Somayeh Baseri - Department of Textile Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran
Mohammad Karimi - Department of Textile Engineering, Amirkabir University of Technology, Tehran, 15914, Iran
Mohammad Morshed - Department of Textile Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran

Cold drawing of PET fibers with the transition of the neck through the material can present a highly oriented structure (mesophase) exhibiting no crystalline order [1]. Mechanicalloading, thermal, and solvent treatments of PET fibers and films as well as their supercritical fluid exposure havesignificant effects on the structure of the fibers [2, 3]. Athorough knowledge of the structural changes induced by supercritical carbon dioxide (scCO2) is essential for designingpolymer processes. As the transient structure has a key role on the ultimate properties of fibers, it will also be interesting tolearn about the post-treatment mesomorphic changes that occur in this structure. Exposure of fibers to scCO2 allows for tailoring desirable structural changes in them without anyenvironmental hazards, designing new polymer processes or improving upon old ones can only be achieved by exactlyknowing the mechanism of microstructure development and the mesomorphic transitions in the oriented PET fibers exposed to scCO2