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.
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.
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.
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.
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 quality of distributive mixing is evaluated via an entropic measure of color homogeneity. We first illustrate this technique in a numerically built rectangular channel representing the unwounded channel of a single screw extruder. We also apply this method for assessing mixing quality of experimentally obtained samples when mixing a color concentrate in ABS resin in a single screw extruder. We discuss application of this technique in numerical simulations of processing equipment.
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.
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.
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.
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.
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.
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.
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.
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.
The performance of Boron Nitride, and its combinations with fluoropolymer as polymer processing aid in the extrusion of Ziegler-Natta polyethylenes is studied by using a capillary rheometer fitted with capillary and crosshead die. Two different techniques of compounding the polymer with the additives are used. In the first technique, both additives (Boron Nitride and fluoropolymer) are compounded together directly into the polymer. In the second technique, the additives are added separately. Improved performance via the second technique is observed.
During the product change from colored into colorless especially at blown film extrusion, long purging times arise because of the long continuing colour haze. The purging behavior has been investigated in low density polyethylene (LDPE) films under variation of the process parameters mass flow rate and temperature. Our analysis shows that the improved purge process control and variation of the process parameter modifications during the purging process reduce the purging time and substandard goods compared to the conventional arrangements. Also the study examines the influence of different color pigments into the purging behaviour.
Thermal translators, along with the connected hardware and software controls, represent the core of automatic control of flexible lips in flat die extrusion. The thermo-mechanical efficiency of said translators has a direct impact on the process for ensuring proper gauge uniformity in film extrusion, thus affecting the quality and the economy of the manufacturing process. This paper will investigate the potential advantages and disadvantages related to translators based on different materials of construction and their basic thermal and mechanical performance. The work presented is the result of analytical and FEA computer simulations.
Compounding of thermoplastics with wood flour or natural fibers presents a number of challenges. The temperature and shear sensitivity of the thermoplastic matrix such as PVC, presence of moisture in the cellulosics, and the critical process temperature limitations of the composite are some of them. Lower shear history and melt temperature during primary compounding operations of such composites generally result in better mechanical properties of the finished product. This paper investigates the suitability of CK Continuous Kneader to surmount the imposed process limitations effectively.
Cable jackets containing carbon black (CB) are one of the most important components in communication and power cable constructions. This jacketing provides protection for the underlying layers from physical abuse, chemical attack, and UV degradation. There are two ways of manufacturing these types of cable jackets: either by fully compounding the product or by blending a combination of a resin and a black master batch (MB). In the latter approach, a main requirement is to have excellent CB dispersion in the MB. Poor dispersion in the MB results in unacceptable mechanical properties and poor UV-resistance in the finished jacket product.This paper describes a series of single screw extrusion experiments which were carried out with let-down resins of different structures, and master batches (MB) to investigate the effects of the resin structure, MB, and extrusion conditions on acceptability of the extrudates for jacketing applications. The MBs employed for this investigation are commercial products of which dispersion is acceptable based on the manufacturing QC testing. Under certain extrusion conditions with these MBs, extrudates had unacceptable surface quality and UV absorption coefficient (termed as ABS, < 400nm ) for a given range of CB content in the finished product (2.5 to 2.7 wt%). The unacceptable properties resulted from poor melt homogenization of the MB with the letdown resin at the extrusion conditions used. Good homogenization was obtained by conducting the extrusion/compounding at higher shear stress. The high shear operation can be accomplished by several methods: selection of lower MI let-down resin (within resin spec); narrow the molecular weight distribution (MWD); lower temperature profile; and higher screw speed. The employment of tighter screen packs also showed some improvement in homogenization. A possible mechanism for the good homogenization (CB dispersion) of the MB will be given.
The effects of multiple-extrusions, up to eleven cycles, on the structure and properties of virgin and nanoclay-filled nylon-12 were investigated. X-ray diffraction and transmission electron microscopy studies showed that the degree of clay exfoliation improves with each successive extrusion sequence up to the seventh cycle. The impact strength of the nanocomposites were enhanced while that of the virgin nylon-12 deteriorated. Regrinding of the nanocomposite resin prior to subsequent extrusion was shown to further improve the clay exfoliation and mechanical performance.
Nylon-12 and nylon-12/clay nanocomposite were recycled by up to eleven times using the melt-extrusion process. Changes in thermal and rheological properties were investigated using DMTA, DSC, TGA, and capillary rheometry techniques. Both materials showed a gradual decrease in phase transition temperatures and storage modulus following repeated extrusions. In addition, the materials melt viscosity increased in response to successive reprocessing. Relative to the nylon-12, the melt viscosity of nanocomposites was reduced by more than 20% and their glass transition temperature was elevated by about 2.0 to 6.5degC depending on the number of extrusion cycles.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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