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Screw Speed (screw + speed)

Distribution by Scientific Domains

Chemistry	68%
Polymers and Materials Science	29%

Selected Abstracts

Effects of extrusion conditions on quality of cassava bran/cassava starch extrudates

INTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 5 2003
Jorge Minoru Hashimoto
Summary Blends of cassava bran and cassava starch were processed in a single-screw extruder. Response surface methodology was used to determine the effect of the concentration of cassava bran (10,50%), barrel temperature (150,210 °C), feed moisture (16,20%) and screw speed (120,180 r.p.m.) on the characteristics of the dried extrudates. All the independent variables were significant (P < 0.05) for radial expansion. The water absorption index (WAI) and water solubility index (WSI) were affected by bran level, screw speed and temperature, while only moisture and temperature influenced specific volume. The maximum radial expansion was found when all the independent variables were at their lowest levels. Lowest-density extrudates (highest specific volume) were obtained at 16,18% moisture and 180,200 °C. An increase in bran level increased the WAI but decreased the WSI when the temperature was higher than 170 °C . Screw speed had a slight effect on those responses, decreasing water absorption and increasing water solubility when changed from 120 to 180 r.p.m. [source]

EXTRUSION COOKING OF BLENDS OF SOY FLOUR AND SWEET POTATO FLOUR ON SPECIFIC MECHANICAL ENERGY (SME), EXTRUDATE TEMPERATURE AND TORQUE

JOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 4 2001
M. O. IWE
Defatted soy flour and sweet potato flour containing 18% moisture were mixed in a pilot mixer, and extruded in an Almex-Bettenfeld single-screw extruder operated at varying rotational speed and die diameter. A central composite, rotatable nearly orthogonal design, which required 23 experiments for three factors (feed composition (fc), screw speed (ss) and die diameter (dd)) was developed and used for the generation of response surfaces. Effects of the extrusion variables on specific mechanical energy (SME), extrudate temperature (ET), and torque (T) were evaluated using response surface analysis. Results showed that product temperature increased with increases in die diameter, screw speed and feed composition. However, the effect of die diameter was greater than those of screw speed and feed composition. Decrease in die diameter with increase in sweet potato content increased torque. Screw speed exhibited a linear effect on torque. [source]

Chemical composition and physical properties of extruded snacks containing crab-processing by-product

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 11 2003
Michael G Murphy
Abstract The crab-processing industries generate millions of pounds of by-product annually, which results in a loss of edible product and presents a considerable waste disposal problem. The purpose of this research was to investigate the use of crab-processing by-product (CB) in the development of a calcium-rich expanded snack. The specific objectives were to examine the effects of type of CB (wet or dry), feed composition and screw speed (150 or 250 rpm) on selected properties of extruded snacks. Product formulations consisting of 0,400 g kg,1 CB combined with corn meal and potato flakes were processed in a twin-screw extruder. The resulting extrudates were analysed for proximate and mineral (calcium, sodium) composition, pH, water activity (aw), total plate count, bulk density, expansion ratio and colour. Both CB type and level of incorporation had significant effects (P < 0.05) on the calcium content, expansion ratio, bulk density and pH of the extrudates. Increasing the CB level resulted in increased calcium content (from 5.1 to 52.4 mg g,1) and pH (from 6.1 to 8.8). Screw speed had no significant effects (P > 0.05) on expansion ratio and bulk density. A high processing temperature (157 °C) and low aw resulted in undetectable microbial growth on the extrudates. This research demonstrates that ground crab-processing by-product can be successfully incorporated into an expanded snack product. Further research will evaluate consumer response to this novel value-added product. Copyright © 2003 Society of Chemical Industry [source]

Changes in the biochemical and functional properties of the extruded hard-to-cook cowpea (Vigna unguiculata L. Walp)

INTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 4 2010
Karla A. Batista
Summary Changes in the biochemical and functional properties of the hard-to-cook cowpea bean after treatment by the extrusion process are reported. The extrusion was carried out at 150 °C, with a compression ratio screw of 3:1, a 5-mm die, and a screw speed of 150 r.p.m. The extrusion caused the complete inactivation of the ,-amylase and lectin and it also reduced the trypsin inhibitor activity (38.2%) and phytic acid content (33.2%). The functional properties were also modified by the process, an increase of 2.5 times in the water absorption index and 3.1% in the water solubility were observed. The digestibility of the hard-to-cook flour of the cowpea bean was improved after the extrusion, with a 55.9% increase in protein digestibility and a 5.9% increase in starch digestibility. [source]

Effect of extrusion parameters on flavour retention, functional and physical properties of mixtures of starch and d -limonene encapsulated in milk protein

INTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 2006
Sri Yuliani
Summary The purpose of this research was to investigate the retention of flavour volatiles encapsulated in water-insoluble systems during high temperature,short time extrusion process. A protein precipitation method was used to produce water-insoluble capsules encapsulating limonene, and the capsules were added to the extruder feed material (cornstarch). A twin-screw extruder was used to evaluate the effect of capsule level of addition (0,5%), barrel temperature (125,145 °C) and screw speed (145,175 r.p.m.) on extruder parameters (torque, die pressure, specific mechanical energy, residence time distribution) and extrudate properties [flavour retention, texture, colour, density, expansion, water absorption index, water solubility index (WSI)]. Capsule level had a significant effect on extrusion conditions, flavour retention and extrudate physical properties. Flavour retention increased with the increase in capsule level from 0% to 2.5%, reached a maximum value at capsule level of 2.5% and decreased when the capsule level increased from 2.5% to 5%. The die pressure, torque, expansion ratio, hardness and WSI exhibited the opposite effect with the presence of capsules. [source]

Effects of extrusion conditions on quality of cassava bran/cassava starch extrudates

An experimental study of single-screw extrusion of HDPE,wood composites

ADVANCES IN POLYMER TECHNOLOGY, Issue 3 2010
Karen Xiao
Abstract Single-screw extrusion experiments were carried out to study the extrusion characteristics of HDPE,wood composites. Three screw geometries (A, B, and C) were used, and the effects of screw speed on output, melting, and pressure profile were studied. Screw A had a much higher compression ratio than screws B and C, which directly affected the melting behavior of the polymers. Screws B and C had the same compression ratio; however, screw C had the same metering capacity as screw A. Therefore, by comparing screws B and C, the effect of feed depth on the solid conveying capacity was investigated. It was found that while screw B had higher outputs than both screws A and C as expected, screw C had a much lower output than screw A for highly filled resins even though they had the same metering capacity. For HDPE, screws A and C showed the same output as expected. Further examinations of the pressure profiles and melting profiles from screw extraction experiments confirmed that screw C showed a severely starved solids conveying capacity for wood-filled resins, which limited the total outputs. Comparing the outputs and pressure generations between theoretical predictions and actual experimental results, it was evident that due to the inaccurate assumption of fully filled channels common in single screw extrusion, both outputs and pressure generations in the extruders were overpredicted. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:197,218, 2010; View this article online at wileyonlinelibrary. DOI 10.1002/adv.20190 [source]

Quantification of dynamic mixing performance of single screws of different configurations by visualization and image analysis

ADVANCES IN POLYMER TECHNOLOGY, Issue 1 2009
A. C.-Y.
Abstract The visualization and image analysis techniques developed by the authors for the study of quantifying the dynamic quality of mixing of a single-screw extruder were employed to investigate the mixing performance of screws of different configurations. The mixing quality was quantified by calculating the variances of the light intensity of the bitmap files cropped from the films taken at the screw length of 15D and 17D of a 45-mm screw diameter single-screw extruder. Temperature and screw speed were the two variables studied. While temperature and back pressure were found to have little effect on the mixing quality, screw speed was demonstrated to be a major factor responsible for the mixing fluctuation observed during extrusion. In fact, screw speed and mixing fluctuation appeared to have a relationship that the higher the screw speed, the bigger the fluctuation (i.e., poorer quality of mixing). The experimental results also revealed that the secondary flight of a barrier screw might be essential to improve the quality of mixing. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:1,15, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20142 [source]

