Evaluation of Rheological Properties and Generation of Cross Orientation of Lamellae and Amorphous Chains in a Thermoplastic Polyester Elastomer

Cross orientation between lamellae and amorphous chains was generated by forming residual crystals during extrusion and melt stretching under temperature-controlled processing conditions in a thermoplastic polyester elastomer (TPEE). Some crystals were not completely melted at a certain temperature slightly higher than the melting temperature of the sample during a heating process, and the survived crystals are called residual crystals. The TPEE exhibited prolonged relaxation at the temperature slightly higher than the melting temperature owing to the formation of the network structure composed of the residual crystals. The formation of the weak network affected the processability during extrusion, such as the swell ratio and the drawdown force. Although polarized microscopy images apparently showed that the average molecular orientation was along the drawing direction, it was found that the lamellar crystals oriented orthogonal to the fiber axis to reduce the hydrodynamic force during extrusion according to the results of multiple structural analyses. The orthogonal orientation of the lamellar crystals should be caused by the high aspect ratio of the lamellar crystals grown from the residual crystals. The orthogonal orientation resulted in a high Young's modulus and yield stress. The method for generating cross orientation of crystalline and amorphous chains will be applied to the preparation of high-performance fibers with high strength and modulus.