Investigating the dependence of elastomeric fracture on temperature and rate

Decades of elastomeric fracture phenomenology resulting from the work of Thomas and Smith demonstrated the remarkable fact that rubbers are stronger and tougher at lower temperatures. The prevailing explanation relates the fracture behavior to polymer viscoelasticity. Given the recent insight and evidence that toughness is influenced by material strength, we examine elastomeric fracture with a different perspective and conclude that chain scission dictates fracture characteristics, including its temperature dependence. Working within selected temperature ranges, stretching is shown to be entirely elastic at a stretching rate less than 0.17 s(-1). We demonstrate that the same temperature and rate dependencies of strength and toughness, observed by Thomas and Smith, also occur in our crosslinked polybutadiene and styrene-butadiene rubber. The temperature effects on rate dependence of strength and toughness are found to be much stronger than that prescribed by the Williams-Landel-Ferry shift factor aT. Moreover, crack propagates, upon either stepwise stretching or during creep, at a much lower speed at lower temperature that cannot be rationalized with polymer relaxation dynamics. Our new interpretation is that a carbon-carbon bond is stronger at a lower temperature. Because backbone bonds are more stable, a higher degree of network stretching occurs before rupture at lower temperatures.