Uniaxially orienred semicrystalline poly(ethylene terephthalate) (PET) and poly(propylene) (PP) films were loaded parallel to draw direction at various temperatures. Changes in the submicroscopical structure of the films under load were examined by small and wide-angle x-ray scattering (SAXS; WAXS) and birefringence measurements. WAXS measurements reveal a decrease of the initial high orientation of the chains in the crystallites during deformation. Simultaneously, an increase of the birefringence was detected, indicating an orientation of chains in the amorphous regions. The alteration of the long period reflections in the SAXS patterns give strong evidence that lamellar stacks with different orientation angles according to load direction are present. Depending on the orientation of stacks, the contribution of lamellar separation to sample deformation alters, giving rise to different amounts of density changes in the stacks. Absolute intensity measurements of SAXS using a Kratky apparatus reveal that lamellar separation occurs preferentially below or in the range of the glass-transition temperature at small strain. With increasing strain and temperatures above the glass-transition slip deformation mechanisms become more important. The formation of microvoids was observed at strain near to elongation at break below or in the range of glass-transition temperature. 相似文献
Morphological changes accompanying the deformation of polypropylene filaments with varying degrees of melt-induced orientation are examined using wide-angle x-ray scattering (WAXS), small-angle x-ray scattering (SAXS), and electron microscopy, and their behavior is compared both to completely unoriented film samples and to very highly oriented, hard elastic filaments. Melt-oriented filaments are shown to deform predominantly by a voiding mechanism at low temperatures (<100°C), and destruction of the lamellas to produce fibrils occurs only after extensive drawing. The bimodal crystal texture of the filaments does not appear to greatly affect the low temperature deformation mechanism. High temperature (>100°C) drawing produces a fibrillar structure containing elongated voids. 相似文献
A thermodynamic analysis of the uniaxial stretching of polyurethanes of various compositions and mechanical histories was carried out by using deformation calorimetry. The initial small strain deformations were found to result from the volume elasticity of the hard phase. The intramolecular energy contributions of the soft blocks were estimated. The hard block contributions were shown to depend on their content and on the degree of sample stretching. The predominant role of the soft component is proved to be manifested only in softened samples with a hard block content not exceeding 30%. The thermodynamics of the softening and hysteresis phenomena were studied. The dependence of the deformation mechanism on the hard block content and mechanical history is discussed.The authors express their thanks to Dr. A. R. Korigodsky and Dr. M. P. Letunovsky for the PU samples. 相似文献
An x-ray study has been made of the structure of a series of ethylene–phosphonic acid copolymers and the parent low-density polyethylene from which they were derived. The phosphonic acid contents (groups per 100 carbon atoms) of the copolymers were: A, 0.8; B, 1.8; C, 2.8; and D, 8.0. Small-angle x-ray scattering (SAXS) results show that the phosphonic acid substituents do not incorporate into the crystal lattice to any appreciable extent, that the substituents have the effect of decreasing the average thickness of the crystal lamellae and increasing the breadth of the size distribution of thicknesses, and that a two-phase model does not adequately account for the observed SAXS invariant. Wide-angle x-ray scattering (WAXS) results show that specimens, A, B, and C are partially crystalline with the polyethylene crystal structure and that D is amorphous. The observed broadenings of the 110 and 200 crystal reflections in the copolymers indicate that the substituents decrease the lateral dimensions of the crystalline lamellae and/or increase the deformation of the lattice due to external strain. Specimen D, completely amorphous according to the WAXS criterion, exhibits the largest value of the SAXS invariant of all the copolymers studied and must thus possess a multiphase structure consisting of small ordered regions and a disordered phase. The results of the study show the structure of the copolymers to be consistent with the fringe-micelle model but do not rule out the folded-chain model, although a regular fold surface is unlikely. 相似文献
In a previous study, the morphologies of a group of paraphenylene diisocyanate (PPDI)-based polyurethane block copolymers were examined. These polyurethanes exhibited a multiphase structure with an interfacial boundary thickness estimated to be on the order of 1 nm and crystallization of the polyoxytetramethylene (POTM) flexible segment. Further studies involving annealing of these polyurethanes are reported here. An annealing time of 4 h was used, and the annealing temperature varied from 125 to 200°C. The samples have been characterized using differential scanning calorimetry (DSC) and with wide- and small-angle x-ray scattering (WAXS, SAXS) in order to determine the effects of annealing on the microphase structure. Annealing increases the phase separation of the two phases as evidenced by sharper endotherms in DSC thermograms and increased intensities in WAXS diffractometer traces. Annealing also slightly increases the transition zone thickness and long-period spacing. At the highest annealing temperature in this study, the long-period spacing increases dramatically due to hard segment domain aggregation. 相似文献
Synchrotron small angle X‐ray scattering (SAXS), wide angle X‐ray scattering (WAXS), and transmission electron microscopy were carried out for an oriented polyethylene‐block‐[atactic poly(propylene)] with a molecular weight of 1.13×105 and a volume fraction of polyethylene of 0.5. Isothermal crystallization at 93°C did not destroy the pre‐formed microdomain, however, with a higher crystallization temperature, the microdomain was more heavily deformed and more crystalline lamella grew. In WAXS profiles, preferential orientation of (020) reflection peak was observed, indicating that the crystalline lamella grew in parallel with the micro domain interface. 相似文献
Summary: The annealing and melting behavior of poly[(R)‐3‐hydroxybutyrate] (P(3HB)) single crystals were followed in real time by synchrotron small‐ (SAXS) and wide‐angle X‐ray scattering (WAXS) measurements. The real‐time SAXS measurements revealed that the P(3HB) single crystal exhibits a discontinuous increase of lamellar thickness during heating. The structural changes as observed by SAXS and WAXS were in response to the thermal properties of single crystals characterized by differential scanning calorimetry.
A series of two‐dimensional small‐angle X‐ray scattering patterns of P(3HB) single crystal mats during the lamellar thickening process. 相似文献
Time-resolved and off-line synchrotron wide-angle and small-angle x-ray scattering (WAXS and SAXS) was used to study the structure formation in poly-p-phenylenebenzobisoxazole (PBO) fibers during various stages of spinning, coagulation, and heating processes. WAXS data could be explained in terms of liquid-crystalline structures of varying degrees of order. A structure model is proposed that is in accordance with the observed SAXS four-point pattern. 相似文献