The prediction of mechanical performance of isotactic polypropylene on the basis of processing conditions

Caelers, Hjm Harm; Govaert, Leon Le; Peters, Gwm Gerrit

doi:10.1016/j.polymer.2015.12.001

Cited by 37 publications

(41 citation statements)

References 63 publications

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“…This illustrates the before mentioned difficulties. For a given crystal phase, the yield stress is correlated to the lamellar thickness; an increase of about 2 nm in the lamellar thickness of α ‐IPP yields an increase of approximately 8 MPa in the yield stress . This gives rise to the presumption that an additional feature like the crystal unit cell structure or the accompanying amount of imperfections affects the level of the yield stress as well.…”

Section: Resultsmentioning

confidence: 99%

Deformation and failure kinetics of iPP polymorphs

Caelers

Parodi

Cavallo

et al. 2017

J. Polym. Sci. Part B: Polym. Phys.

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In this study, the mechanical performance of the different polymorphs of isotactic polypropylene, typically present in iPP crystallized under industrial processing conditions, is assessed. Different preparation strategies were used to obtain samples consisting of almost solely a, b, or c crystals. X-Ray measurements were used to validate that the desired phase was obtained. The intrinsic true stress -true strain response of all individual phases was measured in uniaxial compression at several strain rates (deformation kinetics). Moreover, measurements were performed over a wide temperature range, covering the window in between the glass transition and the melting temperature. The relation between obtained yield stress and the strain rate is described with a modification of the Ree-Eyring model. Differences and similarities in the deformation kinetics of the different phases are presented and discussed. Furthermore, the presence of three deformation processes, acting in parallel, is revealed. The ReeEyring equation enables lifetime prediction for given thermal and mechanical conditions. These predictions were experimentally validated using constant load tests in uniaxial compression.

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Section: Resultsmentioning

confidence: 99%

Deformation and failure kinetics of iPP polymorphs

Caelers

Parodi

Cavallo

et al. 2017

J. Polym. Sci. Part B: Polym. Phys.

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“…The measured scattering intensity could be transposed into the 1D scattering intensity using Lorentz correction. If the electron density differences in one direction are known, the average lamellar thickness l c could be obtained from [40]:…”

Section: Saxs and Waxsmentioning

confidence: 99%

Effect of Rapid Mold Heating on the Structure and Performance of Injection-Molded Polypropylene

et al. 2020

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The tailoring by the process of the properties developed in the plastic objects is the more effective way to improve the sustainability of the plastic objects. The possibility to tailor to the final use the properties developed within the molded object requires further understanding of the relationship between the properties of the plastic objects and the process conduction. One of the main process parameters that allow adjusting the properties of molded objects is the mold temperature. In this work, a thin electrical heater was located below the cavity surface in order to obtain rapid and localized surface heating/cooling cycles during the injection molding process. An isotactic polypropylene was adopted for the molding tests, during which surface temperature was modulated in terms of values and heating times. The modulation of the cavity temperature was found able to control the distribution of relevant morphological characteristics, thus, properties along the sample thickness. In particular, lamellar thickness, crystallinity distribution, and orientation were analyzed by synchrotron X-ray experiments, and the morphology and elastic modulus were characterized by atomic force microscopy acquisitions carried out with a tool for the simultaneous nanomechanical characterization. The crystalline degree slightly increased with the cavity temperature, and this induced an increase in the elastic modulus when high temperatures were adopted for the cavity surface. The cavity temperature strongly influenced the orientation distribution that, on its turn, determined the highest values of the elastic modulus found in the shear layer. Furthermore, although the sample core, not experiencing a strong flow field, was not characterized by high levels of orientation, it might show high values of the elastic modulus if temperature and time during crystallization were sufficient. In particular, if the macromolecules spent adequate time at temperatures close to the crystallization temperature, they could achieve high levels of structuring and, thus, high values of elastic modulus.

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“…This model implies that the reciprocal crystalline lamellar thickness

d_{c}^{- 1}

is governed by supercooling below the equilibrium melting point

T_{f}^{\infty}

that deduced from Gibbs‐Thomsom equation . Although it had been accepted by the main stream of polymer physics society, this model was not able to give excellent explanations of recent experimental findings based on time‐ and temperature‐dependent small angle X‐ray scattering (SAXS) measurements during polymer crystallization and melting . It was always observed that the crystallization temperature T c and the melting temperature T m of polymers were linearly dependent on the reciprocal crystalline layer thickness

d_{c}^{- 1}

separately, which exhibited different slopes and different limiting temperatures at

d_{c}^{- 1}

= 0.…”

Section: Introductionmentioning

confidence: 96%

Crystallization and melting of isotactic polypropylene crystallized from quiescent melt and stress‐induced localized melt

Wang

Chen

et al. 2017

J Polym Sci B Polym Phys

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Temperature dependency of crystalline lamellar thickness during crystallization and subsequent melting in isotactic polypropylene crystallized from both quiescent molten state and stress-induced localized melt was investigated using small angle X-ray scattering technique. Both cases yield well-defined crystallization lines where inverse lamellar thickness is linearly dependent on crystallization temperature with the stretching-induced crystallization line shifted slightly to smaller thickness direction than the isothermal crystallization one indicating both crystallization processes being mediated a mesomorphic phase. However, crystallites obtained via different routes (quiescent melt or stress-induced localized melt) show different melting behaviors. The one from isothermal crystallization melted directly without significant changing in lamellar thickness yielding well-defined melting line whereas stress-induced crystallites followed a recrystallization line. Such results can be associated with the different extent of stabilization of crystallites obtained through different crystallization routes.

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The prediction of mechanical performance of isotactic polypropylene on the basis of processing conditions

Cited by 37 publications

References 63 publications

Deformation and failure kinetics of iPP polymorphs

Deformation and failure kinetics of iPP polymorphs

Effect of Rapid Mold Heating on the Structure and Performance of Injection-Molded Polypropylene

Crystallization and melting of isotactic polypropylene crystallized from quiescent melt and stress‐induced localized melt

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