The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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Investigation of Influences on The Melting of Polyethylene and Polystyrene in a Co-Kneader
The co-kneader is well known for its superior mixing performance and its exact temperature control capabilities. Therefore, it is widely used in the polymer industry for the compounding of shear- and temperature-sensitive materials. In contrast to the considerable amount of scientific work that deals with investigation, modeling or simulation of the process behavior of single and twin screw extruders there are only few studies about the co-kneader. Due to increased quality requirements and the trend for cost reduction by process optimization, this is increasingly becoming a problem for plant construction and processing companies. To address this problem, experimental investigations of the melting behavior of polymer materials in the co-kneader were conducted. In order to determine the melting degree along the extruder length a special barrel was used which can be opened in axial direction. Based on the experimental results, a theoretical consideration for co-kneaders that are operated as plastification extruders is proposed. Therefore a disperse solid melting model is used. A comparison between simulated results and experimental data shows a descent agreement, when the point of melting initiation is estimated accurately.
Reproducibility Analysis of Fiber Length Measur ements During Processing With Twin Screw Extruders
The twin screw extruder is used for processing of plastics. One of the most important processing tasks is the preparation of plastics with fillers and reinforcing materials. For the processing of fibers various recommendations can be found. But in an industrial production, with the same specification and process parameters, the resulting fiber length may differ. These variations must be clearly defined and determined. While process deviations occur during compounding, measurement deviations can be detected in the fiber end length measurements. In order to evaluate the experimental investigations and to use it for model validations, the corresponding deviations must be known beforehand. Within this paper, a reproducibility study will be carried out to ensure the reliability of the experimental investigations. The aim of the work is to determine the fiber length degradation along the screw and their deviations. The investigations in this paper are showing that a producible fiber length reduction is possible.
Influence of Twin Screw Configuration and Processing on Ketoprofen Dissolution in Polymer Blends
The solubility and dissolution enhancement of the poorly soluble drug ketoprofen (KTO) in polymer blends prepared by hot melt extrusion was studied using two different twin screw configurations while changing extrusion processing parameters. Soluplus and Kollidon SR blends were used as solid dispersion excipients. A design of experiments with three melt temperatures, three screw rotation speeds, and three fill factors was performed. Different characterization techniques such as differential scanning calorimetry (DSC), optical and polarized light microscopy, X-ray diffraction (XRD), solid-state nuclear magnetic resonance (ss-NMR), and dissolution testing were used. The results from DSC and XRD showed an amorphous solid solution. An optimal processing condition by twin screw extrusion was found for each screw configuration achieving more than 80% drug release in 8 hours.
Modeling Fully Intermeshing Co-Rotating Twin-Screw Extruder Kneading-Blocks: Part A Conveying Characteristics
Twin-screw extrusion modeling is in most cases based on analytical approaches that are build on considerable geometric simplifications. These approaches give only rough estimations of the processing behavior. More accurate predictions generally require numerical methods with less drastic simplifications. In this work, we analyzed the pressure-throughput behavior in fully-intermeshing double-flighted kneading blocks. First, we conducted a dimensional analysis based on the Buckingham Π-theorem. Second, for each staggering angle, we determined the characteristic angular position that describes the mean throughput. Based on this position, a parametric design study was carried out by varying the identified dimensionless parameters. To solve the complex flow patterns, 3D CFD simulations were conducted. For each design point we evaluated the dimensionless drag flow-rate and the dimensionless dam-up pressure. As an addition to the two established dimensionless conveying parameters A1 and A2, we propose a novel conveying parameter A3. This new parameter simultaneously enables the description of conveying and non-conveying kneading discs. Our results offer considerably deeper insight into the conveying characteristics of kneading blocks. In addition, they can serve as foundation for screw design and process modeling. For a better understanding of the process, we additionally investigated the power consumption and viscous dissipation in Part B of this publication.
