NIPPON GOMU KYOKAISHI
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Special Issue for General Reviews “Fundamentals of elastomers and the latest analysis technology (3)”
Introductory Remarks
General Reviews
  • Analysis of Sulfur Radicals and Insoluble Sulfur by ESR Spectroscopy
    Naoki TERADA, Kenji KOMAGUCHI
    2024 Volume 97 Issue 4 Pages 90-96
    Published: 2024
    Released on J-STAGE: April 23, 2024
    DOIhttps://doi.org/10.2324/gomu.97.90
    JOURNAL RESTRICTED ACCESS
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    Insoluble sulfur (IS), a long chain of sulfur, which is prepared by polymerization of cyclooctasulfur (S8) via thermal ring opening. As IS is very important as a vulcanizing agent for rubber, it is worth enhancing the thermal stability of IS and the yields from S8 for its actual industrial usage such as tire manufacturing processes. Post heat-treatments are effective in the enhancements, but the mechanism remains unclear. This is because the insolubility of IS limits the methods available for characterization. Electron spin resonance (ESR) spectroscopy can detect and identify chemical species having unpaired electrons with high sensitivity. It is widely used to elucidate polymerization and degradation mechanisms of rubber and plastics. IS has radicals at both ends of its linear chain. In this review, we focus on sulfur radicals to characterize IS using the ESR technique and discuss reactivities of sulfur radicals in the polymerization of sulfur via S-S bond cleavage of S8 , the evaluation of sulfur chain length, and the dependence of stability of IS on post heat-treatments in terms of the chain length.

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  • Evaluation of Cross-linking of Rubber and Polymers by TDNMR
    Hideyuki HARA
    2024 Volume 97 Issue 4 Pages 97-104
    Published: 2024
    Released on J-STAGE: April 23, 2024
    DOIhttps://doi.org/10.2324/gomu.97.97
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    TDNMR is a nuclear magnetic resonance spectrometer that observes the relaxation time of protons. TDNMR does not require deuterium solvents as in high-resolution NMR, and can be used to measure samples without sample preparation. This paper introduces an example of using TDNMR to evaluate cross-linking of rubber and polymers. While it is possible to evaluate cross-linking by physical properties based on relaxation time, it is also possible to evaluate cross-linking from a structural viewpoint by using the MQ method, which can detect the effect of residual dipole interactions caused by cross-linking. In addition, examples of the application of the MQ method to polymers will be presented.

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  • An Analysis on Aging Mechanism of Sealing Materials
    Yuichi AOYAGI
    2024 Volume 97 Issue 4 Pages 105-109
    Published: 2024
    Released on J-STAGE: April 23, 2024
    DOIhttps://doi.org/10.2324/gomu.97.105
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    A chemical analysis method was developed to evaluate the degree of chemical degradation for radial shaft seals after driving in a market.
    The obtained samples were analyzed with Fourier transform infrared spectroscopy (FT-IR) and surface hardness measurement. As the driving mileage increased, polymer structure changed and surface hardness increased.
    The degradation of the lip of radial shaft seals was reproduced in a similar environment in our laboratory, and we determined that the factors responsible for degradation are oil additives, temperature, and air. Moreover, the relationship between various types of FKM polymer and their resistance against oil additives was obtained using the molecular orbital simulation method.

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