Structure development of polyesters and their blends in film formation processes

A fundamental study of structure development in cast, single and double bubble, and biaxial film stretching processes of polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and PBT/PET blends was carried out. The deformation mechanisms and physical properties of films were described in terms of various structural parameters. We established a new process technique to fabricate double bubble biaxially orientated films from rapidly crystallizing polymers.; Polyesters were largely stable in various film forming processes. In film casting, the rate of crystallization tended to dominate the processability of materials. The stability of first bubble was substantially improved with an increase in molecular rigidity. In cold-drawing processes, the stability was dominated by the strain hardening behavior of materials.; PBT cast and first bubble films were semicrystalline with only the {dollar}alpha{dollar} phase. Cold-drawn films revealed X{dollar}rmsb{lcub}c{rcub}{dollar}'s of 20-30% and polymorphism. The polymer chains increasingly oriented into the film plane with biaxial stretching. PBT biaxial films had a maximum tensile strength of 210 MPa.; Cast and first bubble films of PET were largely amorphous. PET films stretched in a rubbery state possessed X{dollar}rmsb{lcub}c{rcub}{dollar}'s of 20-35%. PET films exhibited (100) planar orientation with crystallites oriented either to the drawing direction or in the plane of the film. A maximum tensile strength of 400 MPa was obtained.; Twin screw melt extruded PBT/PET blends exhibited equilibrium melting point depression. The interaction parameters {dollar}(chisb{lcub}12{rcub}){dollar} were determined to be negative and composition dependent, ranging from {dollar}-{dollar}0.75 to {dollar}-{dollar}0.55 at 285{dollar}spcirc{dollar}C.; Cast and first bubble films of PBT/PET blends exhibited decreased X{dollar}rmsb{lcub}c{rcub}{dollar} with rising PET content. Cold-drawn blend films possessed a X{dollar}rmsb{lcub}c{rcub}{dollar}'s of 20-45%. The orientation in the PBT phase decreased with increasing PET content while that in the PET phase increased. The mechanical properties of the films generally followed the rule of mixtures.; PEN cast films were largely amorphous. First bubble films developed a maximum {dollar}rm Xsb{lcub}c{rcub} approx 35%{dollar} and highly perfected polymorphic structure. Cold-dawn PEN films had only the {dollar}alpha{dollar} phase and a maximum {dollar}rm Xsb{lcub}c{rcub} approx 48%.{dollar} PEN films possessed (110) {dollar}alpha{dollar} planar orientation.