Silica compounds storage modulus

The B-series of silica samples were also blended with rubber and the compound formulation is shown in Table 17.6. The uncured gums were then tested according to ISO 5794-2 1998. The uncured samples were tested using a Mooney viscometer and an RPA, which measures the dynamic mechanical properties as the samples cure. Figure 17.7 shows the results of these two tests for the Mooney viscosity at 100°C, storage modulus, loss modulus, and tan 8. 

A similar sol-gel process method, via NR rubber solution, was also conducted to study the effect of in situ silica content, which was varied from 15 to 65 phr, on the cure characteristics and mechanical, dynamic mechanical and thermal properties of the silica-NR nanocomposite.Both the Mooney viscosity and cure time of the sol-gel silica-NR compound increased with increasing silica contents and were lower than those of the commercial silica-filled NR compound at the same amount of silica. This is attributed to the fewer amounts of silanol groups in the sol-gel silica as compared to the commercial silica. Better reinforcement of the in situ silica, compared to the normal silica, was confirmed when higher moduli and improved compression set were observed for the sol-gel silica NR vulcanizate. This observation is consistent with the Guth and Gold equation as well as the TEM micrographs results. The sol-gel silica vulcanizate has lower storage modulus but better thermal stability then the commercial silica vulcanizate. 

Fig. 21 Influence of the epoxidlzed rubber content on (a) storage modulus and (b) loss modulus, considering a rubbta- compound filled with 60 phr of silica...

The nonlinear viscoelastic behavior of the composites of natural rubber filled with surface-modified nanosilica was studied with reference to silica loading [191]. The effect of temperature on the nonlinear viscoelastic behavior has been investigated. It was observed that Payne effect becomes more pronounced at higher silica loading. The filler characteristics such as particle size, specific surface area, and the surface structural features were found to be the key parameters influencing the Payne effect. A nonlinear decrease in storage modulus with increasing strain was observed for unfilled compounds also. The results reveal that the mechanism includes the breakdown of different networks namely the filler — filler network, the... 

The incorporation of fillers to elastomeric compounds strongly modifies the viscoelastic behavior of the material at small strains and leads to the occurrence of a non-linear behavior known as Payne effect [49] characterized by a decrease in the storage modulus with an increase in the amplitude of small-strain oscillations in dynamic mechanical tests. This phenomenon has attracted considerable attention in the past decade on account of its importance for industrial applications [50-54]. The amplitude AG = G q—G ) of the Payne effect, where G q and G aie the maximum and minimum values of the storage modulus respectively, increases with the volume fo-action of filler as shown in silica-filled PDMS networks (Figure 4.7a). At a same silica loading, the PDMS network filled with untreated silica displays a much higher G value than the treated one and is much more resistant to the applied deformation (Figure 4.7b). 

---