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Polyvinylidene Fluoride (PVDF): Complete Guide

In the recent years, there has been considerable interest expressed in the polymer Polyvinylidene Fluoride (PVDF). The interest it received because it exhibits strongest piezoelectric properties as compared to any other commercial polymer.

The polymer is widely used in high tech applications such as chemical process equipment, electrical and electronics, specialty and energy related applications.

But, what makes PVDF a high performance plastic in several sectors? Read on to know more…

What is PVDF?


Key Properties and Applications of PVDF PVDF (PVF2 or Polyvinylidene fluoride or polyvinylidene difluoride) is a semi-crystalline, high purity thermoplastic fluoropolymer. With service temperatures up to 150°C, PVDF displays good combination of properties such as:

  • Exceptional chemical resistance
  • High mechanical strength
  • Piezoelectric and pyroelectric properties
  • As well as good processability

Its highly desirable insolubility and electrical properties result from the polarity of alternating CH2 and CF2 groups on the polymer chain.

PVDF is readily melt-processible and can be fabricated into parts by injection and compression molding. As a result, it is commonly employed in chemical processing equipment such as pumps, valves, pipes, tubes and fittings; sensors and actuators etc.

It has many electronic applications, especially as jacketing materials for plenum-rated cable used in voice and video devices and alarm systems. The low flame spread and smoke generation of PVDF is a prime asset in these applications.

PVDF is gaining acceptance as a binder for cathodes and anodes in lithium-ion batteries, and as a battery separator in lithium-ion polymer systems.

Emerging applications of PVDF include fuel cell membranes, and components for aircraft interiors and office automation equipment.

Molecular Structure of Polyvinylidene Fluoride (PVDF)
Molecular Structure of Polyvinylidene Fluoride (PVDF)

Thanks to its excellent combination of properties and processability, PVDF has become the largest volume of fluoropolymers after PTFE.

PVDF is available commercially in a wide range of melt flow rates and with various additives to enhance processing or end use properties. Today, PVDF is sold under a variety of brand names.

» View all PVDF commercial grades and suppliers in Omnexus Plastics Database

This plastic database is available to all, free of charge. You can filter down your options by property (mechanical, electrical…), applications, conversion mode and many more dimensions.

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How PVDF is produced?


PVDF (homopolymers and copolymers) is generally synthesized by the free radical polymerization of 1,1-difluoroethylene (CH2=CF2). The polymerization takes place in the suspension or emulsion from 10-150°C and pressure of 10-300 atm. The material obtained is then processed into film or sheets.

1,1-difluoroethylene - PVDF Monomer
1,1-difluoroethylene - PVDF Monomer
Polymerization
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Structure of PVDF
Structure of PVDF

Chlorotrifluoroethylene (CTFE) or hexafluoropropene (HFP) are most commonly employed to prepare PVDF copolymers.

  • PVDF Copolymers with HFP contain increased flexibility over PVDF homopolymer grades
  • Copolymers with CTFE are among the most flexible PVDF products with excellent low temperature performance and low shrinkage

Copolymers are ideal for wire & cable and tubing applications, which require enhanced flexibility.


Properties of PVDF


Crystal Structure

It is typically a semi-crystalline polymer that is approx. 50% amorphous. It has highly regular structure with most of VDF units joined head-to-tail with very less percentage of monomer units joined head-to-head.

This fluoroplastic exist in four possible conformations named as α, β, γ, and δ phase.

  • The C–F bonds are polar and the highest dipole moment is obtained with the alignment of all dipoles of the polymer in the same direction, corresponding to the β-phase of the PVDF. β-phase is the desirable phase to its piezoelectric characteristics of the polymer.
  • The dipole moments of α crystallites are oriented in opposite directions, resulting in a zero net polarization. 

Alpha- and Beta-phase Structure of PVDF
Alpha- and Beta-phase Structure of PVDF
(Source: Royal Society of Chemistry)


Physical Properties

It has one of the lowest melting points of the commercial fluorothermoplastics, but has highest heat deflection temperature under load.

Polymer Deflection Temperature, °C Melting Point, °C
0.5 MPa 1.8 Mpa
PVDF 148 113 178
PCTFE 126 75 218
PTFE 121 56 327
ECTFE 116 77 240
ETFE 104 74 270
PFA 73 48 310
FEP 70 51 270

The high crystallinity and surface tension properties of PVDF provide very low permeation values compared to other fluoropolymers. PVDF shows low permeabilities to gases and liquids. Though, the permeability of PVDF is influenced by the crystalline degree and the modification of crystalline parts.

Mechanical Properties

As compared to ETFE and ECTFE, PVDF has similar tensile modulus but lower impact strength. Modification with HFP or CTFE lowers the modulus but increases elongation and impact strength.

