2016年1月12日星期二

Part 5 Do you really know PTFE Teflon?

Part5





Half-inch Teflon tubing being extruded, 1955.
Secret of PTFE Teflon 

Next Hardie met with an executive at Du Pont in Wilmington, Delaware. By describing the success of nonstick pans in France, he was able to convince the executive that cookware could be a valuable new market. When the executive objected that the name Tefal was too close to Teflon, Hardie agreed to market his imported French pans under the name T-fal. Later a Du Pont salesman was assigned to accompany Hardie on a visit to Macy’s in New York City. There, in a tiny basement office, a buyer named George Edelstein placed a small order. Hardie was so excited that he sent a victory cable to the French factory. On December 15, 1960, during a severe snowstorm, the T-fal “Satisfry” skillets went on sale for $6.94 at Macy’s Herald Square store. To almost everyone’s amazement, the pans quickly sold out.
Shortly afterward Hardie made his second sale when he telephoned Roger Horchow, a buyer for the Dallas department store Neiman Marcus. Horchow agreed to test a sample skillet even though his store didn’t have a housewares department. He gave the skillet to Helen Corbitt, a cookbook editor who ran a popular cooking school in Dallas. Corbitt loved it, prompting Neiman Marcus to place a large order and run a half-page newspaper advertisement. The store sold 2,000 skillets in a week. Hot-chow later recalled, “Skillets were piled up, still in the shipping crates, as in a discount house, with the salesladies handing them out to customers like hotcakes at an Army breakfast.” The news spread to other department stores. Buyers jumped on the nonstick bandwagon, and Hardie was swamped with orders.
The inventory in Hardie’s barn was quickly exhausted. He phoned France daily to ask for more pans, but the French plant couldn’t work fast enough to supply both sides of the Atlantic. Hardie flew to France to press his case with Grégoire. He even lent Tefal $50,000 to expand its facilities, but it still could not meet the American demand. To cope with the avalanche of orders, which reached a million pans per month in mid-1961, Hardie built his own factory in Timonium, Maryland.
Starting with Apollo, NASA used Teflon cloth and Teflon-coated fibers in its space suits.
Unfortunately for him, around the same time, several major American cookware companies decided that the time was right to start making Teflon pans. Suddenly the market was saturated with nonstick cookware. Because the American companies had no experience with Teflon coatings, much of it was inferior to the French product, and nonstick pans soon acquired a bad name. Just as quickly as the U.S. demand for nonstick pans had soared, it plummeted, and warehouses were filled with unsold stock. Hardie sold his factory and focused on his family’s business. (T-fal cookware, the standard of quality in the, early 1960s, is still being manufactured and is sold in stores in the United States and abroad.)
Despite the problems with early Teflon cookware, Du Pont’s managers still believed that it had enormous potential. So the company commissioned some research. Six thousand consumers, along with a sampling of professionals in the cookware business, were asked what was wrong with Teflon products. The respondents overwhelmingly liked the idea of Teflon cookware; the problem lay with faulty production methods that turned out shoddy pans whose coatings scraped off much too easily.
Du Pont knew that cookware could be more than just a way to sell lots of Teflon. It could also be an invaluable marketing tool, a vehicle to familiarize vast numbers of consumers with Teflon and its properties. Conversely, low-quality merchandise could only harm the product’s reputation. As a result the company established coating standards for manufacturers and initiated a certification program, complete with an official seal of approval for Teflon kitchenware. To verify compliance with its standards, Du Pont performed more than 500 tests per month on cookware at its Marshall Laboratories in Philadelphia.

    The Du Pont certification program was so successful that a marketing survey in the mid-1960s found that 81 percent of homemakers who had purchased nonstick pans were pleased with them. By 1968 Du Pont had developed Teflon II, which not only prevented food from sticking to the pans but was also (supposedly) scratch-resistant. Later generations of Teflon cookware, with thicker coatings and improved bonding, would be introduced under the trade names Silverstone in 1976 and Silverstone Supra in 1986.

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Part3 Do you really know PTFE Teflon?

