Reinforcing fillers silicas

Abstract Plasma polymerization is a technique for modifying the surface characteristics of fillers and curatives for rubber from essentially polar to nonpolar. Acetylene, thiophene, and pyrrole are employed to modify silica and carbon black reinforcing fillers. Silica is easy to modify because its surface contains siloxane and silanol species. On carbon black, only a limited amount of plasma deposition takes place, due to its nonreactive nature. Oxidized gas blacks, with larger oxygen functionality, and particularly carbon black left over from fullerene production, show substantial plasma deposition. Also, carbon/silica dual-phase fillers react well because the silica content is reactive. Elemental sulfur, the well-known vulcanization agent for rubbers, can also be modified reasonably well. 

Silica. The main uses of siUca are in the treads of off-the-road tines for improved chunking and tear resistance and as a component of the bonding system for brass and 2inc-plated steel cord. These are commonly used in radial passenger and tmck tire belt skim stock. In addition the body pHes of steel radial tmck tires, hoses and belts, and footwear use significant volumes of siUca as a reinforcing filler. 

For equivalent particle size the carbon blacks are the most powerful reinforcing fillers. However, fine particle size silicas can be very useful in non-black compounds whilst other fillers such as aluminium hydroxide, zinc oxide and calcium silicate have some reinforcing effect. 

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. 

The reinforcing filler usually takes the form of fibres but particles (for example glass spheres) are also used. A wide range of amorphous and crystalline materials can be used as reinforcing fibres. These include glass, carbon, boron, and silica. In recent years, fibres have been produced from synthetic polymers-for example, Kevlar fibres (from aromatic polyamides) and PET fibres. The stress-strain behaviour of some typical fibres is shown in Fig. 3.2. 

The performance of stabilisers in respect of their physical persistency can also be improved by physical adsorption on surfaces of reinforcing fillers, e.g. of CB or amorphous microground silica [589]. Mineral fillers are well known to adsorb polymer additives, especially stabilisers necessary for processing and... 

The production of modern car tyres uses more than 100 raw materials, most of which are based on petroleum products. Tyres consist of natural and synthetic mbber, typically styrene-butadiene (SBR) reinforcing fillers (e.g., carbon black, silica, clay, calcium carbonate) reinforcing fibres... 

Clays. Clay, which is generally considered a mild reinforcing filler, is used sparingly in tires. It is most often used in white sidewalls or in low performance tires. Clay tonnage in tires woddwide is estimated at 36,0001 annually. Clay can also be coupled to rubber with silanes, and this is the more popular version used in tires. Even with silane coupling, days are still a weak reinforcing filler compared to both carbon black and silica. 

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. 

Most elastomers require reinforcing fillers to function effectively, and NMR has been used to characterize the structures of such composites as well. One examples is the adsorption of chains onto filler surfaces,334,335 and the strong absorption of these chains into bound rubber, for example PDMS immobilized onto high surface area silica.316,320 Another example is the use of NMR to image the filler or polymer itself.336-342... 

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