The void volume of a carbon black expressed as a function of applied pressure, VV, is a carbon black structure property. Structure is a generic term that is a function of the shape irregularity and deviation from sphericity of carbon black aggregates. The greater a carbon black resists compression by having substantial aggregate irregularity and non-sphericity, the greater the compressed volume and void volume. Also, the more that a carbon black resists compression, the greater the energy required to compress the sample per unit void volume.

Structure, traditionally measured by OAN (Test Method D 2414) and COAN (Test Method D 3493), is a property that strongly influences the physical properties developed in carbon black-elastomer compounds for use in tires, mechanical rubber goods, and other manufactured rubber products. Several studies within D24 have demonstrated that void volume data can be used to estimate OAN and COAN numbers of carbon blacks using mathematical models derived from void volume-pressure data and oil absorption data. The models may vary depending on whether dynamic or static void volume measurements are used and the number and types of carbon blacks included within a modeling data set. If necessary, OAN and COAN estimates from void volume models can also be normalized using current SRBs (as practiced in Guide D 4821). Any estimates of OAN or COAN derived from prediction models using void volume-pressure data should be labeled appropriately (that is, Test Method D 6086) to avoid confusion with OAN or COAN data obtained directly from oil absorption methods.

1.1 This test method covers a procedure to measure a carbon black structure property known as Void Volume. Compressed void volumes are obtained by measuring the compressed volume of a weighed sample as a function of applied pressure in a cylindrical chamber by a movable piston with a displacement transducer on the piston mechanism. A profile of void volume as a function of applied pressure provides a means to assess carbon black structure at varying levels of density and aggregate reduction.

1.2 Void volume is an important carbon black structure property that relates to the compounded physical properties for carbon black-filled elastomers including viscosity, modulus, and die swell.

1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.