Comparison of steady-state and transient thermal conductivity testing methods using different industrial rubber compounds

Reliable material data, especially of the thermal conductivity as a function of temperature, are crucial for thevirtual optimization of the rubber injection molding process. Due to the low thermal conductivity of rubbercompounds, typically in the range from 0.15 to 0.4 W m 1K 1, and the fact that the molding of the rubber parttakes place in a heated mold via an energy-based crosslinking reaction, the total cycle time is in the range ofminutes. Consequently, there is a vast potential for optimization of this lengthy production cycle. To determinethe thermal conductivity of seven different rubber compounds, a stationary (Guarded Heat Flow Meter (GHF)),and three transient methods (Plane-Source (TPS), Line-Source (TLS), and Laser Flash Analysis (LFA)) wereemployed. Ancillary, the anisotropic TPS- and the LFA-method require the material parameters specific heatcapacity as well as density. The TPS method also offers the possibility to perform an isotropic and an anisotropicmeasurement of the thermal conductivity. In general, filled rubber systems do not exhibit an isotropic materialbehavior. Due to filler orientation or diffusion of volatile substances to the surface, the values of the thermalconductivity obtained from TPS-method differ significantly from those of GHF or LFA. The TLS-measuredthermal conductivity coincide with the GHF results; however, TLS is limited to rubber compounds containingno cross-linking system, and it is sensitive to emitted volatile substances. To conclude, both the GHF- and theLFA-method provide comparable results for all seven tested rubber compounds.