On-line small-angle and wide-angle x-ray scattering studies on melt-spinning poly(vinylidene fluoride) tape using synchrotron radiation (original) (raw)
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Morphology and phase transition of high melt temperature crystallized poly(vinylidene fluoride
When PVDF is crystallized at temperatures above 155 • C it presents a multiform morphology composed of ringed, non ringed and mixed spherulites. Infrared spectroscopy showed that the ringed spherulites are formed exclusively by the α phase when crystallization takes place at temperatures below 155 • C. Higher temperatures induce a solid-state α → γ phase transformation in these structures, increasing the amount of γ phase with crystallization time. The rate at which this transformation takes place increases with crystallization temperature. The non ringed spherulites, only formed at crystallization temperatures above 155 • C, consist predominantly of the γ phase, crystallized from the melt, with small α phase inclusions. The melt process of the different spherulites, observed by optical microscopy and calorimetric measurements (DSC) showed that the melt temperature of the γ phase, originated from the phase transition, is 8 • C higher than that crystallized directly from the melt. Optical micrographs of samples heated up to 186 • C and quickly cooled allowed visualization of the ringed spherulite regions which underwent the α → γ phase transformation at different crystallization times and temperatures. C 2000 Kluwer Academic Publishers
Polymer, 2000
The early stages of isothermal melt crystallization in linear polyethylene (PE) were investigated via simultaneous synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques. During these stages, noticeable short-range density fluctuations with periodic spacing from 40 to 80 nm were detected (by SAXS) before the identification of three-dimensional crystal ordering (by WAXD). These results are consistent with the recent findings in several other polymers (polypropylene, poly(aryletherketone), poly(ethylene terephthalate) and poly(butylene terephthalate) by our and other laboratories. Some groups have proposed that the spinodal decomposition due to chain conformation in the molten state may act as a precursor to crystallization based on these findings. Detailed examination of the SAXS and WAXD data, however, indicated that the early stages of crystallization also follow the classical nucleation and growth behavior with a simple Avrami expression. The earlier detection of density fluctuations can be attributed to the lower detection limit of crystallinity in SAXS (0.1%) than in WAXD (1%). In addition, we found that the long spacing associated with the SAXS peak decreased slightly with time, which opposed the behavior of the spinodal decomposition.
Macromolecular Research, 2004
The structural changes occurring in the isothermal crystallization processes of polyethylene (PE), polyoxymethylene (POM), and vinylidene fluoridetrifluoroethylene (VDFTrFE) copolymer have been reviewed on the basis of our recent experimental data collected by the time-resolved measurements of synchrotron-sourced wide-angle (WAXS) and small-angle X-ray scatterings (SAXS) and infrared spectra. The temperature jump from the melt to a crystallization temperature could be measured at a cooling rate of 600–1,000°C/min, during which we collected the WAXS, SAXS, and infrared spectral data successfully at time intervals of ca. 10 sec. In the case of PE, the infrared spectral data clarified the generation of chain segments of partially disordered trans conformations immediately after the jump. These segments then became transformed into more-regular all-trans-zigzag forms, followed by the formation of an orthorhombic crystal lattice. At this stage, the generation of a stacked lamellar structure having an 800-Å-long period was detected in the SAXS data. This structure was found to transfer successively to a more densely packed lamellar structure having a 400-Å-long period as a result of the secondary crystallization of the amorphous region in-between the original lamellae. As for POM, the formation process of a stacked lamellar structure was essentially the same as that mentioned above for PE, as evidenced from the analysis of SAXS and WAXS data. The observation of morphology-sensitive infrared bands revealed the evolution of fully extended helical chains after the generation of lamellae having folded chain structures. We speculate that these extended chains exist as taut tie chains passing continuously through the neighboring lamellae. In the isothermal crystallization of VDFTrFE copolymer from the melt, a paraelectric high-temperature phase was detected at first and then it transferred into the ferroelectric low-temperature phase at a later stage. By analyzing the reflection profile of the WAXS data, the structural ordering in the high-temperature phase and the ferroelectric phase transition to the low-temperature phase of the multidomain structure were traced successfully.
Journal of Applied Polymer Science, 2010
The effects of melt-spinning and cold-drawing parameters on the formation of b-phase crystallinity in poly(vinylidene fluoride) (PVDF) fibers and ways of increasing such crystallinity were studied. Fibers were meltspun with four different melt draw ratios (MDRs) and were subsequently cold-drawn at different draw ratios (k). The maximum k value in cold drawing was dependent on the MDR used in melt spinning. The crystalline structure of the fibers was studied mainly with differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results showed that the degree of crystallinity in the fibers was determined by the MDR and that before cold drawing the crystalline structure of the fibers was predominantly in the a form. By cold drawing, a-phase crystallites could be transformed into the b phase. It was established that, under certain conditions of melt spinning and cold drawing, PVDF fibers of up to 80% crystallinity, mainly in the b form, could be prepared. It was further proposed that fibers spun at a sufficiently high MDR consist to a large extent of extendedchain crystals, and this greatly affects the melting point of PVDF. Thus, DSC melting-point data were shown to be insufficient for determining the crystalline phase of PVDF.
