Crack growth resistance in rubber composites with controlled Interface bonding and interphase content

The distinction between abrasion resistance of carbon black and silica reinforced tire tread compounds has drawn attention to the indispensable role of interfacial phenomena on crack growth resistance of rubber composites. Attempts to determine the dependence of interface bonding (from covalent to non-covalent) on crack growth resistance of rubber composites are insufficient without knowledge of the contributions resulting from the interphase (i.e. the volume of rubber chains with restricted mobility). For highly-filled rubbers, the interphase is mainly formed by strong filler-filler interaction and entrapment of rubbers among filler aggregates. Working on the silane-treated silica reinforced rubber, here the alkyl length and the grafting density of silane are systematically controlled to fabricate filler systems with desired surface energy, specified filler-filler interaction and definite trapped-rubber/interphase content. At equal surface energy of fillers one could then change the interface bonding from covalent to non-covalent and study the role of interface on the crack growth resistance. After analyzing the tearing energy of the resulting composites, it was found that the primary factor affecting the fracture strength of highly filled rubbers is the content of the trapped-rubber. The type of interface bonding shared a secondary contribution to the tearing energy values. A slip-stick fracture pattern was observed for the composite with the covalently-bonded interface. A mechanistic model ascribing the relation between the tearing energy and the controlling parameters of the fracture was also proposed.