Tensile and tear behavior of anisotropic double networks of a black-fillednatural rubber vulcanizate

Double networks of a black-filled natural rubber composition have been prep ared by partially curing a sheet, stretching it, and then completing cure. Upon release, a double network retracts to a residual extension ratio, alph a(tau). Samples cut perpendicular to the stretch direction have stress-stra in responses like the isotropic single network, while parallel samples have enhanced stiffness and tensile strength, and reduced extensibility. Tensil e strength is rather weakly dependent on alpha(tau). Tear strengths of the double networks, determined using edge-cut strip specimens, exceed that of the single network for low alpha(tau). However, when alpha(tau) is high, do uble networks have very low tear strengths. Consistent with previous studie s, high tear strengths are associated with extensive longitudinal cracking.