Swelling of filler‐reinforced vulcanizates

TLDR

The study develops a theory to explain the restricted swelling of crosslinked elastomers containing reinforcing fillers in solvents. Assuming complete restriction of swelling at the filler–rubber interface due to adhesion, the authors derive a relation linking the rubber volume fraction in the swollen phase to filler content and a filler‑dependent parameter. The equation fits extensive experimental data on carbon blacks, confirming firm filler–rubber bonding, negligible impact on vulcanization stoichiometry, and illustrating applications to filler reinforcement and vulcanization.

Abstract

Abstract A theory is developed to account for the restricted swelling in solvents of crosslinked elastomers containing reinforcing fillers. Assuming swelling to be completely restricted at the filler‐rubber interface due to adhesion, the following relation is obtained: where v r is the volume fraction of rubber in the swollen rubber phase, V ro is the same quantity referred to on otherwise analogous, unfilled vulcanizate, Φ is the volume fraction of filler, and c a parameter depending on the filler, but independent of Φ and V ro . This equation is shown to hold for a large volume of experimental data on carbon blacks, involving four rubbers, several sulfur vulcanizing systems, five solvents, and a wide range of crosslinking. Conformance with the theory indicates that carbon blacks are firmly bonded to the rubber and that, in the sulfur crosslinking systems investigated, they have no significant effect on the stoichiometry of vulcanization (although they may affect the rate of vulcanization). Illustrative examples of applications of the theory to problems in filler reinforcement and vulcanization are shown.