Mixing immiscible blends in an intermeshing counter-rotating twin screw extruder

ADVANCES IN POLYMER TECHNOLOGY, Issue 2 2006
Ramesh Potluri
Abstract Domain size of 10% dispersed polystyrene in polyethylene was followed in a 34-mm intermeshing counter-rotating twin screw extruder. Variables studied included the effects of barrel temperature, screw speed, viscosity ratio of dispersed-to-continuous phase, and parallel melt versus preblended solids feeds. After steady state was achieved, die samples were quenched for later photomicrographing. The extruder was then stopped and quenched, with subsequent pulling of the screws. From 7 to 12 additional samples were taken along the 18/1 L/D extruder for determination of the mechanism of dispersion and dispersed phase domain size by optical microscopy. At low temperatures, the polystyrene tended to fracture with sharp edges. The fine particles formed in the initial breakup underwent no further size reduction. At higher temperatures, fractured segments had rounder edges, but the size of the small domains remained constant throughout the axial length. There was some evidence of flocculation and coalescence prior to exit through the die. © 2006 Wiley Periodicals, Inc. Adv Polym Techn 25: 81,89, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20065 [source]

Effects of microcompounding process parameters on the properties of ABS/polyamide-6 blends based nanocomposites

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008
Güralp Özkoç
Abstract Melt intercalation method was applied to produce acrylonitrile-butadiene-styrene/polyamide-6 (ABS/PA6) blends based organoclay nanocomposites using a conical twin-screw microcompounder. The blend was compatibilized using a maleated olefinic copolymer. The effects of microcompounding conditions such as screw speed, screw rotation-mode (co- or counter-), and material parameters such as blend composition and clay loading level on the morphology of the blends, dispersibility of nanoparticles, and mechanical properties were investigated. Furthermore, corotating screws were modified to achieve elongational flow which is efficient for obtaining dispersive mixing. The morphology was examined by SEM analysis after preferential extraction of the minor phase. Subsequently, the SEM micrographs were quantitatively analyzed using image analyzer software. The morphology of the blends indicated that processing with counter-rotation at a given screw speed yielded coarser morphology than that of processed with corotation. X-ray diffraction analysis showed that highest level of exfoliation is observed with increasing PA6 content, at 200 rpm of screw speed and in corotation mode. Also, the effects of screw speed, screw rotation mode, and screw modification were discussed in terms of XRD responses of the nanocomposites. The aspect ratio of the clay particles which were measured by performing image analysis on TEM micrographs exhibited a variation with processing conditions and they are in accordance with the modulus of the nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

PROPERTIES of CROSS-LINKED STARCH PRODUCED IN A SINGLE SCREW EXTRUDER WITH and WITHOUT A MIXING ELEMENT

JOURNAL OF FOOD PROCESS ENGINEERING, Issue 1 2004
M. SEKER
ABSTRACT Starch was extruded with sodium hydroxide and sodium trimetaphosphate in order to cross-link it in a single-screw extruder with and without a mixing element at constant screw speed of 90 rpm in the first set of experiments and at similar mean residence time controlled by screw speed in the second set of experiments. For the screw without mixing element in the second set of experiments, screw speed was adjusted to give the similar residence time as the single-screw extruder with mixing element at 220 rpm. Phosphorus content and pasting curves of extrudates showed that starch was cross-linked during extrusion. Replacing the screw without mixing element by the screw with mixing [source]

