Research

27 pages, 3663 KiB

Open AccessArticle

Experimentally Verified Mathematical Model of Polymer Plasticization Process in Injection Molding

by Jacek Iwko, Ryszard Steller and Roman Wróblewski

Polymers 2018, 10(9), 968; https://doi.org/10.3390/polym10090968 - 01 Sep 2018

Cited by 8 | Viewed by 3883

The mathematical model of the polymer plasticization in the reciprocating screw injection moulding machine is presented in this paper. Methods of calculation of the most important flow characteristics, such as the solid bed profile, the pressure and temperature profiles, the mass flow rate, [...] Read more.

The mathematical model of the polymer plasticization in the reciprocating screw injection moulding machine is presented in this paper. Methods of calculation of the most important flow characteristics, such as the solid bed profile, the pressure and temperature profiles, the mass flow rate, the power demand, the screw torque and the energy consumption were analysed. According to the mathematical model, a computer program was developed. Based on the computer program, simulation studies of the injection moulding process were conducted. Thereafter, the experimental studies, evaluating the theoretical model from the accuracy and usefulness point of view, were carried out. Important output quantities, such as the temperature and pressure profiles, the power demand by the screw, the torque on the screw and the screw rotation time were measured. The studies were performed on a specially made research office. The simulation results were compared with the experimental data measured for the most popular polymers and different operating parameters of the injection machine. The experimental studies have indicated the need to introduce some corrections to the mathematical model. Several modifications have been made to the model, mainly related to the methods of stress determining in the polymer layer. Finally, the output characteristics of the plasticization process in the injection moulding are now correctly determined by the model with an average error less than 10%. Full article

(This article belongs to the Special Issue Model-Based Polymer Processing)

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22 pages, 6700 KiB

Open AccessArticle

A Network-Theory-Based Comparative Study of Melt-Conveying Models in Single-Screw Extrusion: A. Isothermal Flow

by Christian Marschik, Wolfgang Roland and Jürgen Miethlinger

Polymers 2018, 10(8), 929; https://doi.org/10.3390/polym10080929 - 19 Aug 2018

Cited by 28 | Viewed by 7139

Abstract

In many extrusion processes, the metering section is the rate-controlling part of the screw. In this functional zone, the polymer melt is pressurized and readied to be pumped through the die. We have recently proposed a set of heuristic models for predicting the [...] Read more.

In many extrusion processes, the metering section is the rate-controlling part of the screw. In this functional zone, the polymer melt is pressurized and readied to be pumped through the die. We have recently proposed a set of heuristic models for predicting the flow behavior of power-law fluids in two- and three-dimensional metering channels. These novel theories remove the need for numerical simulations and can be implemented easily in practice. Here we present a comparative study designed to validate these new methods against experimental data. Extensive experiments were performed on a well-instrumented laboratory single-screw extruder, using various materials, screw designs, and processing conditions. A network-theory-based simulation routine was written in MATLAB to replicate the flow in the metering zones in silico. The predictions of the three-dimensional heuristic melt-conveying model for the axial pressure profile along the screw are in excellent agreement with the experimental extrusion data. To demonstrate the usefulness of the novel melt-flow theories, we additionally compared the models to a modified Newtonian pumping model known from the literature. Full article

(This article belongs to the Special Issue Model-Based Polymer Processing)

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19 pages, 3840 KiB

Open AccessArticle

A Novel Technique for Fiber Formation: Mechanotropic Spinning—Principle and Realization

by Valery G. Kulichikhin, Ivan Yu. Skvortsov, Andrey V. Subbotin, Sergey V. Kotomin and Alexander Ya. Malkin

Polymers 2018, 10(8), 856; https://doi.org/10.3390/polym10080856 - 02 Aug 2018

Cited by 32 | Viewed by 4101

Abstract

We present basic experimental data and the theoretical background of a novel technique for fiber spinning from polymer solutions. The principal feature of the advanced process is realization of phase separation with detachment of a solvent, accompanied by the orientation of macromolecules, under [...] Read more.

