Chemical Properties
Poly(vinylidene fluoride) (PVDF) is made by the polymerization of vinylidene fluoride in aqueous medium under pressure but details of the process
have not been disclosed. Two grades of polymer are available with differing
average molecular weight, namely 300000 and 600000.
Poly(vinylidene fluoride) has good tensile and impact strengths. The polymer has unusual
piezoelectric and pyroelectric properties which have resulted in its use in solid
state switching devices.
The resistance of poly(vinylidene fluoride) to solvents and chemicals is
generally good but inferior to that of polytetrafluoroethylene and polychlorotrifluoroethylene. Some highly polar solvents such as dimethylacetamide
dissolve the polymer at elevated temperature whilst organic amines cause
discoloration and embrittlement. Fuming sulphuric acid leads to suiphonation.
Poly(vinylidene fluoride) has good heat resistance and may be used continuously at temperatures up to 150°C. The polymer may be melt processed
by the standard techniques of injection moulding and extrusion. The polymer
has very good weather resistance. Applications for poly(vinylidene fluoride) include moulded and lined tanks, valves, pumps and other equipment designed to handle corrosive fluids. The polymer is also used in coatings and wire covering.
Chemical Properties
Polyvinylidene fluoride (PVDF) is one of the most rigid and abrasion resistant of the melt-processible fluoropolymers. It has good chemical resistance, though hot sulfuric acid and hot amines can attack it. Like most fluoropolymers, PVDF is inherently flame retardant. It retains useful mechanical properties until 300 degrees F (149 degrees C).
Uses
Poly(vinylidene fluoride) is resistant to most acids and alkalies but it is attacked by fuming sulfuric acid. It is soluble in dimethylacetamide but is insoluble in less polar solvents. Copolymers have been produced with ethylene, tetrafluoroethylene, chlorotrifluoroethylene and hexafluoroethylene. The latter is an elastomer called Viton or Fluorel.
The homopolymer is used as a chemical resistant coating for steel, for tank linings, hose, and pump impellors. The elastomeric copolymer with hexafluoroethylene when cured with hexamethylenediamine is used as a seal, gasket, 0-ring, tubing, coating and lining.
Uses
Poly(vinylidene fluoride) is useful in coatings, film, filter cloth, instrument linings, filtration membranes, pump parts, linings and valves. It is also employed as a material for transducers in devices such as headphones, microphones and sonic detectors. It is also essential for piezoelectric and electrostrictive applications. In addition, it is useful for monofilament fishing lines replacing nylon monofilament. It acts as a standard binder used in the production of composite electrodes for lithium ion batteries. It serves as a high grade insulator for wires, nanomaterials and pressure sensors. It is utilized to make filters which are used to prepare samples for high performance liquid chromatography and other advanced analytical techniques.
Uses
Coatings, film, filter cloth, instrument linings, filtration membranes, pump parts and linings and valves.
Definition
ChEBI: A polymer composed of repeating 1,1-difluoroethyl units.
Production Methods
PVDF, the addition polymer of 1,1,difluoroethene, is prepared
by high-pressure free-radical polymerization in aqueous
systems. It has applications in electric and electronic
devices, as weather-resistant binders for exterior architectural
finishes, and in a number of areas of the chemicalprocessing
industry. The lack of additives and thus the
exceedingly low contamination levels make the polymer
useful in ultrapure water systems, for example, where high
purity is necessary for construction materials.
Production Methods
This product is made by the free-radical chain polymerization of vinylidene fluoride (H2C=F2). This odorless gas which has a boiling point of 82 °C is produced by the thermal dehydrochlorination of 1,1,1-chlorodifluoroethane or by the dechlorination of 1,2-dichloro-1,1-difluoro-ethane.
General Description
Poly(vinylidene fluoride) PVDF is a semi crystalline non-centrosymmetric polymer which exhibits piezo-, pyro- and ferroelectric properties. It is a linear polymer that shows permanent electric dipoles perpendicular to the direction of the molecular chain. These dipoles result from the difference in electronegativity between the atoms of hydrogen and fluorine with respect to carbon. Depending on the processing conditions, PVDF exhibits several different crystalline phases (α,β,γ,δ). The β phase of PVDF is the phase that exhibits the best ferroelectric and piezoelectric properties.
Industrial uses
The properties are generally similar to those ofthe other fluorinated resins: relative inertness,low dielectric constant, and thermal stability(up to about 150°C). The resins (PVF2 resins)are, however, stronger and less susceptible tocreep and abrasion than TFE and CTFE resins.
Applications of polyvinylidene fluoride aremainly as electrical insulation, piping, processequipment, and as a protective coating in theform of a liquid dispersion.
Industrial uses
PVDF can be used with halogens, acids, bases, and strong oxidizing agents, but it is not recommended for use in contact with ketones, esters, amines, and some organic acids.
Although electrical properties of PVDF are not as good as those of other fluoroplastics, it is widely used to insulate wire and cable in computer and other electrical and electronic equipment. Heat-shrinkable tubing of PVDF is used as a protective cover on resistors and diodes, as an encapsulant over soldered joints.
Valves, piping, and other solid and lined components are typical applications of PVDF in chemical-processing equipment. It is the only fluoroplastic available in rigid pipe form.
Woven cloth made from PVDF monofilament is used for chemical filtration applications. A significant application area for PVDF materials is as a protective coating for metal panels used in outdoor service.
A recently developed capability of PVDF film is based on the unique piezoelectric characteristics of the film in its so-called beta phase.
When compressed or stretched, polarized PVDF generates a voltage from one metallized surface to the other, proportional to the induced strain.
Industrial uses
The fluorohydrocarbons are of two kinds: polyvinylidenefluoride (PVF2) and polyvinyl fluoride(PVF). Although similar to the other fluoroplastics,they have somewhat lower heatresistance and considerably higher tensile andcompressive strength.
PVF2, the toughest of the fluoroplastic resins,is available as pellets for extrusion andmolding and as powders and dispersions forcorrosion-resistant coatings. This high-molecular-weight homopolymer has excellent resistanceto stress fatigue, abrasion, and to coldflow. Although insulating properties and chemicalinertness of PVDF are not as good as thoseof the fully fluorinated polymers, PTFE andFEP, the balance of properties available inPVDF qualifies this resin for many engineeringapplications. It can be used over the temperaturerange from –73 to 149°C and has excellentresistance to abrasion.
Solubility in organics
cyclohexanone, DMAC, DMF, DMSO, ethylene carbonate, propylene carbonate
Toxics Screening Level
The screening level for PVDF is 0.1 μg/m3 based on annual averaging.
