ADDITIVES | THERMALLY CONDUCTIVE
Above: Colloids has achieved good thermal conductivity results in polyamides (left) and polyester polymers (right) using its Graphanced masterbatch at low addition levels. The company says as little as 3 wt% of graphene can achieve an increase in thermal conductivity of around 50%
taining polymer composites. The company says it has also collaborated with leading graphene producers in the development of its Graphanced products. It is generally understood that the thermal conductivity of graphene is accomplished by phonons. A phonon is defined as a definite discrete unit or quantum of vibrational mechanical energy (as a photon is a quantum of electromagnetic or light energy). However, when combined in a compound or composite matrix, the morphology of the gra- phene and the many interfaces with the polymer can lead to phonon scattering, negatively affecting the potential thermal conductivity. The appropriate choice of graphene and graphene morphology is critical to unlocking the potential benefits of gra- phene polymer composites, says Colloids. The base resins of the Graphanced product
range include PA6, PA66, PBT, PET, PC, polyolefins, PS, SAN, and various TPEs. Work is underway for development of masterbatches compatible with higher-end polymers such as PEEK and PPS.
Focus on dispersion “Our focus is on dispersion, especially with nanoparticles. As you go down in size to nanome- tre scale, the tendency is for particles to agglomer- ate, to minimise surface energy. We’ve developed our technology to reduce those agglomerates,” says Derek Hepburn, Colloids’ Technical Director. “It’s a question of how much energy you put into the compound when you’re processing it. If you put in too much energy you can start to degrade the polymer or you can start to damage the graphene flakes. It’s a very narrow operating window.” Marios Michailidis, who has a PhD in nanomateri- als and is Colloids’ R&D Technologist leading the new product developments, says that collaboration with the National Graphene Institute (NGI) at the
46 COMPOUNDING WORLD | August 2022
University of Manchester led to the idea of using hybrid systems, combining graphene with other nanomaterials such as carbon nanotubes to develop multifunctional applications that take advantage of the properties of the different materials. Mark Bissett, a Senior Lecturer in Nanomaterials
at the university involved in the collaboration, explains some of the challenges. “There’s quite a lot of parameter space here, and a lot of variables to play around with. Different ratios, different chemical functionalisations of those materials and different processing conditions. And then scaling all that up to the masterbatch volumes that Colloids use,” he says. One problem is that different loadings in the polymer lend themselves to different functionali- ties. For mechanical strength, a low loading of graphene works best while for conductivity (electrical as well as thermal) higher loadings are needed. So some compromise may be involved, depending on the target application. Graphanced was launched at the Compounding
World Expo in Essen in September 2021 and Colloids says it has attracted much interest from customers. Depending upon the final application, the company can develop a solution based on graphene and, if necessary, other 2D materials to meet performance targets. Graphite-based products with a wide range of morphology and particle size distributions are available from Imerys Graphite & Carbon. According to Anna Ellett, a Field Application Engineer, Polymers, says these enable fine-tuning of polymer compound properties such as thermal and electrical conductivity as well as mechanical properties. The company’s Timrex natural and synthetic
graphites and specialty high-aspect-ratio Timrex C-Therm products can confer high levels of thermal
www.compoundingworld.com
IMAGE: COLLOIDS
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