Structural Changes in Poly(ethylene terephthalate) Induced by Supercritical Carbon Dioxide Containing a Cosolvent as a Modifier

Abstract

In order to investigate the structural changes in PET yarn induced by scCO2 treatment and the effect of the additive 1-BuOH on these structural changes, WAXD measurements, DSC analysis and FT-Raman spectroscopy analysis were performed for undrawn PET gut yarn treated with pure scCO2 (120deg, 25 MPa) or scCO2/1-BuOH (120deg, 25 MPa/5.0 mol%). The PET yarn treated with pure scCO2 had a semi-crystalline structure with small and imperfect crystallites and oriented amorphous supermolecular segments. The yarn treated with scCO2/1-BuOH showed higher crystallinity and lower distribution of extended chains, such as oriented supermolecular segments, in the amorphous region than the yarn treated with pure scCO2. Based on these results, we hypothesized on the process of structural change in scCO2 and in scCO2/1-BuOH. We found that the addition of 1-BuOH to scCO2 brings about a significant change in the structure of the PET gut yarn immersed in scCO2.