Fluoroplastic Descriptions

Polytetrafluoroethylene (PTFE) PTFE was discovered in 1938 by research-chemists at Du Pont, but it was not introduced or marketed until 1946. It is a partly crystalline fluoroplastic and belongs to the thermoplastic group (however it is not injection molded). The rare combination of its exceptional properties is essentially due to its molecular structure. The remarkable chemical and thermal resistance results from the linkage force between "C" and "F" atoms and from the nearly complete shielding of the carbon chain by fluorine atoms. PTFE has a thermal resistance of -260°C to +300°C (there is for example no brittleness of boiling helium at -269°C). This temperature range is reached by no other commercial plastic material. But the permanent temperature resistance depends on the load. This means that PTFE can be used from -200°C to +260°C at moderate mechanical load. Labware made of PTFE has a white appearance; its surface is non-adhesive and has excellent slip characteristics. The fabrication of PTFE laboratory devices is done by isostatic pressing processes or they are machined from extruded semi-finished PTFE material.

PTFE-TFM PTFE-TFM is a further development of the classic polytetrafluoroethylene (PTFE). The unique properties of the PTFE were improved in this second generation material. The PTFE-TFM material is characterized by a tighter arrangement of polymers and a lower gas permeability. Additionally, it has an extremely smooth surface and a very low concentration of pores which prevents contamination and makes cleaning easier. The substantially low deformation at load is especially effective at higher temperatures. It is used whenever there is a higher demand for safety and reliability, i. e. in digestion vessels or gaskets.

Tetrafluoroethylene-Perfluoropropylene (FEP) FEP, a molten copolymer of tetrafluoroethylene and perfluoropropylene with a high-molecular, partly crystalline structure, was introduced to the market in 1960. Its mechanical properties and chemical resistance (max. +205°C) are comparable with those of PTFE, however, the upper limit of the permanent working temperature is lower than that of PTFE. FEP is a typical thermoplastic material which can be treated and machined in the usual way using the established methods, although its high viscosity limits the speed of operation. Labware made of FEP is translucent to transparent and non-porous.

Perfluoroalkoxy (PFA) PFA also belongs to the group of molten copolymers with a high-molecular, partly crystalline structure. Compared with PTFE it has additional side chains consisting of perfluorated alkoxy groups. The properties (chemical and thermal resistance) of this thermoplastic fluoropolymer can be compared with those of PTFE. Labware made of PFA is translucent to transparent, non-porous and particularly useful in high-purity work.

Polychlorotrifluoroethylene (PCTFE) PCTFE is a partly crystalline polymer, however, compared with PTFE it has only 3 "F" atoms and 1 "CL" atom. This fluoroplastic is harder than all the other materials of this kind and is particularly characterized by its high deformation resistance. PCTFE is resistant to UV radiation and has the lowest gas permeability rate. Labware made of PCTFE is translucent and non-porous. PCTFE is comparable with PTFE however, with a restricted thermal resistance.

Ethylene-Tetrafluoroethylene (ETFE) ETFE is a modified copolymer of ethylene-tetrafluoroethylene. Compared with the homopolymer PTFE which can be treated only by means of pressing or sintering, the modified copolymer ETFE can be processed as a thermoplastic. This means that this plastic can be injection molded using the appropriate machines. In the laboratory this material is mainly used for items reinforced with glass fibres, i. e. in screw caps or screw joints.

Polyvinylidene Fluoride (PVDF) PVDF is a fluoroplastic material that can be machined or processed as a thermoplastic. It is characterized by a good to excellent chemical resistance. Compared with PTFE, PVDF it is much harder and more rigid. Its functional temperature range, however, is lower than that of the ‚related‘ PTFE. Compared with other fluoroplastics, PVDF displays a series of unique properties, such as its easy processing, the high mechanical values and the low specific weight.

Polyvinyl Fluoride Compared with the regular polymers, PVF, containing fluorine, displays a stronger chemical linkage and thus, a better inherent stability. PVF displays unique properties when used at temperatures ranging from –70°C to +110°C. It even withstands temperatures of approximate. +200°C. Polyvinyl fluoride does not contain a softener. It is resistant to fading and can easily be cleaned due to its dirt-repelling surface. In particular, foils, films and bags for the gas analysis are made of PVF.

Technical Plastics

Polyphenylsiloxan (PPS) PPS is a new material with a high efficiency. This macromolecule consists of phenylene rings and 1 "S" atom. Therefore it is characterized by a good chemical resistance even at high working temperatures. PPS is particularly suitable for the production of molded pieces which are subject to high mechanical and thermal stresses. Injection molding is the most common processing technology for this material; in addition, component parts can be made of semi finished goods by means of cutting. In particular, glass-fibre reinforced compounds are characterized by better rigidity and sturdiness as well as higher dimensional stability under heat than compounds that are not reinforced.