EFFECT OF EXTRUSION COOKING AND SODIUM BICARBONATE ADDITION ON THE CARBOHYDRATE COMPOSITION OF BLACK BEAN FLOURS

JOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 2 2002
JOSE DE J. BERRIOS
ABSTRACT Extrusion cooking and chemical leavening agents such as sodium bicarbonate (NaHCO3), may induce changes in carbohydrate fractions of extruded black bean (Phaseolus vulgaris L.) flours. Bean flours at 20% moisture, with NaHCO3 added at levels from 0.0 to 2.0%, were extruded at a screw speed of 200 rpm. The temperature profile ranged from 23 to 160C. Extruded bean flours with 0.1 to 0.4% added NaHCO3 were selected for sugar analyses based on color and flavor acceptability. The major sugars determined in the bean samples were galactose (0.10%), sucrose (2.08%), and stachyose (2.00%). Extruded samples had an increase in total sugars. Also, an increase in soluble fiber and a decrease of insoluble fiber fractions were observed. Sucrose was the only free sugar which concentration decreased consistently as a result of extrusion processing. Extrusion conditions and the selected levels of NaHCO3 used in this study did not significantly change the oligosaccharide content of the black bean flours. [source]

EXTRUSION COOKING OF BLENDS OF SOY FLOUR AND SWEET POTATO FLOUR ON SPECIFIC MECHANICAL ENERGY (SME), EXTRUDATE TEMPERATURE AND TORQUE

EFFECTS OF EXTRUSION CONDITIONS ON PHYSICOCHEMICAL PROPERTIES OF A MUTANT RICE CULTIVAR, GOAMI2 , HIGH IN NONDIGESTIBLE CARBOHYDRATES

JOURNAL OF FOOD QUALITY, Issue 5 2008
I. CHOI
ABSTRACT A mutant rice Goami2, a cultivar high in nondigestible carbohydrates (NDCs), was extrusion-cooked at feed moisture (20, 25%), screw speed (200, 300 rpm) and barrel temperature (110, 120 and 130C). Effects of extrusion conditions on the physical and functional properties were investigated. NDCs were determined by total dietary fiber (TDF) and resistant starch (RS) contents. Increasing moisture resulted in an increment of density, water absorption index (WAI) and hardness, and a decrement in expansion and water solubility index (WSI). A higher barrel temperature decreased the hardness and increased the WSI probably due to a higher proportion of gelatinized starch. Extrusion caused a reduction in TDF in the extrudates, as well as a significant decrease in RS contents. However, extrudates processed at moisture (%), screw speed (rpm) and barrel temperature (C) combinations of 25/200/110 and 25/200/120 showed no significant difference in TDF contents compared with its raw rice. Multiple regression models showed that feed moisture had the most pronounced effect on extrudate qualities, followed by barrel temperature and screw speed. PRACTICAL APPLICATIONS Rice, being one of the primary dietary sources of carbohydrates worldwide, is the major energy and nutritional sources. In recent years, demands have been increasing for rice with a wide range of value-added properties, such as enhanced nutrient, aroma, color and rice kernel shape, including functional properties. Goami2 is a mutant rice of Ilpumbyeo, a high japonica rice cultivar, and has been revealed to have higher nondigestible fractions. However, Goami2 rice has unsuitable properties for traditional cooking because of the difficulty of gelatinization, which might result in a hard texture of cooked rice compared with that of ordinary rice. On the basis of its nutritional and functional benefits, exploiting the possible utilization of Goami2 for processed food products would increase the potential consumption of Goami2 for various food products. [source]

Kinetics of Lysine and Other Amino Acids Loss During Extrusion Cooking of Maize Grits

JOURNAL OF FOOD SCIENCE, Issue 2 2003
S. Ilo
ABSTRACT: Maize grits were extrusion-cooked in a conical, counter-rotating twin-screw extruder at different barrel temperatures, feed moistures, and screw speeds. Residence time distribution was measured by a dye tracer technique. Experiments with lysine-fortified maize grits showed a 1st order reaction for lysine loss. A detailed kinetic study has been performed for the losses during extrusion cooking of lysine, cystine, and arginine. The 1st-order rate constants were dependent mainly on product temperature and feed moisture, whereas screw speed had no influence. Activation energy of lysine, arginine, and cystine loss was 127, 68, and 76 kJ/mol, respectively. Shear stress significantly affected the rate constants of amino acids loss in extrusion cooking. [source]

