Published by De Gruyter

Volume 18 Issue 3

Issue of International Polymer Processing

Contents
Journal Overview

June 3, 2013

Page range: 217-217

Editorial

June 3, 2013

First in a Series: Polymer Processing in Developing Countries Polymer Processing in Peru

Fernando G. Torres

Page range: 218-218

Screw Extrusion

June 3, 2013

Modeling and Analysis of Helicoidal Flow in a Conical Extruder

A. Sarioglu, J.-A. E. Månson

Page range: 219-225

Abstract

The present paper discusses the unique flow behavior in a new type of extruder. The extruder design is based on a hollow conical assembly of static (stators) and rotating (rotor) parts. Extrusion is achieved from each side of the rotor to provide a two-layer annular product. Flow is helicoidal in the vicinity of the rotor tip and die entry where the polymer layers merge. However, it becomes fully parallel to the main extrusion direction after a certain distance downstream from the rotor tip. Numerical simulations based on the resolution of Navier-Stokes equations using a Generalized-Newtonian viscosity showed that the length of the helicoidal flow depends on die design, viscosity and flow rate ratios between adjacent polymer layers. Analysis of flow variables along the interface showed that the helicoidal flow distance can be increased using a die design inducing lower interfacial shear rate and velocity. When the viscosity ratio and the flow rate of the most viscous polymer are increased, the helicoidal flow can be maintained over a longer distance in the die. Finally, experiments have shown that the advantage of the helicoidal flow is for short fiber orientation in pipes. The fibers are oriented along the streamlines in the hoop direction in the mid-gap of the die; however, they are parallel to extrusion direction in the vicinity of the stators.

June 3, 2013

A Powerful Universal Plasticating System for Single-screw-extruders and Injection-moulding Machines

E. Grünschloβ

Page range: 226-234

Abstract

The plasticating principle, named HELIBAR for single-screw-extruders [1 to 5] is described and recent experimental results with a HELIBAR - extruder Ø 50×34 D are presented. They prove, that with only one barrier-screw the most different thermoplastic polymers can be processed successfully with very high throughput, good process stability, low melt-temperature and good melt-homogeneity. This concerns standard polymers (PE, PP, PS) and so-called technical polymers (PA, PC, PET, PBT, PMMA) as well as soft polymers and elastomers (PVC-W, PUR, TPE, EVA). Besides, this system in a standard design was tested successfully with a fast-running injection moulding machine Ø 70 × 23 D with different polymers (PS, PP, PE-HD). Compared to previous high-performance screws - with the same installed driving power - lower melt temperatures, good melt homogeneities and enhancements of the plasticating power between 20% and 100% were achieved.

June 3, 2013

Cross Channel Flow Velocity and Motion Trajectory of Polymers in a Helical Channel

R. Sikora, E. Sasimowski

Page range: 235-242

Abstract

In reference to the comparison of polymer flow along the helical channel in the screw-based plasticating system in dependence from a kinematical system, which was presented in the previous publication [1], further comparative studies on these models in the range of cross channel flow and resultant flow were conducted. Studies were carried out for both previously described models that is the model with a rotating barrel and the model with a rotating screw. It was stated that polymer cross channel flow velocity and its distribution is different in both models and in both coordinate systems (rectangular coordinate system and helical coordinate system). In a rectangular and helical coordinate system the highest values of the drag (redrag) cross channel flow velocity are the same, the differences occur in the distribution of these velocities. The distribution of the pressure flow velocity is different in both coordinate systems. The conducted analysis of the resultant flow lets us state the differences in the motion trajectory of the polymer particle in both compared models. The spiral lead of the motion trajectory of the polymer particle is higher when the barrel rotates than in the model with a rotating screw. The cause of it lies in different barrel and screw peripheral speeds. Different senses of rotation of the barrel and the screw cause laevorotatory helical motion trajectory when the barrel rotates, and dextrorotatory when the screw rotates, whereas the behaviour of the polymer particle in the vicinity of the screw flight - change of direction by π/2 is the same.

