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  • 1
    Electronic Resource
    Electronic Resource
    Entanglements in polymer solutions under elongational flow: a combined study of chain stretching, flow velocimetry and elongational viscosity (1988)
    s.l. : American Chemical Society
    Macromolecules 21 (1988), S. 250-256 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00179a048
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  • 2
    Electronic Resource
    Electronic Resource
    Diffusion and orientability of rigid-rodlike molecules in solution (1985)
    s.l. : American Chemical Society
    Macromolecules 18 (1985), S. 1443-1453 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00149a015
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  • 3
    Electronic Resource
    Electronic Resource
    Flow-induced scission of isolated macromolecules (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 4022-4028 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We review experimental results on the degradation of stretched polymer molecules in strong extensional flow fields. Atactic polystyrene and polyethylene oxide both show closely central scission along the backbone of the chain. We present a theoretical approach based upon a modified thermally activated barrier to scission model. This successfully describes the scission process as a function of molecular weight and stiffness and strain rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453855
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  • 4
    Electronic Resource
    Electronic Resource
    Stiff and strong polyethylene with shish kebab morphology by continuous melt extrusion (1986)
    Springer
    Journal of materials science 21 (1986), S. 3993-4002 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In a previous work, it was shown that highly oriented fibres with 10 GPa modulus could be obtained by continuous single-stage melt extrusion of a medium molecular weight polyethylene to which 3% ultra-high molecular weight (M w ∼ 3 to 5 × 106) material had been added by solution blending. It was demonstrated that a special interlocking shish kebab structure was responsible for the favourable mechanical properties. In the present work, we succeeded in achieving the same effect from an unblended polyethylene by choosing starting materials with an inherently suitable molecular weight distribution. Both the high and low molecular weight tails of the distribution are very influential: the high tail contributes to the formation of extended-chain fibrils (which constitute the backbones of the shish kebabs), while the low tail affects melt extrudability and strength. Melt strength is important because unusually high tensile stresses are required during wind-up. The wind-up stress was measured and found to be an order of magnitude greater than that encountered in conventional melt spinning — where no shish kebabs are formed. The implications of the above findings for polymer processing, crystal morphology and melt rheology are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02431641
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  • 5
    Electronic Resource
    Electronic Resource
    Stiff and strong polyethylene with shish kebab morphology by continuous melt extrusion (1986)
    Springer
    Journal of materials science 21 (1986), S. 3993-4002 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In a previous work, it was shown that highly oriented fibres with 10 GPa modulus could be obtained by continuous single-stage melt extrusion of a medium molecular weight polyethylene to which 3% ultra-high molecular weight (M w ∼ 3 to 5 × 106) material had been added by solution blending. It was demonstrated that a special interlocking shish kebab structure was responsible for the favourable mechanical properties. In the present work, we succeeded in achieving the same effect from an unblended polyethylene by choosing starting materials with an inherently suitable molecular weight distribution. Both the high and low molecular weight tails of the distribution are very influential: the high tail contributes to the formation of extended-chain fibrils (which constitute the backbones of the shish kebabs), while the low tail affects melt extrudability and strength. Melt strength is important because unusually high tensile stresses are required during wind-up. The wind-up stress was measured and found to be an order of magnitude greater than that encountered in conventional melt spinning — where no shish kebabs are formed. The implications of the above findings for polymer processing, crystal morphology and melt rheology are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00553458
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  • 6
    Electronic Resource
    Electronic Resource
    Thermomechanical degradation of macromolecules (1992)
    Springer
    Colloid & polymer science 270 (1992), S. 307-324 
    Details
    ISSN: 1435-1536
    Keywords: Extensional flow ; degradation ; thermomechanical ; entanglements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Extensional flow techniques are used to investigate thermomechanical scission of polymer solutions from ambient temperatures up to 150°C. We report precise central scission of chains beyond a critical fracture strain-rate. These results can be well accounted for by a Thermally Activated Barrier to Scission (TABS) model. We speculate upon the origin of degradation in simple shear flows and report novel results on degradation in porous media and ultrasonic sound fields, which contain dominant extensional components. Finally, we show how the nature and degree of degradation is affected by concentration and polydispersity. In semi-dilute entangled solutions, the degradation rates increase, are much higher for polydisperse solutions and the scission becomes progressively more random along the chain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00655846
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  • 7
    Electronic Resource
    Electronic Resource
    Fluid flow: Turbulence splits polymers (1984)
    [s.l.] : Nature Publishing Group