A Review on Residence Time Distribution (RTD) in Food Extruders and Study on the Potential of Neural Networks in RTD Modeling

JOURNAL OF FOOD SCIENCE, Issue 6 2002
G. Ganjyal
ABSTRACT: Residence time distribution and mean residence time depend on process variables, namely feed rate, screw speed, feed moisture content, barrel temperature, die temperature and die diameter. Flow in an extruder has been modeled by simulating residence time distribution, assuming the extruder to be a series of continuous-stirred-tank or plug-flow reactors. Others have developed relationships for mean residence time as functions of process variables. Better models can be developed using neural networks. As an example, data from the literature were used to model mean residence time as a function of process variables using statistical regression and neural networks. Neural network models performed better than regression models. [source]

Evaluating Energy Consumption and Efficiency of a Twin-Screw Extruder

JOURNAL OF FOOD SCIENCE, Issue 5 2002
M. Liang
ABSTRACT: Using the results from twin-screw extrusion of corn meal, both energy consumption and extruder efficiency were found to be significantly correlated with screw speed and specific feeding load (SFL). An increase in the SFL decreased the total specific mechanical energy, but increased the extruder efficiency. SFL influenced the extruder efficiency more than the screw speed. Increasing the screw speed from 300 to 450 rpm at a constant SFL level increased the extruder efficiency by 6 to 11%, whereas an increase of SFL from 0.0026 to 0.0038 kg rev 1 raised the extruder efficiency by 30%. Of the mechanical energy consumed per unit mass of extrudate, over 98% were used for shearing or viscous dissipation and less than 1.5% were for pumping during twin-screw extrusion of corn meal. [source]

Extrusion Cooking Process for Amaranth (Amaranthus caudatus L.)

JOURNAL OF FOOD SCIENCE, Issue 6 2000
R.N. Chávez-Jáuregui
ABSTRACT: Amaranth (Amaranthus caudatus L.) extrusion was optimized by response surface methodology (RSM). Response (dependent) variables were: expansion ratio, shearing strength, and sensory texture acceptability. Independent variables were processing temperature and feed moisture. All other process variables (screw speed, screw compression ratio, feed speed, and die diameter) were kept constant (200 rpm, 70 g.min,1, and 3 mm, respectively). The most expanded products also had the best texture and were obtained at 150 °C and 15% moisture. These conditions resulted in greater expansion, greater shearing force of extrudates, greater extrudate surface area per unit weight, and reduced shearing stress at maximum shearing force. This study showed that under conditions that induced the maximum expansion ratio, extrusion produced a highly acceptable snack product based on amaranth flour. [source]

PHYSICOCHEMICAL PROPERTIES OF TEXTURIZED MEAT ANALOG MADE FROM PEANUT FLOUR AND SOY PROTEIN ISOLATE WITH A SINGLE-SCREW EXTRUDER ,

JOURNAL OF TEXTURE STUDIES, Issue 4 2004
E.L. PARMER JR.
ABSTRACT The objective of this study was to establish conditions for the texturization of soy protein isolate and peanut flour mixture using a single-screw extruder. The effects of feed moisture, screw-speed, and barrel temperature on the characteristics of the texturized products were studied. Feed moisture was the most important factor affecting the texture. Feeding ingredients with 22% moisture had the highest water absorption and expansion indices, and Hunter L value (P < 0.05). When the screw speed was above 180 RPM, the meat analog had a 12% decrease in the expansion index and a 5% decrease in moisture content (P < 0.05). When the barrel temperature was increased to 165C, there was a 12% decrease in the water absorption index, and a 23% decrease in the expansion index of the meat analogs (P < 0.05). Overall, an acceptable meat analog could be successfully produced with 22% moisture in the raw ingredient, screw speed at 140 RPM, and barrel temperatures at 150, 155, and 160C for the three temperature zones respectively. [source]

