Increasing Screw Speed Research Articles

Physical characteristics of extrudates from corn flour and dehulled carioca bean flour blend

Extruded products were prepared from a corn flour and dehulled carioca bean (Phaseolus vulgaris, L.) flour blend using a single-screw extruder. A central composite rotate design was used to evaluate the effects of extrusion process variables: screw speed (318.9–392.9 rpm), feed moisture (10.9–21.0 g/100 g) and bean flour level (4.8–55.2 g/100 g) on the specific mechanical energy (SME), sectional expansion index (SEI), longitudinal expansion index (LEI), volumetric expansion index (VEI) and density (D) of the extrudates. The instrumental texture was also analyzed. The independent variables had significant effects on the physical properties (SEI, VEI and density) of extrudates, with the exception of SME and LEI. SEI increased with increasing screw speed, but a higher moisture and bean flour content resulted in decreasing SEI and VEI. The increase of moisture and bean flour increased the density of extrudates. According to texture analysis, some treatments with 30 and 45 g/100 g bean flour did not show significant differences when compared to commercial brand snacks. However, when combined with higher moisture content (≥19 g/100 g) and lower screw speed (≤333 rpm), the results of the expanded product were not satisfactory.

Response Surface Analysis and Process Optimization of Twin Screw Extrusion Cooking of Potato-Based Snacks

The aim of the present study was to optimize the extrusion process for potato-based snacks using response surface modeling approach. A blend of mashed potatoes, rice and chickpea flour was used in the study. The effects of feed moisture, barrel temperature and screw speed on product responses viz. specific mechanical energy (SME), bulk density (BD), water absorption index (WAI), water solubility index (WSI) and hardness was studied using response surface methodology. The blend of potato-rice and chickpea was extruded at different moisture content (12.6–19.4%), screw speed (349–601 rpm) and barrel temperature (116–184C). Feed moisture had significant effect on all product responses, whereas screw speed and barrel temperature, both independent variables, had significant effect on SME, WSI and hardness of the product. Increase in feed moisture reduces SME and WSI and increases BD, WAI and hardness. Increase in screw speed decreases the BD, WAI and hardness of the snacks, whereas increase in barrel temperature decreases the SME, BD, WAI and hardness but increases the WSI. Optimized extrusion parameters for preparation of snacks were 14% moisture, 550 rpm screw speed, 170C temperature. Practical Applications Potatoes are generally processed into flakes, granules and flour by dehydration for using it as raw material for extrusion. Processing costs are very high, so mixing of mashed potatoes with cereal or pulse flour could be an energy-efficient way to use potatoes in extrusion. The consumers are becoming increasingly health conscious and while many admit that pulses are good for them, they are not sure how to use them in diet. There is also a perception that cooking of pulses is difficult and/or time consuming. There is need to find ways to increase consumption of pulses with little extra efforts. This paper explores the optimization of extrusion condition for development of nutritious snacks from potato-chickpea blends.

Melt Processing of Bioplastic Composites via Twin Screw Extrusion and Injection Molding

Polymer composites composed of polyhydroxybutyrates and natural fibers were extruded to investigate the effect of varying screw speed and lubricant loadings. Optical microscopy results show that increasing screw speed can enhance the dispersion of fibers within the polymer composite. At high screw speeds this caused an exothermic reaction to occur within the barrel resulting in the fibers thermally degrading. In terms of mechanical properties considerable increases in flexural properties were observed with the increase in screw speed. However, impact and tensile properties were negatively affected, due in part to the level of fiber attrition.

