Overlapping of different rearrangement mechanisms upon annealing for solution-crystallized polyethylene

Matsuda, Hideo; Aoike, Taku; Uehara, Hiroki; Yamanobe, Takeshi; Kōmoto, Tadashi

doi:10.1016/s0032-3861(00)00893-4

Cited by 45 publications

(63 citation statements)

References 20 publications

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“…The average radius of spherulites equals 3-12 m. 8 The spherulites are formed by lamellae stacks with lamellar thicknesses ranging from 8 to 12 nm. 9 There data were confirmed in [10], where an average lamellar thickness of 11.5 nm was found, but were argued in [11], where an average thickness of 6.5 nm was reported. The average size of lamellae and their curvature, as well as the type of their organization into spherulites, are strongly affected by crystallization conditions, molecular weight, and degree of chain branching.…”

Section: Introductionmentioning

confidence: 89%

The effect of temperature on the viscoelastic response of semicrystalline polymers

Drozdov

Agarwal

Gupta

2004

J of Applied Polymer Sci

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Three series of isothermal torsion relaxation tests were performed at various temperatures ranging from room temperature to T ϭ 120°C on isotactic polypropylene, low-density polyethylene, and linear low-density polyethylene. Constitutive equations are derived for the viscoelastic behavior of a semicrystalline polymer at small strains. A polymer is treated as an equivalent network of strands bridged by temporary junctions (entanglements, physical crosslinks on the surfaces of crystallites, and lamellar blocks). The network is thought of as an ensemble of mesoregions with various activation energies for detachment of active strands from their junctions. The time-dependent response of the ensemble reflects thermally induced rearrangement of strands (separation of active strands from temporary junctions and merging of dangling strands with the network). Stress-strain relations are developed by using the laws of thermodynamics. The governing equations involve five adjustable parameters that are found by fitting the experimental data. This study focuses on the influence of temperature and crystalline morphology of polyolefins on the material parameters in the constitutive relations.

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Section: Introductionmentioning

confidence: 89%

The effect of temperature on the viscoelastic response of semicrystalline polymers

Drozdov

Agarwal

Gupta

2004

J of Applied Polymer Sci

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“…The sliding motion mechanism suggests a diffusion of molecules in-between crystals along the c-axis to form thick lamellae in which the thickness is doubled. [10,13,[17][18][19][20][22][23][24]26] The meltingrecrystallization mechanism emphasizes the melting of thin lamellae and the recrystallization of melted molecules to form thick lamellae. [8,11,20,21,26] In our previous study [34] we have demonstrated a quantized thickening process of a crystal monolayer of PEO with M n ¼ 5 000 g Á mol À1 on the surface of a silicon wafer when the samples were heated from room temperature to an annealing temperature.…”

Section: Full Papermentioning

confidence: 99%

Thickening Processes of Lamellar Crystal Monolayers of a Low‐Molecular‐Weight PEO Fraction on a Solid Surface

Zhai

Gou-liang

et al. 2007

Macro Chemistry & Physics

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Using hot‐stage atomic force microscopy, the thickening processes of monolayer crystals of PEO ($\overline M _{\rm n} $ = 5 000 g · mol−1 and $\overline M _{\rm w} /\overline M _{\rm n} $ = 1.008) from one‐folded (FC1) to extended‐chain (EC) lamellae are experimentally monitored at three temperatures: 50, 52, and 58 °C. At 50 °C some small areas in large FC1 crystals spontaneously thicken into EC crystals. At 52 °C the spontaneously thickened area further expands so as to inductively thicken the entire FC1 lamella into EC lamella. At 58 °C EC crystals first force the adjacent FC1 crystals to melt and then absorb the melted molecules to grow laterally into large EC lamellae till all FC1 lamellae vanish. The three thickening steps express the main thickening process of lamellar crystals from a metastable state to another metastable (or equilibrium) state. The possible mechanisms are discussed in the text.magnified image

