TECHNOLOGY | CONDUCTIVE PLASTICS
Spanish polymer industry research organisation Aimplas, one of the project partners, has devel- oped Peltier devices in the form of self-regulating thermoplastic heating plates that will be installed in the doors of the test vehicles. A conductive thermoplastic compound based on CNTs has already been developed and validated, using cast-extruded sheets (Figure 1). As Aimplas is currently patenting the process, it says it is not able to say more about the CNTs it has used.
Figure 1: Heating effect of self-regulating polymer films produced within the JosPel project Source: Aimplas
Developments heat up As mentioned earlier, CNTs are expected to find application in batteries for EVs. However, there could be another significant EV application for them: heating. The aim of the EU-sponsored JosPel project is to develop an energy-efficient system for optimising interior temperature management in electric vehicles (EVs). The project, which involves 14 partners from nine countries, began in 2015 and ends this October. JosPel is an acronym of Joule and Peltier, two
Right: Measuring the heating
performance of self-regulating polymeric heating materials produced in the EU-funded JosPel project
46
heating effects that are at the core of the project. Joule heating is the process by which the passage of an electric current through a conductor releases heat. In Peltier cells, heat is produced when an electric current flows through a circuit made from two different metals (or in the JoPel project from suitable composites containing CNTs). Heat is emitted at the upper junction and absorbed at the lower. The project organisers’ premise is that many people will not consider buying an EV unless the operating range increases dramatically (EVs compare poorly to most cars on the market today in this respect). The main ways to extend EV range are to increase the engine efficiency, to improve the battery efficiency, to reduce the mass of the car, and to improve energy use in the car. The latter holds considerable scope for improvement as current HVAC technologies reduce the potential operating range of an EV by as much as 25%. The main objective of the project is to achieve a reduction of at least 50% in energy used for passenger comfort and 30% for component cooling in extreme conditions (compared with current EVs).
COMPOUNDING WORLD | February 2018
Focus on single-wall Before graphene arrived on the scene in 2004 – rapidly taking on the mantle of the “Next Big Thing” – the nano-additive to watch was the SWCNT. For a number of reasons, SWCNTs did not find their place, in part due to cost (they were even more expensive than MWCNTs) but also, according to some, the difficulty of dispersing them in plastics compounds. The indications, however, are that these problems are being overcome. OCSiAl has developed a lower-cost production root and, together with a number of key customers, is claiming to have made significant progress in processability. The company claims that the Van der Waal forces that hold the nanotubes together are more or less the same for MWCNTs and SWCNTs, but adds that as MWCNTs are produced as agglom- erates they are inherently more difficult to disperse. OCSiAl advises treating MWCNTs and SWCNTs as two very different materials. “They have hardly anything in common, and thus they impart a number of very different properties,” a spokesper- son for the company says. “While MWCNTs feature many tubes with decreasing diameter that are coiled inside each other, SWCNTs can be thought of as an extremely thin rolled up sheet of graphene.” OCSiAl produces high-purity SWCNTs under the
brand name Tuball. It says the flexibility of its Tuball SWCNTs and the extremely high ratio between their length and mean outer diameter – around 5,000 – leads to an extremely low percolation threshold (the level required to create a conductive network in a matrix polymer). As little as 0.02 wt% of nanotubes is said to be enough to form a three-dimensional, permanent, stable and humidi- ty-independent conductive network in thermoplastics. These ultra-low effective loadings enable bright colours, including white, to be achieved in the final compound. The introduction of SWCNTs does not lead to degradation of the material’s mechanical proper- ties and many even result in
www.compoundingworld.com
PHOTO: AIMPLAS
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