Cold crystallization and thermal shrinkage of uniaxially drawn poly(ethylene 2,6‐naphthalate) by solid‐state coextrusion

Abstract

Abstract Solid‐state coextrusion has been used to prepare uniaxially drawn films from isotropic poly(ethylene 2,6‐naphthalate) (PEN) of a minimum degree of crystallinity (ca. 5%) both below and above its glass transition temperature T g . The onset of cold crystallization ( T c ) of the drawn films has been studied as a function of the extrusion temperature (ET) and the draw ratio (EDR). It has been shown that T c decreases markedly on draw, as much as 95°C, and, at constant draw ratio T c goes through a minimum in the T g region. For undrawn PEN, annealing below 153°C has no significant effect on T c . To evaluate the crystallization rate constant ( k ) and the activation energy ( E a ) of the drawn specimens, a nonisothermal DSC procedure has been used. With increasing EDR, k increases markedly and E a goes down over threefold compared with the undrawn polymer. At high ET, strain‐induced crystallization has also been shown to play an important role in lowering E a for cold crystallization. Thermal shrinkage above T m indicates a high elastic recovery, underlining the efficiency of deformation, ca. 93%, achieved by solid‐state coextrusion.