Silicas, as fillers

Mora-Barrantes, I. Rodriguez, A. Ibarra, I. Gonzales, L. Valentin, J. L., Overcoming the Disadvantages of Fumed Silica as Filler in Composites. 

These new type of resins contain minimum amount of chloride and other mobile ions, such as sodium and potassium, and have become widely used in device encapsulation and molding compounds. The incorporation of fused silica as filler in the epoxy system has drastically reduced the thermal coefficient of expansion of these materials which make them more comparable with the IC die attached substrate materials. The incorporation of a small amount of the elastomeric material (such as, silicone elastomer) to the rigid epoxy has drastically reduced the modulus of the material and reduced the thermal stress of the epoxy material This new type of low stress epoxy encapsu-... 

The formulation of a sulfur-vulcanized styrene-butadiene rubber (R2) mainly contains the rubber polymer and precipitated silica as filler the rest of the components are minor in amount, but they are important to impart adequate vulcanization and protect the rubber from the degradation under use (mainly paraffin wax). The paraffin wax acts as a physical protecting agent against ozone by migration to the rubber surface (Romero-Sanchez and Martin-Martinez 2004). O Figure 43.6 shows the attenuated multiple total internal reflection-infrared spectroscopy (ATR-FTIR) spectrum of the R2 bulk. The main bands correspond to rubber (styrene and butadiene) and silica, and the presence of CH2 moieties are minor corresponding to the paraffin wax. However, the ATR-FTIR spectrum of the R2 surface shows the main bands due... 

Siriwardena, S., H. Ismail, and U.S. Ishiaku, A comparison of white rice husk ash and silica as fillers in ethylene-propylene-diene terpolymer vulcanizates. Polymer International, 2001. 50(6) 707—713. 

Although natural quartz, cristobalite and opal are used as fillers, only synthetic products (fumed and precipitated silicas) find use as fillers in rubber base adhesives. 

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 ... 

Various additives and fillers may be employed. Calcium carbonate, talc, carbon black, titanium dioxide, and wollastonite are commonly used as fillers. Plasticizers are often utilized also. Plasticizers may reduce viscosity and may help adhesion to certain substrates. Thixotropes such as fumed silica, structured clays, precipitated silica, PVC powder, etc. can be added. Adhesion promoters, such as silane coupling agents, may also be used in the formulation [69]. 

More advanced insulations are also under development. These insulations, sometimes called superinsulations, have R that exceed 20 fthh-°F/Btu-m. This can be accomplished with encapsulated fine powders in an evacuated space. Superinsulations have been used commercially in the walls of refrigerators and freezers. The encapsulating film, which is usually plastic film, metallized film, or a combination, provides a barrier to the inward diffusion of air and water that would result in loss of the vacuum. The effective life of such insulations depends on the effectiveness of the encapsulating material. A number of powders, including silica, milled perlite, and calcium silicate powder, have been used as filler in evacuated superinsulations. In general, the smaller the particle size, the more effective and durable the insulation packet. Evacuated multilayer reflective insulations have been used in space applications in past years. 

White pigments such as calcium carbonate, aluminum hydroxide, silica, kaolin, or urea-formaldehyde resin are used as filler. The filler functions as an absorbent of melted components to prevent their adhesion on the thermal head. Thus, the filler is required to be high in oil absorption and not to wear the thermal head. 

Instead of blending them either by dispersing silica powders as fillers within PE, which is a well-developed technology with many applications, or by polymerizing ethylene within the pores of modified9 or unmodified silica,10 now the nanometric physical blending... 

Precipitated silica is used to produce molecular sieves, as an anti-caking agent, and as filler for paper and rubber. Hydrophobic silica is a defoaming agent. 

Silica. The main uses of silica are in the treads of off-the-road tires for improved chunking and tear resistance and as a component of the bonding system for brass and zinc-plated steel cord. These are commonly used in radial passenger and truck tire belt skim stock. In addition the body plies of steel radial truck tires, hoses and belts, and footwear use significant volumes of silica as a reinforcing filler. 

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. 

Inorganic fillers include titanium dioxide. Celite and zinc oxide. Lithium or lead sails of acetic acid, stearic acid or phenol are sometimes used as fillers. Silica and alumina are also feasible. Trimethyl-/ -hydroxyethylammonium bicarbonate has been used as a curing agent. 

The acid-base properties of polymers, fillers and silane additives, as described by Fowkes [14] can be used to predict the effect of silanes on the dispersion of fillers in polymer, and viscosity of the mix. In general, opposites attract (give good dispersion) while like materials repel (poor dispersion) [15]. The effect of cationic silane (Z-6032) on the dispersion of silica (acidic filler) in this particular unsaturated polyester resin (acidic polymer) is shown in Table 6. Addition of Z-6032 in increments to a silica-filled polyester resin lowered the viscosity of the mixture to a minimum at about 0.4% silane based on the filler. 

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