Mixing and Compounding

June 3, 2013

Influence of Low Molecular Weight Additives on Die Extrusion Rheometer Flow of Thermoplastic Melts

S. Ahn, J. L. White

Page range: 243-251

Abstract

An experimental study of slippage induced in various thermoplastics in rheometers by the presence of small amount of low molecular weight additives is described. Capillary and cone-plate experiments are reported. A series of polymers of varying polarity including polyethylene, polypropylene, polystyrene, poly (methyl methacrylate) and polyamide 12 are compared. Five eighteen-carbon amphiphilic ω-compounds are used as additives including octadecanoic acid, octadecanamide, octadecanol, calcium stearate and zinc stearate. The greatest effects were found in polyethylene and polypropylene. Little or no effects are found with the other polymers. The most effective additives were octadecanoic acid and zinc stearate. Octadecanamide and octadecanol had some effectiveness. Mechanisms for this behavior are described.

June 3, 2013

Design of a Static Temperature Scanning Ultrasonic Measurement System and Application to Multi-phase Polymer Systems

G. Adebayo, M. Cakmak

Page range: 252-259

Abstract

A static bench ultrasonic setup was designed and implemented after due consideration for the heat transfer characteristics. The set up allows the measurement of the temperature profile of pertinent ultrasonic variables. The ultrasonic attenuation-temperature profiles in a few compositions of a partially miscible blend of Poly(α-methyl styrene acrylonitrile)/Poly(methyl methacrylate), as well as a PVC compound filled with mineral calcium carbonate fillers of three different particle sizes were followed using this set up. It was found that as the temperature was increased, the attenuation decreases with increase in the PαMSAN content of the blend, reached a peak and then decreases with further temperature increase. The peak value occurred in the 1-phase region while the peak temperature increases with PαMSAN content in the chosen blends. In the filled PVC system, the attenuation also increases with filler loading, especially within the vicinity of typical processing temperatures. The ultrasound technique, if applied to polymer processing, looks promising especially in closed regions along processing equipments.

June 3, 2013

Raman Spectroscopy as an On-line Technique to Monitor Shear Flow Effect on Partially Miscible Polymer Blends

G. Adebayo, P. Koombhongse, M. Cakmak

Page range: 260-272

Abstract

The phase behavior of two partially miscible polymer blends in simple shear flow was monitored on-line by Raman spectroscopy and subsequently with optical light microscopy on the resulting extrudate. Emphasis was placed on investigating the phase behavior in two polymer blend systems of high and low shear viscosity as they flow through a custom built flow cell with slit conduit. Shear flows initiated from one- and two-phase temperatures were monitored in the higher viscosity blend system of poly(α-methyl styrene–co-acrylonitrile) (PαMSAN) and poly(methyl methacrylate) (PMMA). For the second lower viscosity blend of poly(styrene–co-acrylonitrile) (PSAN) and PMMA90, shear flow was conducted at one-phase temperature and various shear stresses. These blends exhibit a lower critical solution temperature (LCST). The chosen blend composition used for PαMSAN/PMMA had the widest miscibility window in view of the high viscosity of the neat polymers, while for PSAN/PMMA90 blend, a composition very close to the LCST was investigated for the shear flow effects. We observed that for a blend composition of PαMSAN/PMMA system, at small temperature gap from the quiescent cloud point curve, the morphological effects due to shear heating overrides other effects. For a lower melt viscosity blend composition of PSAN/PMMA90, shear induced demixing initially occurs at low shear rates, shear-induced mixing regime follows with increasing shear flow prior to the onset of shear heating effects that brings the material to two phase region resulting in creation of locally optically observable demixed regions where the temperature rise due to shear heating across the extrudate are at maximum.

Reactive Extrusion

June 3, 2013

Flow Effects on Polymer Transesterification

I.-K. Yang, C. Y. Hong, P. H. Pan

Page range: 273-276

Abstract

Transesterification between poly–ε–caprolactone (PCL) and polyethylene-terephthalate (PET) under shear flow was investigated. Two types of flow were imposed to the test samples; one is a simple shear and the other is an oscillatory shear. Comparing to reaction at quiescent state, flow provides better conversion to the reaction. For simple shear flow, the rate of reaction increases as the shear rate increases, while under oscillatory flow, increasing the frequency and the amplitude enhances the extent of reaction. Improvements of the transesterification rate by simple shear prevail over those by the oscillatory motion. The results imply that the transesterification is mass transfer limited. The improvement of the reaction rate and the prevalence of the simple shear flow can be interpreted by the convective effect. The small margin between the rates of reaction under flow and at rest can be attributed to the small Reynolds number of the system.

