Modification of PET in high‐speed melt spinning by blending with PEN

Blends of polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) were melt spun using a high‐speed winding process in a single‐screw extruder combined with a spinning setup. The filaments had a single Tm and Tg, which indicates excellent compatibility in both the amorphous and crystalline phases. Birefringence and wide angle X‐ray measurements indicated that compounding PEN into PET suppresses stress‐induced orientation and decreases the stressinduced crystallization in the filaments. Adding PEN to PET relaxes the formation of skin‐core structures for as‐spun fibers and reduces the occurrence of broken filaments. Although the addition of PEN reduced crystallinity, it did not affect the tenacity and the shrinkage of the compounded filaments. The elongation of the fibers could be reduced by 30% to 40%, eliminating the need for a further drawing. These results are attributed to PEN's rigid backbone. Adding PEN to PET improves PETs spinnability during high‐speed spinning.