Part3      Secret of PTFE Teflon 




Another technique involved etching the surface of a piece of Teflon with specially formulated solvents that extracted some of the fluorine atoms. These solvents left behind a thin, carbon-rich surface layer to which conventional adhesives could bond. Yet another solution was to implant fine particles of silica in the Teflon, creating a rough “sandpaper surface” that would also accept adhesives. This method was not as effective as chemical etching, but it was adequate for some purposes. Du Pont chemists also developed fluorocarbon resins that would stick to both Teflon and metal surfaces. And of course, sheets of Teflon could be attached to other items with screws, bolts, clamps, and other mechanical fasteners.
Machine parts requiring a uniform coating could be immersed in a “fluidized bed”—a layer of Teflon powder that was agitated with a stream of air until it behaved like a liquid. The item to be coated was first heated to 650 degrees Fahrenheit and then dipped in the fluidized bed for a second or two. After the excess powder was blown off, a film of one to two thousandths of an inch was left behind. As with other methods, repeated applications were often required to get a thick enough film. This method was especially useful with irregularly shaped mechanical components, such as valves and rotors, as well as with small items like ball bearings.
By 1948 Du Pont had made enough progress to prepare for full-scale production. Two years later the company’s first commercial Teflon plant, designed to produce a million pounds a year, went on line at the Washington Works, on land once owned by George Washington near Parkersburg, West Virginia. Du Pont stepped up its efforts to market Teflon for industrial applications, promoting the use of tape and sheets for insulation in many kinds of electrical equipment. Teflon was also used for gaskets, packings, valve components, pump components, bearings, sealer plates, and hoppers. To help users understand the polymer’s unusual properties and tricky fabrication requirements, Du Pont sent out a team of scientists to advise customers on integrating Teflon into their production processes. Members of the research, manufacturing, and sales staff met regularly to compare notes.
Within a year Teflon was also being used in commercial food processing. Du Pont saw the potential for expansion in this field but decided to proceed slowly. In bread manufacturing, rollers were coated with Teflon to keep dough from sticking. Teflon-lined bread pans and muffin tins became standard equipment in many bakeries. Teflon coatings also stopped dough from sticking to cookie sheets and reduced the number of damaged cookies that had to be thrown away. In candy factories Teflon coated conveyor belts, hooks for pulling taffy, and the cutting edges of slicing machines. In all these applications, Teflon proved much more effective than the old method of coating the surface with oil or grease.
A 1953 Du Pont television commercial showed a Teflon-coated bread pan and boasted that it had “baked 1,258 loaves of bread and ... never had a drop of grease in it.” The first draft of the script for this ad also predicted that frying pans would be coated with Teflon in the future, but that line was deleted before the commercial was filmed. Du Pont was reluctant to market Teflon-coated cookware for home kitchens because of concerns that misuse might lead to injuries and lawsuits. Until the company could be sure that Teflon was absolutely safe in untrained hands, it preferred to stay with industrial users. Nylon, another Du Pont product, had become a great success in consumer products, but it was not subjected to the extreme conditions that Teflon cookware would encounter.
Du Pont’s tests showed that while Teflon could withstand brief exposure to temperatures as high as 1,000 degrees Fahrenheit, it began to soften at 620 degrees Fahrenheit. This was no problem for baking pans, which are rarely subjected to temperatures above 500 degrees, but it could potentially cause problems with pans used on stovetops. Researchers found that at high temperatures, small quantities of gaseous decomposition products were released. Because some of these gases were toxic and might cause temporary flu-like symptoms, adequate ventilation was required. Although the fumes given off by overheated Teflon pans were less toxic than those given off by heated cooking oil or butter, Du Pont decided to proceed with caution. Even as late as 1960 the company sold less than 10 million pounds of Teflon per year, with receipts of a piddling (by Du Pont standards) $28 million. Expanding consumer uses would be the key to boosting sales, but Du Pont had to convince itself that Teflon was harmless before selling it to the housewives of America.

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Part 4 Do you really know PTFE Teflon?

Part4          Secret of PTFE Teflon 

While Du Pont hesitated, an enterprising French couple took matters into their own hands. Marc Grégoire, an engineer, had heard about Teflon from a colleague who had devised a way to affix a thin layer of it to aluminum for industrial applications. The process involved etching the aluminum with acid to create a microscopically pitted surface, covering the surface with Teflon powder, and heating it to just below its melting point, which caused it to interlock with the aluminum surface.
In France, the birthplace of nonstick cookware an advertisement proclaims: "Tefal never sticks."
Grégoire, an avid fisherman, decided to coat his fishing gear with Teflon to prevent tangles. His wife, Colette, had another idea: Why not coat her cooking pans? Grégoire agreed to try it, and he was successful enough to be granted a patent in 1954. The Grégoires were so happy with the results that they set up a business in their home. Starting around 1955, Marc coated pans in their kitchen and Colette peddled them on the street. French cooks, despite their customary reverence for tradition, snapped them up. Encouraged by this reception, the Grégoires formed the Tefal Corporation in May 1956 and opened a factory.
Soon afterward France’s Conseil Supérieur de l’Hygiene Publique officially cleared Teflon for use on frying pans. The Laboratoire Municipale de Paris and the École Supérieur de Physique et Chimie also declared that Teflon-coated cookware presented no health hazard. In 1958 the French ministry of agriculture approved the use of Teflon in food processing. That same year the Grégoires sold one million items from their factory. Two years later sales approached the three million mark.
Du Pont executives, who were aware of these developments in France, decided to seek the approval of the U.S. Food and Drug Administration (FDA) for wider use of Teflon in cooking and food processing. The company tested frying pans and other cooking surfaces under conditions even more rigorous than those used in France. Du Pont’s researchers concluded that utensils coated with Teflon were “unquestionably safe” for both domestic and commercial cooking. In January 1960 the company gave the FDA four volumes of data, collected over nine years, on the effects of Teflon resins in food handling. Within a few months the FDA decided that the resins did not “present any problems under the Food Additives Amendment.” Despite the favorable FDA decision, Du Pont continued to move slowly, since marketing Teflon-coated cookware was not a high priority. Then one man’s enthusiasm nudged Du Pont into action.
Workers in a Tefal factory
Thomas G. Hardie was an American who admired French culture. After graduating from college, he served in the military, worked for the Marshall Plan in Paris, and became a foreign correspondent for an American newspaper chain. Then he entered his family’s business, Nobelt, a Maryland firm that makes textile machinery. During a business trip to France in 1957 or 1958, Hardie met Marc Grégoire at a party on the Left Bank. The Frenchman enthusiastically told Hardie about his business and the factory he was building in a Paris suburb. Hardie was intrigued by Grégoire’s tale of the fast-selling cookware.
After Hardie went home to Maryland, he decided that the popular French pans would sell in the United States too. He went back to Paris to meet with Grégoire, who was reluctant to do business with an American because he didn’t trust Yankees. But Hardie was very persuasive and eventually won Grégoire’s confidence. With visions of quick success, he returned to the States with the rights to manufacture nonstick cookware using Tefal’s process.

During the next two years Hardie called on many American cookware manufacturers, trying to persuade them to make Teflon-coated pans. He had no success because the idea of nonstick pans was simply too new. All these rejections turned Hardie’s business venture into a personal crusade. Although he had no experience in the import business, he cabled the French factory to ship him 3,000 Tefal pans, which he warehoused in a barn on his sheep farm in Maryland. He sent free sample pans, along with promotional literature, to housewares buyers at 200 department stores. Not one of them placed an order.

