engleski

ESR Approach in Studying Rubber and Rubber Composite

The rubber is technically one of the most important materials. Final properties of a rubber material depend on many factors, and between them the most important are structure and (in)homogeneity of rubber matrix, but also the presence of fillers that act as reinforcing agents [1]. The reinforcing effect of fillers is based on the slowdown of the local dynamics of rubber chain segments. Carbon black (CB) is used as common rubber filler during more than 100 years. CB has a specific chemical structure of the surface that leads to strong interaction with the polyisoprene matrix chains. Since rubber products are subject to aging and wear, they must be replaced regularly by new ones. In addition to its good filler characteristics, CB also has a negative side because it fetters the recycling of waste rubber. Therefore, an enormous amount of rubber waste represents a huge environmental problem. This is the reason why the last decades scientists are diligently looking for a new filler that could replace the carbon black. Among many substances, silica, organically modified montmorillonite (OMMT, nanoclay) and multiwall carbon nanotubes (MWCNT) are most frequently investigated. ESR spectroscopy has been proved as a powerful tool in studying segmental motions of polymer chains [2]. Some of composite rubber systems possess an intrinsic ESR signal and can be studied directly by ESR spectroscopy. Contrary, pure rubber, as the majority of rubber composites, possesses no intrinsic paramagnetism and requires the use of stable radicals (most commonly the nitroxides) known as spin probes. This technique gives the possibility to study an effect of the filler on motional behavior of the chain segments. Furthermore, this behavior strongly depends on the interaction between the filler and matrix chains. An overview of the application of ESR spectroscopy in studying matrix inhomogeneity will be presented. Particularly, the influence of various fillers on structural and dynamic parameters in rubber (nano)composites will be discussed [1, 3, 4]. [1] S. Valić, Electron Spin Resonance in Studying Nanocomposite Rubber Materials, in Rubber Nanocomposites: Preparation, Properties and Applications, S. Thomas, R. Stephen, Eds, John Wiley & Sons, 2010, p. 391-405. [2] Z. Veksli, M. Andreis, B. Rakvin, ESR spectroscopy for the study of polymer heterogeneity, Prog. Polym. Sci. 25 (2000) 949-986. [3] M. Petković Didović, D. Klepac, A.P. Meera, S. Thomas, S. Valić, Presence of vacuoles in natural rubber- Cloisite 15A nanocomposites, J. Appl. Polym. Sci. 134 (2017) 44776-44788. [4] A. Ivanoska- Dacikj, G. Bogoeva-Gaceva, S. Valić, ESR spectroscopy as a new method to analyze the synergy between two different nanofillers dispersed in an elastomer matrix, Polym. Test, 73 (2019) 293-299.

ESR ; EPR ; rubber ; composite ; dynamics ; heterogeneity

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