VERSATILE Fluorine Plastics The r a p i d a c c e p t a n c e of fluoroplastics— c o u p l e d with their promising p o t e n t i a l uses, as y e t u n e x p l o i t e d — m a r k these materials as stars of special brightness in the plastics g a l a x y
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J? OR YEARS, chemists had been searching for new plastics that, to an unprecedented degree, could withstand attack by acids, alkalies, and scores of other reagents that swiftly destroyed conventional synthetics. They were searching for radically improved plastics that could b e exposed to
high temperatures without melting, charring, or bursting into flames—or t o s u b zero temperatures without turning brittle and shattering. At the same time, t h e y were looking for altogether new plastics with superior mechanical, electrical, a n d thermal properties—materials that could
Right. Teflon tetrafluoroethylene resin used for inserts in coaxial connectors. Far right. Both the dark packing rings and the white spacers are made of Teflon in this small proportioning pump. Below. The faces of this home sealer are covered with Teflon to prevent sticking. Below center. The rolls on this bread-molding machine are covered with Teflon, eliminating trie need for dusting-flour and rollscrapers and providing a thinner, more uniform sheet. As a valve packing in chemical processing equipment, Teflon is inert to virtually all chemicals, requires no lubrication, and may be used over a wide temperature range
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KEL-F Right. Vessel liner with nozzles fabricated from sheets and tubes of Kel-F to protect metal tower from nitric acid. Seams are being tested for possible leaks. The 18-foot-long liner was inflated for shipping by inserting a plastic bag within it to prevent strains on the Kel-F liner. Typical Kel-F uses include: injection-molded tubesocket base (below), machined fittings (below center), and compression-molded valve diaphragm
known with the exception of molten alkali metals and fluorine. Kel-F, an analog of polyethylene containing both fluorine and chlorine, resists all corrosive agents except molten alkali metals, fluorine, highly halogenated compounds, and various aromatics. In addition to their pronounced chemical resistance, both Teflon and Kel-F are able to withstand exposure to a broad range of temperatures extending all the way from —100° to -|-350 o F. in the case of Kel-F and from — 100° to + 5 0 0 ° F. in the case of Teflon. Because of the outstanding physical and chemical properties of these materials (resulting, in part, from their closely packed structures, in which each carbon is well shielded by halide atoms), fluoroplastics today are proving of vital importance in gaskets for reaction kettles, packing for valves, bellows-type expansion joints for piping, piston rings for pumps, and in a host of other applications. Because of their high electrical resistance, low dielectric loss factor, and zero water absorption, fluoroplastics have captured a prominent place in the nation's electrical industry. Major uses include
be employed effectively where plastics had always failed before. In the late 1930's, after years of research, such materials came into being. They were a versatile new group of polymers, the fluorine plastics. In the vanguard of earliest research on fluorine plastics in the U. S. were such researchers as William T. Miller of Cornell University and Roy J. Plunkett of D u Pont. Their work, carried on independently and, in part, simultaneously, sparked the entire advance of fluorine plastic chemistry. To Dr. Plunkett goes credit for the discovery of polytetrafluoroethylene—Teflon as manufactured by D u Pont and Fluon as manufactured by Britain's Imperial Chemical Industries. To Dr. Miller goes credit for the discovery of polychlorotrifluoroethylene plastic—Kel-F as manufactured by M. W. Kellogg Co. and Fluorothene as manufactured by Union Carbide and Carbon Corp. Today, the only two fluorine plastics manufactured in substantial quantities in the U. S. for general use are Teflon and Kel-F. Teflon, an analog of polyethylene containing fluorine in place of hydrogen, is able to resist attack by all corrosive agents VOLUME