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Part 6 Do you really know PTFE Teflon ?

Part6        Secret of PTFE Teflon 

As Teflon became better known to consumers, rumors began to circulate that it was unsafe. Tales sprang up about how Teflon had caused the mysterious deaths of unidentified workers. In other versions users of nonstick cookware had suffered the flu or seizures after breathing Teflon fumes. Industrial safety bulletins and at least one medical journal warned readers of Teflon’s supposed dangers.
An assortment of industrial parts made from granular PTFE shows the material's versatility and the wide range of applications in which it can be used.
Whenever one of these false reports came to Du Pont’s attention, the company demanded a published retraction. It also published a booklet called The Anatomy of a Rumor that summarized the results of research carried out at Du Pont and elsewhere. In addition, Du Pont tried to set the record straight by acknowledging whatever minor problems could be documented. The company admitted that there had been isolated incidents of “polymer fume fever,” which produced symptoms similar to those of influenza for a brief period but had no lasting effects. It also acknowledged at least one case of a worker suffering “the shakes” after smoking cigarettes that might have been contaminated with Teflon dust. In fact, as early as 1954 Du Pont had instructed its employees not to smoke or carry cigarettes with them while working with Teflon. However, no serious illnesses or injuries had ever been linked to Teflon.
When Teflon cookware was introduced, many national magazines printed articles about the new products. Most discussed the safety issue, and several mentioned the rumors, but none gave any credence to the gossip. Nevertheless, Consumer Reports got so much mail about the rumors after a 1961 article that the editors had to print a second article refuting them again. As late as 1973 Consumer Reports was still receiving mail on the “old bugaboo about nonsticks,” prompting the editors to publish yet another article emphasizing that they knew of “no consumer illnesses resulting from... nonstick cookware in ordinary home use.”
As nonstick cookware became accepted, Teflon made the transition from a low-volume specialty material used chiefly in industry to a mass-market consumer item. Today Teflon is used to insulate fabrics in tablecloths and carpets and to coat the surfaces of steam irons. Teflon plumbing pipes and valves can be found in many new homes; Teflon flakes add toughness to nail polish. In fiber form, as part of the fabric known as Gore-Tex, it is beloved by campers and skiers for its ability to insulate while wicking moisture from the skin. It can also be found in pacemakers, dentures, medical sutures, artificial body parts, printed circuits, cables, space suits, and thousands of other manufactured products. The surest sign of the slippery material’s success is its adoption as a slang term in political discourse, where Teflon is used to describe an officeholder who unaccountably remains popular despite having opinions with which one disagrees.

While the discovery of Teflon was unplanned, the rest of its story is anything but accidental. Plunkett’s training in fluorine chemistry allowed him to recognize what he had found and to analyze its properties, a byway he might not have been able to explore in a smaller firm. When the project grew beyond laboratory scale, he knew he could hand it off to other departments with confidence. Du Pont had the knowledge base to find ways of producing the monomer cheaply enough, controlling the polymerization, applying the useful but hard-to-handle polymer to industrial use, and making sure that consumer products were durable, safe, and reliable. Large research groups can have their disadvantages, but in the case of Teflon, Du Pont’s size was a critical ingredient in its success.

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Part 2 Do you really know PTFE Teflon ?

