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

Chapter 1
adsorption (BET) method. Also pH, chemical composition and oil absorption
are specified. The smallest physically observable primary particle for
precipitated silica is about 15-20µm and for fumed silica it is about 15µm in
size. The surface forces of the small primary particles are so high that many
particles agglomerate to form the so-called secondary particles. Usually the
shear forces generated during rubber mixing is not sufficient enough to
disperse primary filler particles in the rubber. 51
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The secondary particles of silica fillers form further agglomerates.
They form chain-like structures, the so-called tertiary structures. Though the
tertiary structures are also relatively stable, they get more or less shattered by
the shear forces during mixing. 50 The higher the shear forces, the better the
dispersion.
Reinforcement by fillers
Reinforcement is the enhancement of tensile strength, modulus,
abrasion and tear resistance obtained by adding a material like fillers. Active
fillers called reinforcing fillers, interact with polymer molecules through
Van der Waals forces, chemisorption forces and eventually covalent forces. It
is possible to create chemical bonds with the surface of the filler particles
using coupling agents. Reinforcing agents are substances having shape
and structures such as short fibrous forms or powdery form, and are
impregnated with polymers and the moulded product thus obtained possess
remarkable mechanical properties. Interaction between carbon black and
polymer are one of the most important mechanisms of carbon black
reinforcement, often measured as bound rubber. 51 Bellander et al. studied the
influence of pressure and temperature on bound rubber for carbon black-
polybutadiene composites and concluded that elevated pressure and
temperature increased the amount of bound rubber. The reinforcement of
elastomers by particulate fillers, to a large extent depends on polymer