Single Extruder Research Articles

Semi-Solid Processing of Chocolate and Cocoa Butter: Modelling Rheology and Microstructure Changes During Extrusion

This paper describes the development and application of a model that is capable of describing the extrusion behaviour of semi-solid chocolate. The model is based on the flow of a perfect plastic material within an extrusion die. During the isothermal extrusion process, work is carried out and a model has been developed to correlate the work done with the transformation of part of the crystalline triglyceride molecules to the liquid state. Numerical results from finite element calculations are presented for the variation of liquid fat content as a function of position within the extrusion die for a single extrusion, and analytical results are presented for the variation of the average liquid fat content and of the extrusion pressure for sequences of extrusions. The model demonstrates that, in certain situations, changes of a microstructural variable, rather than temperature changes, are necessary in order to describe the dissipation of work during a forming process.

Mechanical and Corrosion Properties of AZ31 Magnesium Alloy Repeatedly Recycled by Hot Extrusion

Machined chips of a magnesium ally were repeatedly recycled by hot extrusion at 673 K, and mechanical and corrosion properties of the recycled specimens were investigated. At room temperature, the recycled specimen with a high repeated number showed high 0.2% yield stress and high tensile strength but low elongation at room temperature. The main strengthening mechanism of the repeatedly recycled specimen was grain refinement strengthening. Inhomogeneous distribution of oxide contaminants adversely affected the elongation. At elevated temperature, the recycled specimen showed low strength and low elongation as the recycling was repeated. The recycled specimen by a single extrusion exhibited a superior corrosion resistance to the reference specimens. On the other hand, the repeatedly recycled specimen showed poor corrosion properties even though a large amount of oxides is contaminated. The deteriorated corrosion properties are caused by the excessive iron contamination which promotes pitting sites resulting from localized galvanic corrosion sites.

Induction of the ABC-Transporters Mdr1/P-gp (Abcb1), Mrp1 (Abcc1), and Bcrp (Abcg2) during Establishment of Multidrug Resistance Following Exposure to Mitoxantrone

Resistance to mitoxantrone is often associated with enhanced drug efflux mediated by members of the superfamily of adenosinetriphosphate-binding cassette (ABC) transporters, i.e. MDR1/P-gp (ABCB1), MRP1 (ABCC1), or BCRP (ABCG2). So far it is unclear whether the same ABC-transporter is always activated from the beginning of mitoxantrone treatment to the end of drug exposure. Here, we demonstrate that the expression of all three extrusion pumps is induced by increasing levels of mitoxantrone resistance, but in the end, merely the overexpression of a dominant single drug transporter, i.e. Mdr1/P-gp, is realized. This upregulation of Mdr1/P-gp was reflected by amplification of the Mdr1/P-gp encoding gene. Short mitoxantrone exposure demonstrated that upregulation of two different transporters, Mdr1/P-gp and Bcrp, was induced. The data indicate that mitoxantrone treatment influences the expression of several ABC-transporters, but in the end, merely a single extrusion pump will be dominant.

Development of an extrusion system for producing fine‐celled HDPE/wood‐fiber composite foams using CO2 as a blowing agent

AbstractThis paper presents an innovative design of a tandem extrusion system for fine‐celled foaming of plastic/wood‐fiber composites using a physical blowing agent (PBA). The plastic/wood‐fiber composites utilize wood‐fibers (WF) as a reinforcing filler in the plastic matrix and are known to be advantageous over the neat plastics in terms of the materials cost and some improved mechanical properties such as stiffness and strength. However, these improvements are usually accompanied by sacrifices in the ductility and impact resistance. These shortcomings can be reduced by inducing fine‐celled or microcellular foaming in these composites, thereby creating a new class of materials with unique properties. An innovative tandem extrusion system with continuous on‐line moisture removal and PBA injection was successfully developed. The foamed composites, produced on the tandem extrusion system, were compared with those produced on a single extruder system, and demonstrated significant improvement in cell morphology, resulting from uniform mixing and effective moisture removal. The effects of WF and coupling agent (CA) on the cell morphology were studied. An increase in the WF content had an adverse affect. The cell morphology and foam structures were improved when an appropriate CA was added. © 2004 Wiley Periodicals, Inc. Adv Polym Techn 23: 263–276, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20016

Simple Medicine

Abbott Laboratories’ diagnostics division claims that the systems improve laboratory workflow. A patented feature of the machines is an automated system called the retest sample handler, which can hold up to 135 sample vials for the i2000sr, 185 for the c8000, and 335 for the ci8200. The samples, which are accessible to a three-axis carrier transport robot, can be picked up in any sequence so they can be retrieved for retesting when it is necessary. Eliminating separate rails and associated fasteners and reducing machining of large surfaces resulted in significant cost savings. In addition, the single extrusion offers improved structural strength in the given space at the lowest weight. Fewer parts minimized tolerance stackup. Electronic components in the original design included circuit boards and cable harnesses in different configurations for each module type. The final design has 18-inch-long circuit boards that can be joined to form a continuous board up to 10-feet long, without cables.

