Crystallinity of Recycled PET Fibers from Chemical and Mechanical Reprocessing

This work investigated the effect of isophthalate (iso) content in poly(ethylene terephthalate) (PET) materials on its degree of crystallinity (χ%) and mechanical properties. Melt blends were prepared from virgin (0 iso-wt.%) and bottle-grade (1.7 iso-wt.%) PET and subsequently spun into fibers. The mechanical and crystallinity properties were determined using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and uniaxial tensile testing. The crystallinity results determined from DSC and XRD quantified the relationship between iso-content and χ% in the materials. It was found that melt-mixing of different isophthalate grades had a lesser effect on melting temperature (Tm) and χ% than chemically recycled random copolymers of terephthalate and isophthalate. It was further shown that random copolymers of <0.25 iso-wt.% had comparable crystallinity to the virgin high-modulus low-shrink (HMLS) materials.