Sulfur vulcanisation relaxation

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)...

In the original paper [47], the authors reported work on the uniaxial tension of plasticised poly(vinyl chloride), sulfur vulcanisates of butyl rubber, and polyisobutylene. Very successful predictions were made at extension ratios up to approximately five. Zapas and Craft [48] applied their formulation to multi-step stress relaxation and creep and recovery of both plasticised poly(vinyl chloride) and polyisobutylene. McKenna and Zapas applied a modified form of the model to the torsional deformation of PMMA [49]. McKenna and Zapas [50] have used the model in the analysis of the tensile behaviour of carbon-black-filled butyl rubbers. 

More precisely, the magnetic relaxation depends on the variable of gelation, i.e., the density of crosslinks, and is closely related to the modulus of elasticity, E, on the one hand and to the swelling ratio, Qm, on the other hand. Long polybutadiene chains are currently randomly crosslinked, using sulfur they can serve to illustrate the NMR approach to the characterisation of vulcanised polymers. It has been shown that the... 

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