Polyetheretherketone (PEEK) PEEK is a partly crystalline thermoplastic which withstands high temperatures. Due to its unique properties this material is mainly used in components that are subject to high mechanical stresses. The high upper working temperature (+250°C), the good chemical stability and resistance to hydrolysis as well as the high mechanical values of this thermoplastic will allow PEEK to become the material of the future. In laboratories, PEEK components are mainly used as HPLC fittings, screw joints or as tubing. Its original color is natural (brown) and its price is considerably higher than that of PTFE or PFA.

Polypropylene (PP) PP is a polymer of ethylene with an isotactic arrangement of methyl groups. It does not belong to the fluoroplastic group. This material can be autoclaved (at +121°C) and is distinguished by good mechanical properties and good chemical resistance almost to its softening point. Labware made of PP is unbreakable and an economical plastic alternative, however, with restricted chemical and thermal resistance.

Polyamides (PA) Polyamides are either condensation polymers obtained from diamine and dicarboxylic acid, for ex.: adipic acid and hexamethylene-diamine or condensation polymers obtained from amino acids respectively from their lactams, for ex.: caproic lactam. In general, polyamides are defined according to the number of "C" atoms of their monomers, e.g.: PA 6 = polycaproic lactam to PA 12 = polylauric lactam. PA 6 is the most commonly used polyamide. All polyamides are characterized by a high toughness, strength and scuff resistance. The application range for this material ranges from simple turned parts, such as screws or nuts, to plain bearing or toothed wheel work.

Polystyrene (PS) Polystyrene is a polymerization product of styrene. Polystyrene is one of the most commonly used plastic materials. For many years it has been processed by injection molding or by extruding or blowing. Because of its structure, polystyrene is transparent, hard and brittle. A disadvantage is its low thermal and chemical resistance.

Polymethylmethacrylate (PMMA) PMMA is an acrylic resin based on methyl methacrylate. It is more known under the trade name ‚Plexiglas‘. On the one hand PMMA is (approx. 60 times) more elastic than window glass, but on the other hand it is also approx. 10 times more permeable than silicate glass. Of course, the hardness of its surface cannot be compared with that of glass, but compared with all the other materials it can easily be polished to high brilliance. Concerning weight it is much more lightweight than normal window glass.

Elastomers

Acrylnitrile-Butadiene-Caoutchouc (NBR) NBR is an elastomer on the base of acrylonitrite-butadiene-caoutchouc which is used as budget priced sealing material (e.g. O-rings for stopcocks). This material has a good resistance in mineral oils and fats and is also resistant to HFA, HFB and HFC-hydraulic fluids. It has a very good elasticity. PERBUNAN (trade name of company BAYER AG) is not resistant to brake fluids on the base of glycol, HFD liquids, aromatic compounds (e.g. benzole), ester, ketone and amines as well as in concentrated acids and caustic solutions. That is why it is not the ideal material for the chemistry.

Fluorcaoutchouc (FPM) Better known as VITON (registered trade name of company Du Pont), FPM is an elastomer on the base of fluorocaoutchouc. Many O-rings, lip seals and sleeves are made of FPM. It has a very good resistance to heat, chemicals, weather and ozone. It is also resistant in sulphurated mineral oils and fats, hardly inflammable HFD liquids (basis phosphor ester or chlorinated hydrocarbons). It is not resistant to anhydrous ammonia, caustic soda and potassium, ketones, ether, dioxane and some amines and organic acids. We often use FPM as sealing material (mostly protected from the medium by a PTFE sealing lip).

EPDM EPDM 3 is an elastomer on the base of ethylene-propylene-diene-caoutchouc which is mostly used for gaskets and O-rings. The main applications are in the area of hot water, steam and lees. It is not resistant to hydraulic liquids on the base of mineral oil but it has a good resistance to weather and ozone. In addition, it is non-ageing. We mainly use O-rings of EPDM for applications where VITON O-rings are not sufficient.

Perfluoro-Caoutchouc (FFKM) The perfluoroelastomer FFKM is an elastic sealing material with natural recovery and good accommodation to the sealing surfaces. It has got the same chemical resistance as PTFE. The FFKM O-rings have a very high chemical and thermal resistance. They can be used at long duration conditions with temperatures up to +260 °C. It is known under the trade names KALREZ of company Du Pont respectively CHEMRAZ of company Greene Tweed.