Hello and welcome to the third part of our plastic additives series. In this post we discuss how to improve the conductivity (thermal and electrical) of polymers by using different filler systems.
Here you can read part 1 and here part 2.
Volume vs weight of fillers
Before we deep-dive, let us clarify an important consideration: volume vs. weight of fillers. For formulating a plastic compound, understanding the volume fraction is key. For compounding we need to translate it to a weight based unit, since it is easiest for the extrusion process to set a weight unit and not volume.
Key is to plot your compound properties as a function of volume percent and not weight percent. It will result in straight lines and not exponential as with weight percentage. Figure 1 shows a PP loaded with different fillers and the filler level is expressed over the volume percentage [1].
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| Figure 1: thermal conductivity of PP and different fillers as a function of filler volume % [1]. |
Thermal conductivity of metals, carbon, and ceramics
Before we compare specific fillers used in plastic compounds to increase the thermal conductivity, we have a look at the thermal conductivity of selected metals, carbon, and ceramics (Table 1). This allows us to get a first feeling for the different thermal conductivity levels, together with the densities.
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| Table 1: overview thermal conductivity of selected metals, carbon, and ceramics |
Electrically conductive and non-conductive fillers for plastic compounds
If you are confronted with the task to improve the thermal conductivity of your polymer, Table 2 can serve as a starting point. If one of the requirements during material selection is to fulfill a certain thermal conductive level, optimal fillers are key. Ceramic based fillers such as Boron nitrite show a high thermal conductivity, however due to the plate shape, it is high in plane direction and lower through plane. Spheric fillers allow for a more uniform conductivity in the final plastic part.
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| Table 2: electrically conductive and non-conductive fillers for plastic compounds. |
Check out part 1 and here part 2 too.
Thanks for reading and #findoutaboutplastics
Greetings,
Herwig
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Literature:
[1] https://phantomplastics.com/plastic-materials-training-from-a-top-expert/learn-about-filled-plastics/
[2] Gächter and Müller: Plastics Additives
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