Structure and mechanical properties of ultra-high molecular weight polyethylene (UHMWPE) films of different draw ratios produced from gel-cast and meltcrystallised samples by multi-stage zone drawing have been studied in order to investigate the structural development and to clarify the role of interfaces between morphological units in the mechanical behaviour. The complex hierarchy of fibrillar structures generating upon neck formation is revealed. It is shown that the rearrangement of initial chain-folded crystallites into a microfibrillar structure occurs inside the volumes of supermolecular structures of larger sizes (spherulites in the melt-crystallised films and stacks of lamellae in the gel-crystallised films), the boundaries between the latter not having disappeared. Both the initial spherulites and stacks of lamellae with internally rearranged microfibrillar structure elongate upon drawing and comprise spindle-like units -macrofibrils -which are well resolved in scanning electron microscopy. Moreover, superfibrils have been revealed in the melt-crystallised films for the first time. They are, as suggested, the remnants of deformed and rearranged nascent polymer particles. Thus, the volume of the drawn films is considered to be full of interfaces. It is suggested that the majority of conformational defects, like chain ends, loops, tie molecules, entanglements, etc., are expelled from fibrillar crystallites in both intra-and interfibrillar regions. In addition to that, the interfibrillar spaces are crossed by tie molecules and micro-and macrofibrils. All of them hinder interfibrillar slip. The differences in creep and recovery of the investigated films are discussed in terms of density of packing and degree of connectivity of various scale fibrillar structural units. The lateral boundaries and the tips of fibrils are considered to be the weakest structural sites from which kink band formation and subsequent fracture of the loaded material begin.
A series of reactor powders of ultrahigh molecular weight (UHMW) polyethylenes with different morphology was melted at 1608C for 5 min and cooled in ice water. Low-frequency Raman spectroscopy was used to characterize the straight-chainsegment (SCS) length distribution of both initial and melt-crystallized materials. A bimodal SCS length distribution was found in the melt-crystallized sample originated from the reactor powder with a very tenuous amorphous phase. In other samples recrystallized from powders with more ordered structure, the SCS length distribution was unimodal and approximately identical. The result is explained in terms of perfection of lamellar crystals formed under limited time and thermal conditions from differently organized initial structure.
With the help of low-frequency Raman spectroscopy, the peculiarity of structural organization of oriented PE produced by multistage zone drawing of melt-crystallized films was studied. The draw ratios varied from DR ¼ 6 to 21 for PEI with M h ¼ 8·10 4 and from 3.5 to 5.7 for PEII with M h < 10 6 :The half widths (Dn) of all observed LAM bands were larger than 10 -20 cm 21 . This means that the bands comprise a continuum of the overlapped elementary bands with Dn < 3 cm 21 because of the wide straight -chain segments (SCS) length distribution. The length (L) of straight segments calculated from LAM-spectra, following a routine procedure, lies in the range from 7 -8 to 60 nm.Weight fractions G MW of the SCS, as functions of their length, have a bell-like shape. Comparison of the SCS lengths with the value of the long periods (D) inferred from SAXS data for the same samples indicates that the lengths do not exceed 2D. The structural interpretation of the data obtained is given on the basis of microfibrillar models of oriented polymers. The peculiarity of the microfibrillar structure in PEI and PEII samples such as crystallite sizes and shapes and concentrations of inter-and intrafibrillar tie molecules, manifest themselves as the shape of G MW (L) functions obtained for PE samples of various M w and DR.
The article is devoted to the study of the method of increasing the capacity at the trans-tailor interchanges providing access to cities, using the example of Belgorod, by introducing the Ramp metering traffic light control system. 4 traffic interchanges at the entrances to the regional center were investigated, geometric parameters of the exits were evaluated. Based on geometric analysis, intensity calculations and time delays, the optimal area for implementing the Ramp metering system is selected.
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