Chemical composition and physical properties of extruded snacks containing crab-processing by-product

Development of a bulgur-like product using extrusion cooking

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 7 2003
Hamit Köksel
Abstract In this study we (1) developed a new bulgur-like foodstuff using a durum wheat cultivar and an extrusion technique, (2) investigated the physicochemical properties of the extrudates produced and (3) sensorially evaluated the end-product after cooking. Durum wheat was processed in a laboratory-scale co-rotating twin-screw extruder with different levels of moisture content of the feed (367, 417 and 455,g,kg,1), screw speed (150 and 200,rpm) and feed rate (2.4 and 2.9,kg,h,1) to develop the bulgur-like product. The effects of extrusion conditions on system variables (die pressure and specific mechanical energy (SME)), physical properties (die swell and bulk density), pasting properties (peak, trough and final viscosities) and cooking and sensory properties of the bulgur-like products were determined. The results indicated that increased feed moisture content resulted in significant decreases in the die pressure and SME values of the extruded durum wheat products. As the moisture content and screw speed increased, the changes in die swell values were not significant. The lowest die swell and highest bulk density values were obtained at the highest feed moisture content. The extrusion variables also affected the pasting properties of the extrudates. Significant increases in each of the pasting properties occurred when the moisture content of the feed was increased. Some of the sensory properties (bulkiness, firmness, stickiness and taste,aroma) improved significantly as the feed moisture content increased, indicating better quality. Increased feed moisture content significantly improved cooking quality as determined by a decrease in colorimetric test results. Extrusion seems to be promising for the production of dry, relatively inexpensive bulgur-like products with acceptable sensory properties. © 2003 Society of Chemical Industry [source]

Dephytinisation of rice bran and manufacturing a new food ingredient

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 15 2001
Wea-Shang Fuh
Abstract Rice bran was extruded at 130,°C and a screw speed of 140,rpm for 20,s to inactivate lipase and prevent lipid oxidation. Although the extrusion process induced further complex formation between phytic acid and protein as well as between phytic acid and starch, nearly 94% of phytic acid in the extruded rice bran could still be removed by solid/liquid extraction conducted at 25,°C for 30,min using hydrochloric acid at pH 2 as solvent and a solvent/rice bran ratio of 15. After the extract had been neutralised and phytic acid removed, it was added back to the rice bran solid to replenish the nutritional and functional components of the solid. The mixture was then dried in a drum dryer to yield a powdered product. The dephytinised rice bran product contained most of the protein, fat, dietary fibre and B vitamins and more than 50% of the oryzanol originally present in the raw rice bran. © 2001 Society of Chemical Industry [source]

Effect of the addition of calcium hydroxide on some characteristics of extruded products from blue maize (Zea mays L) using response surface methodology

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 14 2001
José J Zazueta-Morales
Abstract The aim of this research was to study the effects of calcium hydroxide (0,0.2%) and screw speed (100,180,rpm) on the expansion index (EI), bulk density (BD), penetration force (PF) and specific mechanical energy (SME) values of blue maize meal extrudates. Blue maize meal was extruded using a commercial extruder (Brabender 20DN/8-235-00) with a compression screw ratio of 3:1. A second-order, central composite experimental design was used. It was found that the EI and SME values decreased and the BD and PF values increased when the calcium hydroxide concentration was increased. The screw speed had a significant effect only on the SME and PF values. Quadratic model fitness was shown for all responses, with values of R2,>,0.74, p of F (model) <0.01 and variability coefficient <13.3% (except for PF, 29.18%), and for almost all cases there was no lack of fit (p,>,0.055). Calcium hydroxide concentration showed good correlation (p,<,0.01) with EI (r,,=,,0.81), PF (r,,=,0.60), SME (r,,=,,0.76) and BD (r,,=,0.83). However, screw speed was marginally or not correlated (r,<,0.36, p,>,0.14) with the responses. The results suggest that it is possible to produce appropriate extruded products from blue maize fortified with calcium in an optimised calcium hydroxide concentration and screw speed range of 0.02,0.078% and 117,180,rpm respectively. © 2001 Society of Chemical Industry [source]

