Studies on tyre cords: degradation of polyester due to fatigue

A comparison of physical characteristics of nylon 6, nylon 66 and polyester tyre cords was made. Polyester was found to have excellent dimensional stability in comparison to others. Service conditions of the tyre cords were simulated by applying cyclic compression and tension onto the cord reinforced rubber composite specimens at different strain levels (±10 and ±15%) and time using a Goodrich compression and tension (C-T) fatigue tester. Fatigued cords were taken out from the composites and their ten- sile properties were measured. Polyester was found to have poor fatigue resistance. At very high strain level (±15%) and after 120 h continuous run nylon 66 registered very good fatigue strength retention (80%) while nylon 6 showed 62% retention but polyester cord failed and broke before taking out from the composite. Poor fatigue property of polyester was attributed to the degradation of the cord as observed by decrease in intrinsic viscosity with fatigue time and poor adhesion to matrix. Apart from heat generation, mechanical scission, organic amines present in the rubber compound possibly catalysed the degradation of the polyester cords. Scanning electron microscopy showed a combination of brittle and ductile failure in the polyester filament due to fatigue.