Morphological and Mechanical Properties of Poly(ethylene terephthalate) Gel and Melt Films in Terms of the Crystal Lattice Modulus, Molecular Orientation, and Small Angle X-Ray Scattering Intensity Distribution

Abstract

ABSTRACT:Deformation mechanism of polyethylene terephthalate (PET) gel and melt films was investigated in terms of morphological aspects by scanning electron microscopy, small angle X-ray scattering, and wide angle X-ray difiraction. The morphological properties were discussed in relation to the temperature dependence of the dynamic complex modulus. The storage modulus of the melt film with a draw ratio of 20 was 19.5 GPa at 20°C, while that of the gel film with a draw ratio of 7 was 16.2 GPa. The apparent crystal lattice modulus of the (105) plane was measured by X-ray diffraction. Using the apparent value, the real value of the crystal lattice modulus was estimated to be 118 GPa through a somewhat complicated geometrical treatment. The storage moduli for both the specimens are much lower than the crystal lattice modulus. In order to study the large difference, the crystallite orientation was estimated in terms of the second order orientation factor of the c-axis and the theoretical analysis of small angle X-ray scattering patterns. It turns out that under oriented crystallization, the preferential orientation of the c-axis is attributed to the rotation of crystallites with respect to the stretching direction but not to a crystal transformation from a folded to a fibrous type. Such a orientation mode is thought to hamper ultradrawing to produce high modulus PET films.

Mechanical Properties of Poly(ethylene terephthalate) Estimated in Terms of Orientation Distribution of Crystallites and Amorphous Chain Segments under Simultaneous Biaxially Stretching

“…118 GPa on the basis of the theoretical analysis described elsewhere. 19 This indicates no temperature dependence of crystal lattice modulus of PET along the chain direction, as has been reported for PE 23 PP, 24 and PVA. 10 In contrast, the other crystal moduli decrease with increasing temperature.…”

“…118 GPa, calculated by using the somewhat complicated treatment, 19 on the basis of the crystal lattice modulus of the ( " 1 105) plane at room temperature (see Table II). The intrinsic elastic compliances S ao uv of the amorphous phase needed in the numerical calculation is not quite certain.…”

“…However, the increase in E 0 with increasing is less significant in comparison with the increase under uniaxial stretching. 19 This reason shall be discussed later. The loss modulus at each draw ratio shows two peaks.…”

“…Crystal strain at elevated temperature was provided by a constant-stretching apparatus which has been described elsewhere. 19 For the measurements, the specimen was mounted vertically in the stretching clamps of the apparatus. The intensity distribution was measured with a step-scanning device at a step interval of 0.1 , each at a fixed time of 40 s. The measurements were carried out for the crystal lattice modulus along the reciprocal lattice vectors of the ( " 1 105), (100), (010) and (110) planes.…”

A new three-phase model to estimate the effective elastic properties of semi-crystalline polymers: Application to PET

“…Input data Daubeny et al (1954) showed that the poly(ethylene terephthalate) (PET) crystallises under the triclinic lattice, with the following triclinic unit cell parameters: a = 4.40 Å, b = 6.00 Å, c = 10.84 Å, a = 102°, b = 120°and c = 107°. The PET crystalline phase elastic constants used in our simulation are those determined by Matsuo and Sawatari (1990), at room temperature, and are expressed in an orthogonal basis as follows: GPa The elastic constants of the fully amorphous PET are assumed isotropic with a Young modulus at room temperature E 3 ffi 2.6 GPa, and a poisson ratio t 3 = 0.4 (Bédoui et al, 2006). These parameters were selected to characterize the mobile amorphous phase.…”