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  • Articles  (58)
  • polyethylene  (58)
  • Wiley-Blackwell  (58)
  • American Physical Society
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  • Physics  (58)
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  • 1
    Electronic Resource
    Electronic Resource
    The kinetics and mechanism of polyethylene photo-oxidationPaper presented at the “15th Annual International Conference on Advances in the Stabilization and Degradation of Polymers” in Luzern (Switzerland), June 2-4, 1993. (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 216 (1994), S. 113-133 
    Details
    ISSN: 0003-3146
    Keywords: polyethylene ; photo-oxidation ; weathering ; mechanism ; kinetics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the natural and accelerated photo-oxidation of low-denisty polyethylene (LDPE) films have been studied; different geographical locations have been selected for the natural tests, and a range of temperatures used in the accelerated experiments in a specially built temperature-controlled ultraviolet radiation enclosure. A meaningful correlation between natural and accelerated weathering results was established, by means of an adequate superposition of the effects of UV radiation exposure and temperature. Reasonably detailed and accurate, lumped-parameter, kinetic models of the photo-oxidation process have also been developed, to interpret and predict the results of measurements of carbonyl, hydroperoxide and vinyl absorbances as functions of time and temperature; the models predict the general experimental behaviour, and also that both the formation of hydroperoxides and carbonyl Norrish-I reactions are important initiation steps. More complex models have the potential of interpreting other fine details of the degradation behaviour, namely the generation of other chemical species, and the chain scission and cross-linking process which are directly related to changes in the mechanical properties.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052160108
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  • 2
    Electronic Resource
    Electronic Resource
    The morphology of gel-spun polyethylene fibers, investigated by solid-state 13C NMR (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 2661-2666 
    Details
    ISSN: 0887-6266
    Keywords: polyethylene ; crystal ; oriented amorphous phase ; intermediate phase ; amorphous phase ; conformation ; motion ; disorder ; 13C NMR ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gel-spun polyethylene fibers were analyzed at room temperature with 13C NMR, using both, CP-MAS and BILEV (Bloch-decay with two-level decoupling). The analysis shows the existence of three different components in the fiber sample - a crystal component, an amorphous component and a third component, named the oriented, mobile component. This latter component has a 13 C chemical shift that is similar to the crystalline chemical shift, but with a mobility, expressed by T1, that is closer to the amorphous component. The chemical shift and T1 are as follows: 34.06 ppm and 28.1 s for the crystalline part; 31.70 ppm and 0.3 s for the amorphous part; and 34.06 ppm and 1.8 s for the oriented mobile component. The percentages are 63.2% crystalline; 34.0% oriented mobile, 2.8% amorphous component. Using proton spin-diffusion measurements, it was possible to estimate the domain size of the crystalline and oriented mobile components to be 62.8 and 13.2 nm, respectively, in agreement with the results of a full-pattern x-ray study on the same sample. After melting of the fiber at 450 K and recrystallinzation on cooling, the oriented, mobile component is dramatically reduced. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1994.090321612
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  • 3
    Electronic Resource
    Electronic Resource
    NMR imaging of polyethylene pipes (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 571-576 
    Details
    ISSN: 0887-6266
    Keywords: NMR ; imaging ; polyethylene ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 1H nuclear magnetic resonance (NMR) imaging techniques have been used to image the extrusion aid (EA) in polyethylene (PE) pipe samples. The resulting two-dimensional images show the distribution of EA within the pipe. EA is found to be uniformly distributed in a normal pipe. Examples of degraded pipes, due to exposure to extreme conditions, show migration of EA to the pipes' wall surfaces. NMR images of a normal pipe and two examples of damaged pipes are presented. The imaging technique and the results are discussed. © 1995 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1995.090330405
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  • 4
    Electronic Resource
    Electronic Resource
    Morphologies of microporous polyethylene and polypropylene crystallized from solution in supercritical propane (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 1053-1063 
    Details
    ISSN: 0887-6266
    Keywords: polyethylene ; polypropylene ; supercritical propane ; morphology ; microporosity ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The morphologies of solvent-free, microporous, mechanically self-supporting cylinders of linear polyethylene and isotactic polypropylene, crystallized from solution in supercritical propane, were examined by an SEM technique. The morphology of gels (or foams), obtained with little or no shrinkage from 2% to 35% solutions by weight of polyethylene (99% to 85% porosities), is shown in some detail. Lamellae with very little or considerable mutual organization occur, often in the form of stacks with straight or coiled axes (axialites). Further growth of these can lead to particles with a roughly spherical overall shape and a predominantly radial orientation of the lamellae at the particle surface. Subcooled isotactic polypropylene, on the other hand, crystallizes in the form of perfectly shaped birefringent microspheres of very uniform size. ©1995 John Wiley & Sons, Inc.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1995.090330709
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  • 5