The influence of screw configuration and screw speed of co-rotating twin screw extruder on the properties of products obtained by thermomechanical reclaiming of ground tire rubber

The results of our investigations on the process of continuous thermomechanical reclaiming of ground tire rubber (GTR) carried out using a twin screw extruder are presented. We used a co-rotating twin screw extruder with a special configuration of plasticizing unit, enabling generation of considerable shear forces. The influence of screw configuration and screw speed on breaking of chemical crosslink bonds contained in ground tire rubber are characterized by extrusion parameters, the acetone extract content, the content of the soluble fraction, the degree of reclaiming and the crosslink density of the obtained products. The effect of a secondary curing on the mechanical properties (tensile strength, elongation at break, hardness, resilience and abrasion resistance) of the obtained materials was also determined. It has been established that the thermomechanical reclaiming process depends on shear forces acting on the rubber particles, while the degree of reclaiming increase with the increasing screw speed. A change in screw configuration significantly affects the processing of ground tire rubber during reclaiming process. For example, preliminary pulverization of the fine rubber particles in the first zone of barrel facilitates further processing in the twin screw extruder, which is beneficial in order to decrease the screw torque and the energy consumption in the production of reclaimed rubber. Thermogravimetry analysis (TG/DTG) showed that thermal stability of obtained reclaimed GTR depends strongly on the screw configuration.

Visualization and understanding of the granulation liquid mixing and distribution during continuous twin screw granulation using NIR chemical imaging

Over the last decade, there has been increased interest in the application of twin screw granulation as a continuous wet granulation technique for pharmaceutical drug formulations. However, the mixing of granulation liquid and powder material during the short residence time inside the screw chamber and the atypical particle size distribution (PSD) of granules produced by twin screw granulation is not yet fully understood. Therefore, this study aims at visualizing the granulation liquid mixing and distribution during continuous twin screw granulation using NIR chemical imaging. In first instance, the residence time of material inside the barrel was investigated as function of screw speed and moisture content followed by the visualization of the granulation liquid distribution as function of different formulation and process parameters (liquid feed rate, liquid addition method, screw configuration, moisture content and barrel filling degree). The link between moisture uniformity and granule size distributions was also studied.For residence time analysis, increased screw speed and lower moisture content resulted to a shorter mean residence time and narrower residence time distribution. Besides, the distribution of granulation liquid was more homogenous at higher moisture content and with more kneading zones on the granulator screws. After optimization of the screw configuration, a two-level full factorial experimental design was performed to evaluate the influence of moisture content, screw speed and powder feed rate on the mixing efficiency of the powder and liquid phase. From these results, it was concluded that only increasing the moisture content significantly improved the granulation liquid distribution.This study demonstrates that NIR chemical imaging is a fast and adequate measurement tool for allowing process visualization and hence for providing better process understanding of a continuous twin screw granulation system.

The influence of feed rate and shear forces on the devulcanization process of ground tire rubber (GTR) conducted in a co-rotating twin screw extruder

The search for new ways to recycling of rubber waste has been the aim of many studies conducted by research centers and companies worldwide. The results of our investigations on the process of continuous thermomechanical devulcanization of ground tire rubber using a twin screw extruder are presented. We used a co-rotating twin screw extruder with a special configuration of plasticizing unit, enabling generation of considerable shear forces. Various properties were characterized, such as the influence of the ground tire rubber feed rate and screw speed (shear forces) on the screw torque, acetone extract, sol fraction, and the degree of devulcanization in the resulting products. The effect of a secondary vulcanization on the vulcametric curves was determined, and the mechanical properties (tensile strength, elongation at break, hardness, resilience and abrasion resistance) of the revulcanized material were studied. It has been determined that the devulcanization process depends on the values of shear force and residence time acting on ground tire rubber. The devulcanization degree increases with increasing screw speed and feed rate. The results of repeatability of continuous devulcanization process of ground tire rubber were also determined. Obtained products possess the quality comparable to that of reclaim rubber available on the market.