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“…Formula (20) may be treated as a combination of the Gauss and KWW (Kolhrausch-Williams-Watt) functions. At b ¼ 1, expression (20) is transformed into Eq. (19).…”

Section: Constitutive Equationsmentioning

confidence: 99%

“…(19). Equation (20) was proposed in [40] for the distribution of potential energies of flow units in glasses.…”

Section: Constitutive Equationsmentioning

confidence: 99%

“…Although the time-dependent linear and nonlinear response of polyethylene has been investigated in a number of publications, the effect of temperature on the mechanical properties of LLDPE has not yet been studied in detail. In particular, we are interested in the analysis of the a-relaxation phenomenon, which is conventionally observed in dynamic mechanical and dielectric tests as a pronounced peak on (or change in the slope of) the graph of the loss tangent plotted versus temperature, [15]- [20].…”

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confidence: 99%

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The effect of temperature on the viscoelastic behavior of linear low-density polyethylene

Drozdov

Agarwal

Gupta

2004

Archive of Applied Mechanics (Ingenieur Archiv)

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Observations are reported on linear low-density polyethylene in isothermal torsional oscillation and relaxation tests at various temperatures ranging from room temperature to 110 C. Constitutive equations are derived for the viscoelastic response of a semicrystalline polymer at small strains. The polymer is treated as an equivalent network of strands bridged by junctions (entanglements, physical cross-links on the surfaces of crystallites and lamellar blocks). The network is thought of as an ensemble of meso-regions with various potential energies for rearrangement of strands. Two types of meso-domains are introduced: active, where strands separate from temporary junctions as they are excited by thermal fluctuations, and passive, where detachment of strands is prevented by the surrounding macromolecules. The time-dependent behavior of the ensemble reflects separation of active strands from their junctions and merging of dangling strands with the network. Stress-strain relations are developed by using the laws of thermodynamics. The governing equations involve six material constants that are found by fitting the experimental data. The study focuses on the effects of (i) temperature, (ii) the deformation mode (torsion versus bending), and (iii) the loading program (oscillations versus relaxation) on the adjustable parameters. IntroductionThis paper is concerned with the effect of temperature on the viscoelastic behavior of injectionmolded linear low-density polyethylene (LLDPE) at isothermal deformations with small strains. The choice of this polymer for the investigation is explained by its numerous industrial applications: films for packaging, thin-wall molded components, pipes, irrigation and spray tubes, hoses, geomembranes, etc.Polyethylene is a semicrystalline polymer that contains three different crystallographic forms: monoclinic, hexagonal and orthorhombic. In injection-molded specimens, orthorhombic structures are mainly formed, whereas monoclinic and hexagonal crystallites are produced by polymerization under high pressure (over 400 MPa) and at high temperature, [1].LLDPE is a random copolymer prepared by polymerization of ethylene in the presence of 1-alkenes. The average distance between short branches along the main chain is about 7 nm, [2]. This value coincides with the average segment length found in [3] for metallocene-catalyzed LLDPE. The histograms reported in [3] reveal a wide distribution of segment lengths, with a relatively high probability of segments ranging up to 30 nm, which results in a wide distribution of lamellar thicknesses in LLDPE. The average radius of crystallites is strongly affected by the content of short-chain branches, and it changes from 2.5 to 12 lm depending on the crystallization conditions, [4]. The average lamellar thickness ranges from 8.5 to 10 nm, [4].

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Overlapping of different rearrangement mechanisms upon annealing for solution-crystallized polyethylene

Cited by 45 publications

References 20 publications

The effect of temperature on the viscoelastic response of semicrystalline polymers

The effect of temperature on the viscoelastic response of semicrystalline polymers

Thickening Processes of Lamellar Crystal Monolayers of a Low‐Molecular‐Weight PEO Fraction on a Solid Surface

The effect of temperature on the viscoelastic behavior of linear low-density polyethylene

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