Polyvinylidene Fluoride (PVDF): Properties, Production, & Applications

Polyvinylidene fluoride (PVDF), also known as polyvinylidene difluoride and PVF2, is part of the fluoropolymers family; a group of specialised, versatile polymeric materials with distinct properties that result from the strong bond between their carbon atoms and fluorine atoms and the fluorine shielding of the carbon backbone. PVDF is a specialty polymer with pyroelectric and piezoelectric properties and is used in the manufacturing of diverse high-purity, high-strength, and high-chemical-resistance products for applications in electrical, electronic, biomedical, construction, fluid-systems, oil-and-gas, and food industries [1][2].

Here, you will learn about:

  • What PVDF is
  • How PVDF is produced
  • What the properties of PVDF are
  • Main applications of PVDF
  • How PVDF is used in additive manufacturing 
  • What the market and future applications of PVDF are

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Solvay’s Solef® PVDF for ultrafiltration membranes. (Credit: Solvay)

What is PVDF?

PVDF is a semicrystalline, thermoplastic polymer. Its degree of crystallinity varies in the range of 35 - 70%, depending on the method of preparation [3]. What makes it special is that it has a unique combination of mechanical and electrical properties (i.e., piezoelectricity), retains high standards of purity, and possesses high resistance to most chemicals including solvents, acids, and hydrocarbons.

With the chemical formula (CH2=CF2)n, PVDF sits in the middle between polyethylene (PE: (CH2=CH2)n ) and polytetrafluorethylene (PTFE: (CF2=CF2)n ). Its simple chemical structure gives it the flexibility of PE and some of the stereochemical constraints of PTFE. The different molecular and crystal structures of PVDF change depending on the preparation of the samples [4].

The complex crystalline polymorphism of PVDF cannot be found in other synthetic polymers. There are five known crystalline forms in PVDF: alpha, beta, gamma, delta, and epsilon [5]. The beta phase is the most commonly used form, and together with the alpha and gamma phases constitute the major phases:

  • The alpha phase is nonpolar and is generated in the melting process from melt crystallisation at any temperature. 
  • The beta phase is an oriented phase that results from the mechanical deformation of the specimen via uniaxial or biaxial mechanical drawing below 70 °C. It is the most used for piezoelectric applications.
  • The gamma phase is a special form that develops under specific circumstances. It can be generated through crystallisation at temperatures close to the melting point of the alpha phase via melt casting or solution casting.

 

Production of PVDF

PVDF is produced by free radical polymerisation of the monomer vinylidene difluoride (1,1-difluoroethylene). This process occurs in presence of an emulsion between 10 and 150 °C subjected to a pressure of 10 to 300 atm. 

The PVDF material is processed and fabricated into parts and coatings using melt casting, or processed from a solution such as solution casting, spin coating, and film casting.

  • Melt Casting: the polymer is heated until it melts and is then poured into a mould with the desired shape until it solidifies and cools [6].
  • Solution casting: the polymer is dissolved in a suitable solution to form porous polymer membranes. The polarity, temperature, and molecular weight of the solvent are key factors in the solubility of PVDF [7].
  • Spin coating: the polymer is processed into thin films from the higher beta-phase, where films are stretched or subjected to high pressure or an electric field in order to develop piezoelectric thin film devices [8].
  • Film casting: using a customised extrusion procedure, the polymer is processed into uniform high-quality films or thin sheets. This process is also known as film extrusion [6].

Properties of PVDF

Some of the most characteristic features of PVDF are [1]:

  • Excellent abrasion resistance
  • Good thermal stability
  • Resistance to ultraviolet light (UV) and high energy radiation
  • High resistance to creep under long stress (creep)
  • High resistance to fatigue during cyclic loading
  • High dielectric strength
  • Resistance to most chemicals and solvents
  • Low water absorption; absorbs less than 5% water at room temperature
  • Recognized as mechanically stronger than other fluoropolymers (i.e., PTFE)
  • Meets standards for food processing applications (non-toxic and resistant to bacteria and fungi)

Table 1 summarizes some of the typical mechanical, electrical, and thermal properties of this polymer.

