New PVdF Film May Boost Capacitors for Electric Vehicles

 New applications for specialty films are triggering interesting R&D to stretch their capabilities. I wrote recently about the new polyolefin films that are improving lithium ion batteries. Another example comes from Solvay Solexis, which has developed a biaxially oriented polyvinylidene fluoride (PVdF) film with an equipment partner named Parkinson Technologies. This film could  have important implications for capacitors and electric vehicles.

Fluoropolymer films in general have been in demand due to their toughness and chemical resistance. One example is the booming demand for DuPont’s Tedlar polyvinyl fluoride (PVF) for photovoltaic applciations.

Most PVDF film applications are non-oriented, and the process of producing biaxially-oriented PVDF requires establishing optimal processing conditions. “PVDF has a very narrow process window compared with more typical biax films such as PP and PET,” said Ken Forziati, business development manager at Parkinson. “It’s also very dense–a similar sized roll of PVDF is nearly twice as heavy as other films.”

Parkinson Technologies recently produced a new biaxially oriented PVdF film for Solvay Solexis. This film, successfully produced in the Parkinson in-house Marshall & Williams plastics extrusion and orientation pilot lab, features properties that make it better able to cope with harsh environments. One interesting potential use for biaxially oriented film is in capacitors.

The strong piezoelectricity of PVDF was first observed in the late 1960s. The piezoelectric coefficient of poled thin films of the material were reported to be as large as 10 times larger than that observed in any other polymer. The relative dielectric constant is about 8 for PVdF and 2.1 for PP, for example. Researchers at North Carolina State University announced development in 2007 of PVdF capacitors that allow up to seven times the electrical storage potential as standard capacitors. Powerful capacitors are a possible alternative to batteries in electric vehicles.

The new biax process could overcome some of the limitations observed in highly oriented PVdF films. These include: decay of piezoelectric properties, film shrinkage at elevated temperatures, electrode erosion due to water, curling and fibrillation.

Interestingly, BioSolar also went to the same R&D labs at Parkinson Technologies to study potential manufacturing improvements for its bioplastic films (specifically nylon 11 made from castor oil) for use as backsheets in solar cells as a competitor to a different fluoropolymer, DuPont’s Tedlar.