bioplasticsMAGAZINE_1201

Automotive
PLA and carbon nanotubes
Nanotechnology for automotive applications
Conductivity (S/cm)
1,4
1,2
1
0,8
0,6
0,4
0,2
0
By
A. Tielas, V. Ventosinos, M. de Dios
Plastic Product / Process Area
Engineering & Development Department
Galician Automotive Technological Centre
(CTAG)
Porriño, Spain
PLA/CNT (7%) PLA/CNT (7%)
Talc (10%)
PP/CNT (7%) PP/CNT (7%)
Talc (10%)
Fig. 1. Conductivity measured by the Van der Pauw method
of 15x15x2 mm polylactic acid (PLA) and polypropylene (PP)
pieces filled with the same content of CNT. PLA pieces
exhibit more than five times the conductivity of PP samples.
R impact
Impact
R t=∞
Fig. 2. Resistance profile in a polymer/CNT sample
during an impact.
The continuous development of science is making possible
the design of new materials with properties that were unthinkable
a few years ago. The constant searching for lighter
compounds, durable and compatible with the environment, has
become one of the main goals of many researches today. In this
sense, nanotechnology has quickly revolutionized the whole picture
of current design of high added value materials due to the
unique properties that those composites exhibit in fields as diverse
as electronics, mechanics, optics or magnetism.
Carbon nanotubes (CNTs) perfectly illustrate all the benefits
that nanotechnology can bring, especially in the manufacture
of polymer based nanocomposites. This is due to, among other
reasons, their high electrical and thermal conductivity, which
are transferred to the polymer, even using relatively small loads
of CNTs. Many studies are being carried out to optimize the
fabrication of polymer/CNT compounds, especially to improve the
dispersion of CNTs within the polymer matrix.
The Galician Automotive Technology Centre (CTAG), through its
Engineering and Development department in the area of plastic
products, seeks to explore and exploit all the inherent advantages
of joining together polymer science and nanotechnology.
Committed to the need to preserve respect for the environment
by using, as far as possible, renewable sourced materials, CTAG
currently develops compounds based on polylactic acid (PLA) and
CNTs intended for diverse applications.
Indeed, one of the most interesting properties of PLA/CNT
composites from the standpoint of the practical applicability is
their electrical conductivity. It is known that internal CNT networks
are formed beyond a given threshold concentration of filler, the
point at which a great increase of the electrical conductivity of the
material appears. The electrical behaviour of the polymer also
largely depends on the degree of alignment and dispersion of CNTs
within the polymer matrix. PLA favours the dispersion of CNTs due
to its polar character, and, in fact, PLA/CNT compounds exhibit
in the order of five times the conductivity of PP/CNT composites
(Figure 1).
It has been shown that an external factor that can alter the
disposition of CNTs, further produces conductivity changes in
the sample. This behaviour allows, for example, the detection of
impacts, by conductivity measurements, on pieces made of this
material. The potential applications are vast, from the dynamic
monitoring of structural damage of key parts of a car, to the
localizing and counting of impacts on the surface of an airplane
fuselage (Figure 2).
Based on the same principle, we have developed prototypes
of smart pedals that can detect emergency braking situations
and activate adequate safety measures in case of an imminent
18 bioplastics MAGAZINE [01/12] Vol. 7