Time-Resolved Two-Dimensional Small Angle X-ray Scattering Studies of Oriented Poly(ethylene terephthalate) (PET) Using Paracrystalline Modeling Techniques (original) (raw)
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Polymer, 2003
Two types of SAXS and WAXS experiments have been made using synchrotron radiation to observe the transformation from smectic to crystalline phases in oriented poly(ethylene terephthalate) (PET). In step-anneal experiments, PET was drawn slowly at 30 8C and then observed after annealing at 5 8C steps up to 100 8C. In the other experiments, time-resolved observations were made while drawing at 90 8C at rates up to 10 s 21 . Up to 70 8C the WAXS data in the step-anneal experiments showed the smectic meridional reflection reducing in lateral width, indicating an increase in lateral long range order with annealing. Between 70 and 100 8C, there was a reduction in the intensity of the smectic reflection which correlated with an increase in the intensity of crystalline reflections. The SAXS from the step-anneal experiments showed an intense equatorial streak which has a correlation peak around 20 nm and which diminishes with annealing above 70 8C. It is concluded that this feature is a characteristic of the presence of the mesophase in oriented PET and is due to elongated domains of smectic mesophase with a length . 75 nm and with an interdomain spacing of around 20 nm. Between 70 and 100 8C the SAXS data showed additional diffuse diffraction which correlated quantitatively with the crystalline phase and evolved from a cross-like appearance to a well resolved four-point pattern. The time-resolved drawing experiments were limited by the time resolution of the SAXS detector. They showed the same development of four-point diffuse SAXS patterns as was observed in the step-anneal experiments and a very weak equatorial streak. Differences in phase transformation kinetics between the two types of experiment are attributed to the different chain relaxation processes available under different conditions. q
The development of microstructure in oriented polyethylene terephthalate (PET) during annealing
Polymer, 2007
This work concerns the changes in structural order, which occur when amorphous polyethylene terephthalate (PET) is crystallised by drawing and then subsequent annealing. Real time wide angle X-ray fibre diffraction is used to obtain information about the microstructural changes taking place during drawing and subsequent annealing. The diffraction patterns obtained proved the existence of a liquid crystalline transient mesophase prior to crystallisation. The development of both the mesophase and the crystalline structure are also studied using small angle X-ray scattering during annealing of uniaxially drawn samples held at constant strain. These experiments proved the absence of any microstructure associated with the mesophase and that significant microstructural changes take place only when crystallisation starts to occur.
Polymer International, 2006
Three types of poly(ethylene terephthalate) (PET) were investigated: linear (unprocessed) bottle-grade PET (intrinsic viscosity, IV ∼ 0.82 dL g −1 ); a branched PET produced from linear PET by reactive extrusion with 0.4% w/w pyromellitic dianhydride and pentaerythritol in 5:1 molar ratio (IV ∼ 0.97 dL g −1 ); and a control sample produced from the same linear PET by extrusion under the same conditions without the reactive agents (IV ∼ 0.71 dL g −1 ). A key finding is that the reactive extrusion process, presumably as a consequence of branching and branch distribution, significantly modifies the crystallisation kinetics and changes the final morphology. Using small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC), the crystallisation kinetics of PET was monitored from the melt (270 • C) to a crystallisation temperature of either 205 or 210 • C. The IV of the branched PET was ∼ 21% greater than that of the unprocessed PET, and the rate of melt crystallisation (from DSC measurements) was 510 s for the branched, 528 s for the control, and 640 s for the unprocessed PET. The lamellae spacings measured from the equilibrium SAXS patterns were ∼160 ± 10Å for the branched PET and ∼180 ± 10Å for the unprocessed PET. Such properties offer the potential for new applications requiring high-melt-strength PET.
