Chemical Resistance of PTFE

FIFE is highly resistant to the chemicals listed in Table A.35. The swelling in these chemicals amounts to less than 3% [1054], 

Acetaldehyde Acetic acid 75%, 50°C Acetic anhydride Acetone Acetylene Acrylonitrile Adipic acid, aqueous Alum, aqueous Aluminum chloride Aluminum fluoride Aluminum sulfate Ammonia 

Ammonia, aqueous Ammonia, gaseous, hot Ammonium carbonate Ammonium chloride, aqueous 

Ammonium nitrate, aqueous Ammonium phosphate, aqueous Ammonium sulfate Ammonium sulfide, aqueous Amyl acetate Amyl alcohol Aniline 

Ammonium fluoride, aqueous Ammonium hydroxide Battery acid (accumulator acid) 

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The chemical resistance of PTFE is exceptional. There are no solvents and it is attacked at room temperature only by molten alkali metals and in some cases by fluorine. Treatment with a solution of sodium metal in liquid ammonia will sufficiently alter the surface of a PTFE sample to enable it to be cemented to other materials using epoxide resin adhesives. 

The chemical resistance of PTFE is almost universal It resists attack by aqua regia, hot fummg nitnc acid, hot caustic, chlorine, chlorosulfonic acid, and all solvents. Despite this broad chemical resistance, PTFE is attacked by molten alkali metals, ammonia solutions of such metals, chlorine trifluoride, and gaseous fluonne at elevated temperature and pressure PTFE swells or dissolves m certam highly fluonnated oils near its melting point. Specific lists of chemicals compatible with PTFE are available [/.8]... 

Table 4.1. Chemical Resistance of PTFE to Common Solvents ...

Perfluoroelastomers provide the elastomeric properties of fluoroelastomers and the chemical resistance of PTFE. These compounds are true rubbers. Compared with other elastomeric compounds, they are more resistant to swelling and embrittlement and retain their elastomeric properties over the long term. In difficult environments, there are no other elastomers that can outperform the FPMs. These s)mthetic rubbers provide the sealing force of a true elastomer and the chemical inertness and thermal stability of polytetra-fluoroethylene. 

Substitution of F for H in the C-H bond substantially increases the bond strength from 99.5 kcal/mole for the C-H bond to 116 kcal/mole for the C-F bond. Consequently, thermal stability and chemical resistance of PTFE are much higher than PE because more energy is required to break the C-F bond. Additionally, the size of the F atom and the length of the C-F bond... 

The chemical resistance of PCTFE is good but not as good as that of PTFE. Under certain circumstances substances such as chlorosulphonic acid, molten caustic alkalis and molten alkali metal will adversely affect the material. Alcohols, acids, phenols and aliphatic hydrocarbons have little effect but certain aromatic hydrocarbons, esters, halogenated hydrocarbons and ethers may cause swelling at elevated temperatures. 

In 1989 Du Pont introduced Teflon AF, said to be a copolymer of tetrafluoroethylene and trifluoromethyldifluorodioxol. This amorphous fluoro-polymer has a similar heat and chemical resistance to PTFE but possesses several notable properties, including ... 

Because of its high chemical inertia, the chemical modification of PTFE may appear as a challenge. However, although this polymer resists to acidic or alkaline attacks. 

Polytetrafluoroethylene (PTFE Teflon) was discovered accidently by PlunkettCZ nd commercialized by DuPont in the 1940 s. This polymer has a solubility parameter of about 6H and a high melting point of 327°C and is not readily moldable. Poly-chlorotrifluoroethylene (CTFE, Kel-F), the copolymer of tetrafluoroethylene and hexafluoropropylene (FEP), polyvinylidene fluoride (PVDF, Kynar), the copolymer of tetrafluoroethylene and ethylene (ETFE), the copolymer of vinylidene fluoride and hexafluoroisobutylene (CM-1), perfluoroalkoxyethylene (PFA) and polyvinyl fluoride (PVF, Tedlar) are all more readily processed than PTFE. However, the lubricity and chemical resistance of these fluoropolymers is less than that of PTFE. 

Table 3.21. Chemical Resistance of Filled PTFE Compounds ...

AF, a copolymer of TFA and 2,2-bis-trifluoromethyl-4,5-difluoro-l,3dioxole, display the same chemical resistance as PTFE but is completely amorphous and with the lowest dielectric constant of 1.89 to 1.9 reported so far and unusually high gas permeation rates [750,751]. 

Neat PTFE has several properties which eliminate its need for additives. A very high limiting oxygen index (>95%) means that resin is nonflammable. Its thermal and electric insulation properties and its low friction coefficient means that further improvements are rarely needed. An improvement in mechanical properties may sometimes be needed but this is usually obtained at the expense of chemical resistance because most fillers detract from the chemical resistance of neat PTFE. The addition of NiZn ferrite powder is used to impart ferromagnetic properties to the... 

It is necessary to modify the surface of fluoropolymers to obtain stronger adhesive bonds. Modification or surface treatment alters the structure of the polymer at the surface enabling formation of true adhesive bonds. Mechanical abrasion imparts little improvement and chemical etching is required. Chemical resistance of perhalogenated polymers such as PTFE, PFA, FEP, and PCTFE mandates the use of highly potent agents. 

Properties similar to PTFE, but rigidity significantly higher, anti-friction properties and electrical insulating properties not quite as good. Chemical resistance of ETFE not quite as good. 

In addition to the presence of stable C—F bonds, the PTFE molecule possesses other features which lead to materials of outstanding heat resistance, chemical resistance and electrical insulation characteristics and with a low coefficient of friction. It is today produced by a number of chemical manufacturers such as Du Pont (Teflon), ICI (Fluon), Hoechst (Hostaflon TF), Rhone-Poulenc (Soreflon), Montecatini (Algoflan), Nitto Chemical-Japan (Tetraflon) and Daikin Kogyo-Japan (Polyflon). 

A 50 50 mol/mol copolymer of hexafluoroisobutylene (CH2 = C(CF3)2) and vinylidene fluoride was made available by Allied Chemical in the mid-1970s as CM-1 Fluoropolymer. The polymer has the same crystalline melting point as PTFE (327°C) but a mueh lower density (1.88g/cm ). It has excellent chemical resistance, electrical insulation properties and non-stiek characteristics and, unlike PTFE, may be injeetion moulded (at 380°C). It is less tough than PTFE. 

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