The impact of applied processing history and the postprocessing annealing on the rheological properties of low-density polyethylene (LDPE) have been studied employing various kinds of conventional processing machines. Processing by a corotating twin-screw extruder (Co-TSE) and an internal batch mixer depressed the drawdown force, one of the elastic properties of a melt, to a great extent, even though molecular weight and the polydispersity did not change. On the other hand, the sample processed by a two-roll mill exhibited the drawdown force as high as the original pellets, which is owing to the intermittent stress history instead of the relentless. one in the Co-TSE and the internal batch mixer. Furthermore, the effect of screw configuration in the Co-TSE has also been investigated. It was found that the processing by conveying screws depressed the drawdown force and melt fracture more than that by kneading blocks as long as the torque and the residence time are the same. The large, abrupt, and frequent change in flow direction in the Co-TSE with kneading blocks prohibits the molecular orientation, which leads to disentanglement associated with long-chain branches. (C) 2003 Wiley Periodicals, Inc.

Switching to N 2 or CO 2 for foaming thermoplastics increases cooling requirements for a foam extrusion line. Factors affecting cooling heat transfer and proposed correlations are described. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 69–74, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10035

Plastic energy dissipation (PED) of polymer particulates is, essentially, the energy dissipated during large and repeated plastic deformations of compacted polymer particulates while still in the solid state. PED is higher or much higher than VED, the viscous energy dissipation source of polymeric melts, because the stresses necessary to plastically deform viscoelastic polymer solids are orders of magnitude higher than the stresses needed to support viscous flow. In the last few years our group has demonstrated experimentally the dominant role which PED plays in the heating/melting of solid polymer (compacted) particulate beds in compounding processing equipment, such as twin-screw extruders and counterrotating continuous mixers/melters, in which the deformation of solid polymers is mandatory We have also developed simple empirical methods of predicting the total axial distance needed for melting a given polymer in specific processing/compounding machines and processing conditions, as well as the melting rates, all based on the mechanical energy dissipated during solid particulate compression. This work explores the more complex issue of how the PED behavior of single-component polymers may affect the PED (and the heating/melting) behavior of multi-component polymer blends. (C) 2003 Wiley Periodicals, Inc.

The flow behavior of a Newtonian fluid through special mixing enhancers in a modular intermeshing co-rotating twin screw extruder has been examined. The mixing enhancers are slotted screws and gear mixing elements. Particular attention has been directed to drag and pressure flow characteristics and residence tune distribution in such devices. The data obtained are useful for guidance in the selection of appropriate mixing elements and validation of flow simulation models for twin screw extruders.

This paper investigates the use of a Helical Barrel Rheometer to measure the viscosity of filled polymer systems. A Helical Barrel Rheometer is an online rheometer developed at the Polymer Processing Institute. The HBR allows us to measure the viscosity of polymer systems under conditions close to that encountered in processing. The viscosity measurement does not require measuring either the torque or the flowrate. The rheometer does not require an entrance correction, avoids bridging of filler particles during measurement and also takes care of the orientation of fillers encountered in processing.This paper uses polypropylene/talc as a filled polymer system. Three different concentrations of three different grades of talc were used to measure the viscosity and a comparison with conventional capillary viscometer was made.

The use of a drag flow device such as a twin screw extruder for polymerization and/or copolymerization processes has been studied extensively over the years. Due to the high viscosities (100 to 100 000 poise) that are produced, poor backmixing is experienced in these drag flow devices. As a result, these studies have shown the extruder reactor to exhibit a ''plug flow'' behavior. A drag flow device has been developed that achieves good backmixing with high viscosity materials. This device incorporates two counter-rotating, nonintermeshing, screws; one screw conveying material forward, while the other conveying material backward. Theory suggests that in a plug flow reactor the copolymer composition varies (drifts) as a function of time (position) in the reactor in most cases. Conversely in a micromixed continuous stirred tank reactor (CSTR) the copolymer produced does not drift as a function with position in the reactor. It has also been shown that this drift in copolymer composition becomes more pronounced at higher conversion. Experiments were performed in a counter-rotating nonintermeshing twin screw extruder using the ''backmixed'' configuration and a ''conventional'' configuration. Two copolymer systems were investigated; butyl acrylate/styrene and butyl acrylate/butyl methacrylate. The copolymerizations were conducted at three residence times for each system and configuration to provide materials of a wide variety of conversions (13 to 97 %). Monomer samples were taken at two ports in the extruder and at the die. Samples were analyzed for composition by two methods; FTIR and refractive index (RI). It was shown that the copolymer composition of samples produced in the backmixed extruder reactor does not change significantly as a function of position in the reactor. This is an indication that the copolymer composition does not drift in the reactor. Theoretically this is the behavior that exists with a chain addition copolymerization that occurs in a CSTR. Two methods (RI, FTIR) were used in the copolymer formulation (BA/Sty) and one method (FTIR) was used in the other copolymer formulation (BA/BMA). It was further shown that the difference in copolymer compositions in the two extruder reactors is more pronounced at higher conversions than at lower conversions.

