AbstractElastic and viscous components of the dynamic Young's modulus were measured at strains up to 80 and over a temperature range of −30°C. to +30°C. for natural rubber containing 18 by volume of carbon black. These components were derived from the velocity and attenuation of 1 kcycle/sec. longitudinal waves in stretched filaments. Two types of carbon black were examined, with mean particle diameters of about 0.4 microns (MT black) and 0.04 microns (HAF black). It was possible to represent the strain dependence of the modulus components of the MT‐filled material by the linear relations previously developed for the gum rubber; division by a volume loading factor derived from the Guth‐Simha‐Gold equation gave close agreement with the corresponding values for the gum at the same strain and temperature. The strain dependence of the HAF‐filled rubber was analyzed with reference to the equilibrium modulus‐extension curve. This material showed increases in modulus components much greater than indicated by the volume loading factor and the temperature coefficients of these components were much less than for the gum rubber. The glass‐transition temperature of −65.7°C. for the gum rubber was not significantly affected by the presence of e
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