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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Stagnating Flows at the Screw Tip during Extrusion
Stagnation of polymer materials at the screw tip is a common problem for many extrusion processes with thermoset or thermal sensitive materials. Cured or burnt materials are often found at the screw tip and cause quality problems. Another example is a frequent color change. It may take a long time to purge the old color completely and creates a large amount of scrap.A mathematic model has been developed to simulate the polymer flow at the screw tip. Streamlines and residence time distributions have been obtained to understand the stagnating flow. The screw tip designs have been evaluated with the model. Also evaluated are the gaps between the screw tip and screen pack. The potential solutions to the stagnating flow are discussed.
Single Screw Solids Conveying - Different Polymers and a General Purpose Screw
In this paper we will discuss the differing solids conveying rates of several polymers using a “general purpose square pitch screw.” It is often desired to change polymer in an extruder as the products that are sold in a company change a the time or capital needed to pull the screw an replace it are not available. Often the results are confounding because the rates one obtains are dramatically different for the new polymer. In this paper we will present data for six polymers which demonstrate that the output of a typical solids conveying screw changes substantially as back pressure is increased on the solid bed being conveyed.
Temperature Measurement in Single Screw Extrusion: Late Melting and Thermal Instabilities
Various temperature measurement techniques have been used to investigate thermal profiles in the die of a 60mm single screw extruder, including invasive and wall mounted thermocouples, thermocouple meshes, ultrasound, and infrared. For a general-purpose polyolefin screw, large temperature differences of the order of 20°C were observed over short time periods of less than 1 second, in the exit melt temperature. These instabilities were evident during measurement of bulk melt temperature and are believed to be a result of melting instabilities. Predictive temperature plots obtained from CFD simulations using a commercial software package show qualitative agreement with the empirical results.
Effect of Screw Geometry on Melt Temperature Profile
Thermocouple meshes have been used to measure the temperature profile of polyethylene melt at the exit of a 60mm single screw extruder. Measurements have been made across a 38mm cross-section using a mesh with seven junctions. The meshes are located across the melt and provide temperatures at discrete positions across the flow, from which a thermal map can be constructed. The effect of screw geometry is investigated, with comparisons made between a general purpose polyolefin screw with gradual melting zone, a rapid transition screw, and a barrier flighted screw with a Maddock mixer. Significant differences in melting and temperature profiles were observed between the three extruder screws.
Air vs. Water Cooled Single Screw Extruders
Processors need to know if an air cooled extruder is adequate to their requirements or if they need the higher capacity of water cooling. This decision is often made based on experience, tempered with a fear of guessing wrong. If water cooling was used in the past, many processors are reluctant to try air cooling on a new machine. This paper compares the experimental data of various temperature settings and other operating conditions on a 90mm extruder, precisely repeated with an air and water cooled barrel heater on the same machine with the same screw. The data is then compared and quantified to establish useful guidelines for the application of water vs. air cooling.
A Novel Method of Measuring Viscosity and Tracing the Morphology Evolution Using Single Screw Extruder: The Screw Rheometer
A novel method of using single screw extruder as measuring viscosity and analyzing morphology evolution of polymer blend was elucidated. Combination of a batch wise operation of single screw extruder (the closed discharge condition) and using the modernized high-speed data acquisition system was a key technology of the method. The viscosity measured by “Screw Rheometer” was well matched with that by conventional capillary rheometer. Also the viscosities of rubber like polymers and low viscous materials such as polyamide were also successfully measured. The device also used to observe evolution of morphology for the immiscible polymer blend in controlled shearing state.
Mechanical Properties of Bast Fibers
Bast fibers like flax, hemp or kenaf have excellent mechanical properties which predestine these fibers for reinforcement of composites. The real mechanical properties of the fibers were measured. Diameter of fibers, tensile strength, modulus of elasticity and breaking elongation are available.
Thermal Properties and Structure Development in Film Extrusion Syndiotactic Polystyrene
A study of crystallization behavior and stretching of syndiotactic polystyrene cast film are considered. The isothermal crystallization rate of syndiotactic polystyrene was faster than isotactic polystyrene but slower than isotactic and syndiotactic polypropylene at the same ?T(?T=Tm–Tc). The birefringences of stretched films were developed faster than atactic polystyrene according to their stretching ratio. The crystalline orientation was represented in terms of stretching ratio.
