Increasing Screw Speed Research Articles

Numerical analysis of thermal and mechanical stress profile during the extrusion processing of plasticized starch by non-isothermal flow simulation

Abstract The non-isothermal, non-Newtonian, transient flow of plasticized starch in a co-rotating twin-screw extruder is simulated by using 3-dimensional (3D) computational fluid dynamics (CFD) accompanied by particle tracking simulation. The results show that the maximum stresses are generated at the tip of the screws. These maxima lead to local hot spots with temperatures up to 10 K higher than material temperature at low shear regions. The particle tracking simulation allowed calculating maximum stress distribution among the extruded material, which vary significantly. The results further suggest that increasing screw speed can lead to lower mechanical stresses due to decreased matrix viscosity. Despite the lower mechanical stresses, increasing screw speed still results in the exposure of material to significantly higher material temperature. Overall, results reveal the significance and the necessity of the in-depth analysis of local extrusion conditions by non-isothermal CFD and particle tracking simulations.

Evaluation of PP/Wood Flour Composite Processing Using Computer Simulation

Aiming the development of novel composites reinforced with natural fibers from vegetable origin, it is important the understanding and control of processing parameters in twin-screw extruders. The temperature profile and the screw components, as well as the extrusion speed, compromise the distribution and dispersion of the fibers in the matrix and consequently in their rheological behavior, which reflects in the mechanical, chemical and morphological properties of the composites and products obtained from them. One new tool, used to understand processing parameters in composites, is computer simulation. In this study, we used the WinTXS Software to evaluate the influence of process parameters in the polypropylene matrix composite reinforced with 30 vol% wood flour. Parameters such as shear rate, temperature, melt viscosity, and viscous dissipation were evaluated. It was observed that increasing screw speed, the temperature increased, which results from the viscous dissipation. Under these conditions, the shear rate and melt viscosity were reduced.

Physical and Microstructure Properties of Oyster Mushroom-Soy Protein Meat Analog via Single-Screw Extrusion.

Single-screw extrusion of a fibrous-structured meat analog from soy proteins added with low-grade oyster mushroom was successful. Satisfactory extrudates were obtained at a barrel temperature of 140 °C, screw speed range of 100–160 rpm, and oyster mushroom addition at 0%, 7.5%, and 15% via factorial experiments. Single-screw extrusion equipped with a slit die successfully produced expanded oyster mushroom-soy protein extrudates. However, the increase in the oyster mushroom content significantly decreased (p ≤ 0.05) the expansion ratio of the extrudate from 1.26 to 0.98. This result indicated that adding more oyster mushroom restrained the expansion ratio. The extrudates had a medium density range (max of 1393.70 ± 6.30 kg/m3). By adding oyster mushroom, the extrudates attained a higher moisture content (range = 34.77% to 37.93%) compared with the extrudates containing the protein mixture only (range = 26.99% to 32.33%). The increase in screw speed and oyster mushroom significantly increased (p ≤ 0.05) the water absorption index. The increase in the texturization index was significantly influenced (p ≤ 0.05) by oyster mushroom addition rather than the screw speed. A defined fibrous structure supported the high texturization index and small shape of air cells observed in the extrudates.

Hot-Melt Extrusion Process Fluctuations and their Impact on Critical Quality Attributes of Filaments and 3D-printed Dosage Forms.

Fused deposition modeling (FDMTM) is a 3D-printing technology of rising interest for the manufacturing of customizable solid dosage forms. The coupling of hot-melt extrusion with FDMTM is favored to allow the production of pharma-grade filaments for the printing of medicines. Filament diameter consistency is a quality of great importance to ensure printability and content uniformity of 3D-printed drug delivery systems. A systematical process analysis referring to filament diameter variations has not been described in the literature. The presented study aimed at a process setup optimization and rational process analysis for filament fabrication related to influencing parameters on diameter inhomogeneity. In addition, the impact of diameter variation on the critical quality attributes of filaments (mechanical properties) and uniformity of mass of printed drug-free dosage forms was investigated. Process optimization by implementing a winder with a special haul-off unit was necessary to obtain reliable filament diameters. Subsequently, the optimized setup was used for conduction of rational extrusion analysis. The results revealed that an increased screw speed led to diameter fluctuations with a decisive influence on the mechanical resilience of filaments and mass uniformity of printed dosage forms. The specific feed load was identified as a key parameter for filament diameter consistency.

