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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A Study for Improving the Quality of a Co-Extrusion Blow Molded Bottle
The development and production of a six-layer bottle of ethylene vinyl alcohol/polypropylene for tomato ketchup is described in this paper. The main aim of this study was the analysis of the influence of some processing parameters on the through-thickness structure of the composite. It included a first for the definition of the operating conditions leading to the required bottle structure. In a second stage, and after setting the desired bottle wall structure, the optimum welding conditions were determined. In this study, the mould temperature, the mould closing speed, and the hold time (i.e., time interval between the mould closing and the inflation) were varied according to a L9 Taguchi experiment design. The effect of the processing parameters on the morphology and properties of the pinch-off welding zone was analyzed and the best operating conditions were determined.
Analysis of Permeability and Weld Line Integrity in Multi-Layer Blow Molded Automotive Fuel Tanks
In this study, numerical simulation is used to analyze the blow molding process of an automotive fuel tank. In a first step, 3D simulations employing a shell approximation are used to investigate the deformation of a multi-layer parison as well as the thickness variation for each layer. Next, 2D simulations are used to study the details of the welding line formation. Locally, the shear flow across the parison thickness can no longer be neglected. The position of the interface between the layers is calculated using adaptive meshing to handle the very large deformations. The influence of the rheology on the position of the interface is investigated.
Evaluating Quasi-Simultaneous and Contour Welding for use with the Clearweld™ Process
The Clearweld™ process is a form of through transmission laser welding that enables welding of two clear substrates with minimal effect on the appearance. Aesthetics are especially critical in the medical and packaging industries. The Clearweld™ process can also weld colored or opaque substrates, and reduces the number of color limitations imposed in traditional through transmission laser welding.Single beam contour and quasi-simultaneous welding methods were evaluated for use with the Clearweld™ process to aid users in the selection of beam delivery methods. The welding speed, laser power, and clamping pressures were varied in order to determine the effect on weld strength, amount of collapse, residual color, and weld time. Studies were focused on PETG.
Fiber Graphics in Mold Decoration
The purpose of this paper is to introduce and review basic elements of a newly available IMD material and technology that will impact the way many molded plastic articles will look and feel in the future. Another purpose is to inform molders who now offer IMD product about a new decoration option, a new arrow for the quiver to help create new business by expanding the range of product offerings and/or functionality.This paper is not about how to do IMD, and assumes the reader is familiar with the process. This subject has been described thoroughly in previous ANTEC papers (please refer to presentations by Jeff Applegate and Jordan Rotheiser).Fiber Graphics IMD was developed to help grow this category of decorated plastic; and in the most extreme scenarios, we are seeing a general increase in consumers’ base level of expectations about how they experience the touch and appearance of everyday plastic products and how they should perform. One example of this is: if cell phones do not need to ever slip out of your shirt pocket when you bend over, then why should they?
A Role of an Uneven Temperature Distribution at the Flat Die Inlet on the Die Performance
Flat dies are used for the extrusion of a wide range of flat products. In general, the main requirement to the die design is to get products with a good mass distribution. It is known that a die can be designed well but its performance may become much worse due to uneven material properties at the die inlet. Such a behavior can be studied by a 3D simulation.The described study uses a 3D FEM analysis to investigate an effect of an uneven temperature distribution at the die inlet on the final distribution. The temperature inhomogenity is modeled in two ways. At first a temperature profile created by the heat dissipation is used. In the second case, an L-shaped spindle (valve) is used to generate the temperature irregularity. The spindle orientation was horizontal or vertical to the die axis. In all cases, the influence of the temperature inhomogenity on the final distribution at the die outlet was studied.
Heat Transfer Coefficients and Screw Temperature Profiles in Modular Twin Screw Extrusion Machines
For modular co-rotating twin screw extrusion machines, we developed models of the heat transfer coefficients as well as the screw temperature profile in a machine with both starved regions and fully filled regions. The dependence of heat transfer coefficients on screw diameter, screw rotation speed and power law index of polymer melt was investigated. The screw temperatures were calculated along the screw axis and radial directions as well as compared temperature development difference between these two directions. Calculations are made with dimension of commercial machines with varying screw diameter.
Comparison of Residence Time Distributions for Different Materials in the Same Extrusion Operation
Kinematic modeling has been shown to be important for the understanding and control of co-rotating twin screw extruders. The residence time distribution (RTD) is often used to characterize an extrusion process. Due to the nature of the polymer flow in the extruder, few have felt that the RTD would be independent of material properties for the same extruder setup. To investigate this question, four different polymers, two polyethylenes and two polypropylenes, were processed on the same 30mm Werner and Pfleiderer co-rotating twin-screw extruder (CoTSE) equipped with reflectance optical probes to compare their RTD's. Additionally, each material was tested to determine its complex viscosity, to better understand the phenomena involved.