Some functional properties of extruded orange pulp and its effect on the quality of cookies

Orange pulp was extruded using a Brabender single extruder (20:1 l/D) so as to modify the functional and structural properties of the fibre. The independent variables studied were: barrel temperature (83°C, 100°C, 125°C, 150°C, and 167°C), moisture content (22, 25, 30, 35, and 38g/100g), and screw speed (126, 140, 160, 180, and 194rpm). The feed speed was kept constant at 70g/min. The compression ratio was 3:1, and the die diameter was 4mm. The extrusion process increased the water absorption index (34.86g/100g), water solubility index (134g/100g), and swollen volume (43.75g/100g) and these variables were significantly influenced by the feed moisture content of the raw material and by the barrel temperature. The extruded orange pulp had 74.87g/100g total alimentary fibre, 54.81g/100g insoluble alimentary fibre and 20.06g/100g soluble alimentary fibre. Biscuits of good technological quality and with a good level of acceptance were obtained by means of replacing up to 15g/100g of the wheat flour with extruded orange pulp. The energy value of the biscuits decreased with increased extruded orange pulp content, with reductions of 2.95, 6.62, and 10.67g/100g in total calories as compared to the control.

Effect of process variables on melt velocity profiles in extrusion process using single screw plastics extruder

Single screw extruders are used to generate a continuous flow of molten polymer in many industrial polymer processes. The melt velocity profile as extruded is important in determining the properties of the final product and influences process related phenomena such as die swell and the onset of sharkskin. The factors that influence the velocity profile would be expected to be the melt temperature (this affecting the viscosity of the melt), the screw and die geometry, and the output rate from the extruder. In the present work a thermocouple mesh sensor coupled with a cooled stainless tube has been used to determine velocity profiles in melts exiting from the screw of a single screw extruder. The results show that the technique can be used successfully to determine velocity profiles in the extrusion process.It was found that the main influence on the magnitude of the melt velocity was the extruder screw speed. Melt temperature, and hence melt viscosity, were found to have little effect on the velocity profiles measured. The flow in the centre of the duct was retarded slightly owing to the flow across the screw tip and no rotational component of flow was observed. The velocity profiles measured seemed to be reasonably stable, only small changes being observed in the velocity profiles as the melt flowed along a duct of uniform cross-section, although these changes were limited in nature. Die diameter and length had a limited effect on the velocity profiles generated, although the die entry angle did have a significant effect on the shape of the velocity profile at higher screw speeds.

A Novel System Design for Continuous Processing of Plastic/Wood-Fiber Composite Foams with Improved Cell Morphology

It is believed that the moisture that is inherently present in nondried wood-fibers adversely affects the cell morphology of plastic/wood-fiber composite foams processed in extrusion. Based on this hypothesis, achieving a continuous extrusion-based production of fine-celled plastic/wood-fiber composite foams witha desirable quality would be strongly conditioned by the efficiency of the system designed for uninterrupted wood-fiber moisture elimination. This paper presents an innovative approachin addressing this problem by implementing the well-known cascade devolatilizing system in a chemical blowing agent (CBA) based production of plastic/wood-fiber composite foams. It comprises a moisture-evaporation tandem extrusion system equipped witha vent at the interconnection of the two extruders to serve for purging the moisture in the atmosphere. In order to check the performance of the newly developed system, an experimental study has been carried out for comparing the cell morphology and the volume expansion ratios of the foams obtained by processing identically formulated foamable plastic/wood-fiber composite mixtures using simultaneously the cascade devolatilizing tandem extrusion system and a corresponding single extruder withno vent. The experimental results revealed that the foams produced by using the cascade devolatilizing tandem system exhibited significantly improved cell morphologies and surface quality.

