1. SPECIALTY PLASTICS Polyvinylfluoride (PVF)

2. Polyvinylfluoride (PVF)
Polyvinylfluoride was commercialized by Du Pont in the early sixties. The monomer is manufactured by adding hydrogen fluoride to acetylene.

3. Structure and General Properties
The crystalline melting point is 198°C and the molecular weight is 5x104 to 2x105.
Many properties of PVF resemble those of PVC (low water absorption, resistance to hydrolysis, separation of HF at elevated temperature).
The smaller F atoms result in a higher degree of crystallinity.
The flame resistance is poorer than that of PVC; PVF continues to burn slowly after ignition.

4. Transition Temperatures
Availability
PVF is supplied only as film, weakly oriented or biaxially stretched film is available.
Transition Temperatures
The glass transition temperature is - 20 °C, the crystalline melting temperature 198 °C.

5. Optical Properties
PVF films are transparent to visible and UV light.
In the infrared region radiation with wavelengths between 7 and l2 mm is absorbed.
The refractive index n20D is Three optical axes must be differentiated for oriented films.

6. Resistance to Chemicals
Chemical Properties
Resistance to Chemicals
PVF is resistant to acids, alkaline solutions and many solvents at room temperature.
It is unaffected by boiling in carbon tetrachloride, benzene, acetone and methyl ethyl ketone.
The resistance lies between that of PTFE and PCTFE.

7. Toxicological Assessment
Flammability
PVF burns slowly, i.e. its fire performance is somewhat poorer than that of PVC-U.
Toxicological Assessment
PVF is suitable for use with foodstuffs and is physiologically inert.

8. Processing-1
PVF is supplied only as film.
It can be compression molded.
Cast film is made by pouring a mixture of 25 to 40% PVF and 75 to 60% dimethyl sulfoxide on
to a platen and heating to 130 °C for a short time.
The paste-like mixture can also be extruded in hot oil at 160°C.
PVF films can be welded by heat impulse or high
frequency.

9. Organosols (g-butyrolactone) can also be extruded in a water bath.
Processing-2
Organosols (g-butyrolactone) can also be extruded in a water bath.
High transparency films are obtained by briefly heating the film to 250 °C and quenching rapidly.
Biaxial stretching is carried out in warm solvents (g-butyrolactone, dimethyl acetamide).
PVF films can be welded by heat impulse or high frequency.

10. Typical Applications
The high weathering resistance of PVF makes it suitable for outdoor use as roof covering, cladding, pipe insulation, green houses, solar collectors (transparent to UV).
Corrosion protection for metal panels, plywood and insulating board, road signs, packaging film, shrink tube.

11. Trade Names
Kel-F (3M Co., US)
KF Piezo Film (Kureha Chem. Ind., IP)
Tedlar (Du Pont de Nemours, US)

12. 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)

13. 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
Notched impact strength
Ft lb/in 3
No break
Thermal
Melting Point °C
327
290
216
198
171
Service temperature
in air
without mechanical loading
short-term
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 and 50°C K
100 80 60 20 85
Specific heat capacity
kJ/kg K
1.0
1.2
0.9
Thermal conductivity
W/mK
0.25
0.22

14. Table 1 Guide values of properties of Fluorine containing polymers
Units
PTFE
FEP
PCTFE
PVF
PVDF
Electrical
Volume resistivity
Wcm
>1018
>2.1018
>
3.1013
2.1014
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
Tracking resistance
class C
600
Flammability (ASTM D65)
Non flammable
Clarity
opaque
Transparent -