Effect of material parameters and machine parameters on physical property of extrudates prepared from different blends of sattu and kodo

In the present study extrudates were prepared to identify the optimum machine parameters and prepare good quality ready to eat extruded snacks from a suitable blend of sattu and kodo Extrusion aims at producing a voluminous, expanded, crispy product resembling a baked product. The increase in proportion of sattu and die head temperature increases the water absorption index. The water absorption index achieved a maximum value of 58.5% and a minimum value of 48.7%. The bulk density increases with the increase in moisture content increases in proportion of sattu and the increase in barrel temperature with decrease in die head temperature and increase in screw speed. The bulk density achieved a maximum value of 0.60 g/mm3 and a minimum value of 0.46 g/mm3.

Effects of high-efficiency infrared heating on fiber compatibility and weldline tensile properties of injection-molded long-glass-fiber-reinforced polyamide-66 composites

AbstractGlass fiber composites are prevalent molded materials used in various fields, including aviation engineering, automobile manufacturing, and medical equipment production. The length of a glass fiber affects the mechanical properties of a glass fiber composite. Studies have reported that breakage occurs in long fibers subjected to screw plasticization, injection processes, and geometrical changes in injection molding. Moreover, multigate injection molding can result in weldlines on the final product, consequently reducing its strength. Further exploration is required to determine how product strength is affected by weldlines generated through injection molding with glass fiber composites and how product tensile properties associated with weldlines can be improved. Therefore, this study designed a mold with a vent area and a plug-in mold-surface-heating device to examine changes in the weldlines and tensile properties of long-glass-fiber composite specimens fabricated through injection molding using two melts. The results revealed that fiber length decreased with increasing screw speed; such declines in fiber length affected the tensile strength of the long-glass-fiber-reinforced polyamide-66 composites. In addition, because the arrangement and distribution of the glass fibers were affected by the melt flow rate, melt flow direction, and changes in mold cavity volume, the weldline tensile strength varied with the depth of the vent area. Mold surface heating improved the specimen surface roughness by 5.79% and effectively improved the interfacial adhesion between the fibers and melts, thereby resulting in more favorable weldline tensile strength. This also notably reduced the depth of weldlines produced by the adhesion of two melts.

Possibility to Save Water and Energy by Application of Fresh Vegetables to Produce Supplemented Potato-Based Snack Pellets

The aim of the study was to examine the effect of fresh vegetable addition on processing efficiency, and to ascertain the energy and water consumption during production of potato-based snack pellets. The extrusion-cooking process with a modified single screw extruder was applied at variable screw speeds and amounts of vegetable additives. A mixture of potato flakes, potato grits and starch was used as a basic recipe. The potato composition was supplemented with fresh pulp of onion, leek, kale and carrot in amounts of 2.5–30.0% as replacement of a related amount of potato starch. The water consumption, as well as processing indicators: the production efficiency, the specific mechanical energy (SME), and the total SME requirements during snack pellets processing at the laboratory scale were evaluated. As a result of this work, we found that the amount of applied vegetable additives had little impact on both processing efficiency and SME depending on the screw speeds applied. Moreover, we saw increased processing efficiency with increased screw speed during extrusion. Of particular note, maximum value of processing efficiency was observed if fresh onion was used as an additive at the highest speed screw. Furthermore, the lowest specific mechanical energy consumption was noted for extrudates supplemented with fresh onion addition processed at the lowest screw speed. The most important limiting of water consumption during processing without negative effects on processing efficiency and quality of the final snack pellets was observed if 20% to 30% of fresh vegetables were used in the recipe. We believe that application of fresh vegetable pulp limited the energy requirements by mitigating the drying process of additives.

