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Polytetrafluorethylene (PTFE)

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Presentation on theme: "Polytetrafluorethylene (PTFE)"— Presentation transcript:

1 Polytetrafluorethylene (PTFE)
Chandra Heller Michael Mallicote

2 Discovery Accidentally discovered on April 6, 1938 by Roy Plunkett.
Polytetrafluoroethylene (PTFE) was discovered on April 6, 1938 by Roy Plunkett, a research chemist at DuPont. Plunkett had been working on synthesizing new forms of another DuPont product, Freon®. On this day they were testing reactions using pressurized cylinders of refrigerant gas tetrafluoroethylene (TFE). A cylinder containing TFE, which they had filled themselves, failed to discharge when the valve was opened. Rather than discard the cylinder, which was clearly too heavy to be empty, they decided to cut it open (despite risk for potential explosion). Inside the cylinder they found a white powder. Plunkett put his refrigerant research on hold to study this substance. In time he discovered that the gas has polymerized in the cylinder and more importantly he invented a way to reproduce the TFE-to-PTFE polymerization in the lab.

3 Uses By 1941, PTFE had been patented and had its first brand name Teflon®. By 1946, the resin product was being used to produce machine parts for military and industrial applications. In the 1960s it began its life in the arena of nonstick cookware.

4 Uses (continued) Today it has expanded into a whole family of polymers (resins, films, coatings, moldable forms, powders) and sold under various brand names, including Gore-Tex® and Zylon®. It is used in a wide range of industries from aerospace to pharmaceuticals and is sold in over 40 countries worldwide. PTFE use has increased over the decades. It has uses in the following applications: automotive, medical, household, food packaging, household, textiles, personal care and industrial. There are medical uses for PTFE, such as vascular grafts (used for replacing small arteries (diameter 6 to 8mm or less). PTFE is blood tight, but does allow for cell ingrowth. In household goods, such as cookware, bake ware and small electronics PTFE is used for its nonstick surface qualities. In carpet fibers and paints it is used for the stain resisting qualities and it is also used to coat light bulbs to make them shatter resistant. In the automotive area PTFE is found in windshield wiper blades, oil filters, and lubricants because of its low of friction. It is also found in paint coatings and fabric coatings in automobiles. The use of PTFE in coatings and certain other food contact applications is permitted under FDA regulations. This agent has the name of Zylon® and is used in the paper coating industry. It is a coating on the inside of food wrappers, candy bar wrappers, and popcorn bags as a grease-proofing and as a release agent. Clothing uses PTFE as a fabric protector. Gore-Tex® has a proprietary mechanical heating and stretching process for using PTFE in clothing to allow a breathable watertight fabric. PTFE is also present in the personal care area. It is used in nail polish, hair styling tools, and eyeglass lens coating for both anti-reflective and scratch resisting qualities.

5 Teflon® Monomer F F C C F F tetrafluoroethylene
The monomer of PTFE ( [C2F4]n ), as stated above is tetrafluoroethylene (C2F4). It is comprised of a double bonded two carbon backbone and four fluorine molecules. Fluoropolymers have significantly different behaviors than hydrocarbon chains. Fluorine is a highly reactive element. It the most electronegative of all elements, has unshared electron pairs, and is more easily converted to F- than H is to H-. Bond strength is higher for C-F bonds over C-H bonds (116 kcal/mole vs kcal/mole). F is larger than H, and the C-F bond is more highly polarized than a C-H bond in hydrocarbons. F F tetrafluoroethylene

6 Teflon® Polymer The synthesis of PTFE can be accomplished through emulsion polymerization under pressure, using free-radical catalysts (i.e. peroxides or persulfates) under pressure with oxygen, peroxides, or peroxydisulfates. Polymerization of tetrafluoroethylene is highly exothermic and generates kcal/mole heat.

7 Teflon® Polymer (continued)
PTFE does not branch due to the polarity and strength of the C-F bonds. It does form a helical conformation which helps minimize the steric repulsion of the large fluorine atoms. At temperatures of up to up to 19° C the polymer rotates 180° in the length of 13 carbons. Above 19° C it rotates 180° around in 15 carbons. It is inert to chemicals and solvents up to 300°C. In fact, the only things that react with it above that temperature are molten alkali metals, chlorine trifluoride, and gaseous fluorine. The size of the fluorine atom and the C-F bond length are such that the carbon back bone is blanketed with fluorine atoms which render the C-F bond impervious to attack. It has an initial melting point of degrees Celsius and a secondary melting point of degrees Celsius. PTFE also can temporarily withstand temperatures of 260 degrees Celsius and still have the same chemical properties. PTFE retains its chemical properties in cryogenic temperatures of -240 degrees Celsius. It is very stable in its normal temperature range. Fluoropolymers do not ignite easily and do not sustain flame. To get PTFE to burn on its own you have to provide it with an atmosphere of over 95% oxygen. PTFE has the lowest coefficient of friction of any polymer (Dynamic coefficient of Friction is 0.04) . It is hydrophobic and oleophobic. Oleophobic: lacking affinity for oils.

