Extruder Configuration Research Articles

Process Behavior of Special Mixing Elements in Twin-screw Extruders

Abstract Tightly intermeshing, co-rotating twin-screw extruders are commonly employed for tasks requiring good mixing. The modular structure of both barrel and screw makes it possible to optimize the extruder configuration for a given task. Increasing demands on polymers have resulted in the development of more sophisticated mixing elements. In the framework of this investigation we looked at the pressure-throughput behavior of mixing elements in a conveying, reconveying and conveying-reconveying configuration. Furthermore, the local residence time distribution within those elements was investigated. We developed physical-mathematical models to describe the pressure-throughput behavior observed in the experimental investigations.

Analysis of Mixing in Corotating Twin Screw Extruders through Numerical Simulation

Mixing is a major ingredient in many industrial processes to obtain desired and uniform material properties. Nowadays, many materials, pigments, additives, gas or reactants, are mixed to create new products combining the characteristics of different raw materials to obtain specific product properties. The quality of the mixing, i.e. the uniformity of the mixture, is a key issue that will determine the morphology and the properties of the resulting compound [1, 2]. An insight in the physics of mixing is therefore necessary in order to achieve a good quality of mixing or maintain it when scaling equipment, for example. Such information can now be obtained through the numerical simulation of the transient flow in extruder components. To improve greatly the ease of obtaining such information, a new technique introduced in a finite elements software is presented. This technique simplifies the meshing, reduces the meshes needed and eliminates complex remeshing algorithms to simulate flow in screws, pumps and mixing devices. This technique is validated versus traditional simulation methods (i.e. conforming meshes). 3-D transient numerical simulations of two twin screw extruder configurations are then presented. A further quantitative comparison of their mixing behavior is developed as statistical information (of the RTD, deformations, dispersion, etc.) can be obtained to compare both configurations in a synthetic and quantitative way.

Effects of supercritical CO2 on the viscosity and morphology of polymer blends

Supercritical carbon dioxide (CO2) was used in extrusion for the improvement of polymer blend properties. Various extruder configurations using a twin-screw extruder and a single-screw extruder were designed for investigating the effects of dissolved supercritical CO2 on the viscosity and morphological properties of polyethylene, polystyrene, and their blends. The viscosities of the polymer/CO2 and the blend/CO2 solutions were measured at various concentrations of CO2 and PE/PS blending ratios using a wedge die mounted on the twin-screw extruder. The effect of CO2 on the morphology of PE/PS blends was also investigated using a twin/single-screw tandem system. This system allowed for preferential dissolution of the CO2 into the matrix and/or dispersed polymer phase. By introducing devolatilization to the tandem system, the morphological behaviors of PE/PS blends were investigated on unfoamed filaments. In general, the mixing between two polymers was improved by the dissolution of CO2. The size reduction of the dispersed phase was explained using the viscosity ratio of the two polymers. Finally, the interface between foamed and unfoamed polymers was studied in a bilayer structure produced by using a special configuration of the tandem system. © 2000 John Wiley & Sons, Inc. Adv Polym Techn 19: 300–311, 2000

Evolution of morphology in compatibilized vs uncompatibilized polyamide blends

The development of phase morphology in non-reactive vs reactive polyamide blends with a styrene acrylonitrile (SAN) copolymer and SEBS (a styrenic triblock copolymer with ethylene-butylene midblocks) in a co-rotating twin screw extruder was investigated using electron microscopy techniques. For the polyamide/SAN systems, significant differences were observed between the evolution of morphology in non-reactive binary blends vs blends compatibilized with a reactive imidized acrylic (IA) polymer which is miscible in the SAN phase and has functional groups which are capable of reacting with the amine end groups in the polyamide phase. While a steady decrease in the dispersed phase particle size was observed in general for the non-reactive nylon 6/SAN blends with both increasing screw length and speed, for the ternary nylon 6/SAN/IA blends a dramatic drop in the dispersed phase particle size was observed in the initial region of the screw almost immediately after melting of the pellets followed by some coalescence of dispersed phase in the latter stages leading to a dual population of particle at the exit of the extruder. The extent and onset of coalescence after attainment of minimum particle size in the initial region of the screw in reactive nylon 6/SAN blends was found to be strongly dependent on the screw speed and configuration. The extent of chemical reaction along the extruder screw for reactive nylon 6/SAN blends was dependent on the screw speed, extruder configuration and flow rate. While similar differences in the evolution of morphology were observed between non-reactive and reactive polyamide/SEBS systems, changing the polyamide type from monofunctional (nylon x, e.g. nylon 6) to difunctional (nylon x, y, e.g. nylon 6,6) revealed interesting differences even within these reactive blends. Significant differences in both the development of morphology and reaction profile along the screw were also observed between binary and ternary nylon 6/rubber blends containing similar concentrations of reactive maleic anhydride functionality in the rubber phase using a fixed screw speed and configuration.

Three‐dimensional flow modeling of a self‐wiping corotating twin‐screw extruder. Part I: The transporting section

AbstractA three‐dimensional modeling of the transporting elements in a self‐wiping corotating twin‐screw extruder has been carried out by using the finite element package Sepran (1). This simulation uses the 3D geometry of the channel rolled over the twin‐screw, which consists of the intermeshing and normal areas. The flow profile, the backflow volume, the pressure buildup, the shear and elongation rates, and the adiabatic axial temperature gradient have been calculated by solving the Navier‐Stokes equations and the continuity equation for a Newtonian fluid. These results are given for different extruder parameters such as the throughput of the extruder, the rotation speed of the screws and the helix angle of the screws to better understand the influence of different extruder configurations. This study belongs to a program of research on the self‐wiping corotating twin‐screw extruder that also includes the modeling of the kneading elements (Part II) and, in the future, the study of scale‐up and heat transfer.

Compatibilization of polyester/polyamide blends via catalytic ester‐amide interchange reaction

AbstractIn a series of publications we reported on melt rheology, morphology, and mechanical properties of the poly(ethylene terephthalate)/poly(amide‐6,6) blends (PET/PA). The non‐oriented samples had poor interphase bonding resulting in low impact and tensile strengths. To improve these properties the ester‐amide interchange reaction was carried out in solution and in melt. In the latter case a Brabender Plastograph was used in the mixing chamber or twin‐screw extruder configurations with p‐toluenesulfonic acid as a catalyst. The interchange reaction was followed by 400 MHz proton and 13C nuclear magnetic resonance spectroscopy.