Modeling Fully Intermeshing Co-Rotating Twin-Screw Extruder Kneading-Blocks: Part B Power Consumption
Modeling twin-screw extrusion is commonly based on significant geometric simplifications such as the representation of the flow domain as flat channels. Furthermore, the prediction of the conveying characteristics and power demand of kneading blocks is typically based on their approximation as conveying elements. Considering the accurate flow geometry of fully intermeshing co-rotating twin-screw extrusion kneading blocks we analyzed the power characteristics by means of three-dimensional numerical simulations for Newtonian flow. Therefor we first conducted a dimensional analysis to identify the dimensionless characteristic influencing parameters. Next, we derived novel dimensionless power parameters and then conducted a parametric design study. Our proposed power parameters are capable to simultaneously cover conveying and non-conveying screw elements. The results provide new insights in the power characteristics of kneading blocks and are fundamental for screw design, screw simulation, and scale-up. In Part A.  of this work we focused on the conveying parameters.
New Concept for Melting in Single Screw Extruders
In the late 1950’s Union Carbide’s research engineer, Bruce Maddock, ran several single screw extruder experiments. He established a method to reveal the melting profile in the screw by stopping the screw at speed and quickly cooling it to freeze the polymer. Then he reheated it to create a melt film on the barrel surface so he could pull the screw out. The condition of the polymer in the screw flights was studied. This revealed what Bruce called the solid bed melting mechanism. He showed that at the end of the feed section there was a tightly packed mass of solids in the screw channel. Melting occurred at the barrel surface as the conventional transition section decreased in depth. The melt was scrapped off the screw barrel surface by the rotating screw flight which deposited it into the rear of the screw channel. Thus, the solid bed melting mechanism was discovered. This mechanism has been the basis of all screw designs since. This paper will disclose an alternate melting mechanism which does not use the solid bed theory.
Development of an Analytical Mathematical Modelling Approach for a More Precise Description of Disperse Melting
The melting behaviour in single-screw extruders is of significant importance. For a high-quality extrusion product, a completely molten and thermal homogeneous, in case of a compound or the use of fillers also uniform concentrated, polymer melt is necessary. Due to the striving for the highest possible economic efficiency of the process, screws which can achieve a higher throughput at the same extruder size through higher screw speeds are often used. In these, however, melting no longer takes place in the classical way with a subdivision into melt eddy and solid bed, as was researched in the 1950s and 1960s by MADDOCK and TADMOR and successively extended by many more. Much more the solid bed breaks up into individual solid particles due to high forces or special screw geometries introducing disperse melting. The mathematical description of this process is not as mature as that of classical melting and is therefore the subject of this paper. An analytical mathematical model is presented which allows the calculation of the temperature development in the particle and the variable melting rate in addition to the actual melting process of the disperse melting. The temperature input by dissipation as well as by barrel temperature is considered. By means of an iterative procedure, complete screw geometries can be checked for the melting behaviour. Furthermore, a statistical experimental design based on the model is used to show which factors favor or impair disperse melting.
Evaluation of the Distributive Mixing Quality Based on Particle Tracking and Delaunay Triangulation
In addition to conveying and melting, one of the core tasks of a single screw extruder is the homogenization of the material. Since conventional conveying screws in single screw extruders usually have an inadequate mixing effect, mixing elements at the end of the screw are commonly used to increase the homogenization performance. The melt homogeneity at the end of the screw is very important because it correlates strongly with the product quality and is therefore also directly related to reject rates in the production. However, characterization of the mixing quality is often very difficult because there are many degrees of freedom. In this paper, a new method for characterization of the distributive mixing quality on the basis of 3D CFD simulations is presented. In order to be able to assess the mixing quality, the particle trajectory of an initially defined particle distribution at the inlet of the flow must first be calculated with a particle tracking method. Subsequently, the homogeneity can be characterized by the change in the particle distribution at the end of the flow area. Bin counting is often used for this purpose. However, this method has considerable weaknesses, which will be shown. Consequently, a new characterization method based on the Delaunay triangulation has been developed and implemented in MATLAB. The new method will be demonstrated using selected fictitiously generated as well as simulated particle distributions of some different screw geometries.
Analysis of Leakage Flow in Pressure-Generating Melt-Conveying Zones
In many extrusion analyses, the pumping capability of the extruder screw is overestimated. This is usually due to the effect of the flight clearance being omitted in the mathematical model. The clearance between flight land and barrel surface enables the polymer melt to leak across the flights, thereby reducing the effectiveness with which the screw can pump the polymer melt forward. A few studies have proposed modifications to the widely known pumping model to account for the effect of leakage flow. While most of these consider Newtonian fluids, less attention has been directed towards shear-thinning polymer melts. We propose approximate equations to predict the flow of power-law fluids through the flight clearance of pressure-generating melt-conveying zones. Rather than correct the net material throughput of the single-screw extruder, we locally describe the two-dimensional flow between the flight tip and the barrel surface. Our novel models, which predict the flow rate and viscous dissipation, increase the understanding of the flow of shear-thinning polymer melts across the flights. Implemented in our screw calculation routine (introduced in [1-4]), they also serve as the basic equations for the network elements positioned over the screw flights.