Part 2

Secret Of PTFE Teflon

For about three years Du Pont’s organic chemicals department experimented with ways to produce IFE, also known as TFE monomer, which was the raw material for PTFE. Plunkett and Rebok had produced small batches for laboratory use, but if PTFE was ever going to find a practical use and be produced commercially, the company would have to find a way to turn out TFE monomer in industrial quantities. When the organic group came up with a promising method, Du Pont’s central research and development department began looking into possible polymerization processes.
Spontaneous polymerization of TFE can lead to explosive reactions because heat is released in the process, so it had to be carefully controlled. Experiments by the chemist Robert M. Joyce soon led to a feasible but costly procedure. Meanwhile, Du Pont’s applications group began identifying the properties of PTFE that would be useful in industry, such as its resistance to electric currents and to most chemical reactions. Then came World War II, which gave a large boost to the development of PTFE (and many other technologies).
Scientists working on the Manhattan Project faced the difficult problem of separating the isotope U-235 (which makes up about 0.7 percent of the element uranium in its natural state) from the far more plentiful but inert U-238. The method they settled on was gaseous diffusion, in which a gas is forced through a porous material. Since heavy molecules diffuse more slowly than light ones, multiple repetitions of the diffusion process will yield a gas enriched in the lighter isotopes. Gen. Leslie Groves, director of the Manhattan Project, chose Du Pont to design the separation plant. To make it work, the designers needed equipment that would stand up to the highly corrosive starting material, uranium hexafluoride gas, which destroyed conventional gaskets and seals. PTFE was just what they needed, and Du Pont agreed to reserve its entire output for government use.
For security reasons PTFE was referred to by a code name, K 416, and the small production unit at Arlington, New Jersey, was heavily guarded. Despite the tight security and Du Pont’s efforts to control the polymerization process, the Arlington production unit was wrecked by an explosion one night in 1944. The next morning construction workers stood by while Army and FBI investigators looked for evidence of sabotage. Working with Du Pont chemists, they found that the explosion had been caused by uncontrolled, spontaneous polymerization that was detonated by the exothermic, or heat-releasing, decomposition of TFE to carbon and tetrafluoromethane. When the investigators left, the construction crews took over, working two 12-hour shifts a day. Within two months the unit had been rebuilt with heavy barricades surrounding it.
How Teflon is made from chloroform and hydrogen fluoride
The Manhattan Project consumed about two-thirds of Arlington’s PTFE output, and the remainder was used for other military applications. It proved to be ideal for the nose cones of proximity bombs because it was both electrically resistive and transparent to radar. It was also used in airplane engines and in explosives manufacturing, where nitric acid would destroy gaskets made of other materials, and as a lining in liquid-fuel tanks, whose cold temperatures could make other linings brittle. When the Army needed tape two-thousandths of an inch thick to wrap copper wires in the radar systems of night bombers, it was painstakingly shaved off a solid block of PTFE at a cost of $100 per pound. The high cost was justified because PTFE did a job nothing else could do.
When peace returned, Du Pont decided to go ahead with commercializing PTFE, since its manifold military uses had shown its great industrial potential. With its unmatched knowledge of polymers, the company was in a good position to take advantage of the postwar manufacturing boom. In 1944 the company had registered the trademark Teflon, probably suggested by the abbreviation TFE. The new substance was an ideal fit for Du Pont’s traditional marketing strategy, which was to shun the manufacture of commodity plastics and specialize in sophisticated materials that could command premium prices. Other materials with some of Teflon’s properties were available, but none were as comprehensively resistant to corrosion, and none of the lubricants or low-friction materials then in use were anywhere near as durable or maintenance-free.
Acid corrodes a rod of ordinary plastic but leaves Teflon unaffected.
The company faced significant obstacles before it could produce large amounts of Teflon uniformly and economically. Company chemists had developed several ways to polymerize TFE, but the properties of the resulting product varied significantly from batch to batch. And nearly every step of the manufacturing process raised problems that no chemical manufacturer had faced before. Equipment had to withstand temperatures and pressures beyond previous limits. Even a minute quantity of oxygen would react with the gases used as raw materials, fouling the process lines and valves.
After the synthesis was completed, fabricating Teflon into useful articles raised another set of difficulties. Its melting point was so high that it could not be molded or extruded by conventional methods. A further problem was caused by the very properties that had made Teflon so valuable to begin with. Chemistry students like to joke about the inventor who isolates a substance that will dissolve anything, then cannot find a container to hold it. With Teflon, Du Pont’s chemists faced the opposite problem: How do you make the greatest nonstick substance ever invented bond to another surface?

Research led to the production of Teflon in three basic forms: granules, a fine powder, and an aqueous dispersion. Borrowing the technique of sintering from powder metallurgy, Teflon was compressed and baked into blocks that could be machined into the required shape. In this process the application of heat did not actually melt the Teflon, but it softened the microscopic granules and made them stick together when pressed.  Powder could also be blended with hydrocarbons and cold-compressed to coat wires and make tubing. Aqueous dispersions were used to make enamels that could be sprayed or brushed onto a surface and then baked in place.

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Part 1 Do you really know PTFE Teflon?




Secret Of PTFE Teflon

One of the most versatile and familiar products of American chemical engineering, Teflon, was discovered by accident. There are many such tales to be found in the history of industrial chemistry, from vulcanized rubber to saccharin to Post-Its, all of which were stumbled upon by researchers looking for other things. So common, in fact, are unplanned discoveries of this sort that one might expect would-be inventors to simply mix random chemicals all day long until they come up with something valuable. Yet the circumstances behind the Teflon story show how each step along the way drew on the skills and talents of workers who were trained to nurture such discoveries and take them from the laboratory to the market. Teflon was developed at Du Pont, the source of many twentieth-century chemical innovations. It came about as a byproduct of the firm’s involvement with refrigerants. In the early 1930s a pair of General Motors chemists, A. L. Henne and Thomas Midgley, brought samples of two compounds to the Jackson Laboratory at Du Pont’s Chambers Works in Deepwater, New Jersey. The compounds, called Freon 11 and Freon 12, were chlorofluorocarbons (CFCs)—hydrocarbons in which some or all of the hydrogen was replaced with chlorine or fluorine. GM’s research laboratories had developed the family of Freons for its Frigidaire division, which made refrigeration equipment. They were meant to replace existing refrigerants such as ammonia, sulfur dioxide, and propane, which were less efficient than Freons and either too poisonous or too explosive for residential use.
Having made the basic discovery, GM teamed up with Du Pont to take advantage of the latter’s expertise in manufacturing and research and development.  The two companies formed a joint venture called Kinetic Chemicals, which by the mid-1930s had isolated and tested a wide range of CFCs and put the most promising ones into mass production. The best seller was refrigerant 114 (later called Freon 114), or retrafluorodichloroethane (CF2ClCF2Cl).  Kinetic had agreed to reserve its entire output of Freon 114 for Frigidaire, so in the late 1930s Du Pont was looking for an equally effective refrigerant that it could sell to other manufacturers. One of the chemists assigned to this project was the 27-year-old Roy J. Plunkett, who had been hired in 1936 after completing his doctorate at Ohio State University.
Plunkett was working on a new CFC that he hoped would be a good refrigerant. He synthesized it by reacting tetrafluoroethylene (TFE), a gas at room conditions, with hydrochloric acid. To further this research, Plunkett and his assistant, Jack Rebok, prepared 100 pounds of TFE and stored it in pressure cylinders, to be dispensed as needed. To prevent an explosion or rupture of the cylinder, they kept the canisters in dry ice.
On the morning of April 6, 1938, Rebok connected a canister of TFE to the reaction apparatus he and Plunkett had been using. His standard procedure was to release some TFE into a heated chamber and then spray in hydrochloric acid, but this time, when he opened the valve on the TFE container, nothing came out. A cursory examination did not reveal anything wrong with the valve. Had the gas somehow leaked out? Rebok and Plunkett weighed the cylinder and discovered that most of the gas was still inside. They fiddled with the valve some more, even using a wire to unclog it, but nothing happened.