Response surface optimization of the feed compositions of biodegradable packaging foams

PACKAGING TECHNOLOGY AND SCIENCE, Issue 6 2005
Jinchyau Peng
Abstract Response surface methodology (RSM) was used to analyse the effects of polyvinyl alcohol (PVOH) and calcium carbonate (CaCO3) on the physical and mechanical properties (radial expansion ratio, bulk density, compressibility and spring index) of a biodegradable cushioning extrudate. A rotatable central-composite design (CCD) was used to develop models for the objective responses. The experiments were run at 125°C with a feed rate of 27.8,l/h, screw speed of 215,r.p.m. and die diameter of 3.92,mm. Responses were most affected by changes in PVOH levels and to a lesser extent by CaCO3 levels. Individual contour plots of the different responses were overlaid. An optimum radial expansion ratio of 3.39, bulk density of 0.065 (g/cm3), compressibility of 32.27(N), and spring index of 0.906 were identified at 36% PVOH and 5% CaCO3. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Local residence time, residence revolution, and residence volume distributions in twin-screw extruders

POLYMER ENGINEERING & SCIENCE, Issue 1 2008
Xian-Ming Zhang
This work was aimed at studying the overall, partial, and local residence time distributions (RTD); overall, partial and local residence revolution distributions (RRD) and overall, partial and local residence volume distributions (RVD) in a co-rotating twin screw extruder, on the one hand; and establishing the relationships among them, on the other hand. Emphasis was placed on the effects of the type and geometry of mixing elements (a gear block and various types of kneading elements differing in staggering angle) and process parameters on the RTD, RRD and RVD. The overall and partial RTD were directly measured in-line during the extrusion process and the local ones were calculated by deconvolution based on a statistical theory. The local RTD allowed comparing the mixing performance of mixing elements. Also it was confirmed both experimentally and theoretically that specific throughput, defined as a ratio of throughput (Q) over screw speed (N), controlled all the above three types of residence distributions, be they local, partial or overall. The RRD and RVD do not provide more information on an extrusion process than the corresponding RTD. Rather they are different ways of representing the same phenomena. POLYM. ENG. SCI., 48:19,28, 2008. © 2007 Society of Plastics Engineers [source]

Influence of screw profile and extrusion conditions on the microstructure of polypropylene/organoclay nanocomposites

POLYMER ENGINEERING & SCIENCE, Issue 12 2007
W. Lertwimolnun
Direct melt mixing in a twin screw extruder is a simple and classical technique for preparing nanocomposites by dispersing organoclay in a thermoplastic matrix. In this paper, we focus on organoclay/polypropylene nanocomposites, using maleated polypropylene as compatibilizer. The objective of the work is to characterize the influence of screw profile and processing conditions on the microstructure of the nanocomposite (intercalation and exfoliation). Different screw profiles, more or less severe in terms of mixing elements, have been investigated. For each profile, different processing conditions (feed rate, screw speed) have been tested. Samples were collected both at die exit and all along the screw profiles and analyzed (X-ray diffraction and rheometry). Numerical simulations have been performed to quantify the thermomechanical treatment experienced by the material inside the extruder. For all profiles and operating conditions, a mixed intercalated/exfoliated structure has been observed. Exfoliation increases linearly with the ratio of screw speed to feed rate, but is more important for the less severe profile. Except at low feed rate, intercalation and exfoliation do not change a lot along the screw profile. In many cases, the final microstructure is already obtained after the melting zone of the extruder. POLYM. ENG. SCI., 47:2100,2109, 2007. © 2007 Society of Plastics Engineers [source]

Effect of rotational speed of twin screw extruder on the microstructure and rheological and mechanical properties of nanoclay-reinforced polypropylene nanocomposites

