Effects of Rubber-Curing Chemicals on Tensile Strength of Polyester Yarns

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Abstract
The degradative effects of accelerators of the sulfenamide and thiuram types on polyester tire yarns depends on the stability of the accelerator and the reactivity of the amines generated. Thermal decomposition of the accelerator alone is not sufficient to explain the degradative effects reported by other workers. The complexes formed by the accelerators in the presence of activators, such as zinc oxide and stearic acid, have lower thermal stability than the accelerators alone and release amines at lower temperatures. The formation of the complexes can be shown by differential scanning calorimetry. The findings of this investigation may have important implications with regard to the release of amines during the life of a tire and to the efficient compounding of rubber stock. If, as it appears, the decomposition of TMTM and TBBS occurs more efficiently if they are previously allowed to form a complex, there may be advantages in forming such complexes before addition of the ingredients to the rubber stock. If the ingredients are added separately, the formation of the complex would be controlled by diffusion of the ingredients in the rubber, and incomplete complex formation may result, leaving residues of unreacted components. These would, over a period of time, release more amine, causing degradation of the polyester cord. Advantages of prior complex formation, beside reduction of the above effect, might be lower concentration requirements for the accelerator and possibly better long-term physical properties of the elastomer. As pointed out in the introduction, effects of moisture, which were discussed by Iyengar, were not taken into consideration in this investigation. The conclusions drawn here are therefore strictly applicable only to the thermal decomposition of the accelerators and accelerator-activator complexes. This mode of decomposition is, however, felt to be of major significance for the degradation of polyester tire cords in truck tires during actual use.

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