Property (Standard) PVDF ETFE ECTFE
Melting point, °C, ASTM D 3418 154-184 250-275 236-246
Specific gravity, g/cm3, ASTM D 792 (Solid) 1.75-1.80 1.72 1.7
Tensile Strength @ 23°C, MPa, ASTM D 638 36-56 38-48 45-60
Elongation @ 23°C, %, ASTM D638 25-500 100-350 150-250
Tensile Modulus @ 23°C, MPa, ASTM D 638 1340-2000 830  
Izod impact strength @ 23°C, J/m, ASTM D 256 160-530 no break no break
Coefficient of thermal expansion, ASTM D 696 ~10-4 9 x 10-5 5 x 10-5
Processing temp. range, °C 200-300 300-345 260-300
Dielectric constant, (1 kHz), ASTM D 150 7.5-13.2 2.6 2.6
Dielectric strength, kV/mm, ASTM D 149 260-950 59 80-90
Dissipation factor, (1 kHz), ASTM D 150 0.0163-0.019 0.0008 0.0024
LOI, %, ASTM D 2863 44 30 64

When exposed to flame, PVDF is non-flammable and non-dripped. It is self-extinguishing – It is TL V0 compliant. The LOI is 44%. It also exhibits good resistance to UV light.

Chemical Resistance

The chemical inertness varies between the fluoropolymers such as PTFE, FEP, PFA and MFA exhibit chemical inertness to a wider range of chemicals than do the partially fluorinated polymers such as CTFE (or PCTFE) and ECTFE.

At elevated temperatures, PVDF can be dissolved in organic solvents such as esters and amines, which allows PVDF to be applied as corrosion-resistance coatings on chemical process equipment and architectural panels.

Parts made of PVDF display great resistance to mineral and organic acids, aliphatic and aromatic hydrocarbons, alcohols and halogenated solvents.

Electrical and Piezoelectric Properties of PVDF

Electrical and Piezoelectric Properties of PVDF PVDF is primarily used in wire and cables isolation, thanks to its high dielectric constant and dissipation factor.

However, there poor electrical properties allow the production of PVDF films with piezoelectric and pyroelectric behavior.

There films are prepared from extruded films in B-phase conformation. Both surfaces of the film are metallized and then subjected to high voltage, which leave it permanently polarized.

Such films generate a voltage when stretched or compressed (piezoelectricity) or heated (pyroelectricity) at a temperature close to the melting point. The polymer films also show some ferroelectricity.

Applications of PVDF


  • Energy consuming industries, automotive, military aircraft and petrochemical industries require VDF-based seals, gaskets, lining etc. resistance to corrosive materials

  • Electrical and Electronic Devices: Used for wire insulation/cable jacketing in aircraft and electronics industry, industrial power control systems, high temperature wiring etc.
Applications of PVDF

  • Chemical Processing Equipment: Heat-shrinkable or flexible tubing made from PVDF resin is widely used in high purity water systems, pipes of chemicals, automotive fuel lines etc. It is used on a large scale as a liner for pipes and valves

  • Piezoelectric films are very sensitive transducers with various applications. These films are strong, lightweight and flexible, they can be molded into unique designs and can be glued with commercial adhesives. 

  • PVDF is also widely used in Filtration and separation equipment (filters, membranes, housings)

  • It can also be used as a pyroelectric sensor and laser beam profile sensor in more advanced applications.

  • PVDF membrane can be used as separators in lithium ion batteries, as it has good chemical and thermal stability. These membrane have good mechanical strength, appropriate pore size and shutdown characteristics.


What is PVDF Membrane?


PVDF is one of the most used membrane materials and has received great attentions thanks to its outstanding properties.

Properties such as thermal stability, chemical resistance and processability to form membranes make PVDF ideal for use in biomedical membrane applications and waste water treatment.
PVDF Membranes are Widely Used for Waste Water Treatment
Thank to these features, applications of PVDF membranes are currently found in:
  • Pressure-driven water- and waste-treatment treatment (e.g., microfiltration, ultrafiltration and membrane bioreactor), 
  • Membrane contactors operations (e.g., membrane distillation, acid gas absorption and stripping, volatile organic compounds removal)

Today, most of the commercial membranes are produced via phase inversion method mainly because of its simplicity and flexible production scales (Hence, low cost of production)

But there are certain drawbacks associated with PVDF membranes such as wetting or fouling which can be easily solved by enhancing surface roughness or increasing the hydrophilic nature of the membrane. Though it cannot be absolutely prevented even with modification.

PVDF membranes can be used as separators in lithium ion batteries, as it has good chemical and thermal stability. These membrane have good mechanical strength, appropriate pore size and shutdown characteristics.

They are also used for the manufacture of ion-exchange membranes.

Processing of PVDF


PVDF grades are available in a wide range of melt viscosities as powders and pellets. It can be processed using techniques applicable to standard thermoplastics:

  • Extrusion 
  • Injection, compression and transfer molding
  • Machining

Drying of resin before processing is usually not necessary Care must be taken to eliminate "hang-up" areas where molten resin can collect and thermally decompose if residence time is excessive

Processing temperature: 190 to 280°C

Injection Molding

  • Melt temperature should be between 200-270°C
  • A mold temperature of 50-95°C is recommended 
  • The relatively high melt viscosity of PVDF makes proper mold design an important factor in injection molding
  • The shrinkage (3-4 %) of injected molded pieces, has to be take into consideration during conception

» Check out all PVDF Grades Suitable for Injection Molding

Extrusion

  • In extrusion, attention should be paid to the elimination of dead spots where degradation of polymer can start
  • Extrusion temperature : from 230 to 290°C
  • No extrusion aids, lubricants, or heat stabilizers are needed to extrude PVDF
  • L/D ratio of at least 20 is recommended

» Find Suitable PVDF grade for Extrusion Applications

Commercially Available PVDF Compounds





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