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coatings for magnet wire, insulation for laxial cable, and supports for radar and FM antennas. Moreover, because practically nothing will stick to either Teflon or Kel-F, these polymers are also being put to widespread use on conveyor belts that handle sticky materials, on machinery used to heat-seal plastic films, and on the rollers and other components of breadmaking machinery. Extensive Research Programs Vast, multimillion-dollar research and production programs were undertaken by D u Pont and Kellogg in bringing fluoroplastics to the market place. At the outset, scores of key technical problems demanded solution. For example, ways had to be found not only to speed u p the polymerization of the starting materials but also to bring the rates and extents of polymerization into precise control. Over the years, numerous polymerization initiators were introduced, including oxygen, hydrogen peroxide, sodium persulfate, and organic peroxy compounds. Work went on continuously as researchers sought to improve the properties of the crude poly2689
mers and, a t t h e same time, simplify their conversion -to finished products. As a resrult of extensive research a n d manufacturing programs, enough Teflon and Kel-F were on h a n d during W o r l d War II to rperinit their widespread u s e b y the military. Of possibly even greater importance was the wartime availability of fluoroplastics for major research a n d production jobs in the atomic energyprogram . In particular, fluoroplastics played a vstal role in the Atomic Energy' Commission's uraniurxi-235 plant a t Oak Ridge. Dioring the w a r a n d in the years that followed, much of t h e impetus for the creation of new uses for fluoroplastics stemmed directly from trie must-be-met requirements o f AEC a n d t h e armed forces. T h e U. S . civilian market h a d its first look at fluoToplastics i n 1946. At t h e time, Teflon outrput came entirely from D u Pout's semi-works plant in Arlington, N. J. Now, however, Teflon is produced exclusively in D u Pont's full-scale commercial installation near Parkersburg, W . Va. Since the beginning, Kel-F has been produced at Kellogg's plant at Jersey City, N. J., w h e r e a new installation will b e completed late this year, bringing t h e company's total Kel-F capacity to over 1 million p o u n d s a year. ( See p a g e 2708 ) . Today, Du Pont produces Teflon powder, dispersions, tape, and finishes, while Kellogg's output includes Kel-F granular p o w d e r , dispersions, a n d a variety of Kel-F oils, waxes, a n d greases. T o independent manufacturers h a s gone t h e job of converting these raw materials into such finished prodiacts as fluoroplastic tubes, r o d s , sheets, a n d enamels. Molding Techniques AlthougH Kel-F m a y lack, in part, t h e chemical inertness a n d thermal stability of Teflon, its prime advantage over Teflon is the relative ease with which t h e polymer may be processed in conventional equipment by compression, injection, or extrusion techniques. On the other hand, none of these standard methods can b e applied to the molding of Teflon—a m a t e rial that, unlike ordinary plastics, does not melt oa: flo^v at elevated temperatures. W h e n i t conies to molding Teflon, t h e granular p o w d e r (SO to 50 m e s h ) must first be comipressed a t pressures of about 2000 pounds p e r square inch a n d then heated to temperatures above 620° F . ( t h e temperature at w h i c h t h e crystalline material is transformed into an amorphous g e l ) . ThLs technique, similar to metal sintering, fnas i t s distinct limitations. Not only is it relatively slow b u t it means t h a t t h e molding of Teflon products must b e limited to comparatively simple shapes. Moreover, the only way thin films could b e formed—at least i n the early days—was to shave tliem off cylindrical Teflon blocks. Initially, the production of Teflon enamels anad finishes was out of t h e question. Du JPont chemists w o r k e d on these problems For years i n a concerted effort
