study of the effect of heat treatment on nylon 66 tire cords structure and its physical properties

in this research, the effect of temperature on the physical and chemical behavior of nylon 66 tire cords in the range of 50-200°c and 16 h testing was studied. the results showed that heat treatment considerably reduced the breaking strength of cords. the intensity of reduction of breaking strength below 100°c and above 120°c was more pronounced than intermediate temperatures. the changes in properties above 120°c were attributed to broadening of molecular weight distribution as ascertained by gpc studies. the increase of irregularity in the polymeric chains was ascertained by shrinkage and birefringence studies. it is found that by raising the temperature, both chain folding and thermal degradation occur, because there is decomposition of the amorphous region occurring as evident by ftir spectroscopy and elastic modulus and birefringence studies. the changes in properties below 100°c were attributed mainly to decomposition of the amorphous region. on the other hand the percentage of crystallinity increased and tire cord became more brittle and its tensile strength below 100°c was decreased. the lower reduction of tensile properties in the intermediate temperatures of 100-120°c was due to no change in polydispersity and irregularity of the polymeric chains compared to higher temperatures as well as smaller increase in percentage of crystallinity compared to lower temperature treatments.