A new testing strategy based on the wetting concept for characterizing rubber-filler interaction in rubber compounds and its application to the study of the influence of epoxy groups and non-rubber components on rubber-filler interaction in natural rubber compounds

In the present work, a new testing strategy was proposed to characterize the effect of a functional group on the in-teraction between rubber and filler in a rubber compound. In principle, the filler is mixed into a blend of rubber A and rub-ber B produced by functionalizing the rubber A with a specific chemical group. The phase-selective wetting of the filler is directly related to the effect of the functional group. Based on the new test approach, the impact of the non-rubber components in natural rubber (NR) and its epoxidation on the rubber-filler interaction in carbon black (CB) filled NR compounds was investigated. Accordingly, CB was mixed in three blends consisting of NR/isoprene (IR), deproteinized natural rubber (DPNR)/IR, and NR/epoxidized natural rubber (ENR). The phase selective wetting of CB was quantitatively characterized based on the wetting concept. It was found that proteins and epoxy groups did not affect the affinity between NR and CB, while the linked phospholipids interacted with the CB surface through cation-pi bonding. By fitting the experimentally de-termined selective wetting of CB into the Z-model, the corrected surface tension of NR describing the effect of phospholipids was determined. The proposed test strategy was applied to other NR blends filled with silica and the hybrid CB/silica filler as reference fillers to demonstrate its transferability and verification.