Mesophase as the Precursor for Strain-Induced Crystallization in Amorphous Poly(ethylene terephthalate) Film

Abstract

An in situ study of strain-induced crystallization in an amorphous poly(ethylene terephthalate) (PET) film was carried out by using wide-angle X-ray diffraction with synchrotron X-rays. Results indicated that the mesophase was developed during stretching, immediately upon necking below T g. A sharp meridional peak was observed during the mesophase formation. The d-spacing (10.32 Å) of this peak was smaller than the monomer length, indicating that the chains in the mesophase could be tilted with respect to the stretching direction. Prior to crystallization, the intensity of this peak was found to increase upon stretching. The triclinic PET crystalline structure began to form as the temperature was increased above T g. Then, the corresponding intensity of the d ) 10.32 Å peak was found to decrease. This observation suggests that the triclinic PET crystals form an inclined layered structure, which shifts this peak out of the meridian. A two-dimensional analytical method was used to deconvolute the diffraction pattern into isotropic and anisotropic contributions. The isotropic and anisotropic fractions remained almost constant after stretching was stopped and during crystallization, suggesting that the strain-induced crystallization occurs mainly in the mesophase, supporting the hypothesis that the intermediate mesophase acts as a precursor for crystallization in oriented PET.

Tensile Deformation of Oriented Poly(ε-caprolactone) and Its Miscible Blends with Poly(vinyl methyl ether)

“…3,[15][16][17][18] Being composed of the interpenetrating networks built up by both crystalline lamellae and the entangled amorphous polymeric chains in between, semicrystalline polymers always exhibit a complex deformation behavior under tensile deformation. 1,[19][20][21][22][23] The behavior of the polymers during stretching is generally influenced by both the crystalline and the amorphous phases. 12,[24][25][26][27][28] The small-deformation properties are found to depend only on the nature of crystalline lamellae; whereas the ultimate properties are dominated by the entangled amorphous network.…”

Structure evolution of PET under step-wise and continuous deformation modes: the effect of stress relaxation on the strain-induced morphology

“…Three distinct PET morphologies are developed: i) an unoriented amorphous phase (isotropic); ii) a mesophase with a degree of packing order between the crystalline and the amorphous phase (anisotropic oriented amorphous phase); and iii) a crystalline phase [2,3]. Similar structure development of initially isotropic PET was observed at temperatures slightly below T g [1]. The present study aims at investigating the structure evolution of PET with distinct initial morphologies (quasi-amorphous and ABSTRACT: This study reports about an in-situ deformation investigation under X-ray synchrotron source (Wide-Angle X-ray Scattering, WAXS) of polyethylene terephthalate (PET) following step-wise and continuous stretching modes.…”

“…The availability of synchrotron X-ray radiation made possible to measure in-situ the structural formation of PET films and fibres in real time. Many studies were conducted to investigate the effect of processing conditions and modes of deformation below [1] and above [2,3] T g from glassy PET. During uniaxial deformation above T g of amorphous PET structural development consist of three stages, according to recent models [2,3]: i) molecular orientation occurs due to strong molecular interaction -"orientation" stage; ii) nucleus start to appear as a result of molecular orientation -"nucleation" stage; and iii) crystallization develops through a growth process -"growth" stage.…”

Effect of drawing stress on mesophase structure formation of poly(ethylene 2,6-naphthalene dicarboxylate) fiber just after the neck-drawing point

“…The formation of the β-crystal occurred when the crystallization temperature was high, i.e., 200 or 245°C 2,3 and at take-up speeds above 4.5 km/min. 16 However, the low drawing stress (23 MPa) condition generated β-rich crystals without high-temperature annealing or high-speed spinning. Figure 8 shows d-spacings of the α(010), β(020) and α(100) diffractions.…”

“…Some studies have reported that the mesophase structure is formed after cold drawing of PEN, 4,6 and some researchers including our group have reported the (001') diffraction of PET by in situ analysis during drawing. 8,9,13,15,16 We first communicated the temporal appearance of (001') diffraction, reflecting a quasi-smectic fibrillar structure of PEN. 7 Figure 10 shows the d-spacing of meridional (001') diffraction calculated by Bragg's formula for the three drawing stress conditions.…”