    Electronic Resource
    Electronic Resource
    The effects of annealing on fatigue crack propagation in polyethylene (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 1969-1984 
    Details
    ISSN: 0887-6266
    Keywords: polyethylene ; lamellae ; anneal ; quench ; fatigue crack propagation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Fatigue crack propagation tests on annealed and quenched medium-density polyethylene showed the annealed specimens to have much lower resistance to crack initiation and subsequent propagation. Although the same fracture mechanism, in which the brittle crack gradually becomes more ductile, prevailed in both cases, the voided and fibrillated crack tip root craze in the annealed material was much weaker that the nonfibrillated quenched root craze. Microstructural analyses indicate that the annealed material had separate crystallite populations, whereas the quenched material had a more homogeneous morphology. The highest melting fraction of the annealed material was composed of lamellae that were about 270 Å thick, and the quenched lamellae were estimated to be 160 Å thick. The reduced fatigue crack propagation resistance of the annealed material was suggested to be a result of a lower concentration of tie molecules and its reduced damping capability, compared to the quenched material. © 1995 John Wiley & Sons, Inc.
    Additional Material: 21 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1995.090331312
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  • 6
    Electronic Resource
    Electronic Resource
    Ostwald ripening in immiscible polyolefin blends (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 2281-2287 
    Details
    ISSN: 0887-6266
    Keywords: Ostwald ripening ; polyethylene ; hydrogenated polybutadiene ; blends ; morphology ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The coarsening in the quiescent melt of the phase-segregated particles of a polymer blend, composed of a narrow molecular weight fraction of an unbranched high-density polyethylene (HDPE) and a highly branched (100 ethyl branches/1000 C atoms) hydrogenated polybutadiene (HPB) was studied. The system was effectively binary, due to the narrow molecular weight and composition distributions of each component. The system was composed of 90 wt % of the HDPE and 10 wt % of the HPB and it formed a two-phase system in the melt at 177°C. The blend was precipitated from xylene solution in order to obtain an initially intimately mixed system. This was the third study in a series of studies of the coarsening of phase-segregated particles in polymer blends. This study was unique in that the system studied was binary in this case while the previous systems were multicomponent. Since the present system was binary, exact thermodynamic calculations of the phase state of this system could be applied with a high level of confidence. The droplet phase particles, which were mainly composed of the HPB, were observed to coarsen on storage in the melt for times of from 5 s to 1 h. At the shortest storage time of 5 s the particles had an average radius of about 0.05 μm and coarsened to about 0.2 μm after 1 h storage in the melt state. Particle dimensions were measured by scanning electron microscopy of n-heptane-etched and gold-coated sections. It was found that the volume of the particles increased linearly with time and that the rate constant of coarsening was Kexp = 1.23 × 10-18 cm3/s and this agreed fairly well with the rate constant calculated from Ostwald ripening theory of Kce = 0.86 × 10-18 cm3/s. In contrast the rate constant for direct particle diffusion and coalescence was Kc = 3.6 × 10-20 cm3/s. Since this was two orders of magnitude smaller than the rate constant for Ostwald ripening, it was concluded that, although the linear increase of volume with time was also consistent with the particle diffusion and coalescence mechanism, this was not a significant contributor to the coarsening mechanism. The major cause for the insignificance of the particle diffusion and coalescence mechanism was the high melt viscosity of the matrix polymers. The application of the Ostwald ripening theory to this system could be made with a high level of confidence because it was binary. It was found that the phase concentration of the droplet phase apparently underwent a rapid increase during the first 1-2 min of storage in the melt, indicating that the system did not reach phase equilibrium (i.e., did not completely phase-segregate) for about 1-2 min. This further indicated that the long-time coarsening regime was not entered until after this length of time. The particle size distributions remained approximately self-similar over the period of coarsening, as predicted by Ostwald ripening theory. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1995.090331613
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  • 7
    Electronic Resource
    Electronic Resource
    The critical molecular weight for resisting slow crack growth in a polyethylene (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 1809-1813 
    Details
    ISSN: 0887-6266
    Keywords: slow crack growth ; polyethylene ; critical molecular weight ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An ethylene-hexene copolymer was fractionated into five fractions and the density of short-chain branches was measured for each fraction. The slow crack growth behavior was measured on each fraction by sandwiching the small amount of fractionated resin of about 0.2 g between polyethylene grips. The resistance to slow crack growth was negligible for the three fractions whose Mw was less than 1.5 × 105. For the fourth fraction with Mw greater than 1.5 × 105, the resistance to slow crack growth was very high, being greater than that for the whole resin even though its density of short-chain branches was less than that of the whole resin. It is concluded that a molecular weight greater than 1.5 × 105 is required to create the number of tie molecules that is necessary to produce a high resistance to slow crack growth in this particular copolymer. © 1996 John Wiley & Sons, Inc.
