The strain amplification is one of the recognized causes of the reinforcement of rubber by carbon black. We evaluated strain amplification in nonequilibrium, i.e., stress-strain measurements. Carbon-black-filled rubber compounds were used. In these examples, not only strain but also strain rate is amplified, since it is a dynamic situation. Because the behavior of the gum matrix is strain-rate dependent, strain-rate amplification is also an important aspect of the rubber compound behavior. We presented case studies of strain-rate amplification with several compounds involving variation of gum rubbers and carbon blacks.

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In order to clarify the fatigue behavior of polyester tire cords in tires, the Poly (ethylene terephthalate) tire cords, which were taken out from a bias tire and a radial tire after running, were examined in terms of strength retention, degree of polymerization, molecular chain ends and crystal size. The fatigue modes of two tires were quite different each other. In the case of bias tire, the decrease of cord strength caused by the decrease of degree of polymerization as chemical degradation was found at a shoulder of tire. In the case of radial tire, the decrease of cord strength caused by structural deterioration as fatigue was found around a bead of tire. The relation between decrease of degree of polymerization and content of carboxyl ends on dynamic fatigue test showed that 80% of chain scission was caused by hydrolysis, which agreed well with the result on the thermal degradation under statical state in rubber. It can be presumed that the mechanism of chain scission caused by fatigue is same as that by thermal degradation.

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The reaction of epoxy resin with imidazoline groups on furnace and acetylene black, which was introduced by the treatment of these carbon blacks with 2, 2′-azobis [2-(2-imidazoline-2-yl)propane], was investigated. When a large excess of epoxy resin was reacted with carbon black having imidazoline groups in acetophenone, the epoxy resin was found to graft onto carbon black surface, but no gelation of the epoxy resin was observed. This indicates that epoxy group of the resin reacts with imidazoline groups on carbon black, but another terminal epoxy group of grafted chain no longer reacts with imidazoline groups on another carbon black. The percentage of grafting of epoxy resin (Mn=1400) onto Philblack O increased to 35% after 10h at 150°C and no longer increased after 10h. On the other hand, when small excess of epoxy resin was reacted with carbon black having imidazoline groups in bulk, the percentage of grafting reached to 100% after 50h at 150°C. In the reaction, the formation of gel, however, was also observed. This indicates that the crosslinking reaction of epoxy resin by imidazoline groups proceeds besides the grafting reaction onto carbon black. The crosslinking reaction of epoxy resin preferentially proceeded with the increasing reaction temperature and the increasing charge ratio of carbon black to epoxy resin. Based on the results, it is concluded that the grafting and gelation of epoxy resin by imidazolin groups on carbon black can be controlled by the reaction conditions.

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