Orientation prior to crystallisation during drawing of poly(ethylene terephthalate
Polymer, 2000
Wide angle X-ray scattering data have been recorded during the drawing of poly(ethylene terephthalate) (PET) using a wide range of draw rates (0.05-12 s Ϫ1 ), temperatures (90-120ЊC) and draw ratios. The data were analysed to follow the development of molecular orientation and the onset of crystallisation. The molecular orientation prior to crystallisation has been characterised in terms of the orientation order parameter ͗P 2 cos u͘: The rate of increase of ͗P 2 cos u͘ with draw ratio decreases with both increasing temperature and decreasing draw rate. A superposition of all the data to a common reference temperature of 90ЊC was obtained using a WLF shift factor to provide a master curve showing the dependence of the development of ͗P 2 cos u͘ on draw rate. A comparison of the known chain relaxation motions of PET with the observed relation between draw rate and the onset of crystallisation provides an explanation of a previous discrepancy in the literature concerning the point of onset of crystallisation. For draw rates faster than the rate of the chain retraction motion, the onset of crystallisation is delayed until the end of the deformation process. For draw rates slower than the chain retraction motion, there is evidence of the onset of crystallisation occurring before the end of the deformation process. ᭧
Macromolecules, 1996
The description of the fibrillogenesis pathway and the identification of "on-pathway" or "off-pathway" intermediates are key issues in amyloid research as they are concerned with the mechanism for onset of certain diseases and with therapeutic treatments. Recent results on the fibril formation process revealed an unexpected complexity both in the number and in the types of species involved, but the early aggregation events are still largely unknown, mainly because of their experimental inaccessibility. To provide information on the early stage events of self-assembly of an amyloidogenic protein, during the so-called lag phase, stopped-flow time-resolved small angle x-ray scattering (SAXS) experiments were performed. Using a global fitting analysis, the structural and aggregation properties of the apomyoglobin W7FW14F mutant, which is monomeric and partly folded at acidic pH but forms amyloid fibrils after neutralization, were derived from the first few milliseconds onward. SAXS data indicated that the first aggregates appear in less than 20 ms after the pH jump to neutrality and further revealed the simultaneous presence of diverse species. In particular, worm-like unstructured monomers, very large assemblies, and elongated particles were detected, and their structural features and relative concentrations were derived as a function of time on the basis of our model. The final results show that, during the lag phase, early assembling occurs due to the presence of transient monomeric species very prone to association and through successive competing aggregation and rearrangement processes leading to coexisting on-pathway and off-pathway transient species.
2010
Small-angle X-ray scattering, wide-angle X-ray diffraction and differential scanning calorimetry analysis were carried out to evaluate the evolution of the supermolecular structure of poly(ethylene terephthalate) (PET) during isothermal crystallization and annealing process. PET was crystallized from the melt by isothermal treatments at 226°C. Partially crystallized samples were prepared interrupting the crystallization by quenching, while prolonged treatments were performed to prepare annealed samples. The adopted crystallization procedures allowed to form crystals which developed during primary and secondary crystallization, and the annealing process. On the basis of X-ray data, the lamellar and amorphous phases were unambiguously attributed. The lamellar thickness and the crystallinity progressively enhance with increasing the time of thermal treatment; on the contrary, the long period decreases and this effect is mainly due to the contraction of the amorphous phase. The melting behaviour of the annealed samples indicates that the heating-induced crystal reorganization phenomena are inconsistent. The interdependency between the melting temperature and the crystal thickness allowed to extrapolate the equilibrium melting temperature.
Polymer, 2005
The micromechanical properties (microindentation hardness, H, elastic modulus, E) of poly(ethylene terephthalate) (PET), isothermally crystallized at various temperatures (T a) from the glassy state are determined to establish correlations with thermal properties and nanostructure. Analysis of melting temperature and crystal thickness derived from the interface distribution function analysis of SAXS data reveals that for T a !190 8C the occurrence of two lamellar stack populations prevails whereas for samples annealed at T a O190 8C a population of lamellar stacks with a unimodal thickness distribution emerges. The H and E-values exhibit a tendency to increase with the degree of crystallinity. The results support a correlation E/Hw20 in accordance with other previously reported data. The changes of microhardness with annealing temperature are discussed in terms of the crystallinity and crystalline lamellar thickness variation. Unusually high hardness values obtained for PET samples crystallized at T a Z190 8C are discussed in terms of the role of the rigid amorphous phase which offers for the hardness of amorphous layers constrained between lamellar stacks a value of H a w150 MPa. On the other hand, for T a Z 240 8C the decreasing H-tendency could be connected with the chemical degradation of the material at high temperature.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1995
A purpose-designed X-ray fibre diffraction camera has been used to record the variation in the wide angle X-ray scattering during the drawing and annealing of the organic polymer polyethylene terephthalate. Data were recorded at the Daresbury Laboratory Synchrotron Radiation Source using a Photonics Science electronic area detector interfaced to a Synoptics framegrabber as a series of frames with an exposure time of 40 ms for each frame. Frames could be displayed while the diffraction pattern was being accumulated allowing the experiment to be conducted in a genuinely real-time mode. The draw rate was varied from 20% per min to 72000% per min and the draw temperature from 8O'C to 140°C. The draw ratio in these experiments was designed to be 3.6 : 1. For the highest draw rates essentially all the change in the diffraction pattern was complete in less than 1 s. The degree of crystaiiinity and orientation observed in drawn samples depends on both the draw temperature and the draw rate. In particular for draw rates of 72000% per min the high degree of orientation and crystallinity observed at a draw temperature of 80°C diminishes with increasing draw temperature until for draw temperatures of 14O'C the pattern is essentially unoriented and non-crystalline.
Journal of Applied Polymer Science, 2012
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.