Development of Polypropylene-based Thermoplastic Elastomers with Crumb Rubber by Dynamic Vulcanization: A Potential Route for Rubber Recycling

In our current paper the preparation and properties of thermoplastic elastomer produced by dynamic vulcanization is presented and discussed. We dynamically vulcanized natural and styrene butadiene rubber (NR/SBR) phase by continuous extrusion. Dispersion and in-situ vulcanization of the rubber phase occurred simultaneously in a co-rotating twin screw extruder. We used a random polypropylene copolymer (rPP) as the thermoplastic matrix and untreated crumb rubber (CR) to partially substitute the neat fresh rubber in order to check whether this is a potential recycling route for waste rubber products. We studied the effect of various rubber formulations, various processing conditions (screw speed and configuration) and various CR particle size distributions by characterizing the mechanical performance of the thermoplastic dynamic vulcanizates (TDVs) with tensile and hardness tests and their morphology by evaluating SEM micrographs taken from the fracture surfaces of the tensile specimens. The results showed that increasing screw speed and more high-shear elements in the screw setup led to a finer dispersion of the rubber phase, resulting in improved mechanical properties. The ultimate tensile properties of the best TDVs reached 20.5 MPa in tensile strength and 550 % in strain at break. However, partial replacement of the fresh rubber with untreated CR caused a significant deterioration in mechanical properties, due to poor adhesion between the CR particles and the matrix and rubber. This suggests that some kind of pre-treatment (e.g. by microwave or other devulcanization techniques) is necessary to enhance the surface activity of the CR particles.

Comparing inline extrusion viscosity for different operating conditions to offline capillary viscosity measurements

AbstractDegermed, dehulled cornmeal grits were extruded through a self‐heating single screw extruder with inner restrictions. Constant degree of screw fill was tested at 32.5, 35, and 37.5% w.b. moisture content. The screw speeds tested were 100, 200, and 300 rpm. A novel two hole die was used and showed the melt viscosity to decrease with increased screw speed. The inline data was compared to offline capillary rheometer measurements and showed a decrease in melt viscosity. For example, at 35% moisture content and roughly 110°C the melt viscosity decreased by 32% from offline to 100 rpm for a shear rate of 100 s−1. The melt viscosity change suggested that each process transforms the material differently into two different materials which was supported by RVA pasting profiles. The extruder die temperature increased with increased screw speed and decreased with increased moisture content. The melt viscosity behaved nonlinearly with moisture content due to high temperature rise and starch degradation. The flow behavior index increased with increased screw speed. Overall, the novel two hole die showed general trends of the melt viscosity behavior with operating conditions and made comparisons to offline data.Practical ApplicationsThe extrusion process is an efficient process that can produce a wide range of products at various throughputs depending upon operating conditions and extruder design. Originally developed for the plastics industry, extrusion has been applied to food and pharmaceutical applications. This application comes with increased challenges due to heterogeneous materials that consist of biological macromolecules that are Non‐Newtonian in rheological behavior as well as being susceptible to temperature and shear degradation. The product rheological properties are dependent on extruder design and operating conditions. Unfortunately, measuring the viscosity while extruding can be complicated, time consuming, and expensive. Thus, to facilitate the design of effective future extruders, the viscosity behavior must be able to be predicted from an offline method which is more cost and time effective.

Co-extrusion of corn meal and polydextrose for making high fiber snack food: effects of extrusion screw speed on the product quality

High fiber snack foods are attracting consumers’ attention due to their health benefits. In this research, corn meal and polydextrose are co-extruded with a twin-screw extruder and the screw speed is varied from 150 to 190 rpm. The objective of the research is to evaluate the effects of screw speed on the product quality. As the screw speed is increased, the expansion ratio and crispness of the fried extrudate are enhanced while the bulk density and hardness are reduced. Increase in screw speed results in increased water absorption index and water solubility index of the product. As the screw speed is increased, the mechanical energy of the extrusion process is also increased. The screw speed has significant correlation with the expansion index, bulk density and texture properties of the fried extrudate (p < 0.05).