Rebok (left) Plunket (right) and another chemist, Bob McHarness, reenact the discovery of Teflon

A frustrated Plunkett removed the valve completely, turned the canister upside down, and shook it. Some flecks of white powder floated out. Plunkett and Rebok sawed open several of the storage canisters and found that their interior walls were lined with a smooth, waxy white coating. In his lab notebook Plunkett wrote, “A white solid material was obtained, which was supposed to be a polymerized product.” This entry shows that he instantly understood what had occurred, even though it was generally believed at the time that a chlorinated or fluorinated ethylene could not be polymerized because previous attempts to do so had failed. Something about the combination of pressure and temperature had forced the TFE molecules to join together in long chains, and the resulting compound turned out to have a most interesting set of properties.
Two days later Plunkett noted some additional characteristics of the intriguing substance: “It is thermoplastic, melts at a temperature approaching red heat, and boils away. It burns without residue; the decompositive products etch glass.” He also observed that it was insoluble in cold and hot water, acetone, Freon 113, ether, petroleum ether, alcohol, pyridine, toluene ethyl acetate, concentrated sulfuric acid, glacial acetic acid, nitrobenzene, isoanyl alcohol, ortho dichlorobenzene, sodium hydroxide, and concentrated nitric acid. Further tests showed that the substance did not char or melt when exposed to a soldering iron or an electric arc. Moisture did not cause it to rot or swell, prolonged exposure to sunlight did not degrade it, and it was impervious to mold and fungus.
Plunkett’s next step was to duplicate the conditions that had produced the first batch of polymerized tetrafluoroethylene (PTFE). After experimentation he succeeded in re-creating what had occurred by chance inside the canisters. On July 1, 1939, he applied for a patent (which he assigned to Kinetic Chemicals) on tetrafluoroethylene polymers. The patent was granted in 1941.
The patent application ended Plunkett’s involvement with his discovery, since at that point the problem shifted from fluorine chemistry, which was his area of expertise, to polymer chemistry and process development. Plunkett was named chemical supervisor of Du Pont’s tetraethyl lead plant and stayed with Du Pont in various positions until his retirement in 1975; he was inducted into the National Inventors Hall of Fame in 1985 and died in 1994.
(To be continue ...)


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Extruded PTFE Tubing Properties

Extruded PTFE Tubing Properties

More and more, PTFE tubing is replacing carbon and other metal piping that deteriorates rapidly. Now and for the future, PTFE will continue to serve the industry in critical applications.
Manufacturing Process of PTFE:
CHCL3 + 2 HFCHClF2 + 2 HCl
2 CHClF2CF2 = CF2 + 2 HCL
n CF2 = CF2(-CF2 – CF2 -) n
Tetra-Fluoro-Ethylene (TFE)(PTFE)

Chemical Qualities*: PTFE is inert to the following chemicals
Inorganic ChemicalsOrganic ChemicalsOther
Aqua RegiaAlcoholsBiological Fluids
Hydrofluoric AcidEstersFragrances
Fuming Sulfuric AcidKetonesFood
Chlorosulfuric AcidHighly Halogenated OrganicsPrinting Inks & Dyes
Boiling Sodium Hydroxide SolutionAromatic SolventsLow Level Radioactive Substances
Chlorine GasAminesOxidizers
Hydrogen PeroxideIndustrial Oils
Acid Chlorides
Hot, Fuming Nitric Acid
*Among the only chemicals known to attack PTFE are molten alkali metals and their solutions, chlorine trifluoride, and gaseous fluorine at elevated temperatures and pressures.
Thermal Qualities:
PTFE tubing can withstand temperatures up to 680 °F for limited periods of time.* Under cryogenic conditions, PTFE remains strong down to -320 °F.
*Above 500 °F, mechanical properties become a limiting factor
Electrical Qualities:
PTFE tubing has superb electrical properties, indicated by a low dielectric constant of 2.1 between -40 °F and 480 °F within a frequency range of 5 Hz to 10 GHz.
PTFE tubing is also an excellent insulator with surface resistivity of 3.6 X 1012 ohms (even at 100% relative humidity).
Short time dielectric strengths range from 500 volts/mil (1 mil = 10-3 in) for thicknesses greater than 100 mils to 4000 volts/mil for very thin films.
UV and Radiation Qualities*:
PTFE tubing has excellent UV resistance and weatherability, with a radiation dose threshold for PTFE at 2 – 7 X 104 rads. Absence of oxygen increases radiation resistance by a factor of at least 10.
*Resistance to electron and gamma radiation is relatively poor
Wear and Friction Qualities:
PTFE tubing has a relatively slippery and smooth surface, with a static coefficient of friction of 0.08 and 500 psi load.
The PTFE properties make it particularly suitable for use as bearing pads, under high pressure-low velocity load conditions. Examples are bridge bearing pads, pipe support pads, and mounting pads for heavy manufacturing.
Short List Applications:
  1. Non-Shrink & Heat Shrink Tubing
  2. Heat Exchangers
  3. Coatings
    1. Carburetor Shafts
    2. Medical Catheter Guide Wires
    3. Mold Release
    4. Cryogenic Applications
    5. Automotive Brake Parts
    6. Jet Fuel Filters
    7. Bearing Pads

