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Special Issue "Polymer Processing: Modeling and Correlations Finalized to Tailoring the Plastic Part Morphology and Properties"

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: 31 January 2019

Special Issue Editors

Guest Editor
Prof. Dr. Giuseppe Titomanlio

Department of Industrial Engineering, University of Salerno, Via Giovanni Paolo II, I-84084 Fisciano, Italy
Website | E-Mail
Interests: polymer processing; flow induced crystallization and effect of crystallinity on rheology; morphology evolution during polymer processing; injection molding simulation
Guest Editor
Dr. Vito Speranza

Department of Industrial Engineering, University of Salerno, Via Giovanni Paolo II, I-84084 Fisciano, Italy
Website | E-Mail
Interests: effect of thermomechanical history on final structure of polymeric materials; analysis and numerical simulation of the injection molding process of thermoplastic materials; polymeric materials characterization; atomic force microscopy

Special Issue Information

Dear Colleagues,

The analysis of polymer processing operations is a very wide and complex subject; indeed, during polymer processing, viscoelastic fluids are forced to deform into desired geometries using non-homogeneous velocity and temperature fields down to solidification. The objective of analysis is certainly the identification of processing conditions, which, more and more, are finalized to the optimization of product final properties, which, in their turn, are determined by the final part morphology.

Depending on the operating conditions, the properties of the final part can change even more than one order of magnitude. Properties of interest are certainly the mechanical, optical, barrier properties, the permeability, biodegradability and any other property of practical relevance including the characteristics of the surfaces as its finishing and wettability, which are connected one to the other.

The aim of this Special Issue is to select progresses or reviews in the understanding/description of the phenomena involved along the chain: Processing–morphology–properties. Obviously, along this virtual chain, the modeling may be a very useful approach  and within the objective of understanding  fundamental aspects it may also be relevant to compare selected characteristics of the process and of the material with characteristics of the resulting morphology and then with the properties of the final part. This approach suggested the title: “Polymer Processing: Modeling and Correlations Finalized to Tailoring the Plastic Part Morphology and Properties”.

Prof. Dr. Giuseppe Titomanlio
Dr. Vito Speranza
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • polymer processing
  • modeling morphology evolution
  • morphology of polymeric parts in relation to their processing
  • morphology-properties relationships of polymeric parts
  • polymeric part properties

Published Papers (8 papers)

