Influence of the vulcanization system on the dynamics and structure of natural rubber: Comparative study by means of broadband dielectric spectroscopy and solid-state NMR spectroscopy

• NR dynamics is affected by crosslinks and inhomogeneities at different length scale.
• Sulfur systems feature restricted segmental dynamics compared to peroxide systems.
• Sulfur-cured networks have a homogeneous spatial distribution of cross-links.
• Peroxide-cured networks are heterogeneous at local length-scales.
• BDS and NMR are complementary approaches to study the dynamics and structure of NR.

A study on the effects of the curing systems on the dynamics and network structure of Natural rubber (NR) is performed by using broadband dielectric spectroscopy (BDS) and proton multiple-quantum NMR. Sulfur-cured systems present a restricted segmental dynamics, whereas peroxide-cured systems have the fastest dynamics. Network structure also affects the segmental dynamics of NR. Peroxide-cured networks seem to have more heterogeneous spatial distribution of cross-links, while sulfur-cured networks have inhomogeneities at larger length scales associated to ZnO particles. These structural dissimilarities possibly explain the segmental dynamics behavior and fragility strength of NR. This investigation shows that BDS and NMR are complementary approaches for studying the dynamics and structure of NR. The correspondence between both techniques confirms that the segmental dynamics of vulcanized NR is not solely affected by the number of cross-links, but also by their spatial distribution and nature of these junctions, e.g. C–C or sulfidic bridges with different lengths.

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