Table 1. Typical Properties of PVDF

 

PVDF

Mechanical Properties

Tensile strength (at 23°C)

9 – 120 MPa

Compressive strength (at 23°C)

13.8  - 172 MPa

Elongation at yield (at 23°C)

3.5 – 40 %

Yield strength (at 23°C)

4.8 - 120 MPa

Elastic modulus (at 23°C)

0.03 - 17.1 GPa

Flexural modulus (at 23°C)

0.07 - 20.9 GPa

Density (at 23°C)

0.7 – 1.89 g/cm3

Water absorption (at 23°C)

0.01 - 0.5 %

Electrical Properties

Dielectric strength (at 23°C)

1.4 – 110 kV/mm

Surface resistivity (at 23°C)

1*1010 - 1*1014 Ohm/sq

Dielectric constant (at 23°C)

6 - 8

Volume resistivity (at 23°C)

1*106 - 3.2*106 Ohm.cm

Thermal Properties

Melting point

92 - 342 °C

Specific heat capacity (at 23°C)

665 - 1500 J/kg.K

Thermal conductivity (at 23°C)

0.13 – 0.19 W/m.K

Coefficient of thermal expansion (at 23°C)

2*10-5 – 2.6*10-4 /K

Glass transition temperature

-43.3 – -38.3 °C

Applications of PVDF

Some of the most common applications of PVDF components include [1][2][4]:

  • Filaments for additive manufacturing 
  • High purity semiconductors
  • Wire and cable isolators
  • Biomedical, artificial membranes
  • Nuclear waste processing
  • Pipe and pumping applications
  • General chemical processing
  • Water treatment membranes
  • Food and pharmaceutical processing
  • Battery and sensors
  • Architectural coating

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PVDF for additive manufacturing

Materials with piezoelectric functionalities have the tendency to elongate when subjected to an electric field due to the generation of mechanical strain. These materials have great importance for 3D printing of electronic devices, such as sensors and actuators. 

In addition to its piezoelectric properties, PVDF is lead-free, which renders it favourable in biomedical applications and the food industry. It is also a flexible material, a property needed in applications requiring high displacement. Piezoelectric PVDF sensors have a sensitivity that is directly influenced by the polar phases’ concentration and orientation. The most commonly used 3D printing method that prints PVDF products is filament fused fabrication (FFF), also known as fused deposition modeling (FDM). Here, a PVDF filament is extruded through a heated nozzle, which liquefies the material for printing [9].

A 2017 peer-reviewed study showed the effects of FFF process parameters on the properties of a printed PVDF film, including the in-fill angle, extrusion temperature, horizontal speed, bed material, and applied hot end voltage. The results showed that having relatively fast rates of extrusion together with low extrusion temperatures and high hot end voltages led to higher beta-phase content. PVDF films printed with a high β-phase content demonstrated a small, consistent piezoelectric response after being subjected to a post-printing corona poling procedure [10]. 

Thus, PVDF is recognised as an excellent material for additive manufacturing of piezoelectric devices thanks to its ease of process, flexibility, and biocompatibility.

PVDF filaments for additive manufacturing provide long term performance up to 120 °C, exceptional chemical resistance, high resistance to UV, weathering, and oxidation [11]. The low melting temperature of PVDF makes the filaments accessible to a wider variety of printer models [12].

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Solvay's Solef® PVDF filament. (Credit: IGO3D)

The market and future of polyvinylidene fluoride

The market of PVDF is mainly controlled by pipes and fittings, Li-ion batteries, and semiconductors. The PVDF market is expected to grow at a CAGR of about 5% between 2021 and 2026. The Asia-Pacific region, particularly China, is the largest producer as well as the largest consumer and is expected to continue in the leading position during the same period [2]. 

