Dielectric Behavior of Nonpolar
Polymers and Their Composites: The
Case of Semicrystalline Polyolefins
Stavros X. Drakopoulos, Sara Ronca, and Ignacio Martin-Fabiani
Abstract Polyolefins are thermoplastic polymers used in a wide range of applications, including medical implants, insulating materials, fabrics, and packaging.
The two most popular representatives, polyethylene (PE) and polypropylene (PP),
present linear chemical structures that yield these materials semicrystalline (except
for atactic PP). The versatility of their synthesis enables the fabrication of different
grades, covering a wide range of crystallinities which can reach up to 90%. However,
because of their symmetric aliphatic structure, they do not present a permanent dipole
moment. Their nonpolar nature makes dielectric spectroscopy measurements challenging, as this technique relies on the relaxation of dipoles after the application
of an external electric field. Here, we review different approaches that have been
followed in order to introduce permanent dipoles and render polyolefins dielectrically active, including: (i) addition of probes with a permanent dipole moment,
(ii) oxidation/chlorination to produce dielectrically active chains, or (iii) induced
oxidation in the presence of metal oxide fillers. The introduction of dipoles, either
intentionally or due to the presence of impurities, has enabled the characterization of
the full relaxation spectra of polyethylene and polypropylene as well as the assignment of dielectric relaxations to their respective molecular mechanisms. We then turn
our attention into PE and PP composites for electrical energy storage and insulation
applications. We show how, in these materials, the effect of the polymer matrix and
filler orientation has been proven key to enhance their dielectric breakdown strength.
Keywords Polyolefins · Nanocomposites · Crystallinity · Orientation · Dielectric
probes · Entanglement · Dielectric breakdown strength · Treeing
S. X. Drakopoulos · S. Ronca · I. Martin-Fabiani (B)
Department of Materials, Loughborough University, Loughborough, Leicestershire LE11 3TU,
UK
e-mail: i.martin-fabiani@lboro.ac.uk
© Springer Nature Switzerland AG 2020
T. A. Ezquerra and A. Nogales (eds.), Crystallization as Studied
by Broadband Dielectric Spectroscopy, Advances in Dielectrics,
https://doi.org/10.1007/978-3-030-56186-4_10
243
Polymers and Their Composites: The
Case of Semicrystalline Polyolefins
Stavros X. Drakopoulos, Sara Ronca, and Ignacio Martin-Fabiani
Abstract Polyolefins are thermoplastic polymers used in a wide range of applications, including medical implants, insulating materials, fabrics, and packaging.
The two most popular representatives, polyethylene (PE) and polypropylene (PP),
present linear chemical structures that yield these materials semicrystalline (except
for atactic PP). The versatility of their synthesis enables the fabrication of different
grades, covering a wide range of crystallinities which can reach up to 90%. However,
because of their symmetric aliphatic structure, they do not present a permanent dipole
moment. Their nonpolar nature makes dielectric spectroscopy measurements challenging, as this technique relies on the relaxation of dipoles after the application
of an external electric field. Here, we review different approaches that have been
followed in order to introduce permanent dipoles and render polyolefins dielectrically active, including: (i) addition of probes with a permanent dipole moment,
(ii) oxidation/chlorination to produce dielectrically active chains, or (iii) induced
oxidation in the presence of metal oxide fillers. The introduction of dipoles, either
intentionally or due to the presence of impurities, has enabled the characterization of
the full relaxation spectra of polyethylene and polypropylene as well as the assignment of dielectric relaxations to their respective molecular mechanisms. We then turn
our attention into PE and PP composites for electrical energy storage and insulation
applications. We show how, in these materials, the effect of the polymer matrix and
filler orientation has been proven key to enhance their dielectric breakdown strength.
Keywords Polyolefins · Nanocomposites · Crystallinity · Orientation · Dielectric
probes · Entanglement · Dielectric breakdown strength · Treeing
S. X. Drakopoulos · S. Ronca · I. Martin-Fabiani (B)
Department of Materials, Loughborough University, Loughborough, Leicestershire LE11 3TU,
UK
e-mail: i.martin-fabiani@lboro.ac.uk
© Springer Nature Switzerland AG 2020
T. A. Ezquerra and A. Nogales (eds.), Crystallization as Studied
by Broadband Dielectric Spectroscopy, Advances in Dielectrics,
https://doi.org/10.1007/978-3-030-56186-4_10
243