Print ISSN : 0029-022X
Volume 93 , Issue 11
Showing 1-5 articles out of 5 articles from the selected issue
Regular Papers
  • Naoki TERADA, Katsushige KOUGE, Teppei YAMAGUCHI, Kenji KOMAGUCHI, Shi ...
    2020 Volume 93 Issue 11 Pages 345-351
    Published: 2020
    Released: January 15, 2021

    Insoluble sulfur (IS), which has linear long chain of sulfur and is an allotrope of sulfur, is prepared by thermal ring-opening polymerization of cyclooctasulfur (S8). IS is widely used as a vulcanizing agent for rubber. Enhancing thermal stability of IS and its yield from S8 are important for usage of IS in the tire manufacturing process and its industrial production. Typical procedure for IS preparation has three steps, melting sulfur (S8), cooling the molten sulfur, and post-heating the solidified sulfur that is mixture (Sx) of IS and S8. Our previous investigation demonstrated that the long term post-heat treatments (at 30 °C for 960 h) enhanced thermal stability of the resulted IS without yield loss. Such long term process is not acceptable for industrial preparation of IS. In this paper, we report that the acceptable post-heat treatment condition of the Sx is at 60 °C for 18 hours through the investigation under various post heat treatment conditions. We estimate the apparent reaction rates, elongation reaction of sulfur chains, their scission reaction and formation of S8 by using ESR technique. In addition, the multistep post-heat treatments also enhance thermal stability of the resulted IS with small amount of yield loss.

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Advanced Course on Rubber Science and Technology
  • Chapter 5: Evaporation and Drying
    Masao DOI
    2021 Volume 93 Issue 11 Pages 352-357
    Published: 2021
    Released: January 15, 2021

    When a drop of coffee dries on a dish, many non-equilibrium processes are taking place. The water changes into vapor and diffuses out in air. Inside the coffee, liquid flow is induced by the surface tension, and coffee particles are convected to the edge of the droplets, leaving ring-like stains at the edge. This example demonstrates the complexity and the multi-physics nature involved in the phenomena we are seeing in our everyday life. Here as the last part of this series of lectures, I will discuss a few physics involved in evaporation and drying focusing on two problems, how the evaporation rate is determined, and how the structure of the dried material is determined.

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  • Yoshihide FUKAHORI
    2020 Volume 93 Issue 11 Pages 358-365
    Published: 2020
    Released: January 15, 2021

    When a rigid slider moves over a surface of cross-linked rubber, two kinds of vibration are generated, one being a stick-slip motion, the second being vibrations with a much higher frequency. The high frequency vibration corresponds to the natural resonance frequency of rubber induced during the slip stage of the stick-slip motion, which initiates microcracks on the surface of the rubber. The violent stick-slip motion of the rubber might occur with the same mechanism as observed in atomic motions of metal, in which a large potential energy difference generated between the adjacent atoms when an atom moves on others arranged regularly produces the discontinuous energy dissipation together with the discontinuous movement. In a similar manner, the sticky adhesive area on the surface of the crosslinked rubber produces the large dynamic energy difference stored between the stick and slip stages corresponding to the generation of strain energy, which may cause a high friction coefficient and the discontinuous movement of slider (stick-slip motion).

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  • [in Japanese]
    2020 Volume 93 Issue 11 Pages 366-369
    Published: 2020
    Released: January 15, 2021
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Technical Note