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Title: Superstructure Evolution in Poly(ethylene terephthalate) During Uniaxial Deformation Above Glass Transition Temperature

Abstract

The evolution of superstructure and its relationship with the phase transition during uniaxial deformation of poly(ethylene terephthalate) (PET) at temperatures (90 and 100 C) above its glass transition temperature were investigated by in-situ small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). It appears that deformation at lower temperatures enhances the metastability of mesophase but narrows the strain window for phase transition. Very similar superstructure evolution pathways were observed at both temperatures. In zone I (the plastic deformation zone), WAXD did not show any crystal diffraction peak; however, SAXS exhibited an equatorial streak at the later stage, indicating the formation of a microfibrillar structure. Strain hardening took place in zone II, which could be categorized in two substages. In zone II-a, SAXS showed an X-shaped pattern that coincided with the appearance of crystal diffraction peaks in WAXD. The initial X-shaped patterns possessed strong intensity near the beam stop; the later patterns exhibited a scattering maximum that shifted toward larger angles with increasing strain. Results indicated the formation of a tilted lamellar structure within the microfibrils in conjunction with lamellar insertion. In zone II-b, oval spots appeared at the edges of the X-shaped pattern, which essentially became four-point. In this stage,more » the crystallinity still increased linearly with strain, but the invariant gradually reached an asymptotic value, indicating that lamellar insertion took place at a slower rate. In the final strain-hardening zone (III), the load became linear with strain even though crystallization was reduced. The equatorial long period was found to decrease drastically, suggesting that some microfibrils were split. In addition, a two-point pattern appeared near the central streak, corresponding to a periodic structure with long period of 100 nm. The formation of such a large layered structure and the microfibrillar splitting can be attributed to structural defects such as kinks in microfibrils.« less

Authors:
; ; ; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
914330
Report Number(s):
BNL-78898-2007-JA
TRN: US200809%%27
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Macromolecules; Journal Volume: 39
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; POLYESTERS; CRYSTALLIZATION; DEFORMATION; STRAIN HARDENING; TRANSITION TEMPERATURE; PHASE TRANSFORMATIONS; MORPHOLOGY; national synchrotron light source

Citation Formats

Kawakami,D., Ran, S., Burger, C., Avila-Orta, C., Sics, I., Chu, B., Hsiao, B., and Kikutani, T. Superstructure Evolution in Poly(ethylene terephthalate) During Uniaxial Deformation Above Glass Transition Temperature. United States: N. p., 2006. Web. doi:10.1021/ma052589y.
Kawakami,D., Ran, S., Burger, C., Avila-Orta, C., Sics, I., Chu, B., Hsiao, B., & Kikutani, T. Superstructure Evolution in Poly(ethylene terephthalate) During Uniaxial Deformation Above Glass Transition Temperature. United States. doi:10.1021/ma052589y.
Kawakami,D., Ran, S., Burger, C., Avila-Orta, C., Sics, I., Chu, B., Hsiao, B., and Kikutani, T. Sun . "Superstructure Evolution in Poly(ethylene terephthalate) During Uniaxial Deformation Above Glass Transition Temperature". United States. doi:10.1021/ma052589y.
@article{osti_914330,
title = {Superstructure Evolution in Poly(ethylene terephthalate) During Uniaxial Deformation Above Glass Transition Temperature},
author = {Kawakami,D. and Ran, S. and Burger, C. and Avila-Orta, C. and Sics, I. and Chu, B. and Hsiao, B. and Kikutani, T.},
abstractNote = {The evolution of superstructure and its relationship with the phase transition during uniaxial deformation of poly(ethylene terephthalate) (PET) at temperatures (90 and 100 C) above its glass transition temperature were investigated by in-situ small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). It appears that deformation at lower temperatures enhances the metastability of mesophase but narrows the strain window for phase transition. Very similar superstructure evolution pathways were observed at both temperatures. In zone I (the plastic deformation zone), WAXD did not show any crystal diffraction peak; however, SAXS exhibited an equatorial streak at the later stage, indicating the formation of a microfibrillar structure. Strain hardening took place in zone II, which could be categorized in two substages. In zone II-a, SAXS showed an X-shaped pattern that coincided with the appearance of crystal diffraction peaks in WAXD. The initial X-shaped patterns possessed strong intensity near the beam stop; the later patterns exhibited a scattering maximum that shifted toward larger angles with increasing strain. Results indicated the formation of a tilted lamellar structure within the microfibrils in conjunction with lamellar insertion. In zone II-b, oval spots appeared at the edges of the X-shaped pattern, which essentially became four-point. In this stage, the crystallinity still increased linearly with strain, but the invariant gradually reached an asymptotic value, indicating that lamellar insertion took place at a slower rate. In the final strain-hardening zone (III), the load became linear with strain even though crystallization was reduced. The equatorial long period was found to decrease drastically, suggesting that some microfibrils were split. In addition, a two-point pattern appeared near the central streak, corresponding to a periodic structure with long period of 100 nm. The formation of such a large layered structure and the microfibrillar splitting can be attributed to structural defects such as kinks in microfibrils.},
doi = {10.1021/ma052589y},
journal = {Macromolecules},
number = ,
volume = 39,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • An in situ study of structure formation in amorphous poly(ethylene terephthalate) (PET) during uniaxial stretching at a temperature 30 C above glass transition temperature was carried out using synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques. Three major deformation-induced structure transitions were confirmed. (1) At small strains, the applied load increased initially but leveled off afterward. Sporadic isotropic crystallization without preferred orientation was observed by WAXD, where no hierarchical structure was seen by SAXS. (2) At intermediate strains, strain hardening took place. Although WAXD showed persistent progression of isotropic crystallization, SAXS indicated formation of a layered structuremore » as well as a fibrillar domain in large scale. This behavior is not consistent with the mechanisms for shish-kebab or spinodal-assisted structure formation. Instead, it can be explained by flow-induced demixing of crystal and amorphous phases through layerlike flocking motion perpendicular to the stretching direction. (3) At high strains, the ratio between the applied load and strain was about constant. In this stage, crystal reorientation and lateral crystal growth took place. The corresponding structure changes could be categorized into three subregions. In the first region, the (010) crystalline plane began to orient. In the second region, the (100) crystalline plane began to orient. In the last region, the structure change became stable and the sample eventually broke apart.« less
  • No abstract prepared.
  • No abstract prepared.
  • Thermoplastics like poly(ethylene terephthalate) (PET) can be melt processed into sheet and film formats for a variety of applications. Fabrication of these formats often involves application of a drawing process which can include drafting, tentering, heat setting, detentering, and heat relaxation. These various components add a thermomechanical history to the PET that will influence the glass transition. Thermomechanical analysis (TMA) in both the compressive mode and the tensile mode along with differential scanning calorimetry (DSC) techniques have been applied to a series of seven PET films generated using different drawing processes applied with an Iwamoto Biaxial Stretcher on extruded sheetmore » from a single source. These measurements were undertaken to assign a glass transition temperature for each film. The assigned temperature ranged between 70 C and 94 C. Orientation and heat setting increased the temperature assigned as T{sub g} while detentering both increased and lowered T{sub g} on a direction-specific basis. Both the measurement technique and the assignment protocol employed to determine T{sub g} contributed to differences in the assigned value. DSC results suggested the presence of two amorphous domains (mobile and constrained) in the film oriented uniaxially without constraint. TMA data demonstrated the assigned T{sub g} may be direction specific and not a bulk property in oriented PET films.« less