Relaxation EPDM sulfur vulcanisation

The analytical techniques discussed previously can be used to study the EPDM network as such or its formation in time as well as to determine relationships between the network structure and the properties of the vulcanisates. In a preliminary approach some typical vulcanised EPDM properties, i.e., hardness, tensile strength, elongation at break and tear strength, have been plotted as a function of chemical crosslink density (Figure 6.6). The latter is either determined directly via 1H NMR relaxation time measurements or calculated from the FT-Raman ENB conversion (Table 6.3). It is concluded that for these unfilled, sulfur-vulcanised, amorphous EPDM, the chemical crosslink density is the main parameter determining the vulcanisate properties. It is beyond the purpose of this review to discuss these relationships in a more detailed and theoretical way. 

NMR spectroscopy and solid-state and 13C NMR relaxation-time experiments. However, the sensitivity of solid-state 13C NMR is not as high as that of Raman and IR spectroscopy. For instance, solid-state 13C NMR of sulfur-vulcanised EPDM could only be performed when the ENB unsaturation of EPDM was fully isotopically enriched with 13C NMR [124]. 

A change in T2 relaxation during accelerated sulfur vulcanisation of EPDM rubber is shown as an example in Figure 10.17 [179]. 

Figure 10.17 Dependency of T2 relaxation time as a function of the actual vulcanisation time during accelerated sulfur vulcanisation of EPDM [179]. The line has been included to guide the eye. The vulcanisation temperature was 413 K (140 °C)...

---