The effects of aging and aging under stress on the tear strength of filled natural rubber vulcanizates were investigated. Tear strengths were evaluated using a trouser tear geometry with a constrained tear path. Fracture energies and crack growth rates were determined. Four distinct cracking patterns were observed and characterized. Tear strength significantly decreased and crack deviation was absent at long cure times.
Anaerobic heat aging at 120°C resulted in little change in the tear strength, while aging at 80°C, 100°C or 140°C resulted in a lowering of strength. Heat aging under stress (mechano-chemical) resulted in anisotropy. Tear results were assessed using double network concepts. After mechano-chemical aging at low strain, tear strength decreased slightly, but with enough deformation during aging, it decreased dramatically.
In addition, the effect of various bonding agents on the fracture behavior was studied. A new commercial agent resulted in higher tear strengths than seen for traditional bonding agents.