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.
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.
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 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.
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.
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.
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.
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.
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.
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.
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.
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.
For many decades, the setup and solution of polymer processing models involved use of analytical or numerical methods. These characteristics have changed with the recent digitization of polymer processes and the collection of enormous amounts of data. It is increasingly common to use data-driven modeling techniques to analyze processes, for which analytical and numerical models may not fully describe the process behavior in operational situations. These techniques have significantly extended the set of tools available to the engineer, providing new possibilities of how to develop more accurate process models. As a result, the setup of an appropriate modeling strategy more than ever requires a thorough understanding of the individual modeling techniques. This article was designed to address the potentials and limits of analytical, numerical, and data-based modeling techniques when modeling polymer processes. Moreover, we show how these methods can be combined into one hybrid approach to solve polymer process models not solvable so far. The findings are further illustrated by means of a particular use case, which models the flow of polymer melts in single-screw extruders.
This paper will present the conceptual design of a novel free-rotating mixing sleeve for single screw applications. In contrast to most of the currently available free rotating mixing rings (e.g. the TMR) which primarily have a distributive mixing effect, the mixing sleeve presented in this paper will focus on dispersive mixing. The variety of requirements on dispersive mixing make the structural design and the geometrical layout very complex. Therefore, a method is introduced to couple a full parametric 3D-CAD master model of the mixer with a 3D-CFD-simulation. The aim is to describe a set-up of an automated process to design and optimize the novel mixing element by defining several target figures.
Mesh interface and immersed boundary models are presented as simplifications for the simulative design of dynamic mixing elements for single screw extruders. These simplifications have great potential to cut complexity and cost in both drafting and computation. Results for distributive mixing are compared quantitatively and qualitatively to a non-simplified 3D model. It is found that good agreement with the 3D model is achieved when the simplified models’ throughputs are adjusted for mass conservation.
The design of an extrusion die has been evaluated utilizing a 3-D polymer extrusion simulation software for optimal flow. The flow pattern, pressure, temperature, and shear rate are simulated in the software. The post-die extrudate shape is also simulated to show the improvement by balancing flow velocity in different sections. The combination of 3-D modeling and simulation decreases the time and difficulties for tuning the die during manufacturing.
The use of thermallyconductivepolymersto replaceconventionaltubingmaterialshas the potentialto improveefficiencyof heat exchangedevices. Inthis study,a designof experimentswas conductedto understandthe effectsofextrusionon physicalpropertiesof thermallyconductivetubingfor an MCS.Shearrates and draw downratioswere independentlyvaried,and the tensilepropertiesof the resultingtubingwere measuredand comparedto determinethe effectof each.It was foundthat, in accordancewith previousliterature,shearrate had no substantialeffecton tensilepropertieswhile draw downratiohad a positiverelationshipwith tensileproperties
Colloid prepared with epoxidized soybean oil (ESO) and organically modified montmorillonite (OMMT) has been processed using an ultrasonic twin-screw extruder under various ultrasonic amplitudes and screw rotation speeds. Ultrasonic treatment has significantly increased OMMT dispersion in ESO, according to WAXD and rheological data. Yield strength, storage and loss modulus, complex viscosity and relaxation time of the colloid have been increased with increase of ultrasonic amplitude. Under certain high ultrasonic amplitudes, increase of one to two orders of magnitude have been observed. Creep and recoverable compliance have been decreased with the increase of ultrasonic amplitude. The tremendous changes in rheological properties of the colloid is a result of significantly improved OMMT dispersion with the aid of ultrasonic treatment. With no or low ultrasonic treatment, a higher screw rotation speed has improved OMMT dispersion since it brings more mixing effect. However, at high ultrasonic amplitudes, a higher rotation disrupts jet flow and has led to less dispersion improvement compared with the same colloid extruded at a lower rotation speed.
Peroxide-containing ethylenic polymers are used in many power cable applications. The processes involve extrusion of the polymer compositions to form one or more layers on a conductor, followed by crosslinking in a continuous vulcanization step. To extrude the composition, it is critical to maintain a low discharge temperature so that the peroxide does not decompose significantly during the extrusion process, so as to prevent premature crosslinking. However, with a low discharge temperature, the rate is usually reduced; for some formulations, the rate reduction is dramatic. This paper describes an energy transfer (ET) screw design that enables high rates at acceptably low melt discharge temperatures, or alternatively, yields significantly lower melt discharge temperatures at a given rate than a conventional Maddock mixing screw. The design simulations of the new ET screw were validated experimentally.
Adhesive selection in high dynamic load environments relies heavily on mechanical adhesive properties, including shear, peel and compressive strength. Over time and in the life a part, fatigue can occur to metals, plastics and adhesives. Fatigue weakens the overall strength of these components and can lead to premature failure. In the case of adhesives, shear strength values may depreciate an order of magnitude, from thousands to hundreds of psi due to a life of wear and dynamic movement, which can lead to failure. When selecting an adhesive for bonding a joint, the likely first choice is the adhesive with the highest shear strength with the assumption that the higher the shear strength the longer the part will last. However, upon testing, higher shear strength does not directly correlate to a longer part life. In the case of hybrid adhesives (Loctite® HY4090GY™ and HY4070™) compared to epoxies (Loctite® E-20HP™), the epoxy greatly outperformed the hybrids in shear strength, but the hybrids greatly outperformed the epoxy in limit of endurance. Overall, the methyl methacrylate (MMA) adhesive (Loctite® H8003™) proved to be the most fatigue resistant adhesive tested.
A relatively wide (610 mm) lab-scale microcapillary cast film die was fabricated to aid in the development of this unique film processing technology. Due to the approach used to create microcapillary channels, standard die design techniques for maintaining uniform film gauge (e.g. die lip adjusters) are not applicable. A series of modifications were made to the original die design to improve film gauge. One such modification was the use of computational fluid mechanics (CFD) to improve flow uniformity across the die. Due to the multitude of air pins located near the die outlet, it is impractical to perform direct CFD simulations based on the actual flow geometry. Instead, the flow geometry associated with the comb-like structure of the air pin region is replaced by a porous medium with an equivalent viscous resistance. The primary focus of this paper is a description of the porous medium CFD technique used in the design of the 610 mm wide die.
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