Crystallization of poly(ethylene-co-octene): II Melt memory effects on first order kinetics

Häfele, A.; Heck, Barbara; Hippler, Thomas; Kawai, Tadakazu; Kohn, Peter; Strobl, G.

doi:10.1140/epje/e2005-00023-0

Cited by 46 publications

(61 citation statements)

References 8 publications

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“…81,82 Low magnification AFM images showed the formation of large-scale structures on a length scale of several micrometers. These large-scale structures were then claimed to transform into the final state by a filling of their interior with crystals.…”

Section: Resultsmentioning

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: Resultsmentioning

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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“…5 The same feature has been observed in other polymers as well. 17 In another set of experiments, Strobl and collaborators 13 have shown that the shapes of isotherms and characteristic crystallization times depend on the temperature of the melt T m prior to cooling to the crystallization temperature T c . They have identified two bounds of the melt temperature, one upper (T and T ℓ m , a crossover kinetics between the above mentioned two universal kinetics is observed with the nucleation time progressively decreasing with lowering of the melt temperature.…”

Section: Introductionmentioning

confidence: 98%

“…[6][7][8][9][10][11]15,16 However, there have been several investigations where any possible memory from such remnant crystalline domains is deliberately wiped out, but still observing melt-memory effects during second crystallization. 5,[12][13][14][17][18][19][20][21] As a classic example, Schultz observed that the maximum crystallization rate of linear polyethylene can be significantly lower if the sample was prepared at higher melt temperatures. 5 The same feature has been observed in other polymers as well.…”

Section: Introductionmentioning

confidence: 99%

“…As plausible explanation of this effect, existence of a precursor state, local clustering of chain segments in the molten state, and entanglement effects have been suggested in the literature. 13,17,19 Sometimes a distinction is made between two kinds of memory effects. 21 If the melt temperature is lower than the equilibrium melting temperature, some remnant crystalline domains could linger around and become responsible for melt-memory.…”

Section: Introductionmentioning

confidence: 99%

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Communication: Theory of melt-memory in polymer crystallization

Muthukumar

2016

The Journal of Chemical Physics

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Details of crystallization processes of a polymer at the crystallization temperature T c from its melt kept initially at the melt temperature T m depend profoundly on the nature of the initial melt state and often are accompanied by memory effects. This phenomenon is in contrast to small molecular systems where the supercooling (T 0 m − T c ), with T 0 m being the equilibrium melting temperature, and not (T m − T c ), determines the nature of crystallization. In addressing this five-decade old puzzle of melt-memory in polymer crystallization, we present a theory to describe melt-memory effects, by invoking an intermediate inhomogeneous melt state in the pathway between the melt and crystalline states. Using newly introduced dissolution temperature T

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“…The ''melt memory effect'' has been well known in polymer crystallization. 1,[59][60][61][62][63] Under flow, there are substantial evidences of the formation of long-lived metastable oriented structures, even at temperatures above the normal melting point of the polymer (T mp ). 44,52,[64][65][66][67][68][69][70][71][72][73] The first direct experimental evidence was obtained from rheoRaman 66 studies of polyethylene (PE) melt at 140 8C, a temperature significantly above its melting point.…”

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confidence: 99%

Thermal stability of shear‐induced precursor structures in isotactic polypropylene by rheo‐X‐ray techniques with couette flow geometry

Somani

Šics

Hsiao

2006

J Polym Sci B Polym Phys

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Combined in situ rheo-SAXS (small-angle X-ray scattering) and -WAXD (wide-angle X-ray diffraction) studies using couette flow geometry were carried out to probe thermal stabilty of shear-induced oriented precursor structure in isotactic polypropylene (iPP) at around its normal melting point (162 8C). Although SAXS results corroborated the emerging consensus about the formation of ''long-living'' metastable mesomorphic precursor structures in sheared iPP melts, these are the first quantitative measures of the limiting temperature at which no oriented structures survive. At the applied shear, rate ¼ 60 s À1 and duration t s ¼ 5 s, the oriented iPP structures survived a temperature of 185 8C for 1 h after shear, while no stable structures were detected at and above 195 8C. Following Keller's concepts of chain orientation in flow, it is proposed that the chains with highly oriented high molecular weight fraction are primarily responsible for their stability at high temperatures. Furthermore, the effects of flow condition, specifically the shear temperature, on the distributions of oriented and unoriented crystals were determined from rheo-WAXD results. As expected, at a constant flow intensity (i.e., rate ¼ 30 s À1 and duration, t s ¼ 5 s), the oriented crystal fraction decreased with the increase in temperature above 155 8C, below which the oriented fraction decreased with the decrease in temperature. As a result, a crystallinty ''phase'' diagram, i.e., temperature versus crystal fraction ratio, exhibited a peculiar ''hourglass'' shape, similar to that found in many two-phase polymer-polymer blends. This can be explained by the competition between the oriented and unoriented crystals in the available crystallizable species. Below the shear temperature (155 8C), the unoriented crystals crystallized so rapidly that they overwhelmed the crystallization of the oriented crystals, thus depleting a major portion of the crystallizable species and increasing their contribution in the final total crystalline phase.

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Crystallization of poly(ethylene-co-octene): II Melt memory effects on first order kinetics

Cited by 46 publications

References 8 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

Communication: Theory of melt-memory in polymer crystallization

Thermal stability of shear‐induced precursor structures in isotactic polypropylene by rheo‐X‐ray techniques with couette flow geometry

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