For several years before the beginning of actual warfare with Great Britain, Germany had fostered an intensive study of so-called 'Ersatz' (substitute) materials and many of her large chemical factories had turned to the manufacture of plastics as part of the program of war preparation.
With the entrance of the United States and Japan into the war on Dec. 7, 1941, the role of the former as arsenal for the Allies took on a far broader significance. Shortages of many raw materials began to appear, the list of critical materials became ever and ever larger, and the application of plastics to replace critical metals became increasingly necessary. Moreover, it was found that plastics could fulfill many requirements for which no other materials are suitable.
Because of this sudden strain on available capacity it is not surprising that shortage of many materials soon developed. Early in 1942 the United States Government placed various plastics under priority orders and by the end of the year changed this regulation to strict allocation, so that plastics for nonessential civilian use became almost unobtainable. However, new production facilities were planned, and by the middle of 1943 the capacity for making many plastics will be nearly double that of 1941.
Obviously production figures from enemy countries are not available, in fact, not even from our allies; but based upon United States figures, the 1942 world production of plastics and plastic resins must have reached the staggering figure of 1,000,000,000 lb. At the time of writing this article it is too early to give accurate 1942 figures, but estimates place the value of plastics in the United States as above $450,000,000. We can give reasonably accurate figures for the production of plastics and plastic resins in the United States for 1941, which was approximately 500,000,000 lb. with a value of $160,000,000. Of this amount, about 200,000,000 lb. were used for coatings and adhesives, leaving 300,000,000 lb. as the figure for the group ordinarily classified as plastics.
It is difficult to say in what field plastics have been of the greatest value to the prosecution of the war, but it is certain that in aircraft construction a great deal of aluminum was saved and much plastic was used where no metal was suitable. It is conservatively estimated that the average airplane contains about 200 plastic parts, mostly phenol or urea formaldehydes.
With the above resins as bonding adhesives, large quantities of plywood were used in such places as wings and fuselages in trainer planes, in pulleys, gears, instrument parts and interior fittings. Plywood was also used to great advantage as a substitute for the metal formerly used for machine tools and aircraft drill jigs. Another important and ingenious replacement was that of airplane engine parts previously made of sheet aluminum. These were made of cotton impregnated with phenol formaldehyde and molded into the desired form. Pilot and passenger bucket seats were also made from the same material.
Molded phenolics, usually strengthened by fabric fillers, found extensive use in range finders, oil pump bearings, and propellors. An outstanding advantage of a phenolic propellor is the ease of repair. Various parts of machine tools applied to aircraft making were also made from molded phenolic. These parts were handles, control wheels and knobs, which were made easily distinguishable one from another by using different colored plastics.
The use of acrylic resin in the form of methyl methacrylate which had already found wide application in airplanes was greatly extended. This material became practically indispensable as the transparent sheeting for forming bomber noses, turret tops, domes, cockpit enclosures and other special equipment. It protects the pilot and crew from the weather and the rushing wind and at the same time enables them to enjoy complete vision in all directions. The capacity for making the required methyl methacrylate sheeting was largely expanded, with the unfortunate limitation that large amounts of stainless steel were required.
Nearly as important as the turrets, etc., is the methyl methacrylate being made for tank windows, antenna housings, reflectors for military vehicles, radio parts, marine-engine water strainers, blackout buttons, spotlights, lamps, batteries, gauge glasses, and many similar uses.
In addition to aircraft applications, many other war and essential civilian needs were supplied. For example, plastic-bonded plywood was used for helmet liners, warship steering tubes, and pigeon crates. Phenol formaldehyde was made into washing-machine agitators, electric fans, brake linings, water-meter disks, outboard-motor parts, vacuum cleaners, Venetian blinds, stair treads, camera cases, school desks and chairs.
The vitally important application of nylon as replacement for the silk formerly used in parachutes, while not strictly a plastics application, is well supplemented by the use of nylon monofilament in airplane-engine polishing brushes, paintbrushes for the Army and Navy, surgical sutures and other essential bristling applications.
The paintbrush development alone is a veritable fairy story in which the hog is not only equalled but outdone. Hog bristles grow with a natural taper and the ends split into smaller hairs or 'flags,' useful in the painting art because of their ability to hold and spread evenly a greater amount of paint than a straight unflagged bristle or filament. The nylon filament manufacturer succeeded in making an artificial taper and flag which, while still retaining nylon's superior wearing qualities, are at least three times longer than natural bristles.
Melamine-formaldehyde, because of its high resistance to heat and inertness to fruit juice acids, fats, and oils, was used in increasing amounts. In Great Britain its price was reduced to three shillings per pound, and it found use there for buttons on R.A.F. uniforms, for colored furniture casters, cork replacements, soap dishes, bath spray nozzles, and photograph developing tanks.
An interesting use of urea formaldehyde in Great Britain was in the manufacture of 10,000,000 cups and saucers for the Army.
