Evaluation of the sample temperature increase during the quiescent and shear-induced isothermal crystallization of polyethylene

Martins, José A.; Zhang, W.; Carvalho, Vı́tor; Brito, A. M.; Soares, Filomena

doi:10.1016/j.polymer.2003.09.064

Cited by 6 publications

(5 citation statements)

References 16 publications

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“…18 These three well understood mechanisms provide good predictions to most experimental measurements. However, experiments with large Avrami exponents ͑m Ͼ 3͒, which cannot be explained by these three mechanisms, are also occasionally reported, 8,9,24,29 thus it is necessary to propose a larger value ͑Ͼ2/3͒. Figure 10 presents the fit of distribution model with = 1 to the experimental measurements 9 having a large Avrami exponent at three different temperatures.…”

Section: Resultsmentioning

confidence: 99%

Temperature effects for isothermal polymer crystallization kinetics

Yang

McCoy

Madras

2005

The Journal of Chemical Physics

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We adopt the cluster size distribution model to investigate the effect of temperature on homogeneous nucleation and crystal growth for isothermal polymer crystallization. The model includes the temperature effects of interfacial energy, nucleation rate, growth and dissociation rate coefficients, and equilibrium solubility. The time dependencies of polymer concentration, number and size of crystals, and crystallinity (in Avrami plots) are presented for different temperatures. The denucleation (Ostwald ripening effect) is also investigated by comparing moment and numerical solutions of the population balance equations. Agreement between the model results and temperature-sensitive experimental measurements for different polymer systems required strong temperature dependence for the crystal-melt interfacial energy.

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Section: Resultsmentioning

confidence: 99%

Temperature effects for isothermal polymer crystallization kinetics

Yang

McCoy

Madras

2005

The Journal of Chemical Physics

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“…A Physica MCR 300 rheometer (Paar Physica), with parallel plate (25 mm diameter) and cone-and-plate (25 mm plate diameter and 2° cone angle) configurations, was used to perform the shear stress-growth, oscillatory, and steady-shear experiments. The average true sample temperature was evaluated from the nominal temperature of the experiments following a temperature calibration procedure described previously . This temperature was recorded with an accuracy of ±1 °C, and the gap size was 0.7 mm for all experiments.…”

Section: Methodsmentioning

confidence: 99%

“…The average true sample temperature was evaluated from the nominal temperature of the experiments following a temperature calibration procedure described previously. 16 This temperature was recorded with an accuracy of (1 °C, and the gap size was 0.7 mm for all experiments. For each rheometeric experiment a new sample was used, and the experimental conditions were controlled to ensure data reliability.…”

Section: Methodsmentioning

confidence: 99%

Saturation of Shear-Induced Isothermal Crystallization of Polymers at the Steady State and the Entanglement−Disentanglement Transition

2006

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To provide insight into the formation of shear-induced precursor structures, three apparently unrelated subjects are analyzed and discussed: the saturation of crystallization from sheared polymer melts, evaluated with a new shear DTA instrument, the steady state in steady shear, and the entanglement−disentanglement transition. It is shown that the same large strains that saturate crystallization also lead to a reversible steady state in steady shear, where the viscosity of the sheared melt is constant in time, and their magnitude is only determined by the temperature of the sheared melt. Features of the melt morphology at this state are discussed, and their importance is highlighted to understand the possible mechanisms behind the formation of shear-induced precursors. Measurements of the reptation time for unsheared samples, and samples sheared up to the steady state, allowed the quantification of the entanglements loss during the transition between these two states (around 2/3), which is interpreted as an entanglement−disentanglement transition. The relevance of this result on assumptions of flow models, particularly the constant number of topological constraints, convective constraint release process, and chain stretch, is discussed.

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“…3 Errors resulting from calibration effects, the sample thermal resistance, and heat released during isothermal, nonisothermal, and shear-induced crystallizations were also considered. 4,5 The starting equation of ref 1 is the free-growth overall volume fraction transformed to the solid (crystalline) phase…”

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confidence: 99%

“…Before discussing this work, it must be mentioned that a procedure for dealing with this issue was published by the present author in 2002 for isothermal DSC experiments and in 2003 for nonisothermal experiments, including the application to real processing conditions in the absence of flow . Errors resulting from calibration effects, the sample thermal resistance, and heat released during isothermal, nonisothermal, and shear-induced crystallizations were also considered. , …”

mentioning

confidence: 99%

Comment on “Determination of Nucleus Density in Semicrystalline Polymers from Nonisothermal Crystallization Curves”

Martins

2015

Macromolecules

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Evaluation of the sample temperature increase during the quiescent and shear-induced isothermal crystallization of polyethylene

Cited by 6 publications

References 16 publications

Temperature effects for isothermal polymer crystallization kinetics

Temperature effects for isothermal polymer crystallization kinetics

Saturation of Shear-Induced Isothermal Crystallization of Polymers at the Steady State and the Entanglement−Disentanglement Transition

Comment on “Determination of Nucleus Density in Semicrystalline Polymers from Nonisothermal Crystallization Curves”

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