Multi-dimensional population balance modelling of pharmaceutical formulations for continuous twin-screw wet granulation: Determination of liquid distribution

Two-dimensional population balance model (PBM) is developed in order to model pharmaceutical granules formation in a twin-screw wet granulator. Granule size and liquid content are considered as internal coordinates, while axial length of granulator is considered as external coordinate. Two types of initial liquid distribution are considered for the model development, i.e. constant and linear distributions. The main focus is on modeling and validation of liquid content distribution of granules. Regime-separated approach was used in order to capture the non-homogeneity of the granulator. The plug flow regime is considered for the conveying zone, while well-mixed regime is assumed for the kneading zone of twin-screw granulator. Aggregation and breakage are considered as the main mechanisms for granule formation and size control. Cell average method is used for solution of the PBM based on lumped parameter approach. In order to determine experimentally the distribution of liquid, liquid binder by dye addition was used in the process. The model findings are calibrated and validated by comparing with measured liquid content in each size fraction. The measured data is collected on a 12 mm twin-screw wet granulator using microcrystalline cellulose (MCC) and water soluble dye plus water as binder. The model indicated to be valid for MCC and needs to be validated with further excipients. The results revealed that increasing screw speed led to more uniform liquid distribution. Finally, the model findings indicated that 2D PBM is capable of predicting liquid distribution, and can be used as predictive tool in pharmaceutical continuous granulation.

The Production Efficiency and Specific Energy Consumption During Processing of Corn Extrudates with Fresh Vegetables Addition

Abstract The aim of the work was to determine the influence of screw speed and variable amounts of fresh vegetable additives on selected aspects of extrusion-cooking of corn-vegetable blends. Corn grit as a basic component was supplemented with a fresh pulp of beetroot, carrot, leek and onion in amounts of 2.5-10% in the recipe. The extrusion-cooking was carried out using a single-screw extruder in the temperature range 120-145°C and extrudates were formed into directly expanded snacks. Two indicators were measured: the production efficiency (Q) and the specific mechanical energy (SME) consumption. As a result of the findings it was noted that the rotational speed of the extruder’s screw showed a greater impact on both production efficiency and SME as compared to the variable amounts of applied additives. A tendency to increased efficiency and specific mechanical energy consumption was observed along with the increase of screw speed during processing. The highest production efficiency was observed if fresh leek and onion were used as additives and the highest extrusion speed screw was applied. The largest specific energy consumption was noted during the extrusion-cooking of blends containing fresh carrot and onion addition at high screw speed.

Response surface methodology for evaluation of the effects of screw speed, feed moisture and xanthan gum level on functional and physical properties of corn half products

Effects of screw speed (100–300 rpm), feed moisture (37–47%) and xanthan gum (XG) level (0–1%) on the functional and physical properties of corn half products were investigated and optimized by using three-factor and three-level Box-Behnken design (BBD) under response surface methodology (RSM). Response variables are water absorption index (WAI), water solubility index (WSI), degree of gelatinization (DG), water activity (aw), specific volume and color properties of extrudates. Increased screw speed decreased WAI and aw values and increased WSI values significantly. Specific volume of half products was low for all extrusion combinations and negative correlated with screw speed, feed moisture and XG level. Lightness and yellowness of half products were increased with increases in screw speed, feed moisture and XG level. Low DG for all half products was obtained (46.33–63.36%) because of temperature under 100 °C in last two zones in extruder. Desirability function approach was used to find the optimum extrusion conditions. The optimized combinations of extrusion conditions were found 300 rpm screw speed, 47% feed moisture and 0.44% XG content with a desirability value of 0.991. No significant difference was found between experimental data and predicted values.

Comparison of quality protein maize (QPM) and normal maize with respect to properties of instant porridge

The investigation was carried out to optimize the extrusion conditions for the development of normal maize and Quality Protein Maize (QPM) based instant porridge. The effect of 3 independent variables (moisture content (14–18%), barrel temperature (125–175 °C) and screw speed (400–550 rpm) on the dependent variables (carbohydrate solubility (CS), protein solubility (PS), hydration power (HP) and milk absorption capacity (MAC) was evaluated by using central composite design in response surface methodology (RSM). Feed moisture and barrel temperature exhibited significant affect (p ≤ 0.01; p ≤ 0.05) on PS, HP and MAC, while screw speed showed non-significant (p ≤ 0.01; p ≤ 0.05) affects on HP and CS. Increase in the moisture content and barrel temperature increases the CS and PS of normal as well as quality protein maize porridge. However, increase in screw speed results in decrease in protein solubility. Optimum extrusion conditions for QPM were 14.19–15.36% feed moisture (on dry basis), 411.61–466.50 rpm screw speed and 150ºC barrel temperature. Optimum extrusion conditions for NM were 14.02–14.17% feed moisture (on dry basis), 171.27–173.47 ºC barrel temperature and 404.05 rpm screw speed. Based on the results it was concluded that quality protein maize can be extruded into acceptable as well as nutritious breakfast food.

