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How Different Fillers Affect the Thermal Conductivity of Epoxy Composites

C-Therm clients at the Delft University of Technology recently published an interesting paper in the 2014 Annual Report Conference on Electrical Insulation and Dielectric Phenomena titled How Different Fillers Affect the Thermal Conductivity of Epoxy Composites.  

The work was done in collaboration with researchers from Japan at the IPS Research Center, Waseda University.  

The C-Therm TCi Thermal Conductivity Analyzer was employed for all thermal conductivity testing.  

The researchers noted that polymers are widely uses as insulating materials for a variety of electrical applications but their relatively low thermal conductivity leaves room for improvement.  The inclusion of fillers with a higher thermal conductivity is one approach to increase the thermal conductivity performance of the polymers.

The base material used in the study is an epoxy resin consisting of bisphenol-A diglcidyl ether CY225 and anhydrite hardener HY225.  Four different fillers were added to the base resin.  A highlight on the results on the resin with the SiO2 additive are illustrated in the chart below.

How different fillers affect the thermal conductivity of epoxy composites

The authors of the report note:
All produced epoxy composites exhibit a linear dependence between thermal conductivity and fill grade.

The nanocomposites with SiO2 are presented and compared. The composites with the larger particles consistenly show a higher thermal conducitivity. The results verify that the decrease of particle size leads to the increase of phonon scattering due to the larger surface area. For the same volume concentration of fillers, the interfacial area is much larger in the case of 12nm particles. If we assume that the particles are spherical, the surface-to-volume ratio of SiO2 with an APS of 12nm is nearly 6 times greater than the ratio of SiO2 with an APS of 70nm. Larger interfacial area increases the phonon scattering leading to lower values of thermal conductivity. 

To learn more about application of the C-Therm TCi Thermal Conductivity Analyzer in characterizing composites check out the following archived webinar.

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