Investigation of Melting Mechanism in a Twin Screw Extruder using a Pulse Method and On-Line Measurement
A perturbation method was introduced to investigate the melting phenomena of polystyrene (PS) and polypropylene (PP) blend in a twin-screw extruder. A sliding barrel technique was used to realize the on-line visualization of the processes and to obtain the temperature and pressure profiles along the extrusion region. The melting behavior of PS/PP (80:20) blend was studied under various ratios of the flow rate (Q) over the screw rpm (N). It was found that the melting processes of the PS/PP blend in the TSE can be divided into three sections. Most of the melting occurred in a narrow transition from the partially filled region to the fully filled region. No large deformation of solid polymer pellets was found for all the processes studied here. The relative amount of solid concentration in the flow can be obtained through this perturbation method. It was shown that the solid concentration at the beginning of the fully filled region increased as the ratio of Q/N increased.
Investigation in Power Consumption of Twin Screw Extruders in Respect of Scale-up Theory
In the field of polymer recipe development the homogenization of components is one of the most important points. For reasons of economy on the one side, and to receive a convenient machine configuration on the other, practical investigations are carried out on lab scale extruders. Subsequently the optimized process has to be transferred to an industry scale extruder during a scale-up process.On the basis of temperature and power consumption measurements at a tightly intermeshing, co-rotating twin screw extruder an approach for process transferability is discussed. By keeping the screw diameter constant the influence of throughput on the system energy balance is specified for several polymers. A theoretical approach for partly filled, geometrically similar systems is validated by means of experimental data extracted from a Coperion W&P ZSK-30. The results provide a basis to transfer operating points for co-rotating twin screw extruders.
A Perturbation Method to Characterize Melting during the Extrusion of Polymers and Blends
By means of a novel flow perturbation technique, fundamental details during the extrusion of semicrystalline and amorphous polymers, such as Polypropylene (PP), Polystyrene (PS), or PP/PS polymer blends can be analyzed with respect to the kinetics of melting and energy input. The effects of extrusion conditions such as throughput and screw speed were examined. A specialized, high-speed data acquisition system, the “Extrusion Pulse Analysis System” (EPAS) has been employed to enable on-line monitoring and data analysis based on an imposed mass disturbance to provide a real-time diagnosis of extrusion melting processes in laboratory and manufacturing applications.Using the power response profile of the mass perturbation, four key sequential stages of melting have been proposed for twin-screw extrusion of a single component or polymer blends. A “lubricated melting” mechanism is also proposed for the extrusion behaviors of PP/rubber and PS/rubber blends using an Ethylene copolymer and SBS block copolymer as the minor phase ingredient.
In Line Measurement of the Polymer Melting Behavior in Single Screw Extruders
Existing experimental techniques designed to study melting behavior of polymers inside the screw extruder suffer from limited functions or tedious procedures. Their invasive nature affect friction characteristics and heat transfer, significantly influencing the outcome of measured parameters. This paper presents an in-line, non-invasive measuring technique that can accurately capture experimental data and images from inside the extruder through a small quartz window and a rigid boroscope at short response times using a highly instrumented 45 mm single screw extruder with built-in sensors. By sensing the difference in optical properties between the melt and the solid phase, the melting behavior of high density polyethylene was visualized and measured with this non-invasive technique.
Solid Bed Melting in Single Screw Extruders - An Alternative First Order Mechanism
This paper discusses our initial attempt to model the results presented at ANTEC 2003 which demonstrated that for most of the literature data on solid bed melting careful reanalysis indicates that the solid bed consumption is dominated by melting in the thickness not the cross channel direction. A first order model for the melting is presented which focuses on the melting dynamics in the bed thickness direction. A similar analysis would be necessary for the cross channel direction but is beyond the scope of this paper due to space constraints. The model combines the concepts developed by Tadmor in his classical work with the ideas developed in this laboratory focused on the importance of using the velocities based on the screw rotating.
The Influence of Melt Rheology on the Specific Output Rate of Broad Molecular Weight Distribution Polyethylenes in Single Screw Extrusion
The extrusion (single-screw) characteristics of four broad molecular weight distribution (MWD), linear polyethylene resins are discussed with an emphasis on the output rate. Despite the high molecular weights of the subject polyethylenes, their broad MWD (Mw/Mn range: 10 to 60) does not limit the pressure and torque developed during extrusion. However, the specific output of the four polymers was quite varied. The dependence of the specific output on the melt rheology of the polymers is addressed; specifically, the shear-thinning extent of the melt in the metering section was found to influence output rate. The unique and counter-intuitive temperature-dependence of the shear-thinning character of one of the four polymers will also be addressed in relation to its extrusion characteristics. Lastly, a simple and quick method to evaluate the relative solids conveying efficiencies for various polyethylenes will be presented.