Porosity of starch–proteins extrudates determined from nitrogen adsorption data

Extrudates of potato starch with selected proteins (concentrate of soybean proteins, whey proteins and acidic casein) were produced at 22% raw material moisture, and at various process temperatures and extruder screw speeds. Increase of screw speed and temperature had a significant effect on changes in the specific surface area and porosity of products which were tested with the use of low-temperature sorption of nitrogen. The nitrogen adsorption isotherms plotted are of types II and III according to IUPAC, both for the raw material and for the product. Equation BJH was used to determine the surface area (SBJH), volume (VBJH) and average pore diameter (DBJH). For diameters from 35 Å to 74 Å, the calculated pore volumes assumed values within the range of 23·10−5 cm3/g −55·10−5 cm3/g. Curves of pore size distribution based on average pore diameter within the range of 19.7–23.2 Å indicate a large cumulative volume of pores.Extrusion caused a decrease in the specific surface area of the product, from 0.19 m2/g to 0.32 m2/g. A high correlation was noted between increase in porosity and expansion, and the optimum screw speed and temperature profile.

Influence of process parameters on microstructure and mechanical properties of starch-cellulose acetate/silver sulfadiazine matrices prepared by melt extrusion

Starch-cellulose acetate matrices containing silver sulfadiazine were produced using melt extrusion for application in drug delivery devices (DDDs). The influence of the extrusion parameters (screw speed and temperature) on the morphological and mechanical properties of the matrices was evaluated at three different levels. The microstructural characterization of all matrices showed that an increase in the screw speed enhances the porosity and drug dispersion, while an increase in the extrusion temperature decreases the pore diameter of the matrices. Mechanical results did not show significant differences between the elastic modulus values for the matrices; however, a faster screw speed led to higher ultimate strength and strain at failure values. Results obtained in the dynamic mechanical analysis showed that the glass transition and loss tangent (tan δ) peak values became higher with increasing screw speed and temperature.

EFFECT OF EXTRUSION CONDITIONS ON THE PHYSICAL PROPERTIES OF HIGH PROTEIN SNACKS

Three blends were formulated from corn grits, rice grits and defatted soybean with different percentages. The blends were extruded using a single extruder with different operational conditions: temperature of the extruder ranged from 175 to180o, moisture content of the raw material were (13%, 15, 17 and 19% w.b.), screw speeds were (500, 600, 700, 800, and 900 r.p.m.) and feeding rates were at (1.6, 1.8, 2 and 2.2 kg/min).Therefore, the extrudates were dried at 160 Co for 3min. Technical aspects and other physical and functional properties of the extrudates were studied.The samples were tested for sensory properties at zero time and after three months. Increasing the moisture content decreased the expansion rate while increasing both feed rate and screw speed increased the expansion rate.On the other hand increasing both moisture content and feed rate increased bulk density on contrary increasing screw speed decreased bulk density. In case of water absorption index (WAI), increasing moisture content increased WAI meanwhile increasing both screw speed and feed rate decreased WAI. As for water soluble index (WSI), increasing the moisture content, screw speed and feeding rate decreased WSI. The effect of storage (3 months) on the sensory properties including (taste, appearance, crispiness and overall acceptability) was very slightly since the scores given before and after storage were almost the same.

Droplet breakup and coalescence in a twin-screw extrusion processing of starch based matrix

Formation of oil droplets during twin screw extrusion processing of maize starch was investigated by analyzing the droplet breakup and coalescence mechanisms separately. For this purpose, the flow was characterized by computational fluid dynamics (CFD) using material data derived from online rheological measurements. The simulated results on local flow conditions were coupled to experimental data on the dispersed phase morphology, which was analyzed by confocal laser scanning microscopy (CLSM). This was used to elucidate the influence of process characteristics relevant for droplet breakup and coalescence. The results showed that increasing screw speed does not necessarily result in smaller droplet sizes. This could be related to the contradictory effects: increasing screw speed improves droplet breakup but also increases the rate of coalescence. Smaller droplet sizes were obtained at higher blend viscosities, which could be achieved either by increasing the feed rate or by using screw configuration that applies less mechanical stress. The results suggest that an increase in blend viscosity reduced the rate of coalescence. Moreover, increasing oil content led to an increased rate of coalescence, and therefore to remarkably bigger droplets. Selection of process parameters (e.g. screw configuration, feed rate, screw speed) based on the findings of this study allowed enhancing the dispersive mixing efficiency of triglyceride droplets during extrusion processing of maize starch.

