Executive summaryThe main focus of this paper was the development of a method for the characterization of the reversible extensibility and the stress relaxation under dynamic service conditions. This method can be used for a quantitative evaluation of polymers in dynamically used articles (such as timing belts, engine mounts or seals) as well as for the determination of the molecular mechanisms which generate the stress relaxation and the permanent deformation in polymers.The comparison of an unfilled crosslinked elastomer (peroxidic crosslinked hydrogenated nitrile rubber) with a typical semi crystalline thermoplastic (polypropylene) shows that the deformation behavior of the crosslinked elastomer is primarily controlled by entropy elastic relaxation processes while the deformation behavior of the thermoplastic polymer (PP) is dominated by irreversible flow processes. The characterization of typical thermoplastic vulcanizate‟s (based on ethylene propylene rubber /PP) and filled, crosslinked elastomers (HNBR with the carbon black N330) as a function of thehardness yielded a clear differentiation of the relative permanent deformation and the relaxation behavior. The newly developed relaxation measurement can be used as a tool for the development of novel, improved materials for dynamically used technical rubber goods (such as TPVs or optimized rubber compounds). The results of the EPDM/PP based TPVs can thereby be used as a state of the art reference for commercially available standard grades, the results ofthe filled HNBR compounds may be used as state of the art reference for rubber applications at elevated temperatures.
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Nguồn: Quốc Anh, Cao su Đức Minh
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http://caosu.org/entry.php/114-Characterizing-relaxation-behavior-of-polymers
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