POLYMER ENGINEERING & SCIENCE, Issue 8 2006
Piia Peltola
The morphology and rheological and mechanical properties of nanoclay-reinforced polypropylene nanocomposites were investigated with aid of transmission electron microscopy (TEM), thermo gravimetric analysis, rheometry, and mechanical tests. The organically modified silicate (montmorillonite) was used as a reinforcing material and maleic anhydride-grafted polypropylene oligomer as a compatibilizer to improve the clay dispersion and adhesion. The object of the study was to examine the effect of screw speed of the co-rotating twin-screw extruder on the clay exfoliation and nanocomposite properties. Also, the effect of compatibilizing agent was taken into account. The main result of the study was that nanocomposites showed both intercalated and exfoliated structures depending on the screw speeds of extruder. TEM images revealed that the dispersion of silicate layers was greatly influenced by the screw speed. However, even when the silicate layers were highly exfoliated, there was no remarkable effect on mechanical properties of the nanocomposite. POLYM. ENG. SCI. 46:995,1000, 2006. © 2006 Society of Plastics Engineers. [source]

Assessing local residence time distributions in screw extruders through a new in-line measurement instrument

POLYMER ENGINEERING & SCIENCE, Issue 4 2006
Xian-Ming Zhang
This work aimed at developing a new instrument to measure in real time the residence time distribution (RTD) in screw extruders. The instrument followed the same principle as the one reported in the literature but possessed several important advantages. For example, the detection system had two probes that allowed to simultaneously measure RTDs at any two different locations of an extruder, thus providing the possibility of calculating the local RTD between them by a deconvolution method based on a statistical theory for the RTD. Its performance was evaluated on a corotating twin-screw extruder using anthracene as tracer and polystyrene as flowing material. The effects of various process parameters such as feed rate and screw speed on the RTDs were investigated. The emphasis was placed, however, on the effect of the staggering angle of kneading discs on local RTDs both in the kneading zone itself and its neighboring upstream and downstream screw zones. This work is in support of an ongoing project on the simulation of flow in corotating twin-screw extruders. POLYM. ENG. SCI., 46:510,519, 2006. © 2006 Society of Plastics Engineers. [source]

A study of residence time distribution in co-rotating twin-screw extruders.

POLYMER ENGINEERING & SCIENCE, Issue 12 2003
Part I: Theoretical modeling
A theoretical model to determine the residence time distribution (RTD) in a co-rotating twin-screw extruder is proposed. The method consists of coupling a continuum mechanics approach with a chemical engineering one and allows us to obtain the RTD without any adjustable parameter. The process parameters are obtained using Ludovic® twin-screw modeling software, and ideal reactors are chosen to depict the screw profile. The influence of screw speed, feed rate and viscosity on RTD are described on a fictive screw profile. The predictions of the model are in qualitative agreement with literature data. The key point of this procedure is obviously the correct association between an ideal reactor and a screw element. [source]

Behavior of fully filled regions in a non-intermeshing twin-screw extruder

POLYMER ENGINEERING & SCIENCE, Issue 8 2003
Rajath Mudalamane
Twin-screw extruders are operated with sequential filled and partially filled regions in order to perform the required unit processes. Channel fill length, defined as the length of fully filled regions in an extrusion screw, is gaining importance as a design parameter because of its implications on residence time distribution, distributive and dispersive mixing, and also process stability. A detailed study,experimental and theoretical,of the behavior of fill lengths in response to operating conditions (throughput, screw speed) and screw geometry is presented in this paper. Mean residence times were also measured for each geometry and operating condition. The apparatus consisted of a non-intermeshing counter-rotating twin-screw extruder (NITSE) with a transparent (acrylic) barrel, fed with corn syrup (Newtonian at room temperature). Fill length exhibits a nonlinear relationship with specific throughput (Q/N), with the slope increasing monotonously as the throughput Q increases at a given screw speed N. The mean residence time exhibits a strong linear relationship with inverse specific throughput and inverse fill length. A theoretical model was developed to predict the filled length based on pressure-throughput relationships taken from literature for this system, and the predictions were found to agree very well with experimental observations. [source]