Modification of PET in high-speed molt spinning by blending with PEN

Blends of polyethylene terephthalate (PET) and polyethylene naphthalate (PE N) were melt spun using a high-speed winding process in a single-screw extr uder combined with a spinning setup. The filaments had a single T-m, and Tg , which indicates excellent compatibility in both the amorphous and crystal line phases. Birefringence and wide angle X-ray measurements indicated that compounding PEN into PET suppresses stress-induced orientation and decreas es the stress-induced crystallization in the filaments. Adding PEN to PET r elaxes the formation of skin-core structures for as-spun fibers and reduces the occurrence of broken filaments. Although the addition of PEN reduced c rystallinity, it did not affect the tenacity and the shrinkage of the compo unded 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 PET's spinnability dur ing high-speed spinning.