Numerous properties of PVDF are expected to have an impact in the market of the growing biomedical industry [2]. PVDF is one of the few polymers being used for microporous membranes due to their specific filtration properties as well as for diverse accessory equipment such as pumps, tubing, fittings, and other parts in contact with fluids [13]. High demands on coatings, photovoltaic films, oil & gas products, and electrical applications are also expected to contribute to the growth of this market and its applications [14].

Sources

[1] Drobny, J.G., 2009, Technology of Fluoropolymers, 2nd Edition, CR Press

[2] Grand View Research, Polyvinylidene Fluoride Market Size, Share & Trends Analysis Report By Application, Regional Outlook, Competitive Strategies, And Segment Forecasts, 2019 To 2025, [Online]

[3] Sina Ebnesajjad, 2011, Introduction to Fluoropolymers, In Plastics Design Library, Applied Plastics Engineering Handbook, William Andrew Publishing, 2011, Pages 49-60

[4] Lee S., 2006, Encyclopedia of Chemical Processing, Vol 4, Taylor and Francis, New York

[5] Gregorio  Jr. R., 2006, Determination of the a, b and g crystalline phases of poly(vinylidene fluoride) films prepared at different conditions, Journal of Applied Polymer Science, Vol 6, no. 4, pp 3272-3279, [Online]

[6] Sepehri A., 2012, Development of micro 3D structured polyvinylidene fluoride (PVDF) thin film, Thesis Masters of Science in Mechanical Engineering, San Diego State University 

[7] Solvay, Processing Guide for Polymer Membranes, Technical Bulletin, Special Polymers, [Online] 

[8] Roopa T.S., Murty N, Swathi H. S., Angadi G,  and Harish D.V.N, 2019, Synthesis and characterization of spin-coated clay/PVDF thin films, Bulletin of Material Sciences, Vol 42, No. 15, [Online] 

[9] Marandia M., Tarbutton J., 2019, Additive manufacturing of single- and double-layer piezoelectric PVDF-TrFE copolymer sensors, Procedia Manufacturing, Vol 34, pages 666-671, [Online] 

[10] Porter D.A, Hoang T. V.T., and Bearfield T. A., 2017, Effects of in-situ poling and process parameters on fused filament fabrication printed PVDF sheet mechanical and electrical properties, Vol 13, pages 81-92, [Online] 

[11] Kumasi Sadasivuni K., Deshmuck K., and Almahaaded M.A., 3D and 4D Printing of Polymer Nanocomposite Materials, Processes, Applications, and Challenges, Elsevier, Cambridge MA 

[12] Solvay, 2019, A new material for 3D printing? Solvay’s got it…, [Online] 

[13] Polymer Solutions, 2015, The Impact of Fluoropolymers on the Medical Device Industry, [Online]

[14] Future Market Insights, Polyvinylidene Fluoride (PVDF) Market: Global Industry Analysis and Opportunity Assessment 2014 – 2020, [Online]

Piezoelectricity, defined as the ability of a material to generate an electric field when subjected to mechanical stress or strain, was investigated in polymers of biological nature as well as synthetic optically active polymers since the 1950s. The strong piezoelectricity on oriented polyvinylidene fluoride (PVDF) was first reported by Heiji Kawai of the Kobayashi Institute of Physical Research of Tokyo in 1969. Since his discovery, significant scientific work has been developed towards diverse applications for PVDF products and its copolymers [a][b].

[a]  Fukada E., 2000, History and recent progress in piezoelectric polymers, IEEE Transactions on Ultrasonics Ferroelectrics, and Frequency Control, Vol 47, No. 6, p.1277-90, [Online] Available at 

[b] Brown L.F. and Harris G.R, 2000, Introduction to the Special Issue on the 30th Anniversary of the Discovery of Piezoelectric PVDF, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 47, No. 6, November 2000, [Online] Available at