2.6 Bound rubber measurement
0.25 g of uncured compound (without curatives) was cut into small pieces, put into a metal cage and immersed in toluene at room temperature for 72 h (renewed every 24 h). The sample was removed from the toluene, dried at 50 °C for 24 h, then immersed in toluene again for 72 h at room temperature in either a normal or an ammonia atmosphere. The ammonia treatment was done to cleave the physical linkages between rubber and silica, in order to determine the chemically bound rubber versus bound rubber physical of nature. The sample was finally dried at 50 °C for 24 h. The bound rubber content was then calculated using the following equation [29]:
(equation5)
where m is the weight of sample after extraction, ms is the weight of silica in the sample and mr is the original weight of rubber in the sample.