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I n the course of research on refrigerants, D u Pont's Roy Plunkett ( r i g h t ) /discovered Teflon u p o n cutting open a c y l i n d e r in w h i c h tetrafluoroethylene h a d polymerized. D r . Plunkett's laboratory coworkers i n c l u d e d J a c k Rebok (left) and Robert McHarness to improve the working characteristics of the crude polymer. Finally in 1949, D u Pont announced t h e development of aqueous dispersions of Teflon—a discovery t h a t promptly opened u p immense n e w fields for t h e promising fluoroplasticAt just about t h e same t i m e , Kellogg announced t h e availability of dispersions of Kel-F. W i t h these dispersions as starting materials, manufacturers could produce not only u n s u p p o r t e d fluoroplastic t a p e and film b u t enamels for wiring, coatings for glass fabrics, a n d industrial finishes that could be readily applied with conventional sprayers. W i t h these dispersions, containing 5 0 % solids in the case of Teflon a n d between 30 and 4 0 % solids in the case of Kel-F, fluoroplastic films u p to about 0.0015 inch in thickness can b e formed on solid surfaces. Thicker films t e n d to crack d u r ing the later baking operation. However, if thicker films are essential, these can b e built up in multiple layers if a b a k i n g operation is interspersed b e t w e e n t h e a p plication of each n e w fluoroplastic layer. Fluorine Plastics For C o a t e d Glass Fabrics Among t h e important n e w uses for Teflon a n d Kel-F m a d e possible b y t h e development of fluoroplastic dispersions are coated glass fabrics, w h i c h , unlike untreated materials, will not crack or become brittle even w h e n sharply creased at temperatures as low as —30° F . Currently, such fabrics are b e i n g employed in aircraft electrical systems a n d in such
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household items as ironing p a d s and drapes. Also p r o d u c e d from t h e disp e r s e d polymers a r e fluoroplastic tapes, of value to t h e chemical a n d electrical industries as a gasketing material a n d as a w r a p - o n insulation for motors, generators, a n d electrical cable. P r o d u c t Limitations Despite the impressive strides m a d e in recent years in t h e applications of fluoroplastics, n u m e r o u s technical problems rem a i n unsolved. F o r example, these polym e r s m i g h t prove of considerable value to t h e chemical industry as a corrosionresistant coating for reaction kettles if w a y s could b e f o u n d to improve the m e t h o d s of application and the physical a n d chemical properties of fluoroplastic films applied to t h e interiors of large reaction vessels. A n o t h e r deficiency of fluoroplastics is their limited elasticity, a p r o b lem that is b e i n g solved in a n u m b e r of specialized applications b y t h e i m b e d d i n g of a resilient m e t a l in the plastic itself. Still another p r o b l e m is the development of fluoroplastic coatings that can b e applied to a l u m i n u m a n d similar m e t a l s at t e m p e r a t u r e s b e l o w their transition point— t h e t e m p e r a t u r e at w h i c h t h e metal's tensile strength falls off sharply. Often another barrier to t h e use of fluoroplastics is price. At present, unfabricated Teflon sells for $5.50 a pound, w h i l e Kel-F r u n s t o $12 a pound. Alt h o u g h t h e prices of fluoroplastics h a v e declined markedly during t h e past few years (Teflon originally sold for $ 2 5 a p o u n d in 1944 a n d Kel-F for $29 a p o u n d in 1 9 4 7 ) , these materials are considerably
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more costly than many other plastics. In a great many applications, however, fluoroplastics, in the long run, are far cheaper than any other materials of construction —mainly because of their extended service life, which makes possible a minimum of maintenance costs both for materials and labor. Latest Applications Within the past year or two, new uses for Teflon and Kel-F have soared into prominence. For the laboratory, there are Teflon stopcocks and coated groundglass joints that won't stick, or undergo chemical attack. For the plant, there are
corrosion-resistant fluoroplastic components for plug valves that completely eliminate Tiietal-to-rnetal contact and, at the same time, require no lubrication. In addition, there are fluoroplastic components for diapfiragm valves and new types of Sruoroplastic packing that contain graphJte or asbestos or both. Whaat major new applications for fluoroplastics loom on the horizon? Pump impellers are one application. Another is industrial piping made of fluoroplastics in combination with glass fibers—piping not only zoiore chemically resistant than glass but aJso far less fragile. In the experimental stage are fluoroplastic-coated pa-
The Cover .
