Effect of coupling agent on the morphological characteristics of natural rubber/silica composites foams

The effect of coupling agent on the morphological characteristics of natural rubber/silica composite foams with various silica contents was studied. Bis 3-triethoxysilylpropyl tetrasulfide (TESPT) was used as coupling agent in this system. It could make a chemical bond with the silica particles. By increasing the silica content, cell size of foams was reduced more that 50% and foam density was increased up to 40%. However, compatibilized composites demonstrated about 20% lower foam density and higher cell size. In this case, strong adhesion between the components prevented gas from escaping out. While, in the foams excluded coupling agent the weak adhesion between particles and rubber created an escape path for gas from the interface of components. So, lower cell size and higher density were achieved.