June 3, 2013

A Dynamic Model Accounting for Oscillating Behavior in Reactive Extrusion

L. P. B. M. Janssen, P. F. Rozendal, H. W. Hoogstraten, M. Cioffi

Page range: 277-284

Abstract

A qualitative mathematical model on the oscillating behavior of reactive extrusion is presented. Through the introduction of stagnant volume build up in the die as a result of the ongoing reactive extrusion process, a variable time dependent die resistance emerges. A differential equation for the waxing and waning of stagnant volume in the die is developed. This equation is able to give oscillating behavior for certain extruder parameters and viscosity when coupled to an existing dynamic model of the fully-filled length. The effects of reaction rate, rotational speed, feed rate, die resistance and degree-of-fill are studied.

June 3, 2013

Study on Functionalization of Isotactic PP with Maleic Anhydride in an Internal Mixer and a Twin-screw Extruder

S. M. Ghahari, H. Nazokdast, H. Assempour

Page range: 285-290

Abstract

The grafting reaction of maleic anhydride to molten iPP was investigated in both an internal mixer and a twin- screw extruder. The influence of peroxide content, added maleic anhydride and process variables such as residence time, screw speed and reaction temperature were considered. The rate and level of grafting were quantitatively measured by FTIR and titrometery technics. Maximum level of grafting at constant peroxide content was obtained when concentration of added maleic anhydride reached up to 6%, above which is declined. The rate of grafting increased with increasing the peroxide content. However the β-scission of polypropylene was found to be taken place as a parallel competitive reaction which was intensified with increasing peroxide content. It was demonstrated that it is possible to make an optimization on the grafting reaction on the basis of experimental results in conjunction with a free radical kinetic model developed for this reaction.

June 3, 2013

Quality Aspects on the Power Cable Core Insulation Extrusion and Thermal Curing Process

A. Harlin, P. Huotari

Page range: 291-297

Abstract

The insulated core quality of power cables is directly linked to the performance of the cable in its end-use. The high voltage distribution installations at 10 to 500 kV range are large, expensive, and essential for community. Consequently, the most important quality properties are therefore the expected service life of the cable and its manufacturing costs. Standard cable constructions, with the exception of the extra high voltage (EHV) construction for over 385 kV, have substantial overdimensioning in the insulation layer thickness. Medium voltage cables in the range 10 to 35 kV (MV) are increasingly becoming commodity items and the cost function has become critical to the economic viability of cable production. Insulated core quality depends on the raw materials quality, e. g. the purity of the peroxide cross-linkable PE-LD. The extrusion process and insulation curing process should be considered as the major quality aspects. The total quality of the cable can be assured only if manufacturing is made correct at once. In the following is reviewed the good practice and related aspects based on marked field experience.

Die Extrusion

June 3, 2013

Flow Balancing in Extrusion Dies for Thermoplastic Profiles

Part I: Automatic Design

J. M. Nóbrega, O. S. Carneiro, P. J. Oliveira, F. T. Pinho

Page range: 298-306

Abstract

To achieve a specified geometry for an extruded profile, together with a minimal degree of internal stresses, flow balancing of the die is required. To attain this objective, the flow along a profile die channel must be accurately described, and this demands a computational code able to predict complex 3D non-isothermal flow patterns. In this work new methodologies for flow balancing are implemented and illustrated. The design code developed to carry out the automatic search of a final geometry consists of an optimisation routine coupled with geometry and mesh generators and a 3D computational code based on the finite volume method. The issues discussed and described here encompass recent developments, namely the implementation of two alternative optimisation algorithms for the automatic search of a final solution, the enhancement of the strategies previously developed to balance the flow, some improvements in the routine used to generate the mesh and the adoption of a progressive mesh refinement technique. The examples show that the proposed methodology performs well and the solution is attained in just a few minutes of calculation without any user intervention during the calculation process.

