Some physical characteristics of double-networked natural rubber

A double-networked natural rubber (DNNR) was prepared by a "two-step crosslinking" method, in which the crosslinking was achieved while the natural rubber was in a stretched condition. The swelling behavior, tensile properties, creep, recovery, and permanent set were investigated. Generally, the observed mechanical properties of DNNR, such as the Young's modulus, tensile strength, toughness, creep, recovery, and permanent set, were considerably improved as the residual extension was increased. They were, however, rather inferior to those of a single-networked natural rubber and showed a minimum at a lower residual extension of about 1.55. The degree of crosslinking and elongation at break were not greatly affected by the residual extension.