D.J. Blundell

Characterization of strain-induced crystallization of poly(ethylene terephthalate) at fast draw rates using synchrotron radiation

Abstract Structural changes during fast drawing of poly(ethylene terephthalate) were studied by wide-angle X-ray scattering using synchrotron radiation. Drawing was studied at 80, 90, 100 and 110°C to a final draw ratio of ∼4:1 at a draw rate of ∼ 10s−1. Simultaneous video recording of the sample enabled variation in the X-ray pattern to be correlated with local extension. Essentially all oriented crystallization occurred after final extension. Primary crystallization fits a first-order transformation with little change in the rate of crystallization observed over the 30°C range of temperature. These results show that it can be misleading to rely on crystallinity information obtained when samples from interrupted draw experiments are quenched.

Real time SAXS/stress–strain studies of thermoplastic polyurethanes at large strains

Abstract Simultaneous small angle X-ray scattering (SAXS) and force measurements have been recorded during tensile deformation of two contrasting polyurethane elastomers. The elastomers comprise the same hard and soft chemical segments; in Sample A, the length of the hard blocks is randomised while in Sample B the hard blocks are monodisperse. During deformation of Sample A, the SAXS halo from the mesophase structure deforms to an ellipse with intensification on the meridian. In Sample B, the halo transforms into a four point pattern. The ellipse patterns of A are interpreted in terms of a model based on particles located on a statistical lattice which is subjected to an affine deformation scheme. According to this model, the SAXS patterns of A are consistent with the hard phase regions behaving as embedded particles which separate from each other in an affine manner and which are not impeded by interconnections during the mechanical yield process. In B, the interconnection of the hard phase prevents affine deformation of the structure and involves the formation of a four point ‘lattice’ structure which then subsequently deforms in an affine manner. The differences in behaviour are linked with the segment sequencing which result in the phase regions of Sample A having a lower volume fraction and are consistent with variation in applied stress.

Observations of structure development during crystallisation of oriented poly(ethylene terephthalate)

Abstract 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 °C and then observed after annealing at 5 °C steps up to 100 °C. In the other experiments, time-resolved observations were made while drawing at 90 °C at rates up to 10 s−1. Up to 70 °C 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 °C, 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 °C. 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 °C 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.

Time‐Resolved SAXS/Stress–Strain Studies of Thermoplastic Polyurethanes During Mechanical Cycling at Large Strains

Abstract Simultaneous small‐angle x‐ray scattering (SAXS) and force measurements have been recorded during tensile load/unload deformation cycles of two contrasting polyurethane elastomers. The elastomers comprise the same hard and soft chemical segments; in sample A, the length of the hard blocks is randomized, while, in sample B, the hard blocks are monodisperse. During the initial extension of sample A, the SAXS halo from the mesophase structure deforms to an ellipse with intensification on the meridian. On subsequent loading and unloading, the elliptical halo reverses but with an off‐axis intensification giving the pattern a four‐point character. In sample B, the halo transforms into a four‐point pattern during the first extension. The azimuthal positions of the four‐point maxima move systematically with changing load. However, the azimuthal movement of sample A is in the opposite sense to sample B. The positions of the maxima have been analyzed in terms of an affine deformation scheme of the spatial correlations of the hard‐block domains in real space. The movement of the four points in sample B is consistent with the affine deformation of a two‐dimensional, four‐point reciprocal lattice correlation. The contrasting movement of the maxima in sample A is explained in terms of the affine separation of particulate hard domains in which local spatial correlations between domains is represented by a linear, one‐dimensional lattice.

Microfocus X-ray Diffraction of Spherulites of Poly-3-hydroxybutyrate

The microfocus X-ray beamline at the European Synchrotron Radiation Facility has been used to investigate the variation in molecular orientation and crystallinity in spherulites of the organic polymer poly-3-hydroxybutyrate (PHB). This is the first report of the correlation of optical and X-ray measurements on spherulitic polymer films where X-ray diffraction patterns have been recorded and displayed continuously in real time while the specimen was tracked in steps of 10 mum across an incident X-ray beam with a diameter as small as 10 mum.

