Some aspects of nonisothermal crystallization of polymers. I. Relationship between crystallization temperature, crystallinity, and cooling conditions

Nakamura, Katsuyuki; Watanabe, T.; Katayama, Ken‐ichi; Amano, Toshihiko

doi:10.1002/app.1972.070160503

Cited by 409 publications

(183 citation statements)

References 10 publications

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“…The overall crystallization kinetics theories describe the evolution of the relative degree of crystallization (t) as a function of time t and temperature T. For this simulation the differential form of the model developed by Nakamura et al [13] for a temperature dependent crystallization rate was considered:…”

Section: Crystallization Kinetics Theorymentioning

confidence: 99%

Simulation of warpage induced by non-isothermal crystallization of co-polypropylene during the SLS process

Amado

Schmid

Wegener

2015

AIP Conference Proceedings

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Abstract. Polymer processing using Additive Manufacturing Technologies (AM) has experienced a remarkable growth during the last years. The application range has been expanding rapidly, particularly driven by the so-called consumer 3D printing sector. However, for applications demanding higher requirements in terms of thermo-mechanical properties and dimensional accuracy the long established AM technologies such as Selective Laser Sintering (SLS) do not depict a comparable development. The higher process complexity hinders the number of materials that can be currently processed and the interactions between the different physics involved have not been fully investigated. In case of thermoplastic materials the crystallization kinetics coupled to the shrinkage strain development strongly influences the stability of the process. Thus, the current investigation presents a transient Finite Element simulation of the warpage effect during the SLS process of a new developed polyolefin (co-polypropylene) coupling the thermal, mechanical and phase change equations that control the process. A thermal characterization of the material was performed by means of DSC, integrating the Nakamura model with the classical Hoffmann-Lauritzen theory. The viscoelastic behavior was measured using a plate-plate rheometer at different degrees of undercooling and a phase change-temperature superposition principle was implemented. Additionally, for validation porpoises the warpage development of the first sintered layers was captured employing an optical device. The simulation results depict a good agreement with experimental measurements of deformation, describing the high sensitivity of the geometrical accuracy of the sintered parts related to the processing conditions.

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Section: Crystallization Kinetics Theorymentioning

confidence: 99%

Simulation of warpage induced by non-isothermal crystallization of co-polypropylene during the SLS process

Amado

Schmid

Wegener

2015

AIP Conference Proceedings

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“…The simplest model is a parallel of two kinetic processes noninteracting and competing for the available molten material. The kinetic equation adopted here for both processes is the nonisothermal formulation by Nakamura et al 9,10 of the KolmogoroffAvrami-Evans model. [27][28][29][30] The model is based on the following equation:…”

Section: Theory: Crystallization Kinetics Modelmentioning

confidence: 99%

“…7,8 Several attempts have been made to describe nonisothermal crystallization kinetics with simplifying assumptions [9][10][11][12][13] and procedures have also been developed to determine the relevant rate parameters with no concern on the experimental conditions encountered during processing where drastic solidification conditions are determined by large pressures, stresses, and temperature gradients. 9,10 As a matter of fact, the data obtained from traditional techniques, such as calorimetric cooling ramps, are restricted to few degrees Celsius per second. Such cooling rates are orders of magnitude lower than those experienced by the material during polymer processing.…”

Section: Introductionmentioning

confidence: 99%

Crystallization kinetics of iPP: Influence of operating conditions and molecular parameters

Carrubba

Piccarolo

Brucato

2007

J of Applied Polymer Sci

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An analysis of the crystallization kinetics of different grades of isotactic polypropylene (iPP) is here presented. To describe the crystallization kinetics as a function of molecular and operating parameters, the methodological path followed was the preparation of quenched samples of known cooling histories, calorimetric crystallization isotherms tests, differential scanning calorimetry cooling ramps, wide angle X-ray diffraction (WAXD) measurements, and density determination. The WAXD analysis performed on the quenched iPP samples confirmed that during the fast cooling at least a crystalline structure and a mesomorphic one form. The diffractograms were analyzed by a deconvolution procedure, to identify the relationship between the cooling history and the distribution of the crystalline phases. The whole body of results (including calorimetric ones) provides a wide basis for the identification of a crystallization model suitable to describe solidification in polymer-processing operations, based on the KolmogoroffAvrami-Evans nonisothermal approach. The kinetic parameters, determined for all the materials, are discussed, highlighting the effect of molecular parameters on the crystallization kinetics: molecular mass and distribution, tacticity, nucleating agents, and ethylene units content.

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“…For the polyethylenes the first detailed study of the non-isothermal crystallization was conducted in the 70s by Nakamura et al 9,10 . In the 80's the nonisothermal crystallization of PE as a function of molecular mass was also investigated by Minkova and Mihailov 11 , who studied the kinetics of crystallization of ultra-high molecular mass polyethylene (UHMWPE), high density polyethylene with usual mass (HDPE), and their blends.In the same decade, Eder and Wlochowicz 12 crystallized HDPE at constant cooling rates ranging from 0.5 to 10 °C min -1 .…”

mentioning

confidence: 99%

“…The majority of methods for describing the crystallization kinetics are based on the Avrami equation 17, 18 or its modified forms 9,10,13,19,20 . Ozawa 13 accounted for the effect of cooling rate on dynamic crystallization by properly modifying the Avrami equation to include the constant cooling rate.…”

mentioning

confidence: 99%

Avrami Model Deviations in Polyolefins as Function of the Complexity of the Molecular Structures.

Blanco¹,

Cisneros²,

Belmonte³

et al. 2017

IJAR

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The influence of the complexity of the molecular structure and the cooling rate in the Avrami model fitting has been studied. Kinetics of non-isothermal crystallization of polypropylenes (with different molecular weights), polyethylenes (High Density Polyethylene, HDPE and Low Density Polyethylene, LDPE) and polyethylene wax from molten state were performed under non-isothermal conditions at cooling rates of 3, 10, and 50 °C min -1 . Differential scanning calorimetry (DSC) was used to monitor the crystallization. The results showed that the predicted evolution of relative crystallinity using the Avrami model was a better fit for the polypropylenes and polyethylene waxen than for the polyethylenes due to their molecular structure much more simple and regular. The fitting for higher cooling rates was better than for lower cooling rates for all the materials analyzed and this could be attributable to a predominant homogeneous nucleation at higher cooling rates and predominant heterogeneous nucleation at lower cooling rates. The fitting for HDPE was better than for LDPE at the final stage of crystallization for various cooling rates due to the phenomenon of a slower secondary crystallization. The results showed a better fitting of the Avrami equation for the polypropylenes and polyethylene waxen than for the polyethylenes due to the influence of the branching degree in lamellar thickness and amorphous-layer thickness as the main contributor to secondary process.

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Some aspects of nonisothermal crystallization of polymers. I. Relationship between crystallization temperature, crystallinity, and cooling conditions

Cited by 409 publications

References 10 publications

Simulation of warpage induced by non-isothermal crystallization of co-polypropylene during the SLS process

Simulation of warpage induced by non-isothermal crystallization of co-polypropylene during the SLS process

Crystallization kinetics of iPP: Influence of operating conditions and molecular parameters

Avrami Model Deviations in Polyolefins as Function of the Complexity of the Molecular Structures.

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