Abstract
To investigate the tensile fracture mechanism of rubber vulcanizates, in particular to determine the relationship between the tensile properties and polymer structure, styrene-butadiene copolymers (SBR) with various styrene contents were studied in this paper. The following conclusions were obtained from the results of tensile measurements and physical properties.
(1) Failure for the SBR vulcanizates (carbon black filled), at the temperature region over the necking phenomena, occurred mainly at the site of the main chain, not between rubber molecule and carbon black.
(2) If the number average molecular weight, network chain density and the type of combined sulfur are considered nearly the same, the same molecular motional region (which was discussed from the view of viscoelastic study and nuclear magnetic resonance study in this paper, but it can be mentioned as the glass transition temperature in general) was shifted for the higher temperature side with the increase of styrene content in SBR, and the characteristic temperature for the failure properties (the inflection point for the tensile strength-temperature curve and the maximum point for the ultimate elongation-temperature dependence) was also shifted in the same quantity.
(3) Shifting the tensile data in the same quantity as the transition temperature, only one master curve was obtained for the tensile strength, even if the styrene contents were changed. For the ultimate elongation, however, the master curves were not the same for the various contents of styrene, but the value of the ultimate elongation after shifting decreased with the incresae of styrene parts in polymer. This result was successfully interpreted by the hypothesis that the elongation of polymer molecule depends on the carbon atom in butadiene monomer unit, not on the carbon atom in styrene unit.