Analysis of the dispersive mixing efficiency in a twin-screw extrusion processing of starch based matrix

The flow of plasticized maize starch in a co-rotating twin screw extruder was simulated by using computational fluid dynamics (CFD). Sensitivity of the simulation to the selected viscosity model was analyzed. The results suggest that about 16 times increase in zero shear viscosity has no influence on the flow, whereas a slight change in viscosity at the shear thinning region leads to significant increase in pressure drop along the mixing zone of extruder. Simulation results were validated quantitatively by experimental data. Furthermore, the flow type and profile in the extruder were discussed by using the influence of screw speed and screw configuration as exemplary process parameters. To evaluate the dispersive mixing efficiency, material specific critical capillary number was implemented into particle tracking simulations. Maximum shear stress generated at the tip of the screws was used to calculate the maximum capillary ratio, and therefore to determine the dispersive mixing efficiency. The results show that increase in screw speed led to better dispersive mixing, although the generated shear stresses decreased. To investigate the influence of screw geometry, two different screw configurations were simulated. The results show that the dispersive mixing efficiency can be improved by using reverse kneading blocks at which more particles are exposed to high shear stresses.

Manufacture and characterization of gelatin films derived from beef, pork and fish sources using twin screw extrusion

Gelatin films derived from beef, pork and fish sources were manufactured by twin-screw, co-rotating extrusion. The effect of extrusion processing parameters, namely; screw speed (100–400rpm) and temperature (90, 90, 90, 90°C and 90, 120, 90, 90°C) on the mechanical and barrier properties of gelatin films were studied. Increasing screw speed up to 300rpm improved (P<0.05) tensile strength (TS) and reduced (non-significantly) water vapour permeability (WVP) values for all manufactured gelatin films. However, the WVP of various gelatin film types was reduced (P<0.05) when a screw speed of 400rpm was employed. Increasing the speed of extrusion promoted (P<0.05) increased solubility of films in water. Manufacture of films using a higher temperature profile resulted in films possessing higher puncture strengths (PS), increased water barrier properties with higher water solubility.

Optimization of process variables to develop honey based extruded product

In the present work, the processing variables were optimized to study their effect on functional properties of honey based ready-to-eat expanded snack food. The blends of rice flour, wheat flour and honey were extruded in a twin-screw extruder. Experimental design with temperature (115 to 135°C), screw speed (270 to 350 rpm) and feed proportion (5 to 15%) as independent variables which produced 20 different combinations, were studied using response surface methodology to investigate the effect of these variables on product responses (lateral expansion, bulk density, color, Water absorption and solubility index characteristics). Multiple regression equations were obtained to describe the effects of each variable on product responses. Results showed that increasing the barrel temperature resulted in extrudate with higher expansion, water absorption index, a* value and lower bulk density and L* and b* values. Increasing screw speed resulted in higher expansion, water solubility index, L value and lower bulk density whereas, increasing honey proportion of feed composition resulted in higher a* value, bulk density, water solubility index and lower expansion, water absorption index and L*value. The graphical optimization studies resulted in temperature (119 to 122°C), screw speed (301 to 321 rpm) and feed composition (9.68 to 10.35%) as optimum variables to produce acceptable honey based extrudates. Key words: Twin screw extrusion, honey, response surface methodology, rice flour, wheat flour.

Effects of process variables and addition of polydextrose and whey protein isolate on the properties of barley extrudates

SummaryExtrusion cooking is commonly used in the production of snacks. In the present study, extrudates were prepared using barley flour alone and with the addition of either polydextrose (PD) or whey protein isolate (WPI) and both PD and WPI. Independent process variables were water content of the mass (17%, 20% and 23%), screw speed (200, 350 and 500 rpm) and temperature of section 6 and die (110, 130 and 150 °C). Expansion, hardness, water content, porosity and chemical composition of the extrudates were analysed. