Fluoropolymer Monomer Properties

Fluoropolymer Monomer Synthesis: Tetrafluoroethylene;Hexafluoropropylene;Perfluoroalkyl Vinyl Ethers;Chlorotrifluoroethylene;Vinylidene Fluoride;Vinyl Fluoride.
Properties of Tetrafluoroethylene
Tetrafluoroethylene is a colorless, odorless, tasteless,nontoxic gas which boils at 76.3 C and melts at 142.5 C. The critical temperature and pressure of TFE are 33.3 C and 3.92 MPa. TFE is stored as a liquid; vapor pressure at 20 C is 1 MPa. Its heat of formation is reported to be 151.9 kcal/mole. Polymerization of TFE is highly exothermic and generates 41.12 kcal/mole heatdthe extent of which can be compared with the heats of polymerization of vinyl chloride and styrene, at 23-26 kcal/mole and 16.7 kcal/mole, respectively. 
Safe storage of TFE requires its oxygen content to be less than 20 ppm. Temperature and pressure should be controlled during its storage. Increasing the temperature, particularly at high pressures, can initiate deflagration in the absence of air (TFE degrades into carbon tetrafluoride). In the presence of air or oxygen, TFE forms explosive mixtures in the molar percentage range of 14-43%. Detonation of a mixture of TFE and oxygen can increase the maximum pressure to 100 times the initial pressure.
Properties of Hexafluoropropylene
Hexafluoropropylene is a colorless, odorless, tasteless, and relatively low toxicity gas, which boils at 29.4 C and freezes at 156.2 C. In a 4-hour exposure, a concentration of 3000 ppm corresponded to LC50 in rats. Critical temperature and pressure of HFP are 85 C and 3254 MPa. Unlike TFE, HFP is extremely stable with respect to autopolymerization and may be stored in liquid state without the addition of telogen. HFP is thermally stable up to 400e500 C. At about 600 C under vacuum, it decomposes and produces octafluoro-2-butene (CF3CF¼CFCF3) and octa-fluoroisobutylene.
Properties of Perfluoroalkyl Vinyl Ethers
Perfluoroalkyl vinyl ethers (PAVE) form an important class of monomers in that they are comonomers of choice for the “modification” of the properties of homofluoropolymers in additionto broad use inthe structure of copolymers of TFE. The madvantage of PAVEs as modifiers over HFP is their remarkable thermal stability. A commercially significant example is per-fluoropropyl vinyl ether (PPVE). PPVE is an odorless, colorless liquid at room temperature. It is extremely flammable and burns with a colorless flame. It is less toxic than HFP.
Properties of Chlorotrifluoroethylene
Chlorotrifluoroethylene is a colorless gas at room temperature and pressure. It is fairly toxic with an LC50 (rat) at 4-hour exposure and a concentration of 4000 ppm. It has a critical temperature and pressure of 105.8 C and 4.03 MPa. Oxygen and liquid CTFE react and form peroxides at fairly low temperatures. A number of oxygenated products, such as chlorodifluoroacetylfluoride, are generated by oxidation of CTFE. The same reaction can occur photochemically in the vapor phase. Chlorotrifluoroethylene oxide is a by-product of this reaction. The peroxides act as initiators for the polymerization of CTFE, which can occur violently.
Properties of Vinylidene Fluoride
Vinylidene fluoride, (CH2¼CF2), is [49] flammable and is a gas at room temperature. It is colorless and almost odorless and boils at 84 C. VDF can form explosive mixtures with air. Polymerization of this gas is highly exothermic and takes place above its critical temperature and pressure.
Properties of Vinyl Fluoride
Vinyl fluoride (75-02-5) (fluoroethene) is a colorless gas at ambient conditions. It is flammable in air between the limits of 2.6 and 22% by volume. Minimum ignition temperature for VF and air mixtures is 400 C. Adding a trace amount (<0.2%) of terpenes is effective to prevent spontaneous polymerization of VF. Inhibited VF has been classified as a flammable gas by the U.S. Department of Transportation.
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Fluoropolymer (PTFE) Hose Industrial Applications

