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Fumed silica (FSi) and precipitated silica (PSi) suspensions were used for preparing silica/natural rubber (NR) masterbatches via a latex system. Then, both types of dried silica/NR masterbatch were mixed with other rubber chemicals on a two-roll mill. The results showed that well-dispersed FSi suspension could be prepared by either using the ultrasonic bath or agitator bead mill, while only the agitator bead mill could give well-dispersed PSi suspension. Also, the amount of silica loss in the masterbatches was clearly less than in silica-filled NR prepared by using a conventional method, and the color of the uncompounded FSi/NR masterbatches was lighter than that of the PSi/NR masterbatches. Additionally, the compound viscosity, onset of crosslinking and stiffness of both FSi- and PSi-filled samples progressively increased when silica content was increased. FSi, having higher surface area, imparted the NR samples with higher viscosity and tear strength but, adversely, higher dynamic compression set, heat build-up and rolling resistance than the PSi. However, the beneficial reduction in compound viscosity, heat build-up, compression set, rolling resistance and increment in strength of both FSi- and PSi-filled samples could be achieved by adding bis-(3-triethoxysilylpropyl) tetrasulfide (Si-69). Also, the degree of improvement in dynamic properties after adding Si-69 was greater for the FSi/NR composite. |
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