Chemical Reasoning for PTFE Properties

High C-F Bond Strength & No UV Absorption SitesThermal Stability
Oxidative Stability
Non-Flammability
Chemical Resistance
Resistance to Weathering
Enormous Chain LengthHigh Melt Viscosity
Low Inter-chain ForcesExcellent ToughnessLow Coefficient of Friction
Low Forces Between F Atoms and MoleculesInsolubilityLow Solvent Absorption
High CrystallinityNon-Stick PropertiesLow Water Absorption
No Permanent DipoleLow Dielectric Constant
No Surface ChemistryHigh Static Charge
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2016年1月11日星期一

Introduction of PTFE

话题：ptfe

PTFE-聚四氟乙烯简介

聚四氟乙烯，英文名称：
Polytetrafluoroethylene，简称FTFE
或F4。聚四氟乙烯是四氟乙烯的聚合
物。聚四氟乙烯（Teflon或PTFE），
俗称“塑料王”，是美国杜邦公司的彭
励格（Roy Joseph Plunkett）博士于
1938年发明的，杜邦公司在1945年注册了Teflon?(特富龙?)商标并商业化生产。
PTFE的分子式：
-[CF2 - CF2]n-
PTFE分子中F原子把C－C键遮盖起来而且C－F键键能高特别稳定，除碱金属与氟元素外它不被任何化学药品侵蚀。
PTFE分子中F原子对称，C－F中两种元素共价相结合，分子中没有游离的电子，整个分子呈中性。使PTFE具有优良的介电性能。由于PTFE分子外有一层惰性的含氟外壳，使它具有突出的不粘性能与低的摩擦系数。
聚四氟乙烯具有杰出的优良综合性能，耐高温，耐腐蚀、不粘、自润滑、优良的介电性能、很低的摩擦系数。在PTFE中加入任何可以承受PTFE烧结温度的填充剂，它的机械性能可获得大大的改善。同时，保持PTFE其它优良性能。填充的品种有玻璃纤维、金属、金属化氧化物、石墨、二硫化钼、碳纤纖、聚酰亚胺、EKONOL…等，耐磨耗、极限PV值可提高1000倍。
聚四氟乙烯具有优良的化学稳定性、耐腐蚀性、密封性、高润滑不粘性、电绝缘性和良好的抗老化耐 力。能在+250℃至-180℃的温度下长期工作，除熔融金属钠和液氟外，能耐其它一切化学药品，在王水中煮沸也不起变化。
PTFE工程塑料，可制成聚四氟乙烯管、棒、带、板、薄膜等。一般应用于性能要求较高的耐腐蚀的管道、容器、泵、阀以及制雷达、高频通讯器材、无线电器材等。 分散液可用作各种材料的绝缘浸渍液和金属、玻璃、陶器表面的防腐图层等。各种聚四氟圈、聚四氟垫片、聚四氟盘根等广泛用于各类防腐管道法兰密封。此外，也 可以用于抽丝，聚四氟乙烯纤维——氟纶（国外商品名为特氟纶）。 在聚四氟乙烯已广泛应用于化工、机械、电子、电器、军工、航天、环保和桥梁行业。 PTFE结构式：
PTFE-聚四氟乙烯的特性
耐高温
耐低温 使用工作温度达250℃。 具有良好的机械韧性，即使温度下降到-196℃，也可保持5%
的伸长率。
无毒害 具有生理惰性，作为人工血管和脏器长期植入体内无不良反
应。
力学性能，不粘附 光滑异常，连冰都比不过它，是固体材料中最小的表面张力，
不粘附任何物质。它的摩擦系数极小，仅为聚乙烯的1／5，
这是全氟碳表面的重要特征。又由于氟-碳链分子间作用力极
低，所以聚四氟乙烯具有不粘性。
绝缘性能优异
耐化学腐蚀和耐候性 报纸厚的一层薄膜，便足以抵挡1500V的高压电。 除熔融的碱金属外，聚四氟乙烯几乎不受任何化学试剂腐
蚀。例如在浓硫酸、硝酸、盐酸，甚至在王水中煮沸，其重
量及性能均无变化，也几乎不溶于所有的溶剂，只在300℃
以上稍溶于全烷烃（约0.1g／100g）。
优异的耐候性 不吸潮，不燃，对氧、紫外线均极稳定，有塑料中最佳的老
化寿命。
电性能 聚四氟乙烯在较宽频率范围内的介电常数和介电损耗都很
低，而且击穿电压、体积电阻率和耐电弧性都较高。
耐辐射性能 聚四氟乙烯的耐辐射性能较差（104拉德），受高能辐射后
引起降解，高分子的电性能和力学性能均明显下降。
PTFE-聚四氟乙烯的应用
化工防腐：
利用其耐药品性：氟塑料在耐药品性方面的应用早已不局限于制造密封圈、衬垫、管件，在其他需要耐腐蚀的部件(如管道)上的使用也日益增加。随着原料和加工技术的进步，氟塑料的成型方式又扩大厂选择幅度：如采用注射成型可大幅度提高生产效率，小批量生产时可采用切削加工工艺，聚四氟乙烯粘接和焊接技术的开发使制造大型贮槽和设备衬里有了可能，FEP粉末喷涂工艺使加工更加灵活、方便。半导体生产过程中防腐蚀、防污染已更多地采用氟塑料。