Deriving maximum benefit from the incorporation of fillers into polymers depends upon achieving uniform distribution of well wet-out individual particles. At higher loadings, the best practice is to add the filler downstream in the extruder after the base resin is fully melted. © 2000 John Wiley & Sons, Inc. Adv Polym Techn 19: 54–64, 2000

A counter-rotating nonintermeshing twin screw extruder specifically designed to provide extensive backmixing was used to investigate the molecular weight distribution (MWD) occurring in the polymerization of Butyl Acrylate and the MWD and drift of copolymer content occurring in the copolymerizations of Butyl Acrylate/Styrene and Butyl Acrylate/Butyl Methacrylate. In contrast to almost plug flow characteristics observed in conventional single screw and twin screw extruders, this backmixed extruder has a residence time distribution comparable to a continuous stirred tank reactor, yet provides a positive drag flow regime for high viscosity fluids not available in stirred pots. The polydispersity (M-w/M-n) of chain addition polymerizations carried out in the backmixed extruder was cut in half when compared to those obtained in a conventional (plug flow) extruder, thus producing a more monodisperse polymer, and approached the theoretical value for a micromixed CSTR. The copolymer content of chain addition copolymerizations carried out in the backmixed extruder was demonstrated to be constant as a function of position in the reactor, whereas drift was observed in the conventional (plug flow) extruder.

The flow behavior of a Newtonian fluid through special mixing enhancers in a modular intermeshing corotating twin screw extruder has been examined. The mixing enhancers are slotted screws and gear mixing elements. In addition to pressure and drag flow characteristics, particular attention has been directed to residence time distribution in such devices. The data obtained are useful for guidance in the selection of appropriate mixing elements and the validation of flow simulation models for twin screw extruders.

Rules of thumb are presented addressing aspects of twin screw processing to serve as guidelines for understanding and assessing performance of such equipment. Simple equations permit estimates of drag flow capacity, degree of fill, and residence time. Recommendations are made concerning conducting pilot scale tests and estimating scale-up consequences.

An experimental investigation was conducted to evaluate the performance of three single-screw mixing elements: a Maddock; a Pineapple; and a Twente mixer. The study was designed to focus on the mixers' performance in the mixing of immiscible polymers in the molten state. Two independently controlled melt streams were fed to the mixer and the evaluation of the mixer performance was based on the following criteria: (i) the processing characteristics, namely the pressure drop/rise across the mixer for specific machine and material operating variables; and (ii) the resulting quality of mixing as determined by image analysis of phase morphology on samples collected at the die. The mixing performance was judged both qualitatively, in terms of spatial material distribution, as well as quantitatively, by analysis for the size of the dispersed phase. The blending tests were conducted using three pairs of LDPE/PS systems having different rheological properties. In addition to the experimental work, the flow in the Maddock mixer was simulated using a commercial finite element package (FIDAP). The calculations were done using the experimental conditions and the properties of a pure LDPE phase. The simulation results were used to explain the dispersion data obtained experimentally. © 1998 John Wiley & Sons, Inc. Adv in Polymer Techn 17: 1–17, 1998

The versatile, rugged helical rheometer provides data in excellent agreement with off-line capillary rheometer data, and it can also handle fluids beyond the capabilities of conventional capillary and slit rheometers

