Effect of crystallinity on the viscosity of an isotactic polypropylene

Pantani, Roberto; Meo, Annarita De; Speranza, Vito; Titomanlio, G.

doi:10.1063/1.4937343

Cited by 3 publications

(3 citation statements)

References 12 publications

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“…To consider the interplay between nucleation and flow dynamics, several simple methods have been developed, which is based on either an empirical volume-fraction-dependent viscosity multiplier [229][230][231], or a suspension model [232,233].…”

Section: Andreev and Rutledge's Modelmentioning

confidence: 99%

Polymer crystallization under external flow

Sheng¹,

Chen²,

Cui³

et al. 2022

Rep. Prog. Phys.

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The general aspects of polymer crystallization under external flow, i.e., flow-induced crystallization (FIC) from fundamental theoretical background to multi-scale characterization and modeling results are presented. FIC is crucial for modern polymer processing, such as blowing, casting, and injection modeling, as two-third of daily-used polymers is crystalline, and nearly all of them need to be processed before final applications. For academics, the FIC is intrinsically far from equilibrium, where the polymer crystallization behavior is different from that in quiescent conditions. The continuous investigation of crystallization contributes to a better understanding on the general non-equilibrium ordering in condensed physics. In the current review, the general theories related to polymer nucleation under flow (FIN) were summarized first as a preliminary knowledge. Various theories and models, i.e., coil-stretch transition and entropy reduction model, are briefly presented together with the modified versions. Subsequently, the multi-step ordering process of FIC is discussed in detail, including chain extension, conformational ordering, density fluctuation, and final perfection of the polymer crystalline. These achievements for a thorough understanding of the fundamental basis of FIC benefit from the development of various hyphenated rheometer, i.e., rheo-optical spectroscopy, rheo-IR, and rheo-X-ray scattering. The selected experimental results are introduced to present efforts on elucidating the multi-step and hierarchical structure transition during FIC. Then, the multi-scale modeling methods are summarized, including micro/meso scale simulation and macroscopic continuum modeling. At last, we briefly describe our personal opinions related to the future directions of this field, aiming to ultimately establish the unified theory of FIC and promote building of the more applicable models in the polymer processing.

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Section: Andreev and Rutledge's Modelmentioning

confidence: 99%

Polymer crystallization under external flow

Sheng¹,

Chen²,

Cui³

et al. 2022

Rep. Prog. Phys.

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“…The following are available online at https://www.mdpi.com/article/10 .3390/polym13193236/s1, References [27][28][29] are cited in the supplementary materials.…”

Section: Supplementary Materialsmentioning

confidence: 99%

“…The following are available online at , References [ 27 , 28 , 29 ] are cited in the supplementary materials.…”

mentioning

confidence: 99%

Multi-Scale Simulation of Injection Molding Process with Micro–Features Replication: Relevance of Rheological Behaviour and Crystallization

et al. 2021

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The possibility of tailoring key surface properties through the injection molding process makes it intriguing from the perspective of sustainability enhancement. The surface properties depend on the replication accuracy of micro and nanostructures on moldings; such an accuracy is enhanced with cavity temperature. The simulation of the injection molding process is very challenging in the presence of micro and nanostructures on the cavity surface; this does not allow for the neglect of phenomena generally considered not to influence the overall process. In this paper, a multiscale approach was proposed: in the first step, the simulation of the overall process was conducted without considering the presence of the microstructure; in the second step the outputs of the first step were used as an input to simulate the replication of the microfeature. To this purpose, a lubrication approximation was adopted, and the contribution of the trapped air, which slows down the polymer advancement, was accounted for. A modification of the viscosity equation was also proposed to describe the rheological behavior of isotactic polypropylene at very low temperatures. Concerning the microcavity filling simulation, the modification of the viscosity description at low temperatures consistently describes the process, in terms of polymer solidification. Concerning the replication accuracy, it increases with the cavity surface temperature, consistently with the experimental observations.

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A Criterion for the Formation of Fibrillar Layers in Injection Molded Parts

Pantani

Speranza

Titomanlio

2018

International Polymer Processing

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It is quite well known that the morphology of an injection molded part made by a semicrystalline polymer presents several layers. In particular spherulitic structures are found in the core region, a layer characterized by highly oriented fibrillar morphology (the shear layer) usually follows and a skin layer is often observed at the sample surface. The thickness of the fibrillar layer deeply influences the mechanical properties of the part. In this work, a criterion to predict the thickness of the fibrillar layer is proposed and verified. The criterion is essentially based on the amount of viscous work done when the molecular stretch is higher than a critical value: the molecular stretch should be above a critical value while a critical amount of viscous work is accumulated. In order to tune the parameters, and to validate the criterion, a well characterized polypropylene was chosen as test material, and four different injection molding conditions were analyzed. The criterion is verified by comparing some experimental results with the prediction of the UNISA code (an injection molding software developed at the University of Salerno), good comparison between software predictions and experimental data confirms the suitability of the criterion.

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Effect of crystallinity on the viscosity of an isotactic polypropylene

Cited by 3 publications

References 12 publications

Polymer crystallization under external flow

Polymer crystallization under external flow

Multi-Scale Simulation of Injection Molding Process with Micro–Features Replication: Relevance of Rheological Behaviour and Crystallization

A Criterion for the Formation of Fibrillar Layers in Injection Molded Parts

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