Synthesis of Silicate-Polyamide Nanocomposites via Interfacial Polycondensation
In this work the synthesis of synthetic hectorite layered silicate - polyamide 66 nanocomposites by interfacial polycondensation is investigated to demonstrate the feasibility of the process and to produce viable nanocomposite product via this simple and low-cost process. Optimum reaction conditions and possible post-condensation treatments are identified for further study to obtain higher molecular weight product.
Displacement and Strain Analysis in a Non Homogeneous Material
Electronic holography moiré is applied to the measurement of interfacial conditions between particle and matrix in a non homogeneous rubber material. A tensile specimen is subjected to creep loading. The loads are applied in steps and measurements are carried out at equal intervals of time. The final output is provided by the Holo-Moiré Strain Analyzer and gives the principal strains and their directions in the region of observation. A definition of adhesion as an experimental measurable quantity through the evaluation of contour integrals is introduced.
Applications of Large Volume Processors in Polymer Processing
In recent years, pressure from economic and environmental requirements has been experienced in the field of polymer production. This trend towards single stage operational units, in processes such as low shear devolatilization of elastomer solutions, radical polymerization and polycondensation reactions, phase changing processes and the conversion from batch to continuous operation continues and has lead to the development of large volume, twin shaft horizontal processors (LVPs).These processors have been designed for applications requiring medium to long residence times (20-120 minutes).As an example of this new family of processors, the multi-purpose Reasol®, a new counter-rotating twin shaft processor, is introduced. Trials with model polymers have been performed in a 60L unit at the developer's test center. Its performance is described here by power consumption, RTD (residence time distribution) and self-cleaning and devolatilization efficiency.Trials show that product transport through the new LVP is characterized by a narrow RTD with a high degree of self-cleaning. Typically, the RTD exhibits a Peclet number in the region of 25-35. It is also shown that, unlike typical twin-screw extruders, the shape of the RTD curve is largely unaffected by the rotor speed or mass rate. Furthermore, rotor speed has a relatively small effect on mean residence time thus allowing the freedom to optimize rotor speed with respect to other processing objectives such as heat transfer, surface renewal or shear rate.The indications are that the characteristics of the RTD, power consumption and devolatilization are analogous to more traditional equipment such as twin screw extruders in spite of the larger free volume and residence time and the lower shear.The new LVP is commercially available up to sizes of 12,500 litres net processing volumes.
Predicting Plastic Energy Dissipation (PED) Using Phenomenological Constitutive Equations for Glassy and Semicrystalline Polymer Solids
It has been experimentally demonstrated that Plastic Energy Dissipation (PED) is a dominant melting mechanism in twin-rotor co- and counter-rotating processing equipment. Such devices force compacted polymer particulates to undergo repeated compressive, volume-wise, large compressive deformations, resulting in massive dissipative heating of the solid particulates and rapid melting. The large magnitude of PED has two important consequences: it results in very rapid end efficient volume-wise melting, enabling very fast processing rates and produces a very narrow “age distribution” melt, important for reactive processing. To date the experimental evaluation of PED, during large unconfined compressive cylindrical sample deformations, at appreciable strain rates, can be used to arrive at reasonable engineering estimates of the melting lengths for given polymers in specific processing equipment operating under given processing conditions. But this task involves a large number of PED-evaluation experiments, because of the lack of constitutive equations which are capable of describing the compressive stress-strain behavior of solid polymers at “engineering” strains and strain rates. The object of this presentation is to evaluate and modify existing constitutive relations for amorphous polymers using the large experimental date that have been generated in our laboratories. An acceptable constitutive relation will not only reduce the number of experiments necessary to evaluate PED and estimate melting lengths, but a needed element in the development of PED melting simulation models.
2D Composite Models of Modular Intermeshing Co-Rotating Twin Screw Extruders
A new 2D composite model with the hybrid FEM/FDM was developed for simulating the fully filled and starved regions with the associated pressure profiles of a modular intermeshing co-rotating twin screw extruder. 1D composite models combine the screw characteristic curve of individual element to analysis flow of an entire modular screw and the flow fields of the whole region are not calculated again. Based on the linear relationship of the drag flow rate and the screw rotating speed under the single screw extrusion theory, the new mesh with artificial screw rotation speed boundary conditions was used to simulate the entire flow analysis for the co-rotating twin screw extrusion process in our 2D composite models.To demonstrate applicability, the results provided by our 2D composite models were found to similar to those of 1D composite models, through Fenner’s single screw example. The pressure and filling factor profiles in a modular TEX44 extruder provided by 2D composite models show good agreements with Fukuoka's calculated results and experiment data.