8 Emulsion Polymerization
Initiation: Free radical formation ROOR + Heat → 2 RO Initiation: Formation of new free radicals by peroxide + TFE in aqueous phase RO + CF2=CF2 → RO(CF2–CF2) Propagation: Growth of free radicals by further addition of TFE RO(CF2–CF2) + n CF2=CF2 → RO(CF2–CF2)–(CF2–CF2) Free radicals undergo hydrolysis where a hydroxyl group replaces the peroxide RO(CF2–CF2)–(CF2–CF2) + H2O → HO(CF2–CF2)n–(CF2–CF2) + H+ + HOR HO(CF2=CF2)n–(CF2=CF2) + H2O → COOHCF2–(CF2–CF2) n + 2HF Termination: COOH– CF2–(CF2– CF2) n + COOH– CF2–(CF2– CF2) m → COOH– CF2–(CF2– CF2) m+n COOH Emulsion polymerization is when a liquid monomer is submerged in an insoluble liquid This causes emulsion, the suspension of small micelles of liquid in another liquid because together they are unable to form a solution. Most emulsion polymerizations require an emulsifier, which is a surfactant that helps promote emulsion of the non dissolving liquid. PTFE has the advantage of having no known solvent, making it ideal for emulsion polymerization. The TFE monomer can be dissolved in an inert solvent with the rest of the polymerization system. After polymerization, the PTFE precipitates out of the solution, making it easy to collect.

9 Toxicity The monomer TFE is a confirmed animal carcinogen with unknown relevance to humans. The finished polymer in solid form is inert under ordinary conditions. There is some indication that the powdered forms of PTFE may be carcinogenic if inhaled. Monomer Health Effects Causes acute effects when inhaled, including irritation of upper respiratory tract and eyes, mild depression of central nervous system, nausea and vomiting, and dry cough. Massive inhalation produces cardiac arrhythmia, cardiac arrest, and death. A study by National Toxicology Program has reported kidney and liver tumors in rats and mice, which had exposed to lifetime inhalation of TFE. Relationship to human response has not been established. An exposure limit of 5ppm has been established by fluoropolymer producers. The monomer TFE is a confirmed animal carcinogen with unknown relevance to humans. Polymer Health Effects The finished polymer in solid form is inert under ordinary conditions. Exposure to pyrolytic decomposition products is the principal health concern for the sold forms of PTFE. There is some indication that the powdered forms of PTFE may be carcinogenic if inhaled. Caged pet birds are susceptible to death from hemorrhagic pneumonitis due to accidental overheating of empty PTFE-lined pans. It is important to note that while this is the case with birds there are varying results with the studies performed on pans and human exposure to these overheated pans.

10 Recycling of PTFE It is easy to recycle since no chemical reaction is necessary. Only the extruded forms are recycled (not the resin or powerdered forms). The uses of recycled PTFE are restricted. It is typically ground up into fine powders and used as additives in such products as inks, paints, and cosmetics. It is easy to recycle since no chemical reaction is necessary. Only the extruded forms are recycled (not the resin or powerdered forms) It is separated from impurities and heated to a working temperature. It is then extruded in a long strand which can then be cut down to pellets and shipped to manufacturing companies that use the recycled material. Alternately it is simply ground up to form powders. The incentive to recycle fluoroplastic scrap has a strong economic component due to the high value of these plastics. In reforming the product, the molecular weight is lowered, Lowering of molecular weight adversely affects a number of properties of parts made from recycled fluoroplastics. Because the molecular weight distribution in PTFE is usually not controlled, the uses of recycled PTFE are restricted.  It is typically ground up into fine powders and used as additives in such products as inks, paints, and cosmetics.

11 Questions

12 References Inventor of the Week: Archive. (2000) Teflon.com - the complete resource on Teflon® products by DuPont. (2005) Biomaterials. (2001) Zonyl Packaging: Whistleblower. (2005) Teflon fluorocarbon information. (2001) Polymers. (2004) Ebnesajjad, S. Non-melt Processible Fluoroplastics : The Definitive User's Guide and Databook. Norwich, N.Y. : Plastics Design Library. (2000) Ebnesajjad, S. Melt Processible Fluoropolymers: The Definitive User's Guide and Databook. Norwich, N.Y. : Plastics Design Library (2003) Chemical Structure. (2003) Synthesis. (2003) Burridge, E. PTFE. Eur. Chem. News. 80, 16 (2004) Bingham, E., Cohrssen, B., Powell, C., Eds. Patty's Toxicology. New York : John Wiley. (2001) Useless Information. (2003) DuPont Electronic Materials Keep Mars Rovers Going. (2005) National Toxicology Program. (2005) Learn more about Teflon®. (2005) NIOSH: The National Institute for Occupational Safety and Health. (2005) Recycling. (2003)


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