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

Chapter 1
hardness and abrasion resistance. In the ASTM D 1765 classification for
carbon blacks about 42 commercial blacks were recognized.
1.4.2b. Non-black fillers
22
Non-black reinforcing fillers for rubber include hydrated silica,
calcium silicate, zinc oxide, the fine particle size precipitated calcium
carbonate etc. The use of coupling agent is more relevant with these non-
black fillers. 39-42 Reinforcement by silica and silicates has been reviewed by
Wagner. 43 Non-black fillers include a range of inorganic materials with a
variety of particle shapes and sizes. It is available in a broad range of sizes
from about 10 to 0.015 microns. These fillers can broadly be classified as;
a) fillers used to reduce cost b) semi-reinforcing filler c) reinforcing filler.
Earlier non-black fillers used were mainly naturally occurring minerals or by-
products of manufacturing such as clay, whiting, barytes, zinc oxide, zinc
sulphide, blanc-fixe, mica, asbestos, kieselguhr, magnesium carbonate, iron
oxide, litharge etc. They were used in rubber to reduce tack, increase
hardness, improve durability and reduce cost. 44-46 Other important non-black
fillers being used in the elastomer industry are aluminium hydrate,
aluminium oxide and titanium dioxide.
The need for more reinforcing non-black fillers in many rubber
applications led to the introduction of calcium carbonate, calcium silicates,
hydrated silica and fumed silica between 1940 and 1960. These were
characterized by very small particle size much smaller than the natural
products and similar to the reinforcing carbon blacks. Since then a lot of
developments and refinements in hydrated silica and fumed silica have taken
place resulting in a number of grades for specific applications. 47
Silica
Silica is a crystalline compound occurring abundantly as quartz, sand
and many other minerals and is used to manufacture a variety of materials,