use, chiefly in the manufacture of airplane propellers. Compreg has also been used to some extent for various connector and bearing plates, aerial antenna masts, and tooling jigs. Solid compreg shows promise for use in fan blades, pulley and gear wheels, bearings, and tooling jigs; shuttles, bobbins, and picker sticks for textile looms; high-strength electrical insulators; handles, such as for knives; and various decorative novelties.

Compreg has better strength properties than fabric-reinforced plastics, and it should be appreciably cheaper because veneer is cheaper than fabric, and about half as much resin is used in making compreg as is used in the fabric-reinforced plastics. Compreg may thus replace these plastics in a number of uses.

Impreg and compreg are made with synthetic resins of the phenolic (related to carbolic acid) type. A somewhat similar product can be made with chemicals that, under conditions comparable to those used in manufacturing impreg, form resins of the urea type within the wood. Treatment of wood with these urea-resin chemicals was pioneered by the Forest Products Laboratory, but research was suspended during the war because the phenolic resins appeared more promising. Commercial development of urea treatments was undertaken elsewhere, however, with great fanfare. The laboratory later resumed research with these chemicals to determine whether the properties of wood so treated are as markedly improved as the publicity about the commercial products set forth. This newer research has demonstrated that, on the whole, wood treated with phenolic resins has superior properties to that treated with urea at comparable cost of production.

The chief advantage of urea resins is that they are freer from color and taste than are the phenolic resins. On the other hand, under the most favorable conditions they are only about one-half as effective as phenolic resins in curbing the tendency of wood to shrink and swell with changes in its moisture content. Possible economies resulting from the relative cheapness of urea are in large part nullified by the fact that much more urea resin than phenolic resin is needed to attain even a moderate amount of stability in the dimensions of wood. It is no easier to treat wood with urea than with phenolic resins; assertions that urea can be used to treat dry wood in lumber sizes have not been substantiated by laboratory tests. Such properties as compressive strength and abrasion resistance are no better in wood treated with urea resins than in that treated with the phenolics. Decay, termite, and marine-borer resistance of urea-treated wood appears somewhat inferior to that obtained with phenolic resins.

These findings have led to the conclusion that, while urea treatment may be suitable for a few special applications, its usefulness in its present stage of development appears limited.