Effect of pregelatination on rheology, cooking and antioxidant activity of pasta

The present study explores the possibility of using twin screw extruder for preparation of pregelatinized pasta. The effects of extrusion parameters feed moisture (28 and 32%), barrel temperature (60-105°C) and screw speed (100-200rpm) on pregelatinized pasta were investigated. Prepared pasta was analysed for quality characteristics in terms of cooking quality, degree of gelatinization, color, texture, pasting properties, bioactive composition. Results indicated that higher screw speed improved the cooking quality of pasta and decreased gruel solid loss. Degree of gelatinization revealed positive relation with temperature and feed moisture. Extrusion conditions, altered the color of pasta, a decrease in L*, increase in a* and b* values was observed. Higher peak viscosity was observed at lower barrel temperature and feed moisture. A significant retention in total phenolic content and flavonoid content was observed with higher feed moisture. Extrusion leads to increase in antioxidant activity and firmness upon increasing screw speed and feed moisture.

The effect of extrusion screw-speed on the water extractability and molecular weight distribution of arabinoxylans from defatted rice bran.

Arabinoxylans (AXs) are major dietary fibre in cereals. Recently, AXs have attracted a great deal of attention because of their biological activities. These activities have been suggested to be related to the content of low molecular weight (Mw) AXs, in particular those with Mw below 32kDa. Rice bran is a rich source of AXs. However, water extraction of AXs is difficult and often gives low yield. Extrusion processing has been used to increase the solubility of cereal dietary fibre. The aim of this research was to study the effect of extrusion screw-speeds (80 and 160)rpm on the extraction yield and Mw of water extractable AXs from rice bran. It was found that the extraction of AXs increased significantly with an increase in screw speed and was accompanied by a significant decrease in the Mw of AXs from extruded rice bran. The percentage of very low molecular weight AXs (0.79-1.58kDa) significantly increased with increasing screw speed.

Physico-chemical properties, phytochemicals and DPPH radical scavenging activity of supercritical fluid extruded lentils

A powder blend comprised of lentil flour and pre-gelatinized potato starch was processed using supercritical fluid (carbon dioxide) extrusion (SCFX). The blend was extruded at temperature of 95–99.5 °C and screw speeds of 40, 80 and 120 rpm. The physical properties of the extruded products such as porosity, rehydration rate, expansion ratio, and crispness—improved as the screw speed increased. Furthermore, the density, water solubility index, brittleness, and hardness of the products decreased as the screw speed increased. SCFX increased the transition temperature of starch and protein in lentil flour. Increased screw speed led to increased gelatinization in the starch. Unlike traditionally cooked lentils, no retrogradation of starch was observed for the extruded red lentil products stored at room temperature for 60 days. Compared to raw lentil, SCFX increased the total phenolic and DPPH radical scavenging activity of lentils by 30% and 18%, respectively. In addition, SCFX decreased the trypsin inhibitor content in the lentil flour. Higher screw speeds led to a greater reduction in the trypsin inhibitor content. The SCFX process rendered red lentil flour into a snack-type whole grain product with a more balanced nutritional and antioxidant composition.

Effects of operative conditions on products obtained of starch-oil mixtures by single-screw extrusion.