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  • 8
    Electronic Resource
    Electronic Resource
    Development of a new software for the X-ray structural analysis of polymer crystals by utilizing the X-ray imaging plate system (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 1677-1700 
    Details
    ISSN: 0887-6266
    Keywords: x-ray structural analysis ; polymers ; imaging plate ; direct method ; polyethylene ; polyoxymethylene ; isotactic polybutene-1 ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A software and some useful tools have been developed for identifying individual x-ray reflectional peaks recorded with an x-ray imaging plate system. These techniques were applied to analyze the crystal structure of uniaxially oriented polymer samples. Characteristic features of the present method may be summarized as follows. (1) The indexing of the observed reflections and the determination of the unit cell parameters can be made easily on the display of the computer. (2) The integrated intensity of the individual component of the overlapped reflections can be evaluated quantitatively through the curve separation technique. The Rmerge's for the equivalent reflections were 5-6%, indicating the exact evaluation of the integrated intensities. (3) The thus obtained reflectional data were successfully utilized for the extraction of the initial structural models by the direct method. The actual applications have been made for orthorhombic polyethylene, trigonal polyoxymethylene, and isotactic polybutene-1, giving the refined crystal structures including even the positions of hydrogen atoms in some cases. The reliability factors were 12, 5, and 15%, respectively, for these three polymer cyrstals. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1677-1700, 1997
    Additional Material: 17 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Surface characterization of ion-implanted polyethylene (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 715-725 
    Details
    ISSN: 0887-6266
    Keywords: polyethylene ; ion implantation ; surface structure ; wear ; hardness ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polyethylene (PE) film was implanted with 1000-keV Ar+ ions to a fluence of 5 × 1014 ions/cm2 under high vacuum conditions (2.5 × 10-6 torr) and the film surface was investigated by means of microhardness and microwear measurements, and FTIR/ATR, Raman, and XPS techniques. Ion implantation significantly increased the subsurface hardness and also significantly improved the microwear resistance of the polymer. The implanted surface region of the film was found to consist of two distinct layers. One was the outermost carbon layer with a thickness of the order of 10 nm. In this layer, ca. 75% of carbon atoms were combined by graphitic sp2 and diamond-like sp3 bonds, and the remaining 25% had chemical links with oxygen atoms. Spectroscopic data suggested that the sp2-bonded carbons segregated in graphite-like clusters containing imbedded oxygen atoms, interconnected by the sp3-bonded carbons. The other was the subsurface layer resulting from PE oxidation after ion-beam treatment. This layer was characterized by high contents of O—H and C=O groups as well as ester and double bonds. The chemical composition of the layer was uniform and did not vary over the layer thickness of about 1.4 μm. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 715-725, 1998
    Additional Material: 10 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Temperature and strain-rate dependence of yield stress of polyethylene (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 2177-2189 
    Details
    ISSN: 0887-6266
    Keywords: yield ; polyethylene ; stem length ; crystal plasticity ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The yield stress behavior of a range of polyethylene materials which differ with respect to their short chain branch content has been studied. Measurements carried out over a wide range of temperatures have shown that there is a sudden transition in the behavior of the yield stress at a temperature which is dependent on both the grade of material and the applied strain rate. These results are in agreement with previous results found from analysis of the yield strain behavior.Above the transition temperature the materials all behave in a nonlinear viscoelastic manner, and the yield process is considered as being propagation controlled. Below the transition temperature the materials all behave in an elastic-plastic manner, and the yield process is considered as being nucleation controlled. Below the transition temperature the temperature dependence of the yield stress is determined by the thickness of the crystalline lamellae. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2177-2189, 1998
    Additional Material: 16 Ill.
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