ASTM D4924-89(2012)

Petroleum waxes in rubber compounds are commonly used to provide protection from degradation by ozone under static conditions, that is, when there is little or no flexing of the rubber products. The mode of action for this protection is (1) migration of the wax through the rubber to the surface of the product and (2) the formation of an ozone impervious film on the surface.

This standard classifies the petroleum waxes on the basis of molecular weight. In general, waxes of lower molecular weight (“paraffinic” or “crystalline”) migrate through the rubber more rapidly and form more brittle film than the higher molecular weight waxes (“microcrystalline”). Wax mixtures and blends are commonly used.

No direct inference of suitability for use in a particular rubber compound is made or implied by the classifications herein.

1.1 This classification is intended to establish a classification system and test methods for petroleum waxes used in rubber compounding primarily as a static protective agent or material for unsaturated rubbers such as styrene-butadiene rubber, polyisoprene rubber, natural rubber, chloroprene rubber, acrylonitrile-butadiene rubber, and polybutadiene rubber. These unsaturated rubbers are subject to ozone cracking. Under certain exposure conditions, waxes retard this cracking.

1.2 This classification is applicable to petroleum waxes used as process aids in rubber compounding. It is not applicable to nonpetroleum waxes such as carnuba wax, candelille wax, or ceresin wax, nor to synthetic hydrocarbon waxes such as polyethylene wax. These non-petroleum waxes display a different behavior on gas chromatographic analysis than do petroleum waxes.

1.3 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.