机械工业：
聚四氟乙烯的的摩擦系数小，其静摩擦系数低于动摩擦系数，可用于低速高负荷领域，如在土建、化工、桥梁等结构件中可解决热膨胀和震动引起的伸缩问题。具体应用有：
? 防污染机械(如纺织、造纸、制药、食品机械)的轴承轴套；
? 输送碱、溶剂等非润滑液体的机械(如搅拌机、染色机、泵)；
? 在酸、碱等腐蚀性环境(如电镀浴槽化工设备)下工作的轴套；
? 禁油润滑(如制氧设备)；
? 元油润滑(如超低温冷冻机、液体燃料泵)；
? 油润滑效果不良的环境下(加高温干燥机、炉内台午、炉内传送带)工作的滑动部件；
? 低速高负荷状态下的滑动部件〔可动支承)。
电子电气：
氟塑料是难燃材料，临界氧指数高又耐腐蚀，可作电线的绝缘层。
ETFE、PVDF的绝缘电阻、绝缘强度都高，机械强度也优，可用于计算机、通信机电缆。利用其耐候性、耐辐照等特性可用于油井及核反应堆小的电缆。利用其高频下相对介电常数与介电损耗均低的特点可用于通信设备、高频电了仪器，将PTFE与炭黑、碳纤维这类导电物质混合可作为防静电材料和发热元件材料。PVDF也可制成压电元件用于无线电行业及仪器仪表行业。
医疗器械：
? 人体代用动脉、静脉血管、心脏膜；
? 内窥镜、钳导管，气管；
? 其他管、瓶、滤布等医疗器材。
不粘性产品：
利用氟塑料的不粘性可以制造厨房设备(如不粘锅、点心模具)、高级建筑物的外墙涂层、泡沫塑料成型模具、复印机辊筒等。此外在人造血管、心脏瓣片等医学土物工程材料、气体分离膜、防水透气复合织物等方面的用途也日益广泛。
国内外PTFE聚四氟乙烯产业现状与改性前景
氟树脂由于其独特性能，全球产量与消费量快速增加，目前全球氟树脂的消费量约为12万吨，其中70%左右为聚四氟乙烯 （PTFE）。我国PTFE生产与研究起步较早，但是由于多种因素制约，生产规模和工艺技术整体水平比较低。
我国PTFE产业现状
目前，国内主要生产厂家有上海三爱富股份有限公司、上海氯碱化工股份公司电化厂、济南化工厂、晨光化工研究院二分厂、阜新化工厂等，年生产能力约为 7000吨。我国生产PTFE的基础原料氟石资源丰富，近年来国内部分企业计划引进技术，建设规模装置，国外多家跨国公司也在或计划在中国建设氟树脂项 目，如浙江巨化引进俄罗斯技术合资建设年产能数千吨的聚四氟乙烯装置、常熟国际氟化工园建成后，阿托菲纳公司将进驻投资生产氟树脂、日本大金公司投资 13.3亿元在园区内投资建设聚四氟乙烯装置已经于2002年投产，其它一些公司也纷纷提出入驻的意向，可以预计未来我国PTFE工业将迎来快速发展阶 段。
PTFE加工与应用
PTFE的熔点高、熔融粘度很大，且对于无定形状态下的剪切很敏感，容易产生熔体破裂，因此不能采用熔融挤压、注射成型等常规的热塑性塑料成型工艺，只能采用类似粉末冶金的方法进行烧结成型。 填充的PTFE的制造与PTFE的成型一样，可以采用预成型、自由烧结加工，也可以采用柱塞挤出法成型，上述加工工艺一般适合于一定壁厚的产品，而不适应于PTFE薄膜的加工。
PTFE的改性研究
尽管PTFE具有良好的物化性能，但是也存在一些缺陷，如其机械性能较差、线膨胀系数较大、耐蠕变性差、易冷流、耐磨性差、成型和二次加工困难等，使其应 用受到一定限制。随着我国PTFE产能快速增加，加强PTFE改性技术研究与应用，开发新型高效的PTFE复合材料，已经成为目前国内PTFE的研究与发 展方向。可以通过增强、填充、复配和共混等多种手段对PTFE进行改性，以弥补自身缺陷，主要方法有表面改性、填充改性和共混改性。
一、表面改性
PTFE极低的表面活性和不粘性限制了其与其他复合材料的复合，因此必须对PTFE材料进行一定的表面改性，以提高其表面活性。常用技术有（a），表面活 化技术：可以采用高能射线的辐射使其表面脱氟，在一定装置和条件下与其他材料氟化接枝；用一些惰性气体的低温等离子处理PTFE材料，发生碳-氟或碳-碳 键的断裂，生成大量自由基以增加PTFE的表面自由能，改善其润湿性和粘接性；将PTFE浸入熔融的醋酸钾中，在适宜温度下处理形成具有一定活性的活化 层；PTFE在一定配比的氢氧化钠、二丙烯基三聚氰胺混合液中加热处理，可以提高其表面活性；PTFE经过一定强度和时间的电晕处理，可以形成可胶接的活 化层。（b），化学腐蚀改性：将PTFE经过一定化学试剂处理可以提高其表面活性，这些化学试剂可以是金属钠的氨溶液、萘钠四氢呋喃溶液、碱金属汞齐、五 羰基铁溶液等。（c），表面沉积改性：将PTFE浸渍在某些金属氢氧化物的胶体溶液中，使得胶体粒子沉积在PTFE表面，从而增大其湿润性，改善其表面活 性，而易于与其他材料复合。上述表面改性方法主要适应于PTFE薄膜，改性后的薄膜广泛应用于化工防腐衬里、密封制品及润滑装置的设计与制造中。
二、填充改性
目前填充PTFE制品是产量最大的PTFE树脂产品，通过在PTFE树脂填充无机类、金属类和有机高聚物类等不同填料来改善PTFE的耐压性、耐磨性和冷 却性。这些填料要求能经受住PTFE的烧结温度、不与PTFE反应、另外具有一定粒度并能改善PTFE的一些物化性能。值得注意的是，在国外，PTFE填 充技术都是由PTFE树脂生产厂家完成，而我国则都是由加工生产企业来完成。