June 3, 2013

Flow Balancing in Extrusion Dies for Thermoplastic Profiles

Part II: Influence of the Design Strategy

O. S. Carneiro, J. M. Nóbrega, P. J. Oliveira, F. T. Pinho

Page range: 307-312

Abstract

To achieve a specified geometry for an extruded profile with minimal level of stress gradient induced by pulling, flow balancing of the die is required. To fulfil this requisite, a set of operating conditions and polymer rheological properties is considered during the design step. However, fluctuations of the operating conditions and/or slight variations of the polymer rheological properties are expected to occur during long-term production. Their effect on the performance of an extrusion die will depend, among other things, on the sensitivity of the flow distribution within the die. In this work, an extrusion die is optimised (balanced) using four different design methodologies and the final shapes of the die are compared in terms of their absolute quality (when used in the optimal conditions) and stability to the factors considered. For this purpose, a finite-volume based computational code is used to perform the required simulations of the non-isothermal three-dimensional flows, under conditions defined by a statistic Taguchi technique. The influence of some operating conditions on the flow distribution is assessed and the effect of the polymer melt rheology is also investigated. It was concluded that the use of different design methodologies lead to different results in terms of flow balancing and sensitivity to the factors considered and that the most balanced and stable extrusion die was that generated by the strategy based on the parallel zone thickness control.

Molding

June 3, 2013

On the Residual Stress and Shrinkage in Injection Compression Molding

W.-B. Young

Page range: 313-320

Abstract

Injection compression molding is a process having a compression action in the filling or postfilling stages. This process is suitable for molding of parts with precision features. The success of an injection compression molding process relies on proper design of the mold and selection of process conditions. The main scope of this study is to develop an analysis tool for the residual stresses and shrinkage of an injection compression molding process. A simple thermoviscoelastic model was used to calculate the stress and relaxation developed in the postfilling stage. The model divides the thickness into two regions, glassy and rubbery phases. Residual stress calculation is applied in the glassy region, while the rubbery region is kept at the melt pressure without any strain because of the fast relaxation in this region. The resulted in-mold stress fields are used to calculate the part shrinkage after demolding. The effects of the compression force on the residual stresses and shrinkage of a molding part were also investigated. Higher compression force tends to reduce the part shrinkage but induces a higher level of residual stresses.

About this journal

International Polymer Processing offers original research contributions, invited review papers and recent technological developments in processing thermoplastics, thermosets, elastomers and fibers as well as polymer reaction engineering. For more than 25 years International Polymer Processing, the journal of the Polymer Processing Society, provides strictly peer-reviewed, high-quality articles and rapid communications from the leading experts around the world.
All articles are subject to thorough, independent peer review.
Editor: Polymer Processing Society

Volume 18 Issue 3

Issue of International Polymer Processing

Contents

First in a Series: Polymer Processing in Developing Countries Polymer Processing in Peru

Modeling and Analysis of Helicoidal Flow in a Conical Extruder

Abstract

A Powerful Universal Plasticating System for Single-screw-extruders and Injection-moulding Machines

Abstract

Cross Channel Flow Velocity and Motion Trajectory of Polymers in a Helical Channel

Abstract

Influence of Low Molecular Weight Additives on Die Extrusion Rheometer Flow of Thermoplastic Melts

Abstract

Design of a Static Temperature Scanning Ultrasonic Measurement System and Application to Multi-phase Polymer Systems

Abstract

Raman Spectroscopy as an On-line Technique to Monitor Shear Flow Effect on Partially Miscible Polymer Blends

Abstract

Flow Effects on Polymer Transesterification

Abstract

A Dynamic Model Accounting for Oscillating Behavior in Reactive Extrusion

Abstract

Study on Functionalization of Isotactic PP with Maleic Anhydride in an Internal Mixer and a Twin-screw Extruder

Abstract

Quality Aspects on the Power Cable Core Insulation Extrusion and Thermal Curing Process

Abstract

Flow Balancing in Extrusion Dies for Thermoplastic Profiles

Part I: Automatic Design

Abstract

Flow Balancing in Extrusion Dies for Thermoplastic Profiles

Part II: Influence of the Design Strategy

Abstract

On the Residual Stress and Shrinkage in Injection Compression Molding

Abstract