Improved Polypropylene Thermoformability Through Polyethylene Layering
While the flow forces governing primary melt-based polymer processing techniques, such as extrusion and injection molding, have been extensively studied, characterization of forces in secondary processes such as thermoforming is limited. In this work we utilize multilayer coextrusion to create an extruded film with 100s of alternating linear low density polyethylene (LLDPE) and isotactic polypropylene (iPP) layers; and by extension, 100s of interfaces. The combination of LLDPE, iPP, and these interfaces decreases the elastic storage modulus (E’) and broadens the rubbery plateau observed via dynamic mechanical analysis (DMA). The broadening of the rubber plateau is correlated with an observed improvement in LLDPE/iPP multilayer thermoformability compared to the homopolymer LLDPE and iPP films.
Mitigating Resin Degradation Via Nitrogen Inerting for Single-Screw Extruders
Resin degradation can reduce the value of a product, especially for polyethylene (PE) films. Most of the degradation occurs in the final processing operations using single-screw extruders. There are many reasons why degradation occurs, and screw design is considered the first and best opportunity to mitigate it. The elimination of atmospheric oxygen is the next best option. This paper describes a method for mitigating resin degradation via nitrogen purging at the hopper. Extrusion data are provided that demonstrates the effectiveness of nitrogen purging for PE resins.
Simulation of the Flow in a Bilayer PVC Window Profile Die With Gradually Changing Calibrator Profiles
Simulation of the flow and extrudate deformation in a bilayer window profile die is presented. The shape of the profile was modified during extrudate cooling by changing the shape of successive calibrator profiles. The effect of non-uniform exit velocity, cooling shrinkage and shape of calibrator profiles on extrudate deformation is included in the simulation.
Operating Performance of Free-Rotating Mixing Sleeves in Single-Screw Extrusion
In this paper, an experimental design with three mixing sleeves, two materials and several operating points is carried out to determine the operating performance of free-rotating sleeves in single-screw extrusion. The focus will be on the investigation of the operating parameters: sleeve speed, pressure loss and temperature development. Therefore, an automated method for determining the sleeve speed will be presented.
Product-Related Process Data Acquisition in Blown Film Extrusion
In today’s advanced plastics processing industry, a quality-based control of an entire production line is desirable. This requires a product-related process data acquisition allowing to merge process data and quality data with high accuracy. In this context, an approach for the blown film extrusion process will be presented. An experimental study confirms that the tool of residence time distribution analysis is suitable to identify the system behavior of a blown film line. On that basis, suggestions are made on how to proceed with the implementation of a product-related process data acquisition.
Applying the Shooting Method to Predict the Co-Extrusion Flow of Non-Newtonian Fluids Through Rectangular Ducts
Because of their versatile properties multi-layer polymer products have a high industrial relevance. Process understanding and prediction of the flow characteristics of co-extrusion, hence, is of major importance. When the shear-thinning behavior of polymer melts is to be included in modeling, there is no alternative to numerical solution methods. We present a numerical solver that is based on the shooting method to predict two-layer co-extrusion flows of non-Newtonian fluids within rectangular ducts of infinite width. The pseudo-plastic flow behavior of polymer melts is modeled by the power law according to Ostwald and de Waele. We carried out a dimensional analysis of the governing equations based on the theory of similarity, and identified four independent dimensionless parameters that fully describe the problem. To solve the dimensionless governing equations, we developed a numerical solution procedure. Additionally, we conducted an extensive parametric study by varying these independent dimensionless quantities over a wide range that covers almost all applications in industry. The numerical results offer insights into the influence of the independent parameters on, for instance, pressure gradient, (interfacial) shear stress, velocity profile, and viscosity distribution.