We present basic experimental data and the theoretical background of a novel technique for fiber spinning from polymer solutions. The principal feature of the advanced process is realization of phase separation with detachment of a solvent, accompanied by the orientation of macromolecules, under the action of high extension rates. This is similar in some respects to dry spinning, though the driving force is not diffusion with subsequent evaporation of a solvent but redistribution of polymer-solvent interactions in favor of polymer-polymer and solvent-solvent ones governed by mechanical stresses. A promise of this approach has been demonstrated by experiments performed with polyacrylonitrile solutions in different solvents and solutions of the rigid-chain aromatic polyamide. We examined mechanotropic fiber spinning in model experiments with stretching jets from a drop of polymer solution in different conditions, and then demonstrated the possibility of realizing this process in the stable long-term continuous mode. During extension, phase separation happens throughout the whole section of a jet, as was confirmed by visual observation. Then a solvent diffuses on a jet surface, forming a liquid shell on the oriented fiber. Instability of this cover due to surface tension leads either to formation of separate solvent drops “seating” on the fiber or to the flow of a solvent down to the Taylor cone. The separate liquid droplets can be easily taken off a fiber. The physics underlying this process is related to the analysis of the influence of macromolecule coil-to-stretched chain transition on the intermolecular interaction. Full article

(This article belongs to the Special Issue Model-Based Polymer Processing)

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14 pages, 2404 KiB

Open AccessArticle

Vortical Fountain Flows in Plasticating Screws

by David O. Kazmer, Clemens M. Grosskopf and Varun Venoor

Polymers 2018, 10(8), 823; https://doi.org/10.3390/polym10080823 - 26 Jul 2018

Cited by 5 | Viewed by 3970

Abstract

Variances in polymers processed by single-screw extrusion are investigated. While vortical flows are well known in the fluids community and fountain flows are well known to be caused by the frozen layers in injection molding, our empirical evidence and process modeling suggests the [...] Read more.

Variances in polymers processed by single-screw extrusion are investigated. While vortical flows are well known in the fluids community and fountain flows are well known to be caused by the frozen layers in injection molding, our empirical evidence and process modeling suggests the presence of vortical fountain flows in the melt channels of plasticating screws adjacent to a slower-moving solids bed. The empirical evidence includes screw freezing experiments with cross-sections of processed high-impact polystyrene (HIPS) blended with varying colorants. Non-isothermal, non-Newtonian process simulations indicate that the underlying causality is increased flow conductance in the melt pool caused by higher temperatures and shear rates in the recirculating melt pool. The results indicate the development of persistent, coiled sheet morphologies in both general purpose and barrier screw designs. The behavior differs significantly from prior melting and plastication models with the net effect of broader residence time distributions. The process models guide potential strategies for the remediation of the processing variances as well as potential opportunities to achieve improved dispersion as well as complex micro and nanostructures in polymer processing. Full article

(This article belongs to the Special Issue Model-Based Polymer Processing)

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16 pages, 3088 KiB

Open AccessArticle

Use of Irradiated Polymers after Their Lifetime Period

by David Manas, Miroslav Manas, Ales Mizera, Jan Navratil, Martin Ovsik, Katarina Tomanova and Stanislav Sehnalek

Polymers 2018, 10(6), 641; https://doi.org/10.3390/polym10060641 - 09 Jun 2018

Cited by 7 | Viewed by 3245

Abstract

This article deals with the study of the utilisation of irradiated HDPE products after their end-of-life cycle. Today, polymer waste processing is a matter of evermore intensive discussion. Common thermoplastic waste recycling—especially in the case of wastes with a defined composition—is generally well-known—and [...] Read more.

This article deals with the study of the utilisation of irradiated HDPE products after their end-of-life cycle. Today, polymer waste processing is a matter of evermore intensive discussion. Common thermoplastic waste recycling—especially in the case of wastes with a defined composition—is generally well-known—and frequently used. On the contrary, processing cross-linked plastics is impossible to do in the same way as with virgin thermoplastics—mainly due to the impossibility of remelting them. The possibility of using waste in the form of grit or a powder, made from cross-linked High Density PolyEthylene (rHDPEx) products, after their end-of-life cycle, as a filler for virgin Low Density PolyEthylene (LDPE) was tested in a matrix. It was found that both the mechanical behaviour and processability of new composites with an LDPE matrix, with rHDPEx as a filler, depend—to a high degree—on the amount of the filler. The composite can be processed up to 60% of the filler content. The Polymer Mixture Fluidity dropped significantly, in line with the amount of filler, while the mechanical properties, on the other hand, predominantly grew with the increasing amount of rHDPEx. Full article

(This article belongs to the Special Issue Model-Based Polymer Processing)

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18 pages, 8824 KiB

Open AccessArticle

Computer Modeling for Single-Screw Extrusion of Wood–Plastic Composites

by Krzysztof Wilczyński, Kamila Buziak, Krzysztof J. Wilczyński, Adrian Lewandowski and Andrzej Nastaj

Polymers 2018, 10(3), 295; https://doi.org/10.3390/polym10030295 - 09 Mar 2018

Cited by 33 | Viewed by 6431

Abstract

Experimental and theoretical studies have been performed on the single-screw extrusion of wood–plastics composites. Experimental research has been carried out on the flow and melting of polypropylene (PP)-based composites with different wood flour (WF) content in the single-screw extruder. Based on these experimental [...] Read more.