    Nature 312 (1984), S. 98-98 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] EVEN minute quantities of long-chain molecules can dramatically influence the flow properties of liquids to which they are added, an.effect that has many practical applications. However, limits are set on the usefulness and range of applications of polymer additives by the fact that the longest ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/312098a0
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  • 8
    Electronic Resource
    Electronic Resource
    Designing high-modulus polyethylene with lamellar structures (1984)
    Springer
    Colloid & polymer science 262 (1984), S. 683-690 
    Details
    ISSN: 1435-1536
    Keywords: High-modulus ; polyethylene ; shish-kebab ; melt extrusion ; self-stiffening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In a preceding work we described a method whereby ultra high modulus filaments of polyethylene of essentially lamellar structure could be produced from the melt by a combination of capillary flow and pressure quenching [1]. Here the lamellae are nucleated by flow induced fibrous crystals formed during the extrusion but present in too small amounts to influence the properties themselves. Yet these microfibrils ensure the particular parallel and mutually interlocking arrangement of lamellae which is the source of the ultra high modulus. In the present work we set out to engineer this interlocking parallel lamellar morphology by utilizing preexisting fibrous crystals, as opposed to relying on their coincidental formation during the extrusion. By a judicious choice of the initial starting material and heat treatment conditions our objective was achieved, illustrating that lamellar self-composites with desirable properties can be achieved by planned design of the micro-morphology. As an additional feature these samples displayed ageing effects which have led to improved properties. Analogous phenomena, termed ‘self stiffening’ have been observed previously in drawn fibre products [8]. The presently arising example has now allowed its morphological origin to be identified: this is the delayed crystallization by which the interlocking lamellae fill in the residual interstices, the stage at which the corresponding sample acquires its final modulus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01451539
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  • 9
    Electronic Resource
    Electronic Resource
    Flow of monodisperse polystyrene solutions through porous media (1994)
    Springer
    Colloid & polymer science 272 (1994), S. 1224-1233 
    Details
    ISSN: 1435-1536
    Keywords: Porous media ; monodisperse polystyrene ; elongational viscosity ; entanglements ; elongational flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In this work, we study the origin of the extension thickening commonly observed when solutions of flexible polymers flow through porous media and ideal elongational flows. We have used randomly packed beds of glass beads as porous media. We have performed experiments with closely monodisperse atactic polystyrene of different molecular weights dissolved in organic solvents. The use of a closely monodisperse polymer allowed us to make a more meaningful comparison between the results obtained using opposed jets and porous media flow, as compared to previous works on polydisperse polymers. The results indicate that the coil-stretch transition of isolated polymer molecules in solution cannot be the only mechanism responsible for the extension thickening. It is clear that part of the observed effect is due to the extension of isolated molecules, but the main factor causing a great increase in the elongation viscosity beyond a critical strain rate is the formation of transient entanglement networks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00657774
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  • 10
    Electronic Resource
    Electronic Resource
    The extensibility of macromolecules in solution; A new focus for macromolecular science (1985)
    Springer
    Colloid & polymer science 263 (1985), S. 181-201 
    Details
    ISSN: 1435-1536
    Keywords: Extensional-flow ; solution ; birefrigence ; flexible chain ; rigid-rod
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The paper is a summary of ongoing work in this laboratory laid on foundations of about 10 years standing. It concerns the extensional and aligning effect which appropriately designed elongational flow-fields have on linear macromolecules in solution. In the case of flexible molecules the chains can be fully stretched out, and the corresponding conformational relaxation time, thus determined, provides information on the molecular weight (amongst others providing a new method for determination of the molecular weight distribution), on the coil dimension as relevant to most recent theories, on the draining characteristics of the coil, and on the difference in extension and retraction characteristics. Further, it can provide information on chain flexibility, utilised here in the case of polyelectrolytes where this flexibility can be systematically varied and thus followed. It also signals the onset of associations, geometric entanglements in particular, opening a new window on entanglement behaviour. Also it offers a uniquely definitive method for the study of flow induced chain scission. In addition, these studies reveal how chain extension reacts back and modifies the flow-field producing it with relevance to rheology and fluid transport. Beyond this all, the work shows explicit connections with gelation and absorption phenomena, to the study of which it promises to contribute. In the realm of rigid rod molecules it indicates how elongational flow can promote liquid crystal formation and, more comprehensively, it provides a definitive method for the determination of rotational diffusion as a function of a number of variables. The most salient conclusion in the latter area is the realisation that rigid rods are incomparably less restricted by their neighbours in their rotational frreedom, and are thus correspondingly more orientable than predicted by theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01415506
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