Co-rotating Intermeshing Twin Screw Extruder Research Articles

Preparation and Characterization of PP/Organoclay Nanocomposites with Maleic-Anhydride

Polypropylene (PP)/organoclay nanocomposites were prepared via a melt-mixing method through two-step melt compounding using a co-rotating intermeshing twin screw extruder. Maleic anhydride grafted polypropylene (PP-g-MA) was adopted during compounding as a compatibilizer. Structural investigations via X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed the intercalated morphology of the nanocomposites. The use of PP-g-MA led to not only good clay dispersion but also heterogeneous intercalation. Thermal degradation of the PP nanocomposites was studied by thermogravimetric analysis (TGA). Rheological properties of the PP/organoclay nanocomposites were also investigated via a rotational rheometer in which linear viscoelastic measurements were performed in oscillatory shear with small strain amplitude. Storage (G’) and loss (G”) moduli were found to be increased at all frequencies with increasing clay contents.

Effect of processing conditions on morphology and mechanical properties of compatibilized polypropylene nanocomposites

This work focuses on the influence of processing conditions on the nanocomposites structure, i.e. intercalated or exfoliated, and on the enhancement of mechanical properties of polypropylene (PP) nanocomposites. These nanocomposites were prepared using the melt intercalation technique in a co-rotating intermeshing twin screw extruder. In order to optimise processing conditions, both screw speed and barrel temperature profile were changed. The role of the compatibilizer (maleic anhydride grafted polypropylene) was also studied. The results obtained show that the barrel temperature is a very important parameter: using lower processing temperature, the apparent melt viscosity and, consequently, the shear stress are higher and, therefore, the exfoliation of the clay is promoted. Even using optimised processing conditions, exfoliation of clay can be achieved only when an high compatibility between polymer and clay exists: the PP nanocomposites containing maleic anhydride show an exfoliated structure and a sensible enhancement of mechanical properties while PP nanocomposites without compatibilizer show a structure mainly intercalated and a lower improvement of mechanical properties.

Thermal behaviour of compatibilised polypropylene nanocomposite: Effect of processing conditions

The thermal properties and fire behaviour of polypropylene (PP) nanocomposites were investigated using differential scanning calorimetry, dynamic-mechanical analysis, thermogravimetric analysis and glow wire test. In order to study the morphological structure of the materials obtained, TEM and XRD analyses were also carried out. The nanocomposites were prepared using the melt intercalation technique in a co-rotating intermeshing twin screw extruder. Particular attention was given to studying the influence of different processing conditions (barrel temperature profile and screw rate) and compositions of PP–nanoclay blends (clay content, use of compatibiliser) on the thermal properties of the nanocomposites. The results show that all the properties analysed were strongly influenced by the nanocomposite composition; instead, the processing conditions greatly affect only the dynamic-mechanical properties. DSC curves show that the crystallinity is deeply influenced by the presence of the clay in the matrix, owing to the fact that the filler acts as nucleating agent. DMA curves show that materials processed at low temperature profile and high shear stress, i.e. when a good clay dispersion is achieved, are characterised by an enhanced modulus, thus indicating that the incorporation of clay into the PP matrix remarkably enhances its stiffness and has good reinforcing effects. TGA traces in oxidizing atmosphere show a drastic shift of the weight loss curve towards higher temperature and no variation of the onset temperature (i.e. the temperature at which degradation begins). The TGA analyses in inert atmosphere show instead marked increase of this parameter (about 200 °C) and no shift of weight loss curves. Glow wire results highlight that polymer nanocomposites are characterised by enhanced fire behaviour.

A Physico-Mathematical Model for the Dispersion Process in a Co-Rotating Intermeshing Twin Screw Extruder

To modify the properties of polymers, mineral fillers are frequently added during the compounding process. Due to adhesive forces, these pulverized fillers tend to agglomerate. Therefore, in order to achieve a good homogenisation, it is essential not only to distribute them but also to break down the solid agglomerates. A number of relating models have been published, describing observations (agglomerate rupture, erosion, clustering) made during the dispersion process in a mostly isolated manner. Here, a new model considering each observed effect has been developed in order to get a comprehensive description of the dispersion process. To verify the model, it was implemented into a program for the process simulation of co-rotating twin screw extruders (SIGMA [1]), and thus compared to experimental data. It showed that the model could well describe the experimentally determined data.

Theoretical analysis of the devolatilizing performance of an intermeshing co‐rotating twin‐screw extruder with a type of square‐channel flighted element

AbstractThe local film interfaces in the long vent section of an intermeshing, co‐rotating twin‐screw extruder (ICoTSE) with square‐channel flights (SFs) and the exposure time to the vapor phase were analyzed. A theoretical overall film‐interface geometry factor (OFIGFcal) was calculated from a new devolatilization (DV) model proposed previously by the authors, and the predictions were compared to the experimental results (OFIGFexp) for polystyrene/ethylbenzene (PS/EB). The OFIGF represents a measure of the devolatilization performance of the long vent section. The ratio of the experimental to the predicted apparent film interface areas was 5.5, which demonstrates the enhancing effect of the roughness and bubble‐forming behavior of the film interfaces on DV. The predicted concentrations of EB in the PS melt at the exit of the long vent section agreed well with experimental results.