d. The aim of the study was to evaluate the fat binding and physicochemical properties of the products under conditions of potato starch extrusion containing rapeseed or linseed oil and rapeseed oil with glycerol. The study dealt with the extrudates of potato starch produced with the addition of rape seed or linseed oil and rapeseed oil and glycerol at 22% humidity. The extrudates were obtained at two screw speeds: 80 rpm and 100 rpm. Extrudates containing rapeseed oil and glycerol (R6G) were obtained at a temperature distribution of 115/130/150°C, while those with the participation of rapeseed oil and linseed oil were obtained at 120/135/128°C. Water solubility index (WSI), water absorption index (WAI), specific surface area (SBET) and quantity of fat permanently bound were determined for the products obtained. When oils were added, the solubility of extrudates decreased as compared to the control samples (starch without oil; S). Rapeseed oil added to the starch mixture at the levels of 3 g and 6 g in had no sig- nificant effect on the solubility of the product and amounted to: 80.3–82.6% and 78–79.6%. The largest decrease in solubility (WSI, 55.4–57.1%) was demonstrated for samples with 6% addition of rapeseed oil and 10 g glycerol. For these samples (R6G), a significant increase in the index WAI (376–397%) was recorded. Extrudates obtained with the addition of 3 g of rapeseed oil absorbed slightly more water than those with 6 g of oil added. The specific surface area (SBET 230–256 m2/g) determined from the water vapor adsorption isotherm indicates no statistically significant difference at α = 0.05 for products with rapeseed oil, linseed oil, and controls. A significant increase in the specific surface area (SBET 284–347 m2/g) was observed for samples with 6g rapeseed oil and 10 g glycerol added. For samples with 3 g of rapeseed oil, the amount of bound fat was 1.9–2.1 g/100 g of starch and for 6% the starch percentage was 2.96–3.5 g/100 g. The water solubility of starch extrudates with the addition of oils decreases with an increase   in screw speed. Starch extrudates with linseed oil and rapeseed oil plus added glycerol are characterized by an increase in water-absorption capacity with respect to the control extrudates. The products obtained with the addition of rapeseed oil and glycerol exhibit a significant increase in their specific surface area. The quan- tity of fat permanently bound during extrusion depended on: the oil type, its percentage in the mixture and the screw speed. The linseed oil was the least absorbed in the starch structure, but rapeseed oil binding increased with the increase in its level in the mixture.

Electrical, Thermal, and Morphological Properties of Poly(ethylene terephthalate)-Graphite Nanoplatelets Nanocomposites

Graphite nanoplatelets (GNP) were incorporated with poly(ethylene terephthalate) (PET) matrix by melt-compounding technique using minilab compounder to produce PET-GNP nanocomposites, and then the extruded nanocomposites were compressed using compression molding to obtain films of 1 mm thickness. Percolation threshold value was determined using percolation theory. The electrical conductivity, morphology, and thermal behaviors of these nanocomposites were investigated at different contents of GNP, that is, below, around, and above its percolation threshold value. The results demonstrated that the addition of GNP at loading >5 wt.% made electrically conductive nanocomposites. An excellent electrical conductivity of ~1 S/m was obtained at 15 wt.% of GNP loading. The nanocomposites showed a typical insulator-conductor transition with a percolation threshold value of 5.7 wt.% of GNP. In addition, increasing screw speed enhanced the conductivity of the nanocomposites above its threshold value by ~2.5 orders of magnitude; this behavior is attributed to improved dispersion of these nanoparticles into the PET matrix. Microscopies results exhibited no indication of aggregations at 2 wt.% of GNP; however, some rolling up at 6 wt.% of GNP contents was observed, indicating that a conductive network has been formed, whereas more agglomeration and rolling up could be seen as the GNP content is increased in the PET matrix. These agglomerations reduced their aspect ratio and then reduced their reinforcement efficiency. NP loading (>2 wt.%) increased degree of crystallinity and improved thermal stability of matrix slightly, suggesting that 2 wt.% of GNP is more than enough to nucleate the matrix.

Evaluation of functional properties of extruded snacks developed from brown rice grits by using response surface methodology

Abstract Extrusion behavior of brown rice grits was investigated using twin screw extruder. Feed moisture of the grits was adjusted between 14% and 18%, and extrusion cooking was done at barrel temperature of 130–170 °C and screw speed of 400–550 rpm. The brown rice grits differed significantly with respect to extrusion behavior and extrudate characteristics. Water solubility index (WSI) of extrudates varied from 5.43% to 14.32%, water absorption index (WAI) from 4.72 to 7.81 and bulk density (BD) from 0.065 to 0.188 g/ml. With increase in moisture, BD, WAI and hardness increased, while WSI and SME decreased. Increase in screw speed resulted in lower BD, WAI and WSI whereas resulted in a higher SME. With increase in temperature decrease in SME, BD, WAI and hardness was observed. All responses were most affected by changes in feed moisture, temperature and to a lesser extent screw speed.