Over the last four decades perovskita-type ceramics (zirconium or lead
titanate ceramics) have been mainly used as piezoelectric materials in
acoustic applications, amongst other reasons because of their high
elastic modularity, their high dielectric constant and their low
dielectric and elastic losses. However, and although they have also
been used successfully in many other applications, ceramic
piezoelectric materials have some important drawbacks: limited
deformation, fragility and a high mass density that limit their use in
sectors such as aeronautics or electrical-electronics. These
limitations can be overcome in specific applications using polymeric
piezoelectric materials instead of ceramic ones.
The only piezoelectric polymer that currently exists on the market is
Polyvinylidene Difluoride (PVDF). This semi-crystalline polymer is
characterised by having very good piezoelectric properties, but only
to 90 �C. Thus the interest in synthesising new piezoelectric polymers
capable of maintaining their properties at greater temperatures.
Patent applied for
At GAIKER-IK4 we have developed amorphous piezoelectric polymers to be
employed in conditions of extreme temperature where semi-crystalline
polymers cannot be used. To this end, and after prior work with
different materials, the use of polymides was opted for, given their
excellent thermal, mechanical and dielectric properties. Various
dipolar groups (-CN, -SO2-, -CF3) have been
incorporated into the molecule, varying the number and position of
these groups in order to fix their physical - and consequently, their
piezoelectric - properties. Moreover, it has been shown that the value
for the temperature of vitreous transition is fundamental for these
polymides, as this determines the temperature at which piezoelectric
properties are lost. Specifically, this type of polymers show
piezoelectric stability up to temperatures of 150
�C and do not begin to degrade until above 400 �C.
We have been involved in this line of research at the Plastics and
Composites Area for a number of years now and, particularly as a
result of the research carried out jointly with the Department of
Physical Chemistry at the University of the Basque Country (UPV/EHU),
we have recently applied for a patent in the Oficina Espa�ola de
Patentes y Marcas on �Polymides with piezoelectric properties�.
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