Experiment and Prediction of Polymer Devolatilization in Screw Devolatilizer.

An experimental study on the devolatilizing performances of screw elements with different screw geometries in an intermeshing co-rotating twin-screw extruder (ICoTSE) was conducted using a polystyrene/ethylbenzene (PS/EB) system. The experimental devolatilization (DV) data and literature data obtained in the same type of ICoTSE with a different screw diameter for the same PS/EB system are correlated by the proposed model, where the effect of differences in screw geometries, screw diameters, degree of filling, and fully-filled length in the screw channels as well as changes in the operating temperature caused by the shear heat on DV are taken into account. Furthermore, the difference in the description of the surface renewal DV in a screw extruder between the proposed model and Latinen-type models in the case of ignoring the backmixing of axial dispersion is compared and discussed.

Pumping Characteristics of an Intermeshing Co-rotating Twin Screw Extruder

Abstract The pumping characteristics of several types of screw elements for an intermeshing co-rotating twin screw extruder (ICoTSE) were experimentally studied using molten polystyrene (PS) as a typical non-Newtonian fluid in “LABOTEX30α”. Here, the throughput was regarded as the remainder of drag flow minus pressure flow, based on the previous theoretical and experimental studies with regard to either single or twin-screw extruders. Therefore, the relationship between the throughput and the pressure gradient for a given screw geometry was approximately expressed as a linear dimensionless relation containing two so-called pumping-characteristic parameters which depend on the element geometry and degree of departure of the used fluid from the Newtonian fluid. The pumping-characteristic parameters for two right-hand flighted screw elements (RF) with leads of 0.938D and 0.703D, a neutral kneading disk (NK) and a blister ring (BR) were experimentally determined, and the RF with a lead of 0.938D was taken as an example to observe the effect of the clearance between it and the barrel wall on its pumping-characteristic. The results show that the linear relationship between the dimensionless throughput and the dimensionless pressure gradient for each type of the screw elements used here is a good approximation, and the clearance in the range used here greatly affects the pumping characteristic of the RF. Moreover, the degree of filling and the pressure profile in two kinds of screw configurations used for water-injection foaming devolatilization, which consist of elements with different diameters but with the same dimensionless geometry as those used in this work, were predicted and discussed by using the determined pumping-characteristic parameters under the conditions of given throughput of molten PS and screw speed.

Morphological changes in nylon-6/acrylonitrile-butadiene-styrene reactive blend

The morphological changes of blends of nylon-6 and acrylonitrile-butadiene-styrene (ABS) with reactive compatibilizer [poly(N-phenylmaleimide-styrene-maleic anhydride)] as a function of viscosity ratio of the components, concentration of compatibilizer, and the feed rate have been studied using an intermeshing corotating twin screw extruder. The occurrence of reaction between the amine end group of nylon-6 and maleic anhydride of compatibilizer during melt blending was identified by the solvent extraction and infrared spectroscopy study. It was found that the minimum dispersed phase size occurred at the viscosity ratio (p) = 0.75. Dispersed phase size was decreased significantly by the addition of compatibilizer and tended to equilibrate at about 15 wt % compatibilizer based on the amount of nylon-6. It was observed that the morphology was strongly dependent on the feed rate. The presence of maximum dispersed phase size was observed as a function of feed rate. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1595–1604, 1997

Analysis of morphology development of immiscible blends in a twin screw extruder

Blending processes are primarily carried out in corotating intermeshing twin screw extruders. Because the knowledge about morphology development in such extruders is limited methods to obtain a desired morphology are based on empirical values and screening experiments. For the analysis of morphology evolution, a new special sampling device was developed which enables melt sampling in time periods of less than 10 seconds. With this technique integrated in an intermeshing corotating twin screw extruder, ZSK 40, it is possible to detect morphology development along the extruder screw nearly in real time. The performance of the developed method was verified by observation of morphology development in a polypropylene/polyamide-6 blend system along a screw section. A difference in morphology development caused by a variation of the screw rotational speed was observed. Furthermore, drop deformations in partially filled screw sections could be detected. © 1997 John Wiley & Sons, Inc. Adv in Polym Techn 16: 1–10, 1997

Effects of processing parameters on the in situ compatibilization of polypropylene and poly(butylene terephthalate) blends by one‐step reactive extrusion

This paper concerns the effects of processing parameters on the in situ compatibilization of polypropylene (PP) and poly(butylene terephthalate) (PBT) blends by one-step reactive extrusion in a corotating intermeshing twin screw extruder. This in situ compatibilization process was characterized by a sequential arrangement for the free radical grafting of glycidyl methacrylate (GMA) onto PP and the interfacial compatibilization reaction between the GMA functionalized PP and the terminal carboxylic group of the PBT. Among the processing parameters examined were feed rate (Q), screw speed (N), and specific throughput (Q/N). Their effects were evaluated by the associated mechanical properties of final blends in terms of elongation at break and impact strength. Results showed that elongation at break and impact strength increased virtually linearly with decreasing Q or N. Moreover, for a particular Q/N, they increased with decreasing Q with a concomitant decrease in N. Further analysis of these results showed that it is through residence time that these parameters affect the performance of the above mentioned in situ compatibilization process. © 1996 John Wiley & Sons, Inc.

