Solid‐state structural evolution of poly(ethylene terephthalate) during step uniaxial stretching from different initial morphologies: An in situ wide angle x‐ray scattering study

Abstract

This work reports an in situ wide-angle Xray scattering (WAXS) study of the structural evolution of PET with distinct initial morphologies during step uniaxial stretching in the solid state. Two types of samples were analyzed under synchrotron X-ray radiation, namely quasi-amorphous (QA) and semicrystalline (SC) (with 2D and 3D order). Results show that initially different QA morphologies evolve following the same stages: (i) stage I (before neck), at almost constant orientation level the amorphous phase evolves into mesophase; (ii) stage II (neck formation), there is a rapid increase of polymer orientation and the appearance of a periodical mesophase from the highly oriented mesophase; (iii) stage III (necking propagation), there is a leveling off of the average polymer orientation together with partial conversion of the periodical mesophase and mesophase into highly oriented amorphous. The behaviors of the two SC morphologies are completely distinct. A 2D order crystalline morphology evolves with stretching likewise the QA through three stages: (i) at early stages of deformation the polymer orientation remains unchanged while the amorphous phase amount increases slightly, stage I; (ii) in stage II, a fast increase of polymer orientation is accompanied by large formation of mesophase; and (iii) in stage III there is the level off of polymer orientation as the chains approach their finite extensibility and the 3D crystalline order is achieved. Evolution of SC sample with 3D crystalline order mainly features constant orientation increase together with mesophase increment. Structure deformation models are suggested.

In situ WAXS/SAXS structural evolution study during uniaxial stretching of poly(ethylene therephthalate) nanocomposites in solid state: Poly(ethylene therephthalate)/montmorillonite nanocomposites

“…Homogeneous stress-strain curve and selected 2D WAXS patterns for solid state uniaxial stretching of neat PET (note: a mismatch in the WAXD patterns is observed on the neck region due to neck formation out of the incident X-ray point). 39 At this stage of deformation samples morphologies were considered to be composed of three phases: (i) amorphous (ii) mesophase, and (iii) periodical mesophasemesophase with conformational periodicity perpendicular to the stretching direction. Such accumulation time was set as a lowest as possible for considered strain rate.…”

“…As the strain increases, the WAXS patterns can exhibit a pair of meridional mesomorphic reflection ð103Þ at about 2H ¼ 25.8 , 37,38 indicating conformational regularity, and called periodical mesophase, PM. 39 At this stage of deformation samples morphologies were considered to be composed of three phases: (i) amorphous (ii) mesophase, and (iii) periodical mesophasemesophase with conformational periodicity perpendicular to the stretching direction. The area of fitted ð103Þ peak profile was used to determine the mass fraction of the PM.…”

In situ WAXS/SAXS structural evolution study during uniaxial stretching of poly(ethylene terephthalate) nanocomposites in the solid state: Poly(ethylene terephthalate)/titanium dioxide and poly(ethylene terephthalate)/silica nanocomposites

“…Equipmental setups were as follows: WAXS: Sample‐to‐detector distance of 145 mm and 2D WAXS patterns were acquired with accumulation time of 20 s. Samples were stretched at a constant cross‐head velocity of 2 mm min −1 (strain rate of 0.002 s −1 ). Such accumulation time was set as a lowest as possible for considered strain rate . WAXS was calibrated by means of a crystalline PET sample. SAXS: Sample‐to‐detector distance of 3025 mm and 2D SAXS patterns were acquired with accumulation time of 30 s. Samples were stretched at a constant cross‐head velocity of 5 mm min −1 (strain rate of 0.006 s −1 ). …”

“…The mass fractions of the individual phases were taken as the ratio of the area for each phase to the total area of the equatorial profile. As the strain increases, the WAXS patterns can exhibit a pair of meridional mesomorphic reflection at about 2θ = 25.8°, indicating conformational regularity, and called PM . At this stage of deformation, the morphologies of the samples were considered to be composed of three phases: (i) amorphous, (ii) mesophase, and (iii) PM, mesophase with conformational periodicity perpendicular to the stretching direction.…”

The effect of hot multistage drawing on molecular structure and optical properties of polyethylene terephthalate fibers

“…The drawing behavior of PET has been studied extensively over many years and different workers have highlighted different features, from the purely mechanical aspects to the structural changes [1][2][3][4][5][6][7][8][9][10][11][12][13] . When PET fiber structure is deformed by hot multistage drawing process, individual crystalline regions slide past each other, to take up a new position, where they are held together just as strong as in the origin material, owing to the formation of fresh, inter-atomic bonds.…”