Crystal thickness distributions from melting homopolymers or random copolymers

Crist, Buckley; Mirabella, Francis M.

doi:10.1002/(sici)1099-0488(19991101)37:21<3131::aid-polb22>3.0.co;2-m

Cited by 81 publications

(81 citation statements)

References 23 publications

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“…A comparison of the crystal thickening of these two polymers is shown in Figure 3. The crystal (lamella) thickness distribution of the copolymer in Figure 2, calculated from G-T theory, 63 is shown in Figure 4. Note that the overall range of crystal thickness in Figure 4 is only about 1-1.5 nm.…”

Section: Resultsmentioning

confidence: 99%

“…To make a specific comparison between these results and the expected melting behavior of an assumed, bimodal crystal thickness distribution, the crystal thickness distribution for the poly(ethylene-1-octene) [5.2 mol % 1-octene] was calculated by a method based on G-T theory. 63 These calculations were done using the DSC data shown in Figure 9. The lamella thickness distribution (not shown) was used to construct a plot of lamella thickness versus temperature and is shown in Figure 9 as unfilled squares.…”

Section: Resultsmentioning

confidence: 99%

“…59 The dimension calculated from DSC data, using G-T theory, is a volume average, since it is based on an increment of crystal thickness with respect to an increment of mass that melts (assuming equal density of all crystals). 63 There is no clear relationship between the two types of averages. Another critical problem that may complicate the interpretation of the SAXS data is that, depending on the type of melting which occurs, the SAXS pattern may not change as expected.…”

Section: Resultsmentioning

confidence: 99%

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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%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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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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“…Enthalpy of fusion was used to calculate the percent crystallinity using fusion enthalpy for a 100 % crystalline PE of 290 J/g [18]. Lamella thickness was calculated using the Gibbs-Thomson equation [19,20]:…”

Section: Materials Characterizationmentioning

confidence: 99%

Molecular and morphological studies to understand slow crack growth (SCG) of polyethylene

Fawaz¹,

Deveci²,

Mittal³

2016

Colloid Polym Sci

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Slow crack growth (SCG) is a time-dependent brittle-type failure that polyethylene (PE) pipes suffer from when under low stress levels. This study discusses the relation of morphological, molecular weight and molecular weight distribution, rheological, thermal and tensile properties of different PE materials with SCG behavior obtained from the crack round bar (CRB) test, strain hardening (SH) test, and notched pipe (NPT) test. It was observed that increasing the molecular weight and its distribution, short-chain branches, co-monomer content and length, as well as lateral lamellar area increased the SCG resistance and the subsequent time to failure. This was attributed to the enhanced interlamellar entanglement and tie molecules that resisted deformation for a longer time. In addition, SCG resistance was found to decrease with decreasing lamella thickness and degree of crystallinity (within similar molecular weight range). A decrease in the SCG resistance was observed on increasing the onset degradation temperature. Despite the lack of correlation established from tensile tests in the elastic region, SH and CRB values were found to be directly related. As strain hardening modulus increased, time to failure also increased. Zero-shear viscosities also reflected the SCG resistance properties of the samples, as CRB values increased with increasing zero-shear viscosity.

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“…It should be noticed, however, that the use of the Thomson-Gibbs equation to estimate lamellar thickness from DSC data has been the subject of controversy in the literature, especially for ethylene/a-olefin copolymers. [16][17][18] Cho et al have recently expressed the Thomson-Gibbs equation as: [19] l…”

Section: Limitations To the Quantitative Determination Of Lamellar Simentioning

confidence: 99%

High Speed SSA Thermal Fractionation and Limitations to the Determination of Lamellar Sizes and Their Distributions

Lorenzo

Arnal

Müller

et al. 2005

Macro Chemistry & Physics

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Summary: The technique of successive self‐nucleation and annealing (SSA) has been applied using differential scanning calorimetry (DSC) to a model hydrogenated polybutadiene prepared by anionic polymerization and to a commercial Ziegler‐Natta ethylene/1‐butene copolymer. Here, it is shown that the use of high scanning rates (50 °C · min−1) in the SSA protocol can reduce the thermal fractionation time to only 78 min in length (if 6 fractions are produced with a fractionation window of 5 °C), taking into consideration the need to compensate the increment in heating rates by reducing the sample mass. This time is much shorter than those previously achieved by thermal fractionation in the literature, where fractionation times of 12 or 24 h are common. Potentially, much higher rates could be employed by further reducing the fractionation times by SSA. For the first time, a distribution of lamellar thicknesses has been obtained by transmission electron microscopy after SSA fractionation and compared to distributions calculated by the Thomson‐Gibbs equation. It is shown that the results are highly dependent on the equilibrium melting temperatures employed in the calculations, and it is recommended that the values of lamellar thicknesses obtained are checked by comparing with methylene sequence lengths derived from calibration measurements available in the literature. The Thomson‐Gibbs equation is useful for comparing lamellar thickness distributions obtained by SSA with different polymers only on a semi‐quantitative basis.

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Crystal thickness distributions from melting homopolymers or random copolymers

Cited by 81 publications

References 23 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

Molecular and morphological studies to understand slow crack growth (SCG) of polyethylene

High Speed SSA Thermal Fractionation and Limitations to the Determination of Lamellar Sizes and Their Distributions

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