Abstract
The combination of vulcanizing agents is an adequate strategy to develop multiple networks that consolidate the best of different systems. In this research, sulfur (S), and zinc oxide ( ZnO) were combined as vulcanizing agents in a matrix of carboxylated nitrile rubber (XNBR). The resulting dual network improved the abrasion resistance of up to ~15% compared to a pure ionically crosslinked network, and up to ~115% compared to a pure sulfur-based covalent network. Additionally, the already good chemical resistance of XNBR in non-polar fluids, such as toluene and gasoline, was further improved with a reduction of up to ~26% of the solvent uptake. A comprehensive study of the molecular dynamics was performed by means of broadband dielectric spectroscopy (BDS) to complete the existing knowledge on dual networks in XNBR. Such analysis showed that the synergistic behavior that prevails over purely ionic vulcanization networks is related to the restricted motions of rubber chain segments, as well as of the trapped chains within the ionic clusters that converts the vulcanizate into a stiffer and less solvent-penetrable material, improving abrasion resistance and chemical resistance, respectively. This combined network strategy will enable the production of elastomeric materials with improved performance and properties on demand.
Highlights
IntroductionElastomers usually undergo a crosslinking process of their polymeric chains (known as vulcanization), which gives them their characteristic elastic behavior
Elastomers usually undergo a crosslinking process of their polymeric chains, which gives them their characteristic elastic behavior
The MH value increases with the amount of zinc oxide (ZnO) due to the increase in the ionic crosslinks points in the matrix that cause a greater resistance to shear deformation [14]
Summary
Elastomers usually undergo a crosslinking process of their polymeric chains (known as vulcanization), which gives them their characteristic elastic behavior. The benefits of the carboxylic group over different properties that were being discovered were adequately collected in multiple reviews of the literature [2,4]. It was not until the work of Eisenberg, in which a molecular model (currently in vigor) was presented with the aim of understanding ionic crosslinking as a complex and fascinating structure. With the appearance of carboxylated nitrile rubber (XNBR), and its better performance in multiple properties compared to its original rubber (nitrile rubber, NBR), numerous studies have focused on enhancing its characteristics and improving its processing. The use of different systems in XNBR has been a constant since each type of crosslink (ionic and covalent) has a particular contribution on the properties of the rubber, and together, they deliver the best of both networks
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