Performance Characteristics of Elongational Mixing Screws
Elongational mixing (EM) screws have recently become commercially available. Elongational flow allows more efficient mixing, particularly dispersive mixing. Elongational mixing reduces viscous dissipation relative to shear mixing. This results in lower motor load and reduced melt temperatures. This paper will present detailed operational data of a 90-mm mixing screw producing cast film and a 130-mm mixing screw with a special barrier section producing filled polyolefin film. Data produced with the elongational mixing screw is compared to a conventional mixing screw.The data indicates that elongational mixing screws allow increases in output and product quality while at the same time reducing motor load and melt temperature. The ability of elongational mixing screws to disperse gels is a particular advantage in film extrusion.
Melting of Polymer Blends in a Shear Field - Experimental Investigation
The melting of polymers is one of the most difficult problems of the modeling of the process behavior in screw machines. Because it is a complex task to analyze and visualize this phenomenon directly in the extruder, experimental studies are often inadequate. Therefore a model apparatus with parameters close to processing conditions, which can generate a shear flow, was developed. With this apparatus, it is possible to analyze optically the structural modifications during the melting of polymer pellets in a surrounding melt. The melting process can be observed directly with a CCD camera attached to a microscope. In order to quantify the influence of the different parameters, investigations have been performed. For the melting, the most important factors are the material properties of the melt and the granule, the temperature field in the pellet as well as the environment and the flow characteristics.
Real-Time Crystallinity Measurements in a Multilayer Blown Film
Online measurement of crystallinity development in a multilayer blown film using Raman spectroscopy is discussed. The Raman spectrum of a multi-layer film consists of superimposed spectra from the individual layers. For polyethylene (PE) and polypropylene (PP), some peaks are distinctly different but some overlap (1295-1350 cm-1). Offline Raman experiments were used to measure the contribution of polypropylene from the total integral intensity calculated in the range 1295-1350 cm-1, so that crystallinity evolution can be calculated for the two components. Preliminary results suggest that Raman spectroscopy is a useful technique to monitor crystalline growth of PE and PP in multi-layer blown films.
Stability Analysis of the Nonisothermal Film Blowing Process
The stability of film blowing process has been investigated using the governing equations taking care of nonisothermal nature of the process. In this study, on top of the linear stability analysis, employing a newly-devised numerical scheme, the hitherto unavailable transient solutions of film blowing dynamics have been obtained for the first time to produce temporal portrayal of draw resonance instability strikingly close to experimentally observed profiles. Many interesting aspects of the film blowing stability have also been revealed including multiple steady states and their diverse stability characteristics.
Effect of Crystallization Kinetics on the Morphology of Linear Low-Density Polyethylene Blown Films
Previous real time studies during the fabrication of a blown film have reported that the imparted molecular orientation is dependent not only on the stresses acting at the freeze line but also on the crystallization process that takes place along the axial distance. In this study, the relationship between the crystallization kinetics, as estimated using real-time Raman spectroscopy measurements, and the film morphology was investigated for linear low-density polyethylene (LLDPE) blown films. Crystallization half-time (t0.5), defined as the time taken for the polymer to reach 50 % of its equilibrium crystallinity, was proposed as a single parameter to relate the processing conditions with the orientation of the films. The results showed an asymptotically decreasing relationship between crystallization half-time and the a-axis orientation factor for a range of processing conditions.
Rheological Evaluation of the Processability of Polyethylenes for Extrusion Coating
The two key processability characteristics of low-density polyethylenes (LDPE) in extrusion coating applications are principally concerned with the degree of neck-in (NI) and the drawdown ability (DD). Molecular structures like long chain branching (LCB) and molecular weight distribution (MWD) have strong influence on these processability parameters, which, in turn, can be correlated with the melt elasticity of the polymer at processing conditions. These molecular structures effects on melt elasticity can suitably be studied by shear and extensional rheologies. A range of extrusion coating LDPE grades have been rheologically characterised and two models relating their extrusion coating processability parameters (NI and DD) and their melt elastic properties have been established. These new rheological parameters and models enable rapid quality controls and evaluation of potential materials, from catalyst development to products scale-up, for extrusion coating applications, with the desirable processability in terms of NI and DD.
Computational Design of U-Profile Die and Calibrator
The objectives of this work are three-fold: 1) to validate that an open profile product can be made using simulation alone to design a die (design rules of thumb are not applied), 2) assess the role of the calibrator in shaping the free surface of the extrudate, and 3) quantify the heat transfer in a vacuum calibrator and assess how such data can be used to design calibrators for other products. The scope of this paper includes: 1) three-dimensional flow simulation to design a die to make a U-shaped extrusion, 2) experimental trials to validate the mass flow balance through the die and the cooling performance of the calibrator, and 3) comparison of the heat transfer data obtained during calibration trials to published data for profile calibrators.
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