Effect of fly ash silica and precipitated silica fillers on the viscosity, cure, and viscoelastic properties of natural rubber

The viscosity, cure properties, storage, and loss moduli and tan delta of natural rubber (NR) filled with the same amounts of precipitated silica (PSi) and fly ash silica (FASi) fillers were measured. The fillers were treated with bis[3-triethoxysilylpropyl-]tetrasulfide (TESPT), or, used in the rubber untreated. TESPT is a sulfur-containing bi-functional organosilane that chemically adheres silica to rubber and also prevents silica from interfering with the reaction mechanism of sulfur cure. The dispersion of PSi and FASi in the rubber was investigated using scanning electron microscope (SEM). The effects of silica type and loading and surface treatment on the aforementioned properties were of interest. The SEM results showed that the FASi particles were larger in size and had a wider particle size distribution when compared with the PSi particles. The viscosity of the compounds decreased progressively with mixing time, and the compounds with FASi had a lower viscosity than those filled with PSi. The treatment with Si69 had no beneficial effect on the dispersion of the fillers in the rubber matrix. At low temperatures, the type and loading of the filler had no effect on the storage and loss moduli of the compounds, but the effect was more pronounced at high temperatures. There was also evidence from the tan delta and glass transition temperature (T-g) measurements that some limited interaction between the filler particles and rubber had occurred because of TESPT. Copyright (C) 2008 John Wiley & Sons, Ltd.