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Research

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Open AccessArticle Multi-Objective Optimizations for Microinjection Molding Process Parameters of Biodegradable Polymer Stent
Materials 2018, 11(11), 2322; https://doi.org/10.3390/ma11112322
Received: 18 October 2018 / Revised: 11 November 2018 / Accepted: 15 November 2018 / Published: 19 November 2018
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Abstract
Microinjection molding technology for degradable polymer stents has good development potential. However, there is a very complicated relationship between molding quality and process parameters of microinjection, and it is hard to determine the best combination of process parameters to optimize the molding quality
[...] Read more.
Microinjection molding technology for degradable polymer stents has good development potential. However, there is a very complicated relationship between molding quality and process parameters of microinjection, and it is hard to determine the best combination of process parameters to optimize the molding quality of polymer stent. In this study, an adaptive optimization method based on the kriging surrogate model is proposed to reduce the residual stress and warpage of stent during its injection molding. Integrating design of experiment (DOE) methods with the kriging surrogate model can approximate the functional relationship between design goals and design variables, replacing the expensive reanalysis of the stent residual stress and warpage during the optimization process. In this proposed optimization algorithm, expected improvement (EI) is used to balance local and global search. The finite element method (FEM) is used to simulate the micro-injection molding process of polymer stent. As an example, a typical polymer vascular stent ART18Z was studied, where four key process parameters are selected to be the design variables. Numerical results demonstrate that the proposed adaptive optimization method can effectively decrease the residual stress and warpage during the stent injection molding process. Full article
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Open AccessArticle Structural Formation of UHMWPE Film Tracked by Real-Time Retardation Measurements during Uniaxial/Biaxial Stretching
Materials 2018, 11(11), 2292; https://doi.org/10.3390/ma11112292
Received: 23 October 2018 / Revised: 9 November 2018 / Accepted: 10 November 2018 / Published: 15 November 2018
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Abstract
This work reports on an experimental study of the stretching of ultra-high molecular weight polyethylene (UHMWPE) film in various uniaxial/biaxial stretching modes at various temperatures and stretching speeds. We examined the stress-birefringence relationship as a stress-optical rule (SOR) under uniaxial stretching and evaluated
[...] Read more.
This work reports on an experimental study of the stretching of ultra-high molecular weight polyethylene (UHMWPE) film in various uniaxial/biaxial stretching modes at various temperatures and stretching speeds. We examined the stress-birefringence relationship as a stress-optical rule (SOR) under uniaxial stretching and evaluated the stress-optical coefficient (SOC). Wide-angle X-ray diffraction (WAXD) measurements were applied to evaluate the contribution to birefringence of the crystalline and amorphous phases and to characterize stretching modes. In simultaneous biaxial stretching, the melting temperature (Tm) proved critical to structural formation. We applied thermal analysis techniques and tensile testing to evaluate higher order structures after each stretching mode. Full article
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Open AccessArticle Chaotic Manifold Analysis of Four-Screw Extruders Based on Lagrangian Coherent Structures
Materials 2018, 11(11), 2272; https://doi.org/10.3390/ma11112272
Received: 14 October 2018 / Revised: 4 November 2018 / Accepted: 9 November 2018 / Published: 14 November 2018
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Abstract
The four-screw extruder (FSE) is a novel equipment for polymer processing. In this paper, from a new viewpoint of Lagrangian coherent structures (LCS), two-dimensional fluid transport and chaotic mixing characteristics within three kinds of novel industrial FSEs are explored based on LCS to
[...] Read more.
The four-screw extruder (FSE) is a novel equipment for polymer processing. In this paper, from a new viewpoint of Lagrangian coherent structures (LCS), two-dimensional fluid transport and chaotic mixing characteristics within three kinds of novel industrial FSEs are explored based on LCS to better understand the flow and mixing natures in the FSEs. Firstly, based on the finite-time invariant manifold theory, the finite-time Lyapunov exponent (FTLE) and LCS of FSEs are calculated by considering the different initial time. Hyperbolic LCSs from the FTLE maps are adopted to identify chaotic mixing manifolds in FSEs. Moreover, particle tracking and Poincaré sections are used to illustrate the different fluid motions in the above three isolated regions. Finally, the effects of relative rotating directions and layout of four screws on the chaotic manifolds in FESs are discussed in order to enhance local mixing performance. Furthermore, quantitative mixing measures, such as the segregation scale, logarithmic of stretching, and mean-time mixing efficiency are employed to compare the mixing efficiencies in three kinds of FSEs. The results show that the relative rotating directions and positions of four screws can change the chaotic manifolds and increase mixing performance in local poor mixing regions. FTLE and LCS analysis are helpful to better understand the chaotic mixing nature in the novel screw extruders. Full article
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Open AccessFeature PaperArticle Silk as a Natural Reinforcement: Processing and Properties of Silk/Epoxy Composite Laminates
Materials 2018, 11(11), 2135; https://doi.org/10.3390/ma11112135
Received: 3 October 2018 / Revised: 24 October 2018 / Accepted: 26 October 2018 / Published: 30 October 2018
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Abstract
With growing environmental awareness, natural fibers have recently received significant interest as reinforcement in polymer composites. Among natural fibers, silk can potentially be a natural alternative to glass fibers, as it possesses comparable specific mechanical properties. In order to investigate the processability and
[...] Read more.