Degradation Profiles of Potato Starch Melts Through a Capillary Tube Viscometer

The effects of time-temperature and strain history on potato starch melts at 150 °C were investigated by use of a capillary tube viscometer. Reciprocating and single extrusions were performed in this study. Shear stress at single extrusion decreased gently as initial heating time increased, while shear stress at reciprocating extrusion decreased rapidly as the number of extrusion strokes increased. A high degree of cold water solubility was obtained by reciprocal extrusion at lower moisture content. From the results of gel filtration it could be concluded that starch molecules were depolymerized by high and reciprocal shear stress. According to these results time-temperature history was more effective on the depolymerization of starch molecules and degradation of starch granules at higher moisture content, while strain history was more effective at lower moisture content.

In situ composites: effect of elongational flow velocity on thermotropic liquid crystalline co-polyester fibrillation in thermoplastic/TLCP systems

This study focuses on the TLCP fibrillation process in a thermoplastic (PP) matrix during melt blending. The process of blending includes a single extrusion process in a twin-screw extruder with compatiblization and injection moulding of the extrudates. The TLCP, VA950 in situ fibrillation, compatiblization with PP and retainment of fibrils in the injection-moulded samples has already been achieved in our earlier study. However, the fibrillation process remains a complex issue. There are many factors like viscosity ratio, capillary number, composition, and flow speed which will affect the fibrillation. The elongational flow seems to be a more important factor affecting the TLCP fibrillation. The present study aims to identify the important factors which influence the TLCP fibrillation at their near-critical conditions. The morphological features and mechanical properties show that the compatiblization and elongational flow speed are very important for effective fibrillation.

The Strain Sensoring Behavior of the Melt-extruded Ethylene-vinyl Acetate (EVA)/carbon Black Composites Filament

In this study, Ethylene-vinyl acetate (EVA) based composites filament, with four different volume fraction of the nano-sized carbon black particles (NCB) were produced by melt mixing using a single extruder. The morphology of the EVA/NCB was studied using SEM, where a 3-D network of the NCB was presented. Thermal gravity analysis (TGA) measurement was utilized, denoting the degradation temperature of EVA, and presetting the actual volume fraction of NCB in the composites. Mechanical properties, e.g. elongation at break, tensile strength of the EVA/NCB filament was studied. Most importantly, the strain sensoring behavior of the EVA/NCB was investigated ultilizing a tensile testing machine coupled with a pico-ammeter. The gauge factor for various strain range, as well as the relative change of the resistance during the cyclic measurement of the NCB/EVA composites was calculated. Moreover, the measured data were fitted using some mathematical modellings, which reveals the potential of the strain sensoring behavior of the NCB/EVA composites in this study. Overall, this study introduces a durable NCB/EVA composites using as strain sensor oriented to industrial large-scale production, and the proposed modelling provides an effective evaluation method on its strain sensoring behavior.

Activation of bovine oocytes by specific inhibition of cyclin-dependent kinases.

Activation of bovine oocytes by experimental procedures that closely mimic normal fertilization and allow to obtain haploid oocytes is essential both for intracytoplasmic sperm injection (ICSI) and for nuclear transfer. Therefore, with the goal of producing haploid activated oocytes, this study evaluated whether bohemine, either alone or in combination with ionomycin, is able to activate young matured bovine oocytes. Furthermore, the effect of bohemine on the patterns of DNA synthesis after pronuclear formation as well as changes in histone H1 kinase and MAP kinase activities during the process of activation were studied. Our results with bohemine show that the specific inhibition of CDKs in metaphase II bovine oocytes induces parthenogenetic activation in a dose-dependent manner (25, 50, and 100 microM, respectively), either alone (3%, 30%, and 50%) or in combination with ionomycin (30%, 70%, and 87.5%). A single pronucleus and extrusion of the second polar body was observed (97%) when Ca(2+) influx was stimulated in the presence of bohemine, although pronuclear formation without polar body extrusion was observed when bohemine was used alone. Bohemine-activated oocytes started to synthesize DNA in the first hour (37%) after their removal from bohemine-supplemented medium (6-7 hr post-activation; hpa). A high synchrony in the S-phase was registered with more than 85% of parthenotes actively synthesizing DNA 8 hpa. By contrast, DNA synthesis was absent in oocytes cultured for 4, 6, and 8 hpa in the presence of bohemine and a low rate was observed by those cultured for 18 hr (30%) in bohemine-supplemented medium. This confirms the ability of the inhibitor to arrest the cell cycle in the G1/S boundary for at least 8 hr. A drop in histone H1 kinase activity was observed in bohemine-activated oocytes. The activity of MBP kinase decreased later than histone H1 kinase and even 4 hr after inomycin-bohemine treatment at least half of this activity was still detectable. Then, the MBP kinase activity decreased and the lowest level could be seen 6-8 hpa. In summary, our study shows that in vitro matured bovine oocytes can be successfully activated by a synthetic inhibitor of CDKs. This effect can be improved by combination with ionomycin. The targeting of CDKs in the way to activate bovine oocytes can be an approach to improve the efficiency of mammalian oocyte activation.

