Thermal Shrinkage and Orientation-Induced Crystallization Behavior of Successive-Biaxial Drawn Poly(phenylene sulfide) and Poly(ethylene terephthalate) Films.

Abstract

The structure development of poly(phenylene sulfide) (PPS) and poly(ethylene terephthalate) (PET) films in successive-biaxial drawing process was studied through the analysis of the structural change of films with thermal shrinkage. When the first and second step draw ratios were equal, molecular chains showed preferential orientaion along the second step draw direction. After the thermal shrinkage of the equal-biaxial drawn samples with the draw ratios of 2.0 for PPS and 4.0 for PET, the directions of crystal orientation (c-axis orientation for PPS and a*-axis orientation for PET) changed from the second step draw direction to the first step draw direction. Both polymer films with lower draw ratios became almost isotropic, whereas the crystal orientation directions of the higher draw ratio films (c-axis orientation for both samples) remained intact with the thermal shrinkage. Accordingly it was speculated that these par-ticular draw ratios for both polymers correspond to the boundary between the formation of the oriented crystalline embryo and the completion of the fiber structure formation. In other words, the crystalline embryos can rotate during the second step drawing and the thermal shrinkage process, while the crystals cannot rotate anymore after the fiber structure was completely developed.