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materials | Thermally conductive compounds


Figure 1: Thermal conductivity of PA66 and compounds containing 45% by weight of conductive filler (ref45, 44.95% boron nitride and 0.05%


nanodiamond; and 44.9% boron nitride and 0.1% nanodiamond


Source: Carbodeon


approach the thermally conductive thermoplastics market in 2012 (it is also exploring the use of nanodia- mond to improve the tribological properties of poly- mers). It supplies the nanodiamond material to compounders as a filler together with guidance on use. There is no charge for usage or process knowledge. The nanodiamonds are spherical particles with a


diameter of less than 10nm and with functional groups covalently bonded to their surface. Carbodeon’s synthe- sis and processing methods enable it to offer three different options for the surface chemistry: the first two comprise an amine or hydrogen that results in strongly positively-charged particles; the third is carboxylated and results in strongly negatively charged particles. Selection of the most appropriate type of surface chemistry is made based on the specific polymer and the other fillers in the particular application. The small particle size and surface function enables


dispersion of the particles either throughout a polymer matrix or over the surface of a filler particle. Myllymäki says that the combination of extreme physical proper- ties of diamond coupled with very strong interaction between these particles and surrounding materials at nanoscale are the factors that bring such large improvements to compounds. He emphasises that this is achieved with a small enough fraction of nanodia- mond to make the application economic – the nanodia- mond filler adds from €5/kg to the price of a compound.


Carbon’s share Whether diamonds prove to be a compounder’s best friend is yet to be seen. In the meantime, more mundane forms of carbon currently hold a large share of the conductive compounds market. Imerys Graphite & Carbon says that last year it observed significant growth in sales of graphite-based thermally conductive additives for polymers, especially for metal part


46 COMPOUNDING WORLD | February 2017


substitution in automotive applications. “Thermoplas- tics are certainly the main field of application but also elastomers are showing some interest,” says Polymer Applications Development Scientist Daniele Bonacchi. Aside from LED heat sink applications, other more specific applications that need a certain degree of thermal conductivity are also being developed, Bonacchi says. “Another application that deserves attention is cold touch. Highly thermally conductive materials provide a better sensation when touched, giving a metallic like feeling,” he notes. On a corporate level, with the growth in demand for


graphite—including natural graphite for thermally conductive plastics—and with Imerys wanting to increase its market share in this sector, the company has been looking for ways to complement its existing natural graphite production in Canada. Late last year, Imerys partnered with Gecko Namibia as controlling party in a joint venture to develop a site in Namibia for the production of natural graphite for use in various applications. “Since a very high percentage of our Lac Des Iles


production [in Canada] is meant for the North American market, Namibia is an excellent opportunity to expand natural graphite distribution in that territory and other geographical areas, thanks also to favourable logistics,” says Bonacchi. Production is scheduled to start in the first half of this year, and Imerys is already providing product samples. “In this growth scenario, we realise that cost effective solutions, based on more conventional


Figure 2: In-plane thermal conductivity in injection moulded 2.0mm thick plaques produced in PA6 and PP with 50% natural graphite Source: Imerys Graphite & Carbon


www.compoundingworld.com


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