With growing environmental awareness, natural fibers have recently received significant interest as reinforcement in polymer composites. Among natural fibers, silk can potentially be a natural alternative to glass fibers, as it possesses comparable specific mechanical properties. In order to investigate the processability and properties of silk reinforced composites, vacuum assisted resin transfer molding (VARTM) was used to manufacture composite laminates reinforced with woven silk preforms. Specific mechanical properties of silk/epoxy laminates were found to be anisotropic and comparable to those of glass/epoxy. Silk composites even exhibited a 23% improvement of specific flexural strength along the principal weave direction over the glass/epoxy laminate. Applying 300 kPa external pressure after resin infusion was found to improve the silk/epoxy interface, leading to a discernible increase in breaking energy and interlaminar shear strength. Moreover, the effect of fabric moisture on the laminate properties was investigated. Unlike glass mats, silk fabric was found to be prone to moisture absorption from the environment. Moisture presence in silk fabric prior to laminate fabrication yielded slower fill times and reduced mechanical properties. On average, 10% fabric moisture induced a 25% and 20% reduction in specific flexural strength and modulus, respectively. Full article
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Open AccessArticle Replication of Micro- and Nanofeatures in Injection Molding of Two PLA Grades with Rapid Surface-Temperature Modulation
Materials 2018, 11(8), 1442; https://doi.org/10.3390/ma11081442
Received: 22 July 2018 / Revised: 7 August 2018 / Accepted: 9 August 2018 / Published: 15 August 2018
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Abstract
The production by injection molding of polymeric components having micro- and nanometrical surfaces is a complex task. Generally, the accurate replication of micro- and nanometrical features on the polymeric surface during the injection-molding process is prevented by of the low mold temperature adopted
[...] Read more.
The production by injection molding of polymeric components having micro- and nanometrical surfaces is a complex task. Generally, the accurate replication of micro- and nanometrical features on the polymeric surface during the injection-molding process is prevented by of the low mold temperature adopted to reduce cooling time. In this work, we adopt a system that allows fast heating of the cavity surface during the time the melt reaches the cavity, and fast cooling after heater deactivation. A nickel insert with micro- and nanofeatures in relief is located on the cavity surface. Replication accuracy is analyzed by Atomic Force Microscopy under different injection-molding conditions. Two grades of polylactic acid with different viscosity have been adopted. The results indicate that the higher the cavity surface temperature is, the higher the replication accuracy is. The viscosity has a significant effect only in the replication of the microfeatures, whereas its effect results are negligible in the replication of nanofeatures, thus suggesting that the interfacial phenomena are more important for replication at a nanometric scale. The evolution of the crystallinity degree on the surface also results in a key factor on the replication of nanofeatures. Full article
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Open AccessArticle Preparation Nano-Structure Polytetrafluoroethylene (PTFE) Functional Film on the Cellulose Insulation Polymer and Its Effect on the Breakdown Voltage and Hydrophobicity Properties
Materials 2018, 11(5), 851; https://doi.org/10.3390/ma11050851
Received: 21 April 2018 / Revised: 14 May 2018 / Accepted: 16 May 2018 / Published: 21 May 2018
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Abstract
Cellulose insulation polymer is an important component of oil-paper insulation, which is widely used in power transformer. The weight of the cellulose insulation polymer materials is as high as tens of tons in the larger converter transformer. Excellent performance of oil-paper insulation is
[...] Read more.
Cellulose insulation polymer is an important component of oil-paper insulation, which is widely used in power transformer. The weight of the cellulose insulation polymer materials is as high as tens of tons in the larger converter transformer. Excellent performance of oil-paper insulation is very important for ensuring the safe operation of larger converter transformer. An effective way to improve the insulation and the physicochemical property of the oil impregnated insulation pressboard/paper is currently a popular research topic. In this paper, the polytetrafluoroethylene (PTFE) functional film was coated on the cellulose insulation pressboard by radio frequency (RF) magnetron sputtering to improve its breakdown voltage and the hydrophobicity properties. X-ray photoelectron spectroscopy (XPS) results show that the nano-structure PTFE functional film was successfully fabricated on the cellulose insulation pressboard surface. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) present that the nanoscale size PTFE particles were attached to the pressboard surface and it exists in the amorphous form. Atomic force microscopy (AFM) shows that the sputtered pressboard surface is still rough. The rough PTFE functional film and the reduction of the hydrophilic hydroxyl of the surface due to the shielding effect of PTFE improve the breakdown and the hydrophobicity properties of the cellulose insulation pressboard obviously. This paper provides an innovative way to improve the performance of the cellulose insulation polymer. Full article
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Open AccessArticle “Skin-Core-Skin” Structure of Polymer Crystallization Investigated by Multiscale Simulation
Materials 2018, 11(4), 610; https://doi.org/10.3390/ma11040610
Received: 16 March 2018 / Revised: 6 April 2018 / Accepted: 13 April 2018 / Published: 16 April 2018
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Abstract
“Skin-core-skin” structure is a typical crystal morphology in injection products. Previous numerical works have rarely focused on crystal evolution; rather, they have mostly been based on the prediction of temperature distribution or crystallization kinetics. The aim of this work was to achieve the
[...] Read more.
“Skin-core-skin” structure is a typical crystal morphology in injection products. Previous numerical works have rarely focused on crystal evolution; rather, they have mostly been based on the prediction of temperature distribution or crystallization kinetics. The aim of this work was to achieve the “skin-core-skin” structure and investigate the role of external flow and temperature fields on crystal morphology. Therefore, the multiscale algorithm was extended to the simulation of polymer crystallization in a pipe flow. The multiscale algorithm contains two parts: a collocated finite volume method at the macroscopic level and a morphological Monte Carlo method at the microscopic level. The SIMPLE (semi-implicit method for pressure linked equations) algorithm was used to calculate the polymeric model at the macroscopic level, while the Monte Carlo method with stochastic birth-growth process of spherulites and shish-kebabs was used at the microscopic level. Results show that our algorithm is valid to predict “skin-core-skin” structure, and the initial melt temperature and the maximum velocity of melt at the inlet mainly affects the morphology of shish-kebabs. Full article
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Review

