Untreated silica fillers

Figure 1. Plots of T p vs. filler content for treated and untreated silica fillers. O — iPPO + untreated silica. = iPPO MeSiCl treated silica. 3 = overlapping point.

Fig. 10 SEM images (magnification 100,000 x) of untreated silica (a) and PA-silica filler (b)...

Figure 18 shows the bound rubber content of samples filled with untreated silica, plasma-treated silicas, and silane-modified silica, as representative of the filler-polymer interactions. Samples SPTh and SPA show the highest bound rubber contents, and the ST the lowest value. The SPPy sample shows a bound rubber content slightly lower than that of SU. 

Thus, silica or fumed silica is truly the work-horse filler of the silicone industry. One attribute of silica fillers, when of the proper particle size and properly dispersed, is their transparency in the polymer. This allows the preparation of the clear silicone sealants commonly used. The silicas can either be untreated or treated by any of several methods.This treat-... 

Surface treatments for Cab-O-Sil influence the viscosity and thixotropic properties of an adhesive as shown in Figure 3.19 where MS-5 is untreated Cab-O-Sil , TS-720 is treated with polydimethylsiloxane, and TS-610 and TS-530 are treated with dimethyldichlorosilanes. The silica filler treated with polydimethylsiloxane (TS-720) produces greater van der Waals forces of attraction and thus higher viscosity compared to TS-610 and TS-530. ... 

The amount of polysiloxane-based plasticizer depends on a combination of factors including the required modulus of rubber, the amount of silica filler, and the type of silica filler (treated or untreated with silane). 

Figure 1 shows the results of the rheology study at a filler volume fraction ( > of 0.11. Untreated silica is not represented because at such volume fractions the solid structure is too strong to be measured with the available equipment. 

Untreated silicas in PVC compounds show a decrease in yield stress with increasing particle content and size, which is higher when the filler particles are irregular in shape than when the compounds are filled with particles of spherical shape. To improve the adhesion at the particle/matrix interfaces, treatment with a silane coupling agent (y-aminopropyl methyldiethoxysilane) increases the yield stress generally, and more so with irregular shaped than spherical particles. 

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). 

Fig. 9.67 Plots of Tp against filler content for isotactic poly(propylene oxide) with silica additives, o polymer plus untreated silica polymer plus Me4SiCl treated silica. (From Cole and St. Pierre (247))...

Figure I. Reinforcement of silicone gums by carbon blacks (including nonrreinforcmg NR), silica powder (both surface-treated T and untreated NT), and titanium dioxide. The increase in modulus per unit dose and filler concentration depends on filler particle size.

The higher amounts of bound rubber for all samples filled with plasma-treated silica demonstrate an improved filler-polymer interaction between the plasma-treated silica and the polymers in the blend compared to untreated and silane-treated silica. The highest filler-polymer interaction for the PPy-silica can be due to the best compatibilization effect of PPy-silica with both polymers in the blend, as... 

For silica in SBR, a polyacetylene coating gives the lowest filler-filler interaction, a good filler-polymer interaction, and the best dispersion compared to untreated and the other plasma-treated samples. However, for the stress-strain properties, the polythiophene-treated sample gives the best results. This shows the importance of sulfur moieties on the surface of the filler, which form a secondary network in the cured materials. In the blend of S-SBR and EPDM rubbers, the situation is less conclusive. The Payne effect, the bound rubber, and... 

The different results for untreated fillers (Omyalite 90, Calofort U, Silica Tixosil 365 and Tixosil NM61), and surface treated fillers (Omyalite 95T, Calofort S) are reported in Table 2. 

The -potential of colloidal silica surface treated by acrylate copolymers is affected by pH. The -potential of untreated colloidal silica at a pH of 4 is -7 mV and it decreases to -32 mV at a pH of 7. Modification of the surface of colloidal silica changes its surface properties and behavior. In another study on filler modification, hydroxyapatite was modified for medical applications with several differ-... 

Applications The following use was made of infrared and Raman specfroseopy identification of surface groups on treated and untreated fumed silica, identification of silica functional groups and coatings by Raman spectroscopy, silane deposition on various fillers, surface grafting of barium sulfate by acryloamide grafting of wood fiber, specbal absorption of filler,crystallization of polymer in the presence of filler, absorption of polyacrylate on alumina, deformation of fibers in composites by Raman... 

The physical properties of cured polysiloxane materials are dramatically influenced by fillers (1,2). So-called non-reinforcing (extenders) and reinforcing fillers are typically used the most common reinforcing filler is silica. High surface area silica, called fumed silica, is formed by burning the product mixture obtained from the trichlorosilane (TCS) reaction of equation 8. Only a small amount of untreated... 

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