Orientation changes during the cold drawing and subsequent annealing of PEEK

Abstract Two-dimensional wide- and small-angle X-ray scattering (WAXS and SAXS) patterns have been recorded at the Daresbury Synchrotron Radiation Source in time-resolved studies of changes in orientation and crystallinity during annealing of cold drawn samples of poly(aryl ether ether ketone) (PEEK). An amorphous PEEK film drawn uniaxially to a draw ratio of 2.0 was observed to give a well oriented non-crystalline WAXS pattern. The drawn film was then held at constant length and diffraction patterns recorded while the sample temperature was raised at 15°C min −1 from ambient to the glass transition temperature ( T g = 145°C) and beyond. WAXS patterns were recorded with an exposure time of 5s. Close to T g there was a sudden loss of orientation so that the diffraction pattern resembled that given by the specimen before cold drawing. This absence of crystallinity and orientation persisted for ∼45s after which the unoriented non-crystalline pattern began to be gradually replaced by a highly crystalline oriented pattern. This loss of orientation within a non-crystalline specimen close to T g is consistent with a change from a molecular orientation associated with pseudo-affine deformation to an orientation associated with a stretched rubbery network. From parallel studies, the dramatic changes in the WAXS pattern were found to be correlated with changes in the small angle diffraction. Significant features in the SAXS pattern were not observed until the temperature was ∼150°C when the meridionally oriented central maximum began to develop. With increasing temperature this maximum gradually broadened in the meridional direction until at ∼160°C it developed into a distinct meridional peak at a spacing of 140 A. During subsequent annealing the intensity of this peak increased but its spacing did not change. Also, the half width of this peak in the direction parallel to the equator did not vary during annealing, suggesting that the lateral dimension of the crystalline regions within the specimen does not change during crystallite growth.

Formation and decay of a smectic mesophase during orientation of a PET/PEN copolymer

An analysis has been made of time resolved wide angle X-ray scattering during the deformation of a 50%poly(ethylene terephthalate)/50%poly(ethylene 2,6naphthalate) copolymer at 120°C at a draw rate of the order of 10 s−1. During the initial fast deformation a meridional reflection associated with a smectic mesophase is observed to form. After the initial deformation, the mesophase reflection decays at a rate of about 1 s−1. During the decay, the lateral halfwidth of the meridional reflection increases indicating attrition of the smectic mesophase regions from the lateral interfaces. The sample deforms in a non-uniform manner. After the applied deformation ceases, the sample continues to thin down in the region of the X-ray beam. This is attributed to the lack of crystallisation during the 5 s timescale of observation. Analysis of the azimuthal profile of the strong inter-chain diffuse diffraction at ∼2.8 nm−1 shows that the mesophase is associated with extended chains with a characteristic high alignment of segments along the deformation. During the period of decay of the mesophase it is proposed that the chain segments can be effectively divided into just two components: oriented mesophase and isotropic amorphous regions. The analysis indicates that the proportion of the mesophase varies from 80 to 40% during the observed decay period.

Micro-SAXS and force/strain measurements during the tensile deformation of single struts of an elastomeric polyurethane foam.

A microdeformation stage based on a piezoelectric crystal actuator capable of measuring the force applied to micrometre-sized polymeric samples is described. Laboratory force/strain measurements on a single strut of an elastomeric polyurethane foam have been conducted for the first time. The device has also been used on the microfocus beamline at the European Synchrotron Radiation Facility to collect microbeam small-angle X-ray scattering data simultaneously with strain and force measurements during the time-resolved tensile deformation of a single strut of elastomeric polyurethane foam.

Time-resolved X-ray wide angle scattering studies of the effect of draw rate and temperature on the development of orientation and crystallinity in PET

Abstract 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 72 000% per min and the draw temperature from 80°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 crystallinity and orientation observed in drawn samples depends on both the draw temperature and the draw rate. In particular for draw rates of 72 000% 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 140°C the pattern is essentially unoriented and non-crystalline.

Investigation of the variation in orientation and crystallinity in poly(ethylene terephthalate) containers using microfocus X-ray diffraction.

The microfocus X-ray beamline at the European Synchrotron Radiation Facility has been used to investigate the variation in molecular orientation and crystallinity in the wall of a container fabricated from poly(ethylene terephthalate). Two-dimensional wide-angle X-ray scattering patterns were recorded and displayed in real time as the specimen was tracked across the incident X-ray beam enabling the measurement of textural changes to be made with a spatial resolution of ~2 mum.