Content area
Full Text
ABSTRACT
Migration of compounding ingredients is an important factor in the overall properties and performance of rubber articles containing a number of layers for example, a tire, a hose or a conveyor belt. In certain cases, migration of compounding ingredients before, during and after vulcanization in rubber compounds can be of benefit. For example, waxes and p-phenylenediamines antiozonants rely heavily on the migration mechanism to provide optimum protection of rubber products during service against degradation by ozone. In addition, the dispersion of compounding ingredients such as oil, curatives, and antidegradants can be enhanced by diffusion within rubber. In other cases, however, diffusion across a rubber-to-rubber interface can be detrimental to performance. Diffusion will change the distribution of materials which in turn may result in changes in mechanical properties, loss in adhesion or antidegradant protection, and staining of lightcolored products. Thus, a better understanding of the migration of chemical additives in rubber could provide the desired distribution of ingredients for obtaining the optimum compound performance.
I. INTRODUCTION
Migration of compounding ingredients before, during and after vulcanization in rubber compounds has been recognized as an important factor in the overall properties and performance of rubber articles such as a tire. In certain cases, diffusion or migration of compounding ingredients can be of benefit. Waxes1,2 and p-phenylenediamines antiozonants2,3 rely upon migration to provide optimum protection against degradation by ozone and fatigue. In addition, the dispersion of compounding ingredients such as oil, curatives, and antidegradants can be enhanced by diffusion within a particular rubber compound.4 In other cases, however, diffusion across a rubber-to-rubber interface can be detrimental to performance by causing a change in the distribution of materials which may result in a change in physical properties, a loss in adhesion or antidegradant protection, or staining of light-colored products.3-5
Curative migration should be of particular concern in an uncured compound such as a tire since it contains many interfaces between different rubber components with various cure systems. The literature has established that several commonly used curatives such as sulfur, sulfenamide accelerators and sulfur donors will diffuse quite readily across a rubber-to-rubber interface.4-7 Published diffusion data on rubber chemicals are, however, sparse probably due to the relatively complicated measurement techniques involved.
Radioisotope tracing is highly accurate and lends...