Texture development in uniaxially drawn polyethylene tape

Gerrits, N. S. J. A.; Young, Robert J.

doi:10.1007/bf00549180

Cited by 14 publications

(9 citation statements)

References 23 publications

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“…The plasticity of crystalline materials is well known to proceed through crystal slip processes due to the nucleation and propagation of dislocations. Plastically deformed semicrystalline polymers display structural features such as kinks, bands, twinning, phase change, and texturing,1–15 which thoroughly support the occurrence of such mechanisms. Active dislocations in chain‐folded polymer crystals should have their glide plane parallel to the chain stems in the crystal because CC bond scission is prohibited in plasticity.…”

Section: Introductionmentioning

confidence: 75%

Dislocation approach to the plastic deformation of semicrystalline polymers: Kinetic aspects for polyethylene and polypropylene*

Séguéla

2002

J Polym Sci B Polym Phys

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The plasticity of semicrystalline polymers is analyzed in the framework of Young's dislocation model under the assumption of nucleation of screw dislocations from the lateral surface of the crystalline lamellae. It is proposed that the driving force for the nucleation and propagation across the crystal width of these screw dislocations relies on chain twist defects that migrate along the chains stems and allow a step‐by‐step translation of the stems through the crystal thickness. Such defects are identified as thermally activated conformational defects responsible for the so‐called crystalline relaxation. Dislocation kinetic equations are derived. Plastic flow rates attainable by dislocation motion in polyethylene and polypropylene are assessed with frequency–temperature data of the crystalline relaxation. Comparisons are made with experimental strain rates that enable homogeneous plastic deformation. In addition to temperature, the crystal lamellar thickness, which is a basic factor of the plastic flow stress in Young's dislocation model, is a major factor in dislocation kinetics through its influence on chain twist activation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 593–601, 2002; DOI 10.1002/polb.10118

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Section: Introductionmentioning

confidence: 75%

Dislocation approach to the plastic deformation of semicrystalline polymers: Kinetic aspects for polyethylene and polypropylene*

Séguéla

2002

J Polym Sci B Polym Phys

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“…This process is facilitated by the motion of dislocations [89]. Several research groups have interpreted the deformation of PE (in stages (ii) [91] and (iii) [46] of drawing) as such a sliding on crystal planes parallel to the [001] chain direction [47,92]. This process has been termed "chain slip".…”

Section: Slip On Crystal Planesmentioning

confidence: 99%

“…Thus, the chain-diffusion process resulting from chain rotation-translation as described in this work, while distinct from crystal-plane chain slip of refs. [46,91], should be able to account for most of the reported observations.…”

Section: Slip On Crystal Planesmentioning

confidence: 99%

Polymer ultradrawability: the crucial role of α-relaxation chain mobility in the crystallites

1999

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An explanation of the varying (ultra)drawability of semicrystalline polymers is proposed, based on NMR evidence of αc‐relaxation‐associated helical jumps and chain diffusion through the crystallites of polyethylene and several similarly “αc‐mobile” polymers; these include isotactic polypropylene, poly(ethylene oxide), poly(oxymethylene), poly(tetrafluoroethylene), poly(vinyl alcohol), and several others. The chain motions provide a mechanism by which hot drawing of these polymers can extend an initially formed fiber morphology by an order of magnitude to draw ratios > 30, without melting. A second class of polymers, including nylons, poly(ethylene terephthalate), syndiotactic polypropylene, isotactic polystyrene, and isotactic poly(1‐butene) (form I) lack a crystalline α‐relaxation and the associated chain mobility. Therefore, these polymers are “crystal fixed” and drawability is limited to draw ratios < 14, arising mostly from break‐up of crystalline lamellae and deformation of the amorphous regions. On this basis, we can explain which polymers are drawable to high draw ratios, given a sufficiently low level of entanglement. The motion through the crystallites is thermally activated and the applied stress only biases the direction of the jumps; this explains the crucial role of temperature and rate in tensile drawing and solid‐state extrusion processes. The behavior of the crystal‐fixed, poorly drawable polymers strongly suggests that melting, straight chain pull‐out, and sliding on crystal planes are not significantly operative during ultradrawing, and that weak intermolecular forces are not a sufficient condition for ultradeformation. Various stages of drawing are distinguished and other models of ultradrawability are discussed critically.

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“…This observation can be related to the striking change of slope in the stress-strain cur ve. 14,15 At ® rst, plastic¯ow is m ore likely governed by a combined activation of the two slip systems, including eventual cross slip, 17 which means change of slip plane due to the com mon slip direction [001]. Beyond the plastic strain Î 5 0.3, the (010)[001] slip system takes a predominant part.…”

Section: Resultsmentioning

confidence: 99%

Plastic Deformation of Polyethylene Studied by Infrared Dichroism

Elkoun¹,

Séguéla²,

Depecker³

1999

Appl Spectrosc

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Infrared dichroism measurements have been carried out to investigate the plastic deformation mechanisms of homogeneous and heterogeneous ethylene copolymers issued from the metallocene and the Ziegler–Natta catalyses, respectively. The two copolymers having the same density display significantly different plastic behavior that should result from different mechanisms of crystal slip. Such mechanisms are analyzed on the basis of the main crystal slip systems (100)[001] and (010)[001] having the higher shear compliances. Attention is focused on the Schmid factor, S, of the slip planes, which is the ratio of the resolved shear stress acting on each slip plane to the applied tensile stress. From the orientation functions of the three crystallographic axes of the orthorhombic unit cell, the Schmid factor of the two slip systems is determined as a function of plastic strain. The heterogeneous copolymer exhibits somewhat higher data for the (010)[001] slip, which suggest a preferred activation of this system during the yielding stage. In contrast, the homogeneous copolymer displays close values for the two slip systems, indicating that plastic flow is more likely governed by a combined activation of the two slip systems, and with eventual cross slip owing to the common [001] slip direction.

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Texture development in uniaxially drawn polyethylene tape

Cited by 14 publications

References 23 publications

Dislocation approach to the plastic deformation of semicrystalline polymers: Kinetic aspects for polyethylene and polypropylene*

Dislocation approach to the plastic deformation of semicrystalline polymers: Kinetic aspects for polyethylene and polypropylene*

Polymer ultradrawability: the crucial role of α-relaxation chain mobility in the crystallites

Plastic Deformation of Polyethylene Studied by Infrared Dichroism

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