Mechanism of silica reinforcement in CPE/NR blends by the use of rheological approaches

Blends of elastomeric chlorinated polyethylene (CPE) and natural rubber (NR) at blend composition ratio of 80/20 CPE/NR with various precipitated silica loadings were prepared. By the use of rheological approaches, a mechanism of silica reinforcement was proposed. Results obtained reveal that the viscoelastic behavior of blends is influenced remarkably by loadings of silica. A cure promotion phenomenon is found as silica is loaded due probably to the strong silica-CPE interaction and/or a reduction in curative absorption on silica surfaces. A strong Payne effect is observed, which is increased by a rise in silica loading, implying a formation of pseudocrosslink via a physical interaction, which could be disruptedat high strain of deformation. The proposed mechanism of silica reinforcement based on the formation of pseudocrosslink is validated by the deactivation of silanol groups on silica surfaces using silane-coupling agents. The bis-(3-triethoxysilylpropyl) tetrasulfane (Si-69) is found to be more effective in suppressing the pseudocrosslink than 3-thiocyanatopropyl triethoxy silane (Si-264), which is thought to be the result of its larger amount of alkoxy groups at a given silane loading.