Effects of processing parameters on thein situ compatibilization of polypropylene and poly(butylene terephthalate) blends by one-step reactive extrusion

This paper concerns the effects of processing parameters on the in situ compatibilization of polypropylene (PP) and poly(butylene terephthalate) (PBT) blends by one-step reactive extrusion in a corotating intermeshing twin screw extruder. This in situ compatibilization process was characterized by a sequential arrangement for the free radical grafting of glycidyl methacrylate (GMA) onto PP and the interfacial compatibilization reaction between the GMA functionalized PP and the terminal carboxylic group of the PBT. Among the processing parameters examined were feed rate (Q), screw speed (N), and specific throughput (Q/N). Their effects were evaluated by the associated mechanical properties of final blends in terms of elongation at break and impact strength. Results showed that elongation at break and impact strength increased virtually linearly with decreasing Q or N. Moreover, for a particular Q/N, they increased with decreasing Q with a concomitant decrease in N. Further analysis of these results showed that it is through residence time that these parameters affect the performance of the above mentioned in situ compatibilization process. © 1996 John Wiley & Sons, Inc.

Simulation of Continuous Polymerization in a Modular Intermeshing Co-rotating Twin Screw Extruder

Abstract A method of modeling chemical reactions in a modular inter-meshing co-rotating twin screw extruder is described. This is applied to simulate the anionic polymerization of caprolactam. Calculations are made for specific modular screw configurations. The screw configurations included both screw elements and kneading disc blocks. Reaction conversion and temperature rise were calculated along the screw axis. The results are compared to experiment.

A study of degradation of high density polyethylene in a corotating intermeshing twin screw extruder

AbstractA study of the effect of extrusion conditions on the degradation of high density polyethylene was carried out. The extent of degradation was quantified by dynamic viscometry. The effect of barrel temperature profile, screw speed, and feed rate on the degradation of high density polyethylene was determined. The viscosity response of high density polyethylene is complex with respect to extrusion conditions. Residence time studies were carried out to correlate the viscosity data. Simulations of simple theoretical models give an insight into the flow behavior of the polymer in a twin screw extruder.

Fluid Mechanics of Distributive Mixing in a Modular Intermeshing Corotating Twin Screw Extruder

Abstract A theory of distributive mixing in a modular intermeshing corotating twin screw extruder is described. This is based on the Spencer – Wiley premise of representing mixing through interfacial area increase and its relationship to shear strain. The increase of interfacial area in both screw elements and kneading disc elements is analyzed. The flow in screw elements has a figure eight configuration but basically is analogous to flow in a single screw extruder. The primary mixing mode in these machines is within the kneading disc elements. A model for increase of interfacial area, which includes backflows through kneading disc tips, is developed. The kneading disc and screw element models are combined to compute interfacial area development in modular twin screw machine. We consider that modular twin screw extruders often have regions of starvation. To apply this model it is necessary to know flow configurations such as may be determined by a composite model of the total flow such as has been developed by the authors and their coworkers in earlier papers.

Non-Newtonian flow modelling in the screw regions of an intermeshing corotating twin screw extruder

We model the low of a non-Newtonian fluid obeying a power-law model through the screw elements of a self-wiping intermeshing corotating twin screw extruder. The flow is modelled for a power-law viscosity function using both a finite element method and a lubrication theory modified FAN procedure. The finite element method yields machine direction and transverse velocity fields. The screw pumping correlations developed from the two methods agree within ten percent.

Improved Model of Flow in the Kneading Disc Region of an Intermeshing Co-Rotating Twin Screw Extruder

Abstract A new modelling analysis and simulation of flow in the kneading disc region of an intermeshing corotating twin screw extruder is presented. The modelling takes account of the complex flow behavior between the intermeshing kneading discs. This leads to alternate expansions and compressions of the local volume between the intermeshing regions and the chamber wall. This fluctuating volume modifies the flow fields and acts as a pump.

An improved theory of metering in an intermeshing corotating twin‐screw extruder

AbstractAn improved analysis of flow in the screw elements of an intermeshing corotating twin screw extruder is presented. The new theory based on an isothermal Newtonian fluid model allows explicit consideration of the geometry of the intermeshing region. Flow rates are computed as a function of the pressure gradients and screw speeds. Both left‐handed and right‐handed screws are considered.