1. SPECIALTY PLASTICS Polyvinylidenefluoride (PVDF)

2. Polyvinylidenefluoride (PVDF)

3. General Description
Introduced by Pennwalt Corp. in 1961, PVF2 or PVDF is a high molecular weight homopolymer.
The monomer an be obtained from trichloroethylene by reacting with hydrofluoric acid and the action of metallic zinc on the difluorodichloroethane formed.
The partially crystalline polymer contains over 57% w/w fluorine.

4. Particular advantages of PVDF are:
- high mechanical strength, stiffness and toughness,
relatively resistant to high and low temperatures
- tough even at low temperatures,
- good chemical resistance.

5. Structure and Properties
The degree of crystallinity depends on the history of the molding.
Rapid cooling of thin­ walled moldings and film results in transparent products; slow cooling or annealing at 135 °C lead to highly crystalline products with high stiffness and compressive creep strength.

6. Availability
PVDF is supplied in various grades as:
granules for injection molding and extrusion,
as powder and
as 45 to 50% dispersions in organic solvents (dimethyl phthalate & diisobutylketone).

7. Mechanical Properties
Transition Temperatures - PVDF has a glass transition temperature Tg of 40 °C, a crystallization temperature of 140 °C and a melting point of 171 °C.

8. Thermal Properties
PVDF can be used over the range -60 to +150°C.
It withstands temperatures as follows without any noticeable degradation:
- 150°C over 1 year,
- 260°C up to 12 hours,
- 240 °C up to 30 minutes,
- at 480 °C it decomposes within a few minutes.
Copper, aluminium and iron catalyze decomposition.

9. Electrical Properties
Like PVF, PVC and PVDC, the polar nature of PVDF precludes its use for high frequency applications.
The volume resistivity is greater than 1015 W at 30 °C making it highly suitable for use in the mains frequency range.
The dielectric strength (1 mm film) is 22 kV/mm, the surface resistance exceeds 1013 W,

10. Resistance to Chemicals
Chemical Properties
Resistance to Chemicals
PVDF is resistant to acids (apart from fuming nitric acid), alkaline solutions, solvents, aromatic, aliphatic or chlorinated hydrocarbons, oils, fats, fluoro-refrigerants.
It is not resistant to primary amines at elevated temperatures, hot acetone (thin films), strongly polar organic compounds such as dimethylformamide, diethyl acetamide, cyclohexanone, ketones, esters.

11. Weathering Resistance Resistance to Radiation
PVDF deteriorates slightly outdoors.
Resistance to Radiation
PVDF is resistant to UV; there is slight degradation in the range 200 to 400 nm.
Its resistance to high energy radiation is superior to that of other fluoroplastics.

12. Toxicological Assessment
Flammability
PVDF is classified as V-0 to UL94. The oxygen index is 44%.
Toxicological Assessment
There are no restrictions on the use of
PVDF with foodstuffs.
It is non-toxic.
Gases liberated during processes must be
ventilated.

13. Processing - 1
Injection molding, extrusion and coating are the most important methods of processing PVDF.
The storing temperature of coatings produced by spraying, dipping or casting is 190 to 215°C.

14. Processing-2
It is absolutely essential that the surfaces of plasticizing screws in injection molders or extruders do not contain any boron.
Boron-containing products such as various glass fiber materials or MoS2 are incompatible with PVDF and cause spontaneous decomposition of the product during processing (fire, vaporization).
This can also occur with colorants, fillers and reinforcements not certified by the manufacturer. Suitable pigment concentrates are available.

15. Joining -1
Welding
Welding with round nozzle °C
Welding with high speed nozzle °C
Heated tool welding 230 °C
Melt pressure 0.5 bar
Welding pressure 2 bar
HF welding is suitable for wall thicknesses up to 2 mm
Ultrasonic welding: near and remote field methods .

16. Joining-2
Bonding
PVDF with PVDF: solvent adhesives as for PVC-U
PVDF with PVDF or other materials: two-pack adhesives based on Epoxide resin.
Surfaces to be bonded must be roughened.

17. Typical Applications
Seals, pump and valve components, membranes, transparent rigid pipes (for HF and HC!), fittings, linings for pipes, vessels and autoclaves. films for packaging pharmaceuticals, medical instruments, shrink tubing, corrosion- and weather-resistant laminates for wood and metal, cable sheathing, monofilaments for manufacturing filter cloth and piezo and pyroelectrical films for hydrophones, infrared detectors, respiration monitors, muscle sensors and security equipment.
Modification of the relatively stiff homopolymer has resulted in more flexible grades thus opening up new applications. The melting range of the modified material is 162 to l65°C.

18. Typical Applications-1
Seals, pump and valve components, membranes, transparent rigid pipes (for HF and HC!), fittings, linings for pipes, vessels and autoclaves. films for packaging pharmaceuticals, medical instruments, shrink tubing, corrosion- and weather-resistant laminates for wood and metal, cable sheathing, monofilaments for manufacturing filter cloth.

19. Applications-2
Piezo and pyroelectric films for hydrophones, infrared detectors, respiration monitors, muscle sensors and security equipment.
Modification of the relatively stiff homopolymer has resulted in more flexible grades thus opening up new applications. The melting range of the modified material is 162 to l65°C.

20. Trade Names
Kynar (Arkema Inc.)
Dycon (Dyncon, US)
Kureha (Kureha Chern. Ind., IP)
Solef (Solvay Solexis, US)
Hylar (Solvay Solexis, US)
Dykor (Whitford Corp. US)

21. Further Reading
BRYDSON, J.A, Plastics Material, Butterworth Heinemann, oxford, New Delhi (2005)
DOMININGHAUS.H, Plastics for Engineering, Hanser publishers, Munich, New York (1998)
CHARLESS A . HARPER, Modern Plastics Hand Book McGraw –Hill, New York (1999)

22. Table 1 Guide values of properties of Fluorine containing polymers
Units
PTFE
FEP
PCTFE
PVF
PVDF
Density
g/cm3
1.7
Water absorption (23°C, 24h) %
0.04
Mechanical
Tensile strength
N/mm2
25-36
22-28
32-40
49-127 46
Elongation at break
Tensile modulus of elasticity
408
350
1800
840
Thermal
Melting Point °C
327
290
216
198
171
Service temperaturein air without mechanical loading
short-term C
300
250
180
long-term
205
150
Glass transition temperature
127 45
-20 40
Heat deflection temperature
121 70
126
Coefficient of linear expansion between 0- 50°C K
100 80 60 20 85
Specific heat capacity
kJ/kg K
1.0
1.2
0.9

23. Transparent - transluscent
Table 1 Guide values of properties of Fluorine containing polymers
Properties
Units
PTFE
FEP
PCTFE
PVF
PVDF
Electrical
Volume resistivity
Wcm
>1018
>2x1018
>1.20x1018
3x1013
2x1014
Surface resistance W
1017
1016
Dielectric constant
<2.1
2.1
8.5
7.72
Dissipation factor, tan d (103Hz)
0.0002
0.015
0.018
Dielectric strength
kV/mm
800
Flammability (ASTM D65)
Non-flammable
Clarity
opaque
Transparent - transluscent