Sequential Mixing Methods of Environmentally Benign Nanocomposites from Cellulose Acetate/Plasticizer/Organoclay System
Injection molded nanocomposites have been successfully fabricated from cellulose acetate (CA), triethyl citrate (TEC) plasticizer and organically modified clay. The effect of sequential mixing methods and plasticizing conditions on the performance of these nanocomposites has been evaluated. The mechanical and thermal properties of nanocomposites are correlated with the XRD and TEM observations. Cellulosic plastic-based nanocomposites with 75-minute pre-prasticized CA/TEC/organoclay showed the best exfoliated structure.
Application of GRP for Chimney Liners Exposed to Sulfur Dioxide and Sulfur Trioxide
Innovative development and application of a multilayer GRP structure for chimney liners exposed to sulfur dioxide and sulfur trioxide are described.The structure is made by winding. It includes a chemical proof layer, a constructional layer and an external layer.Inspections have shown no deterioration of GRP after three months of operation. GRP are affective constructional material of the universal purpose.
Novel Technique for Predicting Long Term Resistanse of Chemical Resistant GRP
A novel technique of estimating the lifetime of chemical resistant GRP is described.Destruction of GRP is considered as a heterogeneous chemical reaction of the first or zero order with constant energy of activation.Based on these estimations, it is recommended to use GRP for chimney liners exposed to sulfur dioxide and sulfur trioxide. Received results were used for forecasting of service life of GRP.
Rheological, Thermal and Mechanical Behavior of Polyolefins/Sea Shells Composites
The rheological, thermal and mechanical behavior of polypropylene (PP) and high density polyethylene (HDPE) filled with sea shells composites at different concentrations of filler were investigated. The composites were prepared by extrusion and injection molding. Most filler addition to composites promoted a slightly increase on the melt viscosity, improve the tensile modulus and the thermal stability in all composites studied.
Study on the Characteristic of Axial Circular Flow Field in Co-Rotating Intermeshing Twin-Screw Extrusion
In order to improve the mixing ability and elongate the mean residence time in twin-screw extruders, the axial circular flow was introduced in this study. A non-intermeshing section was set in the co-rotating twin-screw extruder, in which one screw was equipped with reverse conveying elements and the other with forward conveying elements. In the current work, a three-dimensional simulation of the flow in the axial circular flow section was developed by FEM package, ANSYS. Based on the calculated pressure and velocity profile, the pressure-throughput behavior and mixing ability of the axial circular flow section were discussed. Compared with the conventional conveying elements, the circular flow section has reduced ability to conveying but its distributive mixing capability was largely increased. Visualization experiments showed that the simulation results were in good agreement with the experimental outcomes.
3-D Modeling of Polymerization in Conveying Screw Element in Twin-Screw Extruder
The polymerization of ?-caprolactone in fully intermeshing conveying screw elements of co-rotating twin screw extruders was simulated with Fluent. The effects of the pitch on the element, temperature, flow rate, and screw rotating speed upon the reaction progression were investigated. It was found that the back-flow in the screw element affects the progress of polymerization. The simulation result from 3-D model differs significantly from 1-D model, especially in relation to slow reactions. This is because reaction is very sensitive to temperature change, and the value of heat transfer coefficient at the barrel and screw surface used in 1-D model may not represent the real conditions in extruders.
Investigation on Extrusion Property of PSE?Polygon Screw Element in Co-Rotating Twin Screw Extruder
PSE (Polygon Screw Element) is a new screw element, designed to meet the development of co-rotating twin-screw extruders toward high rotating speed and excellent mixing capability. In the present study, a three-dimensional flow field simulation of PSE element was carried out by the ANSYS FEM package. Pressure profile and shear stress profile were obtained. The mixing ability of PSE element was also analyzed. The simulation results of the flow field in PSE element were verified by experiments. It was found that the energy consumed in PSE element is smaller, whereas its mixing ability is better than the kneading block. Furthermore, PSE element is suitable for the fiberglass reinforced processing.
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