Visual and microscopy analysis was performed on solid carcasses collected from the split-barrel Twin-Screw Mixing Element Evaluator (TSMEE) (1) to study melting phenomena and mechanisms of single-component polymers in twin-screw kneading blocks. The results were interpreted in terms of dissipative phenomena such as interparticle frictional heat generation, irreversible deformation and break of the particulate solids and viscous energy dissipation of the resulting melt or melt solid mixtures. Simple estimates of the thermal energy generated by each Of the above phenomena were carried out for a number of polymer systems of different particulate size and solid and melt properties. The contributions of each dissipative phenomenon on the heating of Polypropylene (PP) powder or pellets, LDPE and PET were experimentally evaluated.To better understand the effect of the particulate size distribution on the melting of PP powders, batch melting experiments were conducted with a regular Brabender batch mixer at the Polymer Processing Institute and with the glass end plate fitted apparatus of Dr. Chi-Kai Shih at his DuPont Laboratories.

Dispersive mixing of immiscible polymer blends as well as polymer systems containing solids is achieved in compounding equipment at two stages of the system's processing experience: first, while one or more of the polymer components are melting, and second, after all polymer components have melted. That is, the first mode of dispersive mixing occurs during the melting mechanism of ''dissipative mix melting'' (Ref. 1), while the second is melt-melt mixing.During the compounding of a given blend system, there are a number of processing parameters that can be changed in order to improve mixing. These range from machine operating variables to the addition of processing aids. If such processing changes fail to produce the desired morphology, the most common change to consider is the screw geometry. This, in practice involves a trial and error procedure, or the use of an existing database built from prior experience.The role which the thermomechanical and rheological properties of the blend component play in dissipative mix melting and melt-melt mixing has not yet been well understood. The reason for this is that although most blend systems have components which are strongly non-Newtonian and strongly viscoelastic, the thinking and rules of thumb for mixing such materials has been heavily influenced by the analysis of G. I. Taylor (Ref. 2), who in 1932 addressed the phenomenon of the dispersion of a single Newtonian droplet by a Newtonian matrix flowing in laminar shear flow.This paper addresses the strong role that the rheology of blend components, under processing conditions, play in laminar dispersive mixing of polymer blends. From a practical point of view, if the dispersion mechanisms and rates of dispersion depend on the component rheology, then such knowledge can lead us to the selection of advantageous mixing element designs and processing conditions.The experimental results were obtained in dispersive mixing carried out in devices developed in the Polymer Mixing Study (Ref. 3). Such model devices include the Couette Flow Intensive Mixer (CIM) (Ref. 4), where a constant shear stress is applied on the blend components and the Twin Screw Mixing Element Evaluator (TSMEE) (Ref. 5), where the mixing flows are those encountered in actual mixing/compounding operations. The TSMEE will be described in the body of this paper together with its on- and off-line morphology determination capabilities and its in-line rheology sensor.The low-density polyethylene (LDPE) and polystyrene (PS) polymers studied were selected because they cover a wide spectrum of rheological properties.

A new versatile on-line rheometer has been developed for monitoring process viscosities. The principle of this rheometer is based upon measuring the pressure differential across one flight of a special extruder wherin the helix is cut in the barrel rather than in the screw.On-line data from the new rheometer agree well with off-line capillary rheometer data. The new rheometer can also handle fluids beyond the capabilities of conventional capillary or slit rheometers.The relationship of wall shear rate for closed Couette flow has been determined for power law fluids.

The need for rapid process adjustment to maintain or achieve a desired product quality has led to the development of in-line and on-line techniques for process monitoring in the plastics industry. In large production setups, any time that a process parameter is changed, or a fluctuation in the process occurs, the time required for off-line analysis to check product quality is long enough for the generation of large quantities of material of unknown characteristics (1).On-line and in-line methods are increasingly in use for several reasons. For example, some applications process materials which may exhibit drastic changes once taken from the process line for off-line analysis, thus presenting challenging sampling procedures. In some other cases, factors such corrosiveness and toxicity preclude the use of off-line methods, and require closed-loop product evaluation techniques.This paper addresses recent developments in in-line/on-line sensors for monitoring blend rheology and morphology to evaluate the extent of mixing and/or reaction in continuous compounding equipment. Areas of possible applications as well as limitations of these sensors are discussed.