The present research work was carried out to investigate the tensile behaviour of yarns spun from inherently flame-retardant Polyester Fibres (Trevira CS), produced on most common spinning systems. Trevira CS fibres were successfully processed on popular spinning systems such as Ring spinning, Rotor spinning and Air-jet spinning to produce 20 Ne yarns. The tensile behaviour of Ring-spun, Rotor-spun, Air-jet-spun yarns has been investigated at varying specimen lengths and high extension rates. It is observed that the increase in specimen length from 200 mm to 500 mm decreases continually the yarn tenacity, breaking extension, but increases the breaking work and the modulus. The Rotor-spun yarn exhibits a minimum reduction in tenacity while the Air-jet-spun yarn shows a greater drop in tenacity and breaking extension when tested at longer specimen lengths. Amongst all yarns, the Ring-spun yarn exhibits highest tenacity and modulus followed by Rotor- spun yarn and Air-jet-spun yarn. The yarn tenacity, breaking extension, modulus, breaking work, breaking time are found to be logarithmic functions of specimen length. The increase in extension rate from 5 m/min to 400 m/min considerably increases the yarn tenacity but does not have a regular effect on its breaking extension. The percentage increase in tenacity is higher in case of Ring-spun yarn followed by the corresponding Rotor-spun and Air-jet-spun yarns. All these observations ascribe to the nature of the responses of the constituent fibres in the yarns and differences amongst the structures of these yarns.
