High modulus filaments of polyethylene with lamellar structure by melt processing; the role of the high molecular weight component

Bashir, Z.; Odell, J. A.; Keller, A.

doi:10.1007/bf02396944

Cited by 99 publications

(84 citation statements)

References 18 publications

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“…44 Subsequent studies of stress-induced crystallization of polyethylene elucidated this mechanism and revealed the detailed structure of these morphological units, which were called shish kebabs. [45][46][47][48][49][50][51][52] The detailed structure of polyethylene shish kebabs were revealed in recent studies, showing that the shish were sub-lm to $10 lm in length, $2-3 lm in diameter and contained $10-50 extended chain segments. 51,52 Also, a blend study revealed that mainly ultra-high molecular weight polyethylene chains ($5-6 Â 10 6 weight-average molecular weight) were involved in shish formation by a coil-stretch mechanism.…”

Section: Stress-induced Crystallizationmentioning

confidence: 99%

Crystallization and melting of polyethylene copolymers: Differential scanning calorimetry and atomic force microscopy studies

Mirabella

2006

J Polym Sci B Polym Phys

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ABSTRACT:The HoffmanLauritzen theory of secondary, surface nucleation and growth was primarily relied upon for about 40 years after its introduction in about 1960 to rationalize the crystallization of flexible chain polymers into lamellar crystals. However, in about 1998, Strobl and coworkers introduced a different model for crystallization, based on the stagewise formation of lamellae. Two major components of this model were as follows: (1) the concept of the formation of a mesomorphic melt as a precursor to crystallization and (2) the control of the melting temperature range of lamellar crystals of homogeneous polyolefin copolymers by an inner degree of order or perfection rather than on the crystal thickness. The first concept is in disagreement with the HL theory and the second with the Gibbs-Thomson theory, which associates melting temperature with lamella thickness. In the present study, differential scanning calorimetry and atomic force microscopy were successfully employed to monitor the in situ quiescent crystallization of polyethylene homopolymer and copolymer. In the present study, evidence was not found to support the concept of lamellae with equal thickness melting over a broad temperature range. Some evidence was found that might be interpreted to support the concept of a mesomorphic melt as a precursor to crystallization. At present, the model promoted by Strobl and coworkers appears to be at an uncertain stage at which strong proof or disproof are not available. However, this alternative model has injected a new vitality into the study of crystallization of flexible chain polymers.

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Section: Stress-induced Crystallizationmentioning

confidence: 99%

Crystallization and melting of polyethylene copolymers: Differential scanning calorimetry and atomic force microscopy studies

Mirabella

2006

J Polym Sci B Polym Phys

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“…[1][2][3][4][5] Crystallinity affects many of the material properties, from mechanical to optical. [1][2][3][4][5][6][7][8][9] Semicrystalline polymers are stiffer than amorphous and tend to be opaque. However, universal rules are difficult to establish because these materials exhibit a processing-structure relation; i.e., the final properties are affected by the processing conditions.…”

Section: Introductionmentioning

confidence: 99%

Crystallization and Precursors during Fast Short-Term Shear

2009

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This paper deals with structural and morphological developments during flow-induced crystallization of molten isotactic polypropylene (iPP). Several authors have invoked the formation of precursors in the early stages of this process. However, it is not clear whether these precursors can be generated and can crystallize already during flow. We address this issue using X-ray scattering (SAXS and WAXD) with a high image capturing rate during and immediately after a strong shear pulse to the undercooled melt. Eventually, we provide the first in situ evidence of formation of flow-induced precursors (FIPs) of crystallization generated applying shear to a fast crystallizing melt of flexible macromolecules, like iPP. Moreover, it is shown that a rheological classification can be used to define the flow conditions promoting FIPs formation. In fact, when molecular stretch is achieved, we found that shear rate is the parameter dominating the formation of structures during shear. When the shear rate is high enough, crystals with a high degree of orientation are formed during a brief shear pulse. Whereas, for low shear rates, crystalline structures do not develop during a brief shear pulse. However, the equatorial streak of intensity in SAXS points to the formation of high density domains with fibrillar morphology. These dense and noncrystalline scatterers are metastable precursors of crystallization. After cessation of flow, they nucleate and assist the radial growth of stacks of lamellae. Eventually, this sequence of events leads to the well-known shishkebab morphology.

