Effect of liquid natural rubber on interfacial interactions of SiO₂/NR composites prepared by wet mixing method

The silica/natural rubber (SiO₂/NR) composites was prepared by wet mixing technology with liquid natural rubber (LNR) as compatibilizer. The tensile fracture surface morphology, Payne effect, glass transition temperature (T_g), bound rubber contents and crosslink density of SiO₂/NR composites were characterized by SEM, rubber processing analyzer (RPA), differential scanning calorimetry(DSC), swelling method and nuclear magnetic resonance instrument. The effect of LNR on the rubber-filler interaction was also investigated. The results show that SiO₂ particles are tightly encompassed by NR and fracture surfaces appear toughness fracture in the presence of LNR. The Payne effect of SiO₂/NR composites is obviously decreased under certain amount of silica SiO₂. T_g is observed from -59.57℃ to -56.61℃ and bound rubber content is observed from 40.24% to 44.02% when the mass ratio of SiO₂ to NR is 60:100. The interfacial interaction of SiO₂/NR composites quantitatively evaluated by Lorenz-Park equation is strengthened in the presence of LNR. Nuclear magnetic resonance test shows that the crosslink density has great enhancements and transverse relaxation time (T₂) decrease for modified SiO₂/NR composites, T₂ decreases 4.20 ms, 5.84 ms and 7.86 ms when the mass ratio of SiO₂ to NR are 30:100, 50:100 and 70:100, respectively, which can be ascribed to the stronger filler-rubber interfacial interaction that limites the extensibility of NR chains with incorporation of LNR. It is revealed that LNR has good compatibility, which contributes to strengthening interfacial interaction of SiO₂/NR composites.