Jump to: Research

Open AccessReview Additive Manufacturing of Metallic and Ceramic Components by the Material Extrusion of Highly-Filled Polymers: A Review and Future Perspectives
Materials 2018, 11(5), 840; https://doi.org/10.3390/ma11050840
Received: 26 April 2018 / Revised: 11 May 2018 / Accepted: 16 May 2018 / Published: 18 May 2018
Cited by 4 | PDF Full-text (7209 KB) | HTML Full-text | XML Full-text
Abstract
Additive manufacturing (AM) is the fabrication of real three-dimensional objects from metals, ceramics, or plastics by adding material, usually as layers. There are several variants of AM; among them material extrusion (ME) is one of the most versatile and widely used. In MEAM,
[...] Read more.
Additive manufacturing (AM) is the fabrication of real three-dimensional objects from metals, ceramics, or plastics by adding material, usually as layers. There are several variants of AM; among them material extrusion (ME) is one of the most versatile and widely used. In MEAM, molten or viscous materials are pushed through an orifice and are selectively deposited as strands to form stacked layers and subsequently a three-dimensional object. The commonly used materials for MEAM are thermoplastic polymers and particulate composites; however, recently innovative formulations of highly-filled polymers (HP) with metals or ceramics have also been made available. MEAM with HP is an indirect process, which uses sacrificial polymeric binders to shape metallic and ceramic components. After removing the binder, the powder particles are fused together in a conventional sintering step. In this review the different types of MEAM techniques and relevant industrial approaches for the fabrication of metallic and ceramic components are described. The composition of certain HP binder systems and powders are presented; the methods of compounding and filament making HP are explained; the stages of shaping, debinding, and sintering are discussed; and finally a comparison of the parts produced via MEAM-HP with those produced via other manufacturing techniques is presented. Full article
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

1. Authors: Giuseppe Titomamlio, Vito Speranza

2. Author: Roberto Pantani

3. Author: Cengiz Altan

4. Tentative Title: Development of Higher-order Structure of UHMWPE film Under Uniaxial/Biaxial Stretching with High-speed Modes 

    Authors: Y. Hashimoto, Y. Ohta, S. Nishitsuji, T. Kurose, H.Ito

5. Author: Xiangzhe Zhu

6. Author: Meiling Xue

7. Author: Jitao Liu 

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