Polymer, 2020
Recent efforts attempting to in-situ track the polymer film formation during film blowing are summarized. The specially designed film blowing apparatus is firstly introduced, where the air ring is aligned along with the die, and it's capable of installation in the synchrotron beamline (SR-beamline). Later on, detailed structural evolution of different polymeric systems during film blowing, including polyethylene (PE) and poly(butylene adipate-cobutylene terephthalate) (PBAT), are obtained with the assistance of simultaneous acquired Small-and Wide Angle X-ray Scattering (SAXS/WAXS). The transient structure evolution information from oriented polymer melt to final crystalline tubular film clarifies the contribution of the crystallite-based network to final macroscopic performances. Also, the experimental results have shown the influence of intrinsic molecular characteristics and external processing parameters on the formation of stable tubular bubble. Additionally, the post-modification of the blown film, including stretching and surface treatment is also discussed. Current experimental efforts are expected to provide more detailed parameters for mathematical modeling of film blowing, which could help us modify or develop new numerical models.
In situX-ray characterisation of isotactic polypropylene during melt spinning
Plastics, Rubber and Composites, 2006
In fibre production, draw induced crystallisation and orientation are the dominant factors that influence the properties of the final end use article. These properties depend on processing conditions; in particular, the rate of temperature change, which affects crystallinity, and the stress applied during the drawing process, which affects orientation and may also facilitate crystallisation. Polymer crystalline regions can be characterised by wide angle X-ray scattering (WAXS) and small angle X-ray scattering (SAXS). An X-ray system capable of in situ determination of fibre structure as it develops during processing has been designed and installed at Clemson University, allowing simultaneous measurement in the WAXS and SAXS regions from the extruder exit and down the spinline. Results from the in situ study of isotactic poly(propylene) with determinations of crystallinity and crystalline orientation from WAXS patterns, and lamellar long period from SAXS patterns, diameter, temperature and velocity, at varying distances from the exit of the extruder are presented.
Macromolecules, 1996
In this paper, we present results of morphological studies during long time melt crystallization and subsequent melting in poly(aryl ether ether ketone) (PEEK). Morphological changes were monitored via small angle X-ray scattering (SAXS). SAXS data were analyzed via a combination of the correlation and interface distribution functions. Our analysis indicates the following: (1) The semicrystalline morphology is best described by a three-phase, dual lamellar stack model. Stacks of a finite number of lamellae and interlamellar amorphous layers are separated from each other by interstack regions of amorphous material (liquid pockets). (2) Secondary crystallization occurs via the formation of secondary lamellar stacks within the liquid pockets. Secondary lamellae are thinner than primary lamellae (70 Å vs 120 Å), and the amorphous layer thicknesses are about 47 Å in both stacks. (3) The low endotherm observed during a heating scan is associated with the melting of the secondary lamellae. (4) At room temperature, the semicrystalline PEEK material is in a state of dilational stress (negative hydrostatic pressure) which may originate from the secondary crystallization process in constrained liquid pockets.
Macromolecules, 2000
The early stages of polymer melt crystallization using fractionated isotactic polypropylene (iPP) as a model system were investigated via simultaneous synchrotron small-angle X-ray scattering (SAXS)/wide-angle X-ray diffraction (WAXD) and laser light scattering (LS) techniques. Since the crystallinity in the early stages is very low, the issue of the crystallinity detection limit of WAXD was addressed. This was done by using solutions of n-paraffin (C 33H68) in dodecane (C12H26) at different concentrations (as low as 1%). The precipitated fraction simulated the degree of crystallinity in polyethylene since n-paraffin essentially completely crystallized and dodecane remained liquid at the measurement temperature. A modeling method was also used to simulate the WAXD profiles to check the effect of crystal size at low crystallinity. With these two methods, we conclude that our WAXD procedure is capable of detecting crystallinity from 0.5% to 1%. During the early stages of iPP isothermal crystallization, noticeable short-range density fluctuations with average periods from 20 to 24 nm (by SAXS) were seen prior to the observation of three-dimensional ordering of the crystalline R-form (by WAXD). The spacing associated with the peak of the SAXS was found not to increase with time, being constant or a possible initial decrease, which is consistent with the formation of a finite lamellar structure. Furthermore, larger objects with dimensions growing from 300 nm were observed with the more sensitive technique of polarized light scattering, prior to the detection of the lamellar period by SAXS. The development of the crystallinity as measured by WAXD as well as SAXS and light scattering are all consistent, which follow the same Avrami equation, suggesting that the early stages of crystallization as measured here follow classical nucleation and growth.
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