Cellulose acetate-butyrate, because of its resistance to moisture, enjoyed a large market with an estimated United States production of 7,000,000 lb. This thermoplastic resin, as well as cellulose acetate, found application in many aircraft parts where the strength of fabric-filled phenol formaldehyde was not required. Cellulose acetate in the form of transparent sheeting was used in glider and motorcycle windshields, windows for blimps, and because of the scarcity of methyl methacrylate, acetate was used for the transparent enclosures of trainer and observation planes and in many auxiliary and secondary construction points. In England it was made into transparent tanks to hold deicing fluid in Lancaster bombers. Other uses were plumbing fixtures, shatterproof window coatings, wire insulation in the form of tape, cork for speaker field coils and bobbins, identification tags, lenses for gun sights, clothespins, fish-net floats, salt and pepper shakers, laboratory windows, rifle trigger guards, and fluorescent instrument panels. This latter application is of great value to pilots because a very small source of infra-red light can be used to illuminate instrument panels without making the plane visible to the enemy. Heavy transparent sheets were installed as machine guards and safety devices in many munitions plants.
An interesting use of cellulose acetate was in the form of army bugles. Here ten ounces of cellulose acetate replaced two pounds of brass which had been required to make a twenty ounce bugle. Cellulose acetate and other thermoplastics also replaced the brass in a large variety of garden-hose fittings.
In Great Britain a type of plastic not entirely new, but a recent arrival, consists of three parts hydrolyzed lignocellulose and one part phenol formaldehyde, and it was used for fuse covers and plugs, bayonet scabbards and fire control panels.
The application of styrene to the manufacture of synthetic rubber started the construction of styrene plants with a capacity of over 200,000 tons per year. These plants were not producing to any great extent in 1942, and consequently a considerable portion of styrene normally available for plastics was used for pilot-plant production of synthetic rubber. A large amount of polystyrene did, however, find its way into molded combs for the armed forces, into signal lenses and into instrument dials.
A real newcomer, the so-called Columbia Resin CR-39 which is reported to be diallyl glycol dicarbonate, was used experimentally for transparent aircraft enclosures. It was unfortunately only in pilot-plant production in 1942. It has greater abrasion resistance than any other transparent plastic. Its monomer is relatively high-boiling and it can be polymerized under relatively low pressure with but little shrinkage.
One of the large plastic production groups is that of the vinyl resins which as polyvinyl chloride or as the chloride acetate copolymer found increased use as rubber substitutes. Approximately 12,000,000 lb. of these resins were thus used in the first six months of the year with a resultant saving of 18,000,000 lb. of rubber. It is believed that the production capacity of the copolymer containing over 92 per cent polyvinyl chloride will soon reach an annual rate of over 25,000,000 lb. This high molecular weight resin found valuable application in cable and wire insulation for shipboard use and special sheetings for aircraft accessories. The uses for a lower molecular weight resin having a polyvinyl chloride content of less than 92 per cent were rigid sheets for aircraft windshield and cockpit covers, waterproofed goods including hospital sheeting, engine covers, army raincoats, and binocular covers. Other applications were special protective paints, paper coatings, certain chemical tank linings, printing plates, and stirrup-pump hose. Germany made great strides in the use of polyvinyl chloride for valves, tubes, and conduits.
Ethyl cellulose and 'Saran' (polyvinylidine chloride) were produced in increased quantity. The former was used as flexible ice-cube containers, projection screens and motorcycle grips, and the latter was made suitable for injection molding.
Polyvinyl acetate was not only used as an intermediate in the manufacture of polyvinyl alcohol, polyvinyl acetals and vinyl chloride copolymers, but in its own right became a commercially important resin used primarily as an adhesive in water emulsion. These adhesives were used in bonding textiles, paper, cork, leather, etc., and also in the manufacture of printing inks, textile sizings, special sealing compounds for packages, shoe cements, and shoe impregnating compounds. Another vital use of this material is in the manufacture of sulfa drugs in which approximately 7 per cent of the current production is used.
Polyvinyl alcohol made from polyvinyl acetate was used for solvent resistant tubing, vibration dampers, shock absorbers, foot-pedal coverings, pulley facings, textile finishes, paper specialties, aircraft, automobile and refrigerant hose. Polyvinyl acetal, a condensation product of polyvinyl alcohol and aldehyde, was used for the waterproofing of raincoats, pontoons, and hospital sheetings, wire insulations, fuel-tank liners, gas masks, shatterproof glass for tanks and armored cars and laminating cement for sealing special envelopes and packages.
Thiokol, which was given great prominence as a rubber substitute, was also used as gasoline hose and in the bulletproof linings of gasoline fuel cells.
Because of the necessity for secrecy, a great many uses of plastic in the war effort may not be mentioned at the present time but will result in amazing revelations after the war has ended. As in the case of World War I, the intense pressure of necessity has compressed into months developments that might have taken years to achieve under less urgent conditions.