Fluoropolymer hoses are widely used in chemical processing, chemical transfer, chemical filling, and compressed gas transfer/filling applications. Hoses are lined with PTFE, FEP or PFA and can be reinforced with a range of materials such as rubber …
All of the Fluoropolymer hoses consist of an extruded PTFE core. PTFE has an excellent flex life,handles high temperatures and offers superior chemical and corrosion resistance. Additionally, PTFE can be extruded with a static dissipative innercore to prevent the attraction of dust and other particulate and reduce the build-up of static charges.
In the case of a PTFE hose, static electricity is caused when a nonconducting fluid flows at a high velocity through the PTFE natural core tube. When a static charge builds up in the tube of a PTFE hose, it will look for the path of least resistance to ground. If the tube is nonconductive,then the path of least resistance may be to pierce through the wall of the PTFE tube to the conductive Stainless Steel Braid and eventually to the metal fittings and back-to ground through the equipment to which the hose assembly is connected.
The purpose of a static dissipating tube on the inside of the hose is to provide an acceptable path of least resistance and allow the static build-up to dissipate through the core tube to the metal fittings and eventually to ground.

FLUOROPOLYMER HOSE CONSTRUCTION

Fluoropolymer hoses
1. Core
Contains Media
Materials: Natural or Static-Dissipative PTFE with a Smoothbore or Convoluted Core


2. Reinforcement
Provides Resistance to Internal Pressure
Materials: Stainless Steel


3. Jacket or Protective Sleeve
Protects Reinforcement
Materials: Silicone, Polyurethane

 

 

FLUOROPOLYMER HOSE FEATURES

  • ƒ Excellent chemical compatibility
  • ƒ Handles extreme temperatures to +450°F
  • ƒ Environmentally safe
  • ƒ Low moisture permeability
  • ƒ Low friction minimizes pressure drops and deposits 

FLUOROPOLYMER HOSE APPLICATIONS/MARKETS

  • ƒ Chemical transfer lines
  • ƒ General hydraulics
  • ƒ Compressed air/gases
  • ƒ Adhesive dispensing
  • ƒ Coolant Lines
  • ƒ Medical Gases 

