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Studies on the use of nano zinc oxide and modified silica in NR, CR ...

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Chapter 8<br />

implemented method for prepar<strong>in</strong>g high pure amorphous <strong>silica</strong> with low<br />

energy process.<br />

150<br />

Silica has been <strong>use</strong>d as an important re<strong>in</strong>forc<strong>in</strong>g agent <strong>in</strong> rubber<br />

compounds toge<strong>the</strong>r with carb<strong>on</strong> black. 11-15 Mix<strong>in</strong>g <strong>of</strong> <strong>silica</strong> <strong>in</strong>to rubber<br />

compound <strong>of</strong>fers a number <strong>of</strong> advantages <strong>in</strong> tear strength, abrasi<strong>on</strong>, heat<br />

resistance, hardness, high modulus, high resilience, improved roll<strong>in</strong>g<br />

resistance, reducti<strong>on</strong> <strong>in</strong> heat build–up <strong>and</strong> <strong>in</strong>crease <strong>in</strong> <strong>the</strong> compound<br />

adhesi<strong>on</strong> <strong>of</strong> multi comp<strong>on</strong>ent products. Re<strong>in</strong>forcement is usually def<strong>in</strong>ed as<br />

improvement <strong>in</strong> abrasi<strong>on</strong>, tear, cutt<strong>in</strong>g <strong>and</strong> rupture resistance, <strong>in</strong> stiffness <strong>and</strong><br />

hardness <strong>of</strong> vulcanized compounds through <strong>the</strong> <strong>in</strong>corporati<strong>on</strong> <strong>of</strong> f<strong>in</strong>ely<br />

divided m<strong>in</strong>eral particles. The most important factor <strong>in</strong> <strong>the</strong> capability <strong>of</strong><br />

certa<strong>in</strong> m<strong>in</strong>erals to impart re<strong>in</strong>forcement to elastomers is <strong>the</strong> average particle<br />

size. Re<strong>in</strong>forcement is readily obta<strong>in</strong>ed with particle sizes smaller than 100nm<br />

<strong>and</strong> semi re<strong>in</strong>forcement with particle sizes smaller than 1000 nm. Particles<br />

larger than 10 3 nm do not have re<strong>in</strong>forc<strong>in</strong>g capabilities or have detrimental<br />

acti<strong>on</strong>. 16 But <strong>the</strong> particles chemical structure is also a decisive factor. Silica has<br />

a number <strong>of</strong> hydroxyl groups <strong>on</strong> its surface, which results <strong>in</strong> str<strong>on</strong>g filler-filler<br />

<strong>in</strong>teracti<strong>on</strong>s <strong>and</strong> adsorpti<strong>on</strong> <strong>of</strong> polar materials by hydrogen b<strong>on</strong>ds. S<strong>in</strong>ce<br />

<strong>in</strong>termolecular hydrogen b<strong>on</strong>ds between hydroxyl groups <strong>on</strong> <strong>the</strong> surface <strong>of</strong><br />

<strong>silica</strong> are very str<strong>on</strong>g, <strong>silica</strong> can aggregate tightly exhibit<strong>in</strong>g a complex<br />

geometry, from elementary particles to aggregates, agglomerates <strong>and</strong> clusters<br />

with dimensi<strong>on</strong>s from 0.05 to 40 µm. This property can ca<strong>use</strong> a poor<br />

dispersi<strong>on</strong> <strong>of</strong> <strong>silica</strong> <strong>in</strong> a rubber compound. 17<br />

Nowadays many attempts have been made to prepare mesoporous<br />

<strong>silica</strong> from <strong>the</strong> natural resources beca<strong>use</strong> <strong>of</strong> cost sav<strong>in</strong>g <strong>and</strong> envir<strong>on</strong>mental<br />

issue. From rice husk, soluble sodium <strong>silica</strong>te is extracted us<strong>in</strong>g caustic soda.<br />

The development <strong>of</strong> new mesoporous <strong>silica</strong> with properties different than <strong>the</strong><br />

precipitated <strong>silica</strong>, especially <strong>the</strong>ir high BET surface areas <strong>and</strong> <strong>the</strong>ir organized

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