Reinforcing fillers fumed silicas

Reinforcing fillers Fumed silica (Si(>2) Thixotropic reinforcing agents... 

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... 

Fumed silica has an ultimate particle size as small as 5 nm, which is finer than hydrated precipitated silica. With a conventional Banbury mixer, a filler this fine would be very difficult to disperse in a general-purpose elastomer compound. Fumed silica can be dispersed using a dough mixer in a gum silicone to achieve the ultimate reinforcement improvement. Fumed silica costs more to produce than hydrated precipitated silica. 

Fumed silicas (Si02). Fumed silicas are common fillers in polychloroprene [40], natural rubber and styrene-butadiene rubber base adhesives. Fumed silicas are widely used as filler in several polymeric systems to which it confers thixotropy, sag resistance, particle suspension, reinforcement, gloss reduction and flow enhancement. Fumed silica is obtained by gas reaction between metallic silicon and dry HCl to rend silica tetrachloride (SiCU). SiC is mixed with hydrogen and air in a burner (1800°C) where fumed silica is formed ... 

Reinforcing fillers (active) Fumed Silica (Si02) precipitated calcium carbonate (CaCOi) carbon black Thixotropic reinforcing agents (non-slump), adjustment of mechanical properties (cohesion) provide toughness to the elastomer as opposed to brittle materials. 

Silicone polymers when cured into elastomers by themselves are weak, gel-like materials. For this reason, fillers must be used to provide reinforcement. The type of fillers (qv) used in silicone sealants varies widely two of the most common fillers are fumed silica and calcium carbonate. 

Fumed silica, a highly reinforcing filler, is usually added in amounts ranging from 6 to 20%. Silica is most often used when a high strength sealant is desired. Several silicas having different surface areas are available and surface treatment with silanes may be used as well. 

This technology was first commercially applied to polyurethane blend [121] and patented as Rimplast (for Reactive Injection Molding), but many polymers have since been blended with polysiloxane thanks to this method polyethylene [122], polypropylene [122,123], polyamide [124-130], polyesters [128,131-133], poly(phenylene ether) [134], fluorocarbons [135] and many more. Many of them include reinforcing fillers such as fumed silica. The silicone base involved can moreover contain reactive groups such as the epoxy group [136,137]. A typical silicone base useful for these blends was de-... 

Fumed silica acts as a highly reinforcing filler in silicone elastomers. Its activity results fi-om its highly dispersed particle structure, high surface area and surface energy. To better understand the interplay of these properties first studies on gas adsorption of hexamethylsiloxane on hydrophilic and silylated silica have been conducted. The shape of the adsorption isotherm revels the existence of low- and high-energy adsorption sites, the latter qualitatively seem to be related to reinforcement of the silicone elastomer. Further quantitative studies in this field are needed. 

The tensile strength of cross-linked polysiloxane elastomers is low, but can be markedly improved by reinforcement with a filler. The material of choice is fumed silica with high surface area, which can increase the strength by a factor of 20. It is thought that the silica particles agglomerate to form a three-dimensional network within the siloxane, greatly reinforcing the stmcture. 

Figure 5.6 shows that pyrogenic manufacturing gives excellent control over particle size distribution and median particle size. These grades of fumed silica differ in properties and require a different technological approaches to their dispersion since small particle size filler is more difficult to disperse. At the same time, smaller particle sizes give more transparent products and better reinforcement. 

Cab-O-Sil . [Cabot] Fumed silica for mfg. of glass, water glass, refractories, abrasives, ceramics, enamels, petrol, prods. filler in cosmetics rubbn reinforcing agent as anticaking and defoaming agent abrasive thickener, dispersant... 

Silica, then, is an important part of all or nearly all silicone sealants. If the sealant is clear, silica s probably the only filler. If the sealant is opaque, silica may or may not be present for reinforcement but it s almost always present for flow control. The single drawback to fumed silica is cost therefore, only a minimum quantity is used and there is a continual search for ways to use less. 

Other silica fillers can be used as well. One such filler is ground quartz. This also has SlOH on the surface and it also ties in, but has a much larger particle size, lower surface area and lower relative density of SiOH. Because of this, it gives much less reinforcement on an equal weight basis when used as a replacement for fumed silica. 

FX-90Q instrument and infrared spectra were recorded on a Nicolet MX-1 or Digilab FTS 2 FT-IR instrument. All norbornene resins and intermediates were completely characterized via HPLC, NMR, FT-IR, and GC analytical techniques and gave satisfactory results. Silicone prepolymers were compounded with 35% of a reinforcing fumed silica filler and photoinitiator. All formulations were cured under a medium pressure mercury vapor lamp until constant durometer values were obtained. Differential photocalorimetric studies were carried out on a DuPont Model 930 photocalorimeter in air at several temperatures. D)mamic mechanical analyses were performed on a Polymer Laboratories DMTA instrument. Organic resins were analyzed as single cantilevered beams at 1 Hz frequency with a temperature scan of 5°C per minute. Silicone dastomers were analyzed under the same conditions. 

Dynamic mechanical thermal analysis of several of the norbornene functional organic resins and the silicone resins gave relatively unremarkable results. The maximum for tan 5 peaks were in good agreement with Tg detamiined by DSC. The silicone elastomer (with 35% fumed silica as reinforcing filler) exhibited a Tg of ca. -90°C and a Tm at ca. -30 C which is typical for this type of polymer. 

Another example of the effect of fillers on improving bond strength is reported for a silicone RTV-1 sealant formulated with Cabot Corporation s Cab-O-Sil LM-130 and TS-720 materials. Cab-O-SU fumed silicas are very effective reinforcing agents due to the very-large surface area available for polymer/filler interactions. The very low, 45 psi, tensile strength of the unfilled silicone increased to 210 psi with 14 phr of LM-130 fumed silica and to 150 psi with the same level of TS-720 fumed sUica. ... 

Chem. Descrip. Fumed silica CAS 112945-52-5 EINECS/ELINCS 231-545-4 Uses Thickener, thixotrope, antisettling agent for paints/coatings, phar-maceuticals/cosmetics (toothpaste, tablets, powds., aerosols, suspensions, ointments, creams), diazo paper, printing inks, PVC plastisols, rubbers, adhesives reinforcing filler in silicone rubber flow aid for powds., pigments, and salts Features Hydrophilic... 

Fumed silica is widely used for the reinforcement of polydimethylsiloxane (PDMS) elastomers. The intermolecular interaction of the filler surface with the PDMS matrix controls this process [1, 2] so that understanding which factors influence the interaction at the filler/PDMS interface has become a crucial point for further development of the technology. Among the factors of interest there are the... 

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