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“…On the other hand, as mentioned in Introduction, TEM observations showed that shish (extended chain crystal) had a diameter of $10 nm. [7][8][9][10] These observations suggest that shish-kebab has hierarchic structure in a wide spatial scale. In this work we studied the hierarchic structure using small-angle neutron scattering in a very wide Q range.…”

Section: Small-angle Neutron Scatteringmentioning

confidence: 73%

“…For example, even size of shish-kebab structure is not still fully understood. About 30 years ago, Keller and co-workers observed shish-kebab structure in polyethylene (PE) using transmission electron microscope (TEM), [7][8][9][10][11] showing shish of $10 nm in diameter and several mm in length. This has been assigned to extended chain crystal.…”

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confidence: 99%

Quantum Beam Studies on Polymer Crystallization under Flow

Kanaya

Matsuba

Ogino

et al. 2007

Polym J

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ABSTRACT:One of the longstanding issues in polymer science is crystallization of polymers under flow, especially formation of the so-called shish-kebab. Recent progress in quantum beam technology shed light on the substantial nature in the shish-kebab formation. In this paper we review our recent experiments on polymer crystallization under flow using time-resolved depolarized light scattering, small-angle and wide-angle X-ray scattering and small-angle neutron scattering in a wide spatial scale from 0.1 nm to several tens mm. These studies revealed that the shish-kebab formation is governed by a competition between the crystallization rate and the chain relaxation rate. Small-angle neutron scattering study on an elongated blend of deuterated low molecular weight and protonated ultra-high molecular weight polyethylenes showed that a long cylindrical object 2 mm in diameter and 12 mm in length was formed from deformed network of ultra-high molecular weight chains, which included three shishs (or extended chain crystals) 9 nm in diameter. 1-3 In order to obtain desired properties of polymers it is necessary to control the final structure of polymers in the processing. Therefore, many researches have been carried out on polymer crystallization under flows for many decades to elucidate the crystallization mechanism and control the final structure. One of the famous issues in the research filed is structure and formation mechanism of the so-called shish-kebab, which consists of long central fiber core (shish) surrounded by lamellar crystalline structure (kebab) periodically attached along the shish, and it is believed that the shish-kebab structure is a structure origin of ultra-high strength and ultra-high modulus fibers. [4][5][6][7][8][9][10] This is one of the reasons why so many studies have been performed on the structure and the formation mechanism of shish-kebab. In spite of the great efforts there are still many unsolved problems in the shish-kebab. For example, even size of shish-kebab structure is not still fully understood. About 30 years ago, Keller and co-workers observed shish-kebab structure in polyethylene (PE) using transmission electron microscope (TEM), [7][8][9][10][11] showing shish of $10 nm in diameter and several mm in length. This has been assigned to extended chain crystal. On the other hand, large and long objects with diameter of several mm aligned along the flow direction are often observed in some polymers 24,28 using optical microscope (OM). This long object is apparently similar to the shish structure but the spatial scale is very different. It must include the kebab inside judging from the spatial scale. These observations suggest that shishkebab has hierarchic structure in a wide spatial scale. However, few papers did not deal with the hierarchic structure of the shish-kebab structure. One of the reasons is difficulty to study the shish-kebab structure in a wide spatial range simultaneously, in addition, kebab structure is overlapped on the shish structure, so that it is not easy to...

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High modulus filaments of polyethylene with lamellar structure by melt processing; the role of the high molecular weight component

Cited by 99 publications

References 18 publications

Crystallization and melting of polyethylene copolymers: Differential scanning calorimetry and atomic force microscopy studies

Crystallization and melting of polyethylene copolymers: Differential scanning calorimetry and atomic force microscopy studies

Crystallization and Precursors during Fast Short-Term Shear

Quantum Beam Studies on Polymer Crystallization under Flow

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