IMAGES FOR FLUOROPOLYMER HOSE

Fluoropolymer Hose

About PTFE’s Physical Properties

The structure of PTFE molecules
PTFE, poly(tetrafluoroethene), is made by polymerising lots of tetrafluoroethene molecules.
PTFE's Physical Properties
This simple diagram for PTFE doesn’t show the 3-dimensional structure of the molecule. In the simpler molecule poly(ethene) the carbon backbone of the molecule just has hydrogen atoms attached to it, and the chain is very flexible – it definitely isn’t a straight molecule.
However, in PTFE, the fluorine atoms in one CF2 group are big enough to interfere with those on the neighbouring groups. You need to remember that each fluorine atom will have 3 lone pairs sticking out from it.
The effect of this is to inhibit rotation about the carbon-carbon single bonds. The fluorine atoms will tend to line up so that they are as far apart as possible from neighbouring fluorines. Rotation will tend to involve a clash of lone pairs between fluorines on adjacent carbon atoms – and this makes rotation energetically unfavourable.
The repulsions lock the molecules into a rod-like shape with the fluorines arranged into very gentle spirals – a helical arrangement of the fluorines around the carbon backbone. The rods will then tend to pack together a bit like long thin pencils in a box.
This closely touching arrangement has an important effect on the intermolecular forces as you will see.
Intermolecular forces and the melting point of PTFE
The melting point of PTFE is quoted as 327°C. That’s quite high for a polymer of this sort – so there must be sizeable van der Waals forces between the molecules.
But . . . several web sites talk about PTFE having very weak van der Waals forces. If it had very weak van der Waals forces, it would be a gas – not a fairly high melting point solid. So we have a problem here!
Why do people claim the van der Waals forces in PTFE are weak?
van der Waals dispersion forces are caused by temporary fluctuating dipoles set up as electrons in the molecules move around. Since PTFE molecules are large, you would expect the dispersion forces to be large as well, because there are a lot of electrons which can move.
It is generally the case that the bigger the molecule, the greater the dispersion forces.
However, there is a problem with PTFE. Fluorine is so electronegative that it tends to hold the electrons in the carbon-fluorine bonds closely to itself – so closely that the electrons are prevented from moving as much as you would expect. We describe the carbon-fluorine bonds as not being very polarisable.
van der Waals forces also include dipole-dipole interactions. But in PTFE each molecule is sheathed in a layer of slightly negative fluorine atoms. The only interactions possible between molecules in this case are repulsions!
So the dispersion forces are weaker than you might expect, and dipole-dipole interactions are going to tend to cause repulsion. It is no wonder that people claim that van der Waals forces are weak in PTFE. You don’t actually get repulsion because the effect of the dispersion forces outweighs that of the dipole-dipole interactions, but the net effect is that the van der Waals forces will tend to be weak.
And yet PTFE has a high melting point, and so the forces holding the molecules together must be strong.
How can PTFE have a high melting point?
PTFE is very crystalline in the sense that there are large areas where the molecules are lying in a very regular arrangement. Remember that PTFE molecules can be thought of as long thin rods. These rods will pack very closely together.
That means that although PTFE molecules can’t generate really big temporary dipoles, the dipoles that are produced can be used extremely effectively.
So are the van der Waals forces in PTFE weak or strong?
I think you could argue it both ways! If you had PTFE chains arranged in such a way that the chains didn’t have much close contact, then the forces between them would be weak, and the melting point would be low.
But in the real world, the molecules are closely touching. The van der Waals forces may not be as strong as they could be, but the structure of the PTFE means that they are felt to the maximum effect, producing overall strong intermolecular bonding and a high melting point.
Non-stick properties and friction
Virtually every site that I have looked at treats the relative lack of friction of PTFE and its non-stick properties as if they were the same effect. I don’t think that’s true.
The non-stick properties
This is about why things like water and oil don’t stick to the surface of PTFE, and why you can fry an egg in a PTFE-coated pan without lots of it ending up stuck to the pan.
You need to consider what forces might hold other molecules to the PTFE surface. Possibilities might include some sort of chemical bonding, van der Waals forces or hydrogen bonds.
Chemical bonding
Carbon-fluorine bonds are very strong, and there is no way that any other molecule could get at the carbon chain to enable any sort of substitution reaction to take place. No sort of chemical bonding could take place.
van der Waals forces
We’ve seen that the van der Waals forces in PTFE aren’t very strong, and only work to give PTFE a high melting point because the molecules lie so close together and there is very effective contact between them.
But it is different for other molecules approaching the surface of the PTFE. A relatively small molecule (like a water or an oil molecule) will only have a small amount of contact with the surface, and will only produce a small amount of van der Waals attraction.
A large molecule (like a protein, for example) isn’t going to be rod-like and so, again, there isn’t going to be enough effective contact between it and the surface to overcome the low tendency of the PTFE to polarise.
Either way, van der Waals forces between the PTFE surface and whatever is around it are going to be small and ineffective.
Hydrogen bonds
The PTFE molecules on its surface are completely encased in fluorine atoms. Those fluorine atoms are very electronegative and so will all carry some degree of negative charge. Each fluorine also has three lone pairs of electrons sticking out.
Those are exactly the conditions needed for hydrogen bonding to be possible between lone pairs on the fluorines and hydrogen atoms in water for example. But it clearly doesn’t happen – otherwise there would be strong attractions between PTFE molecules and water molecules and water would stick to the PTFE.
In November 2013, an Iranian PhD student pointed out to me a 1997 paper by Dunitz and Taylor with a title “Organic Fluorine Hardly Ever Accepts Hydrogen Bonds”. If you are interested, you can find it from this site if you have the right access.
They found that only a tiny number of compounds containing C-F bonds would form hydrogen bonds, whereas compounds like HF or the F- ion formed strong hydrogen bonds.
What they didn’t come up with, however, was any definite explanation for this, although they suggested that a possible explanation could lie in the fact that the fluorine atom holds its electrons very tightly in towards the nucleus, and as a result the C-F bond isn’t very polarisable. The electrons won’t move sufficiently towards a hydrogen from water (or anything similar) in order for a hydrogen bond to form.
Personally, I have a problem seeing why that is different from the situation in H-F or a fluoride ion, both of which can form hydrogen bonds with water.
And their final sentence said:
“At the same time, it has to be admitted that, in spite of the vast amount of work on hydrogen bonding over the years, the chemical factors influencing the strength of hydrogen bonds (especially factors influencing H-bonding acceptor ability) are still not completely understood.”
Summary
There are no available methods for other molecules to attach themselves successfully to the surface of the PTFE, and so it is has a non-stick surface.
The low friction
PTFE has a very low coefficient of friction. What this means is that if you have a surface coated with PTFE, other things will slide on it very easily.
What follows is just a quick summary of what is happening. This comes from a 1992 paper called Friction and wear of PTFE – a review which is available free from this link.
At the start of sliding, the surface of the PTFE fractures, and lumps are transfered to whatever it is sliding against. That means that the PTFE surface tends to wear away.
As sliding continues, the lumps are spread out to a thin film.
At the same time the surface of the PTFE is dragged out into an organised layer.
The two surfaces in contact now both have well organised PTFE molecules which can slide over each other.
What holds the PTFE layer onto the substance it is sliding against is quite complicated, and thoughts on this may have changed since the paper was written. If you are interested, you will find it discussed on the page numbered as 203 of the paper (page 11 of 19 on my pdf reader).