Simulating Flow through Channels with novel Cross-Sections: Pressure Drops and Flow Coefficients
Despite the evolution of several new die concepts since the invention of spiral mandrel dies in the 1960s, the basic geometry of the spiral grooves themselves remained unchanged. The cross section of the groove is u-shaped, i.e. consists of a rectangular and a semi-circular area. Typically, the spiral grooves abruptly merge into the annular gap, forming sharp edges. These edges negatively affect process performance e.g. by potentially damaging the polymer chains or provoking deposits. Rounding off these edges ease the effect to some extent, but alternating the general shape of the cross section has obviously a much better potential to influence the process characteristics of the die. This paper systematically investigates spiral mandrel dies with channels of different cross-sections: type I is u-shaped, as it is normally used for spiral dies, type II is u-shaped with one side inclined at 45 degrees and type III is a wider variation of the u-shape. To calculate the pressure drop along channels with such cross-sections, it is common practice to use correction factors. These so-called flow coefficients correct the error introduced by the geometrical simplifications necessary to obtain analytical solutions. This paper presents flow coefficients calculated from CFD results for the given cross-sections.
Advances in Extrusion Blow Molding of Post-Consumer Resin
Demand for increased recycled content in various applications has driven innovation toward incremental step change in recycled material quality. In pursuit of increasing recycled content usage in extrusion blow molding applications, considerations must be made for the preservation of mechanical properties via the prevention of thermal and oxidative degradation during both the recycling and molding processes. In order to understand the importance of timely implementation of solutions like stabilizer blends, a set of experiments was run on extrusion blow molded articles to illustrate the rate of performance decay that occurs between the recycler and the molder. This analysis proposes pathways to improve upon current recycled content utilization while simultaneously improving end-use properties.
Evaluation of Sub and Near Critical Carbon Dioxide for Low Processing Temperature of Medical Thermoplastic Polyurethane
Incorporation of thermosensitive active pharmaceutical ingredients for manufacturing multifunctional polymeric medical device is still limited as they can be deteriorated in the hot-melt extrusion process. In this study, the potential of sub and near-critical carbon dioxide used as a green plasticiser was injected to hot melt extrusion process of Pellethane thermoplastic polyurethane to decrease process temperature. Its thermal and rheological behaviour were also evaluated. The resultant extrudates were characterised using parallel-plate rotational rheometry and differential scanning calorimetry. The process temperature decreased from 185 to 160 °C. The rheology indicated that the reduction of melt viscosity to 36.36% and 40.04% at 600 and 1000 psi, respectively. The results indicate that the employment of scCO2 as a transient plasticiser is a viable aid to conventional hot-melt extrusion and offer more opportunities for thermosensitive drugs to be more thermally stable in the molten stream of Pellethane thermoplastic polyurethane.
Filterability of Raven 1300 Ultra Carbon Black For Fine Denier Fiber Applications
Carbon blacks can offer improved performance over dyes in fiber and textile applications in polyester, polyamide and polypropylene resins. Their stringent cleanliness and superior filterability are of critical importance for successful fine denier fiber applications. In this study, the filterability of Birla Carbon’s fiber black Raven 1300 Ultra was evaluated after compounded in PET resin via twin-screw extrusion and a Farrel continuous mixer (FCM). The carbon black demonstrates excellent filterability performance via twin-screw extrusion and an FCM compounding processes. FCM was explored to make atypical PET masterbatches with higher carbon back loadings beyond 30%. However, a further study focusing on improving dispersion and filterability of highly loaded PET masterbatches is warranted to better serve the fiber application.
Analysis of the Advantageous Process and Mixing Behaviour of Wave-Dispersion Screws in SSE
In the plastics processing industry, the improvement of the economic efficiency of extrusion lines is important. This is achieved, especially in single-screw extrusion, by an increased throughput at a constant machine size. In order to guarantee high melt quality, new screw concepts are being developed in addition to conventional screws. These include wave-dispersion screws, which are designed to break up the solid bed at an early stage so that the melting and homogeneity behavior is optimized. This paper deals with the experimental comparison of two wave-dispersion screws with a common barrier and 3-section screw. The maximum achievable throughput and in particular the melt quality with regard to thermal and material homogeneity are investigated in order to detect possible advantages of the screw concepts. Here it has been shown that both better thermal and material homogeneity with simultaneously higher possible throughputs can be achieved by wave-dispersion screws.
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