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.
