Dielectric Behavior of Nonpolar Polymers and Their Composites …
259
Fig. 11 DC conductivity as a function of filler volume concentration of polyethylene nanocomposites with carbon nanofibers (CNF, solid symbols) or multi-wall carbon nanotubes (MWCNTs,
empty symbols) [67]. Reproduced with permission from Linares et al. Macromolecules 2008, 41,
7090–7097
4.3 Polypropylene Composites
Polypropylene is currently the material of choice for capacitor applications over
several other polymers (e.g., polystyrene, polyethylene terephthalate) due to its very
low dissipation factor (tanδ < 0.001), superior dielectric strength (~700 MV/m),
thermal stability (130 °C < T m < 170 °C), and its easier melt processing [53, 68].
Advancements in the chemistry of polyolefins has resulted into isotactic polypropylene (iPP) exhibiting an isotacticity of 97–99% and very low impurity concentration
(30 ppm), facilitating processing and bringing its melting point of around 165 °C [69].
In industrial settings, the financial aspects related to the manufacturing conditions
play a significant role on the choice of material. For the aforementioned reasons,
polypropylene has remained the best option for over half a century. Since 1963
and the MAGVAR invention from General Electric, biaxially oriented polypropylene films have been employed in capacitor applications, as they provide a thin and
efficient energy solution for the storage and recovery of electrical energy [68]. The
orientation in these films can be achieved through several methods, including simultaneous stretching in two perpendicular directions utilizing an apparatus such as the
one presented in Fig. 12. However, in industry, the prevalent approach is the tubular
process, which enables continuous production of BOPP [70].
During the earliest tests on unoriented polypropylene, it became clear that orientation is paramount to achieve time endurance, as an increase in dielectric breakdown
strength by at least a factor of 2 is achieved with the orientation process. Nash
259
Fig. 11 DC conductivity as a function of filler volume concentration of polyethylene nanocomposites with carbon nanofibers (CNF, solid symbols) or multi-wall carbon nanotubes (MWCNTs,
empty symbols) [67]. Reproduced with permission from Linares et al. Macromolecules 2008, 41,
7090–7097
4.3 Polypropylene Composites
Polypropylene is currently the material of choice for capacitor applications over
several other polymers (e.g., polystyrene, polyethylene terephthalate) due to its very
low dissipation factor (tanδ < 0.001), superior dielectric strength (~700 MV/m),
thermal stability (130 °C < T m < 170 °C), and its easier melt processing [53, 68].
Advancements in the chemistry of polyolefins has resulted into isotactic polypropylene (iPP) exhibiting an isotacticity of 97–99% and very low impurity concentration
(30 ppm), facilitating processing and bringing its melting point of around 165 °C [69].
In industrial settings, the financial aspects related to the manufacturing conditions
play a significant role on the choice of material. For the aforementioned reasons,
polypropylene has remained the best option for over half a century. Since 1963
and the MAGVAR invention from General Electric, biaxially oriented polypropylene films have been employed in capacitor applications, as they provide a thin and
efficient energy solution for the storage and recovery of electrical energy [68]. The
orientation in these films can be achieved through several methods, including simultaneous stretching in two perpendicular directions utilizing an apparatus such as the
one presented in Fig. 12. However, in industry, the prevalent approach is the tubular
process, which enables continuous production of BOPP [70].
During the earliest tests on unoriented polypropylene, it became clear that orientation is paramount to achieve time endurance, as an increase in dielectric breakdown
strength by at least a factor of 2 is achieved with the orientation process. Nash