The Thermal Diffusivity and Conductivity of Natural Rubber Compounds

Abstract

New methods of measuring the conductivity and diffusivity of rubbers from ambient to 250°C have been developed. The method of measuring diffusivity described in this paper is simple to use and very much quicker than previous methods, the whole temperature range being covered in about half an hour. The accuracy is about 5%. Two disk-shaped samples are used, 48 mm diameter and 2 mm thick, but the geometry can be changed to accommodate samples of varying thickness. The method is suitable for anisotropic samples but, because the measurement is made over a small area, they must be homogeneous. Diffusivity and conductivity measurements have been made on a series of carbon-black-loaded natural rubber compounds. Both thermal properties depend on temperature, type of rubber, and the type and quantity of carbon black. Empirical equations have been obtained relating diffusivity and conductivity to temperature and black loading. These fit the data to better than 10%.

Thermal Conductivity of Rubber Compounds Versus the State of Cure

“…The molding parameter optimization method described previously6 requires the use of a reliable prediction model for the thermal and kinetic history of the molded compound. The quality prediction depends strongly on the accuracy of the thermophysical parameters, especially the thermal conductivity 7. For the same polymer sample, the available values for the thermal conductivity show important differences depending on the measurement technique and experimental conditions.…”

“…In addition, the evolution of the thermal conductivity of a rubber molded part as a function of molding parameters (temperature and pressure) and vulcanization progress must be considered. Several works deal with the temperature,7–11 pressure,12–16 and filler17, 18 effect on thermal conductivity evolution of rubber compounds.…”

Experimental and simulative investigation of a multistage 2K injection molding process of PA6 and EPDM

“…The thermal conductivity of a rubber compound depends on the type of rubber, the amount of filler/ plasticizer used-carbon black increases the conductivity, plasticizers reduce it above the glass transition temperature of the rubber-the thermodynamic state and other parameters. 26 The measurements were made on already vulcanized samples. There is controversy in literature as to whether the thermal conductivity of the rubber depends on the progress of the crosslinking reaction.…”

Simulation of curing of a slab of rubber

“…The initial and boundary conditions are not compatible only at time t = 0. We assume that thermal diffusivity and conductivity of rubber does not depend on temperature and is taken to be approximately 4.2 × 10 −2 cm 2 /min and 0.12 J/min/K (refer to data for HAF black in Hands and Horsfall [10]). The rate of heat generated per unit volume unit rate of change of crosslink density (q) is taken as 1.98 × 10 5 J/mol.…”