Characterization of Higher-Order Structure of Poly(ethylene-2,6-naphthalate) Treated with Supercritical Carbon Dioxide

Abstract

We have prepared poly(ethylene-2,6-naphthalate) (PEN) films having higher-order structure with fine crystallites using a supercritical carbon dioxide (scCO2) treatment technique at a relatively low-temperature range, from 110 to 170 °C. After the scCO2 treatment, the glass transition temperature Tg decreased by more than 50 °C, and the PEN films were crystallized. Long-term change in the FT-IR absorbance intensity at 2335 cm-1 (CO) was in good agreement with the change in Tg. The large decrease in Tg was attributed to the sorption of the CO2 molecules into the PEN film. Moreover, the increase in the treatment pressure increased the amount of absorbed CO2 and reduced Tg, which can promote crystallization. The higher-order structure, long period, lamella, and interface thickness of the crystallized PEN films were calculated from the one-dimensional correlation function by SAXS. These parameters were all linearly related to the treatment temperature. The crystallite size obtained from the Scherrer equation d...