Experimental and theoretical studies have been performed on the single-screw extrusion of wood–plastics composites. Experimental research has been carried out on the flow and melting of polypropylene (PP)-based composites with different wood flour (WF) content in the single-screw extruder. Based on these experimental observations, elementary models of the process phenomena have been proposed and a global model of the process has been developed. This global computer model includes the models of solid conveying, melting dependent on the wood flour content, melt flow in the screw, and melt flow in the die. 3-D non-Newtonian finite element method (FEM) screw pumping characteristics have been applied to model the melt flow in the metering section of the screw. The model predicts the extrusion output, pressure and temperature profiles, melting profile, and power consumption. The model has been validated experimentally. An effect of material slip on the extruder operation has been discussed including both slipping in the screw/barrel surfaces and in the extruding die. Full article

(This article belongs to the Special Issue Model-Based Polymer Processing)

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22 pages, 16284 KiB

Open AccessArticle

The Effect of Irradiation on Mechanical and Thermal Properties of Selected Types of Polymers

by David Manas, Martin Ovsik, Ales Mizera, Miroslav Manas, Lenka Hylova, Martin Bednarik and Michal Stanek

Polymers 2018, 10(2), 158; https://doi.org/10.3390/polym10020158 - 07 Feb 2018

Cited by 48 | Viewed by 9336

Abstract

This article deals with the influence of electron-beam radiation on the micro-mechanical, thermo-mechanical, and structural properties of selected polymers. In the search for the desired improvement of polymers, it is possible to use, inter alia, one particular possible modification—Namely, crosslinking—Which is a process [...] Read more.

This article deals with the influence of electron-beam radiation on the micro-mechanical, thermo-mechanical, and structural properties of selected polymers. In the search for the desired improvement of polymers, it is possible to use, inter alia, one particular possible modification—Namely, crosslinking—Which is a process during which macromolecular chains start to connect to each other and, thus, create the spatial network in the structure. In the course of the treatment of the ionizing radiation, two actions can occur: crosslinking and scission of macromolecules, or degradation. Both these processes run in parallel. Using the crosslinking technology, standard and technical polymers can acquire the more “expensive” high-tech polymeric material properties and, thus, replace these materials in many applications. The polymers that were tested were selected from across the whole spectra of thermoplastics, ranging from commodity polymers, technical polymers, as well as high-performance polymers. These polymers were irradiated by different doses of beta radiation (33, 66, 99, 132, 165, and 198 kGy). The micro-mechanical and thermo-mechanical properties of these polymers were measured. When considering the results, it is obvious that irradiation acts on each polymer differently but, always when the optimal dose was found, the mechanical properties increased by up to 36%. The changes of micro-mechanical and thermo-mechanical properties were confirmed by structural measurement when the change of the micro-hardness and modulus corresponded to the crystalline phase change as determined by X-ray and gel content. Full article

(This article belongs to the Special Issue Model-Based Polymer Processing)

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17 pages, 2953 KiB

Open AccessArticle

Vacuum Thermoforming Process: An Approach to Modeling and Optimization Using Artificial Neural Networks

by Wanderson De Oliveira Leite, Juan Carlos Campos Rubio, Francisco Mata Cabrera, Angeles Carrasco and Issam Hanafi

Polymers 2018, 10(2), 143; https://doi.org/10.3390/polym10020143 - 02 Feb 2018

Cited by 22 | Viewed by 7363

Abstract

In the vacuum thermoforming process, the group effects of the processing parameters, when related to the minimizing of the product deviations set, have conflicting and non-linear values which make their mathematical modelling complex and multi-objective. Therefore, this work developed models of prediction and [...] Read more.

In the vacuum thermoforming process, the group effects of the processing parameters, when related to the minimizing of the product deviations set, have conflicting and non-linear values which make their mathematical modelling complex and multi-objective. Therefore, this work developed models of prediction and optimization using artificial neural networks (ANN), having the processing parameters set as the networks’ inputs and the deviations group as the outputs and, furthermore, an objective function of deviation minimization. For the ANN data, samples were produced in experimental tests of a product standard in polystyrene, through a fractional factorial design (2^k-p). Preliminary computational studies were carried out with various ANN structures and configurations with the test data until reaching satisfactory models and, afterwards, multi-criteria optimization models were developed. The validation tests were developed with the models’ predictions and solutions showed that the estimates for them have prediction errors within the limit of values found in the samples produced. Thus, it was demonstrated that, within certain limits, the ANN models are valid to model the vacuum thermoforming process using multiple parameters for the input and objective, by means of reduced data quantity. Full article

(This article belongs to the Special Issue Model-Based Polymer Processing)

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