填充材料主要有：无机填充材料，主要有玻璃纤维、石墨、二硫化钼和碳纤维等；金属填充材料，通常采用铁、铜、铅、钼、钨、银等金属及其氧化物来填充PTFE，尤其是铜及其合金最为常用；有机填充材料主要是有机纤维和高分子聚合物。
三、共混改性
共混改性主要是利用PTFE的优异特点对一些树脂进行合金化处理，目前研究与应用前景看好，如PTFE/PA、PTFE/POM、PTFE/PC、PTFE/PI、PTFE/PPO、PTFE/PEEK、PTFE/PPS、PTFE/PES等合金产品层出不穷。
PTFE改性聚甲醛（POM）：
POM具有极好的力学、化学和电性能，广泛应用于汽车、电子、精密机械和建材。国内采用冷压-热烧结工艺研制出一系列不同 PTFE含量的的POM/PTFE的共混物，可以明显改善摩擦磨损性能、韧性、抗蠕变性和外观；还有通过高速混合PTFE和增韧增容改性后的POM挤出造 粒制得合金粒料，使改性后POM的摩擦磨损性能得到现状改善，其改善机理在于PTFE转移膜的形成；国外通过机械共混方法制备多种POM/PTFE共混 物，即POM分别与PTFE、涂覆偶联剂PTFE、经过化学处理的PTFE等数种PTFE共混，结果表明经过化学反应处理的、加偶联剂的PTFE与POM 之间产生很强的粘附作用，具有非常优异的性能。
PTFE改性聚苯硫醚（PPS）：
PPS缺点在于耐冲击性能较差、而且加工成型困难。由于PTFE惰性表面很难与PPS进行粘接，日本从提高表面亲和力的观点出发，采用增溶剂以降低两相界面张力，并采用在高剪切速率下进行混炼的技术，使该非相容体系合金化。
国内利用PPS粉与混合剂混磨后，加入PTFE粉制成涂料，使得涂层具有优异的摩擦磨损性能、附着性、柔韧性和防粘性，其混合剂一般采用乙醇、水、二氧六 环十二烷基磺酸钠的体系。PTFE/PPS合金解决了PPS熔体流动速率高、难以直接模塑成型的问题，在300℃以上仍能保持较高的力学性能，主要用于耐 腐蚀的泵、阀、垫圈，以及动态密封、轴套、汽车引擎阀盖、色谱仪滑动密封件和导向件等。
PTFE改性聚酰胺（PA）：
PA添加PTFE主要是提高其滑动性，据资料介绍，当PTFE填充量大于10%时候，PA的减摩耐磨性明显得到提高，如在 PA体系中同时添加能于、与其部分相容的线型低密度聚乙烯/丙烯-苯乙烯的共聚物5%，PTFE10%，二者协同效应非常好，无论是从提高复合材料的性 能，还是降低成本方面考虑，都是非常理想的改性方法。
PTFE改性聚酰亚胺（PI）：
PI作为一种新型的工程塑料主要用于航空航天工业，近年来应用拓展到电子、汽车等领域。国外由33%PTFE、2%炭黑和 65%可溶性PI组成的复合材料是摩擦磨损性能十分优异的无油润滑材料，如国外rtp公司采用热塑性聚酰亚胺与PTFE进行共混或添加其他磨耗剂与填料的 技术开发了rtp4200系列产品，可用于汽车发动机罩下部件、航空航天设备和办公电子设备等。
PTFE改性聚醚醚酮（PEEK）：
PEEK复合材料在航空航天、电子电气等领域获得广泛应用。国内研究单位利用PEEK的良好力学性能和高耐热性、 PTFE的低摩擦系数，配以助剂改进加工工艺，通过熔融共混制备PEEK/PTFE共混物，并用玻璃纤维/碳纤维混合纤维增强以提高其力学性能，开发一种 工艺性能好且能注射成型的无油润滑、耐高温、低摩擦的材料，用作高温发动机部件。
PTFE改性聚间苯二甲酰间苯二胺(PMIA)：
PMIA是一种力学性能、耐高温性远高于其他脂肪族的聚酰胺，为了进一步改善材料的摩擦学性能，需要采用 润滑性填料改善摩擦磨损性能。国内利用高速混合装置使PMIA粉末PTFE充分混合，并通过压缩浇铸得到样品，经过实验表明，当PTFE含量为20%时候 共混物具有最低的摩擦系数。
PTFE改性线型低密度聚乙烯(LLDPE)：
采用PTFE对LLDPE改性可以有效延长其寿命，如果国外报道利用γ射线辐射粉体PTFE，同时用硅烷偶 联剂处理，用表面处理后的PTFE填充改性LLDPE后，不仅可以提高PTFE和LLDPE的粘接性，又可以提高共混物的力学性能，通过测试LLDPE的 加工性和紫外线稳定性得到明显提高。
另外，PTFE与其他多种工程塑料的共混国内外也进行大量研究，如PTFE与无定型高聚物聚醚砜（PES）进行共混，可以明显提高PES的润滑性能，英国ICI公司和日本住友化学相继开发出PTFE改性的系列耐磨耗的PES新产品；PTFE与聚苯醚（PPO）共混物特别适合制成整体和大型轴承部件；聚（邻 苯二甲酸-二酚基丙烷）树脂是一种非晶性透明聚合物，具有很多优异性能，采用PTFE改性后，可明显提高其耐化学性和自润滑性；日本帝人化成开发的 PTFE与聚碳酸酯共混合金特别适宜生产机械、车辆、电器等设备的齿轮凸轮和轴承等制品。
在线型PTFE链上引入少量非氟基团，进行嵌段接枝以破坏其对称性，从而得到可热塑性塑料加工方法加工的改性PTFE，加工性能大为改善，日益受到业内重视，另外如PTFE分散液、PTFE微粉和膨胀型PTFE等因为加工性能优异倍受重视。

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