Poly Vinyl Fluoride (PVF)

Poly Vinyl Fluoride (PVF):

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

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.

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.

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 1.45. Three optical axes must be differentiated for oriented films.

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.

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.

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.

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.

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.