Thermal stability of polycarbonate composites reinforced with potassium titanate whiskers: effect of coupling agent addition

Polycarbonate (PC), and PC/potassium titanate (K 2Ti 6O 13) whisker composites were extruded in a single extruder. Methyltrimethoxy silane (C 4H 12O 3Si) and tetrabutyl orthotitanate (C 16H 36O 4Ti) were used as coupling agents for these specimens. Differential thermal analysis (DTA) and thermogravimetric (TG) measurements showed that the methyltrimethoxy silane coupling agent had little influence on the thermal stability of PC. On the other hand, the glass transition temperature ( T g ) and 5% weight loss temperature ( T −5%) of the extruded PC treated with tetrabutyl orthotitanate were much lower than those of PC treated with methyltrimethoxy silane. For the PC/potassium titanate whisker composites, both the T g and T −5% tended to shift to lowest temperatures with the use of a methyltrimethoxy silane coupling agent. The results indicated there is a synergistic effect between methyltrimethoxy silane and potassium titanate in degrading PC during compounding.

Morphology development of in situ compatibilized semicrystalline polymer blends in a co‐rotating twin‐screw extruder

AbstractThis paper concerns the morphology development of in situ compatibilized semicrystalline polymer blends in a co‐rotating, intermeshing twin‐screw extruder, using polypropylene (PP) and polyamide 6 (PA‐6) blends as model systems. The morphology of in situ compatibilized blends develops much faster that of mechanical ones. The size of the dispersed phase (PA‐6) undergoes a 104 fold reduction from a few millimeters to sub‐micron during its phase transition from solid pellets to a viscoelastic fluid. The final morphology is reached as soon as the phase transition is completed, which usually requires only a small fraction of the screw length in a co‐rotating twin screw extruder. Screw profiles and processing conditions (screw speed, throughput and barrel temperature) control the PA‐6's melting location and/or rate, but do not have significant impact on the ultimate morphology and mechanical properties of in situ compatibilized blends. The finding that morphology of PP/PA‐6 reactive blend develops rapidly makes it possible to produce compatibilized PP/PA‐6 blends by the so‐called one‐step reactive extrusion. It integrates the traditionally separated free radical grafting of maleic anhydride onto PP and the compatibilization of PP/PA‐6 into a single extrusion step.

Texture formation in bulk iron processed by simple shear

The preferred orientation of grains in iron after conventional deformation by cold rolling or drawing is characterized as sheet or fiber texture respectively. The main texture component in the rolling direction is [110](001). For the case of wire drawing, again, the [110] direction aligns with the wire axis. A novel method of straining materials called equal channel angular extrusion (ECAE), has recently been developed. This new processing method has the capability of introducing large amounts of plastic strain into bulk material in a relatively uniform manner without a reduction in workpiece cross-section. The processing concept is elegant; press a block of solid material through a constant cross-section tunnel composed of two intersecting channels. The purpose of the work reported here is to determine which kinds of texture are developed by three basic schemes of multipass ECAE. The schemes examined include what are termed route A, route B and route C. Route A maintains the same orientation of the shear plane and shear direction relative to the extrusion direction during all extrusions. Route B involves rotating the billet +90{degree} about the extrusion direction before each even numbered extrusion and {minus}90{degree} before each odd numbered extrusion. Route C processing includes an evenmore » number of extrusion passes with a +180{degree} or {minus}180{degree} rotation of the workpiece around the extrusion direction before each extrusion. Conventional sheet and fiber textures can be developed in bulk iron by using multipass ECAE processing. A shear texture results after a single extrusion. Multipass extrusions that return structural elements to their original shape after an even number of passes result in a texture that shows characteristics of both shear and the original texture.« less

In situ compatibilization of polypropylene and poly(butylene terephthalate) polymer blends by one-step reactive extrusion

