Abstract: An investigation of the structure and mechanical behavior of melt-spun isotactic polypropylene (iPP) fibers subjected to thermal treatment in an inert atmosphere is described. Two iPP formulations, Basell Pro-fax PH835 and ExxonMobil Achieve 3854, synthesized by the Ziegler-Natta and metallocene catalysts respectively, and spun at take-up velocities of 1000 to 3000 m/min are consider…