CHARACTERIZATION OF NONIDEAL NETWORKS BY STRESS-STRAIN MEASUREMENTS AT LARGE EXTENSIONS

It is shown how a characterization of unfilled, amorphous rubber netwo rks can be evaluated from uniaxial stress-strain measurement data. Bes ide the cross-linking density, the relative scission probability durin g the curing procedure is evaluated, which determines the amount of da ngling free chain ends and the number of trapped entanglements. These values are found from the C2 term of the Mooney-Rivlin equation by usi ng the predictions of a tube model. A necessary requirement for applyi ng stress-strain measurements at large extensions is the consideration of the finite extensibility component of the reduced stress. It is ta ken into account by using a numerical procedure, which derives from a series expansion of the inverse Langevin approximation. The experiment al results found at natural rubber networks cross-linked with thiuram (TMTD) and peroxid (DCP) show that network defects cannot be neglected in the DCP networks. They are assumed to be connected to the worse te nsil strength properties compared to the TMTD networks.