This paper concerns the in situ compatibilization of immiscible polypropylene/poly(butylene terephthalate) (PP/PBT) blends by a one-step reactive extrusion process. By one-step reactive extrusion, we are referring to functionalization of the PP with a monomer bearing a desired functional group and the subsequent interfacial reaction of this functionalized PP with the PBT, where the whole operation is carried out in a single extrusion process. Three monomers, acrylic acid (AA), maleic anhydride (MA) and glycidyl methacrylate (GMA), which are potentially reactive towards the car☐ylic and/or hydroxyl groups at the chain ends of the PBT, were melt grafted on to the PP by free-radical reactions. A comparative study showed that GMA is more effective in compatibilizing the PP/PBT blends. Optimization of chemical parameters (initial concentrations of GMA and peroxide) and processing conditions (the sequence of addition of the materials, devolatilization of residual GMA, etc.) allowed us to obtain compatibilized PP/PBT blends with a fifteen- to twentyfold improvement in elongation at break and impact strength over an uncompatibilized PP/PBT blend. The in situ compatibilization performance of this one-step reactive extrusion process was comparable with that of a classical two-step process. In this latter case, the first extrusion step was to functionalize the PP with GMA, and the second one being the interfacial reaction between the functionalized PP and the PBT.

High Lysine Extruded Products of Quality Protein Maize

Ahstract: Extrusion-cooking is used by several food industries to produce expanded snack foods, ready-lo-eat cereals and pet foods frorn corn rneal. A snack food utilising normal rnaize and quality protein rnaize (QPM) as its rnain ingredient was developed and characterised. The extrusion process was perforrned in a Mapirnpianti single cooker extruder. Processing conditions were single screw with a screw speed of 150 rpm, and a die with 20 die-nozzle orifices with openings of 2 rnm of diameter. The die head zone was heated at 110°C by electrical resistance. Compressed air was circulated around the barre1 to rnaintain precise control oC the ternperature. Moisture content of sarnples were 150 and 200 g kg-'. The extruded producis showed low density and high expansion degree. Optimum expansion index was obtained with flours processed at 150 g kg-' of rnoisture content in both maize samples with better characteristics for QPM extrudates. The white colour values were highest for QPM cornpared to Hr128 extruded products.

Devolatilization: A critical sequential operation for in situ compatibilization of immiscible polymer blends by one‐step reactive extrusion

AbstractThe main objective of this study was to show that an efficient removal of residual monomers is very important for in situ compatibilization of immiscible polymer blends by one step reactive extrusion. One‐step reactive extrusion means that when compatibilizing two immiscible polymers with one polymer containing potential functional groups and the other being chemically inert with respect to these functional groups, functionalization of the chemically inert polymer and its subsequent interfacial reaction with the functional polymer are accomplished in a single extrusion process. Two model blend systems were chosen: polypropylene/poly(butylene terephthalate) (PP/PBT) and high density polyethylene/polyamide 6 (HDPE/PA6). A co‐rotating intermeshing twin screw extruder was used to process these blends. Glycidyl methacrylate (GMA) and maleic anhydride (MA) were used to functionalize PP and HDPE, respectively. Results showed that the mechanical properties of both blends in terms of elongation at break and impact strength were improved to a much greater extent with up‐stream devolatilization compared with down‐stream devolatilization.

Morphology in Blends of a Thermotropic Liquid Crystalline Polymer and Polypropylene

Abstract By monitoring the development of morphology a novel dual extrusion process from the point that the thermotropic liquid crystalline polymer (TLCP) stream meets the matrix material to the final drawn strand, a clear mechanism for the development of the TLCP reinforcement is presented. It was found that under appropriate mixing configurations the fibrillar TLCP morphology seen in strands produced from this method originate at the onset of mixing in the phase distribution system and are subsequently refined as the melt passes through the static mixing elements. The axially continuous morphology seen at the entrance of the die is maintained and further developed as the blend passes through the die and is drawn. In contrast, strands produced using the single extruder blending or the dual extrusion method with excessive mixing produce a droplet morphology prior to the die. At a very low concentration of TLCP, the droplets are too small and well dispersed to sufficiently coalesce and deform into fibrils in the elongational flow field of the die and drawing process. These phenomena result in an undesirable morphology for self reinforcement which clearly has been seen in the measured mechanical properties of the strands.

Influence of time‐temperature history and strain history on the melt rheology of soy protein isolate at an elevated temperature

Summary.Reciprocating extrusion and single extrusion experiments were performed using a completely air‐tight capillary extrusion viscometer in order to elucidate the effects of time‐temperature history and strain history on the melt rheology of soy protein isolate (SPI) at an elevated temperature (140°C). Both histories produced a decrease in the measured pressure drop during extrusion and these effects were strongly dependent on the sample moisture content. For moisture contents above 41% (dry basis), the time‐temperature history effect was predominant more in decreasing the measured pressure drop, whereas the strain history effect was more influential at moisture contents below 30% (d.b.)