Roy Plunkett, Discoverer of Teflon, Wins Coveted John Scott A w a r d TN
1816, John Scott, a chemist of Edinburgh, Scotland—a man about whom practically nothing is known— gave to the city of Philadelphia $4000. With this sum, awards were to be presented to "ingenious men and women who make useful inventions." Over the years, the John Scott Award (originally $20, now $1000) has gone to such scientific notables as Madame Curie, Thomas Edison, Guglielmo Marconi, Orville Wright, Irving Langmuir, and Alexander Fleming. This month, another name was added—Roy J. Plunkett, chemist, discoverer of polytetrafluoroethylene or Teflon. To Dr. Plunkett this month went not only the award, the citation, and the scores of congratulations but also the John Scott Medal, a great copper disc simply inscribed: "To the most deserving." The discovery of Teflon goes back to 1938, when, as a young Du Pont chemist, just two years out of college, Dr. Plunkett was engaged in research on new fluorine-containing refrigerants. Among the many reagents stored in the laboratory at the time was tetrafluoroethylene—under ordinary pressures, a gas. By chance, Dr. Plunkett discovered one day that, although all of the tetrafluoroethylene gas had been discharged from one of the stored cylinders, the container weighed appreciably more than it did when empty. Cutting open the cylinder, Dr. Plunkett found, encrusted on the inner surface, a thick layer of a dense, white solid that, to the touch, seemed almost exactly like wax. Altogether unlike wax, however, the new material was able to withstand a wide range of temperatures despite exposure to virtually all of the most powerful corrosive rer gents known. The chance discovery of Teflon might never have been made if Roy Plunkett
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had not been the type of alert, trained obseo-ver who, seeing the unexpected, knew how to make the most of it. Dr. Plun&kett acquired part of the scientific training he needed at Manchester College in Indiana. After receiving his bachaelor's degree from Manchester in 193^, h e transferred to Ohio State University, where, at the completion of graduate research on carbohydrates, he received his Ph.D. in 1936. Throughout his college days, Dr. Plunkett worked his way through school, holding down odd jobs as a farm hand, clothing salesman, tutor, dishwasher, fount dry helper, graduate assistant, and part—time janitor in the university dormitories. Early Spadework Fresh out of college, Dr. Plunkett joined the Jackson Laboratory of the Du Pont Co. There he did much of the early spadework on Teflon. However, the job of perfecting Teflon and of extending its applications was left to others. Six months after Teflon was discovered, Plunkett accepted an appointmenL-t as chemical supervisor of Du Ponfc's tetraethyllead plant. Recognized by top management as a man. who knevr the ropes both technically and administratively, Dr. Plunkett was quickly upgraded in the Du Pont organization. -In 1945, he became superintendent of the TEL plant. Later, in 3.949, he was appointed superintendent of the Ponsol colors area and, in 1950, assistant manager of the Chambers Works. His associates these days have a way of referring to his tour of cltity in the colors department as "tha_t time when Roy was passing thro-ugh/' Ai: the first of this year, Dr. Plunkett became manager of the chemical development section of Du Pont's Organic
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per and fluoroplastic dispersions pigmented in over a dozen colors. Currently, experimental work on fluoroplastics is going on full time not only at Du Pont, Kellogg, and at dozens of other chemical companies (particularly Minnesota Mining and Mfg. Co. and Firestone Tire and Rubber Co.) and in the laboratories of numerous users and fabricators of fluoroplastic Today, because so many varied uses for fluoroplastics have caught on so rapidly and because so many new, important uses lie promisingly ahead, it's no wonder these up-and-coming synthetics are classed among the glamour babies of the American plastics industry.
Chemicals Department. Currently, in his new post at Orchem, Plunkett has his eye on the development of such major products as dyestuffs, neoprene, tetraethyllead, pharmaceutical intermediates, fluorine compounds, refrigerants—but not Teflon. Although discovered in the Orchem laboratories, Teflon is today the province of the Polychemicals Department, whose many and diversified operations include the production of plastics. Yen for Antiques Obviously, it's not all work and no play for Roy Plunkett. Besides being a crackerjack bridge player, Dr. Plunkett is a seasoned collector of antiques. His varied collection of pressed glass, for example, comes to almost 400 pieces, picked up on dozens of motor trips to everywhere from Maine to Louisiana. Evenings, he's quite apt to be found in his home basement, refinishing some choice pieces of early American furniture. The Plunketts, including their two youngsters, Pat and Mike (ages 7 and 10), have an ideal setting for the family antique collection. Several years ago, they moved into historic Seven Stars Tavern, north of Sharptown, N. J. This landmark, built in 1762 and restored in 1941, was originally, in pre-Revolutionary War days, a stop-off point in the stagecoach run from Burlington to Salem, N. J. Says Dr. Plunkett: "We had a whole house full of antiques to start with, so moving into a place like Seven Stars was naturally intriguing/' Dr. Plunkett, a tall, energetic man who seems to fit Hollywood's image of the dashing young executive, is vice president of the Gloucester-Salem Council of the Boy Scouts of America and a former director of the Du Pont-Penns Grove Country Club. In addition, this year, he served as chairman of the Red Cross fund drive for all of Salem County. His friends wonder how he finds the time. But then, executives like Roy Plunkett, skilled in the manufacture of chemicals, seem to have a flair for manufacturing time as well.
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