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

Chapter 2
2.2.6 Bound rubber content
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Bound rubber is the rubber that is trapped by the filler aggregates
after mixing. The rubber chain are attracted either physically or chemically to
form a rubber shell on the surface of the silica particles. The rubber fraction
of an uncured compound is amount of rubber that is not extracted when it is
exposed to a good solvent.
The mixture samples were cut in small pieces and put over a stainless
steel sieve (40 µm meshes), then extracted with toluene for 4 days and finally
dried for one day at 80°C. Contents of bound rubber were determined from
the weights of the samples before and after the extraction.
The BRC is calculated from the weight of the residue after extraction
(b), the weight of the initial mixture (m), and the amount of silica present in
the initial mixture (a), determined by calcination at 600° C.
BRC %= [(b-a) / (m-a)] x 100………………………….. ……….. 2.5
The BRC can be related to the amount of rubber in the mixture before
the extraction and was calculated using the equation 2.5. 11
2.2.7 Ozone resistance
Ozone resistance was determined according to ASTM D 518 method
B. Samples were exposed to ozonised air in an ozone chamber (MAST Model
700-1) for 12 hrs. The concentration of ozone was maintained at 50 pphm at
20% strain and the inside temperature at 40°C. The ozone cracks developed
on the samples were observed by a lens and the photographs were taken.
2.2.8 Thermogravimetric analysis
The thermograms of natural rubber, silica composites are recorded
with a thermogravimetric analyzer Q–50, TA instruments. It is computer