Typical Properties of Fluoropolymers(PTFE,FEP,ETFE,PVDF,PCTFE)

Properties of Fluoropolymers
PTFE Properties:
The Steel Industry and Chemical Processing Industry have been using fluoropolymer tubing products from materials like PTFE and hoses for many years for transferring highly caustic or corrosive chemicals. 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.
PTFE 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
PTFE 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.
FEP Properties:
Electrical FEP exhibits most of the properties of PTFE. However, because of its excellent electrical FEP properties, FEP tubing is a valuable and versatile electrical insulator.

Fluoropolymers (PTFE,PCTFE,PVF,PVDF) Properties

Fluoropolymers are produced from alkenes in which one or more hydrogen atoms have been replaced by fluorine. The most important members are polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), poly(vinyl fluoride) (PVF) and poly(vinylidene fluoride) (PVDF)

Due to the weak van der Waals forces, polyfluoroolefins have a very low coefficient of friction and very low surface tension and, due to the stability of the (multiple) carbon-fluorine bonds, excellent chemical resistance, which increases with the number of fluorine atoms in the repeat unit. They can be used both at high and very low temperatures and possess outstanding resistance to weathering (UV-resistance). Most fluoropolymers are also totally insoluble in most organic solvents and stable in concentrated acids and bases.

Fluoropolymers Properties

The largest-volume polyfluoroolefin is polytetrafluoroethylene (PTFE). This polymer has unique performance properties. It has outstanding thermal, electrical and chemical resistance and can be used both at very high (up to 530 K) and extremely low temperatures. Its coefficient of friction is among the lowest of all polymers (self-lubricating and non-stick). PTFE cannot be dissolved in any common solvent below its melting point. It is ideal for applications where broad chemical resistance, high durability, wide service temperature range, excellent dielectric properties, low friction, and non-stick are required. The properties of PTFE – high crystallinity, very high melting point (600 K), and very high melt viscosity – do not allow its processing by the usual process methods for plastics. Instead, similar to metal forming, the granular resins are processed by compression moulding at ambient temperature followed by sintering above the crystalline melting point.

Various copolymers of tetrafluoroethylene (PFA, FEP, ETFE) and other fluoropolymers with lower melting point and crystallinity were developed to overcome the lack of melt processability of PTFE. Among these, poly(vinylidene fluoride) (PVDF) is noteworthy. These resins are some of the easiest to process fluoropolymers. PVDF has high tensile and impact strength, and excellent resistance to tensile creep and fatigue. Like PTFE, it exhibits high thermal stability.