Polyvinylidenedifluoride - PVDF

Polyvinylidenedifluoride (PVDF) is a white, semi-crystalline, and semi-opaque engineering thermoplastic that can be processed by melting and is very expensive.

Although it is not as good as PTFE, it has good temperature and general chemical resistance. It has good abrasion and radiation resistance. In addition, it has high dielectric losses but is somewhat stronger and stiffer than most (melt-processable) fluoropolymers.

PVDF has a highly dipolar molecule which means the correct morphology results in valuable piezo- and pyro-electric properties.

The preferred form is called the ß phase or Form I, where in the predominantly "head to tail" polymer chains have an all-trans extended planar zig-zag form with the dipoles of neighboring chains parallel to one another.

This is formed from the more common Alpha phase (Form II) by mechanical deformation followed by electrical polarisation at relatively high electrical fields.

In practice, both biaxial and uniaxial mechanical orientations are used which, after poling, give a different balance of piezo-/pyro-electric properties.

Polymer Type

Thermoplastic

Advantages

Polyvinylidenedifluoride (PVDF) is the highest tensile strength of all processable fluorocarbons. It has good radiation resistance (better than other fluorocarbons), is melt processable and has a good abrasion resistance. Good general chemical resistance, although inferior to PTFE.  Maximum use temperature 150°C (300°F).  Useful piezo-electric properties.

Disadvantages

High dissipation factor. Processing machinery needs to be very clean. Normally cannot reinforce with glass fibres due to decomposition initiated by boron. Poor resistance to fuming acids.

Applications

Applications of PVDF include chemical process industry – bearings, pipes, pipe fittings, vessels and linings (all especially for the chemical processing industry), wire insulation, chemical laboratory apparatus, heat-shrinkable tubing, and piezo-electric devices

PVDF is used for wire insulation Image Credit: ShutterStock/schankz

PVDF is used for wire insulation Image Credit: ShutterStock/schankz  

Typical Properties

Property Value
Density (g/cm3) 1.76
Surface Hardness SD80
Tensile Strength (MPa) 35
Flexural Modulus (GPa) 1.7
Notched Izod (kJ/m) 0.18
Linear Expansion (/°C x 10-5) 16
Elongation at Break (%) 50
Strain at Yield (%) 9.5
Max. Operating Temp. (°C) 150
Water Absorption (%) 0.04
Oxygen Index (%) 43
Flammability UL94 V0
Volume Resistivity (log ohm.cm) 14
Dielectric Strength (MV/m) 13
Dissipation Factor 1 kHz 0.06
Dielectric Constant 1 kHz 7
HDT @ 0.45 MPa (°C) 121
HDT @ 1.80 MPa (°C) 82
Material. Drying hrs @ (°C) 4 @ 90
Melting Temp. Range (°C) 260 - 300
Mould Shrinkage (%) 3
Mould Temp. Range (°C) 80 - 90

Source : Abstracted from Plascams

For more information on Plascams please visit RAPRA Technology Ltd.

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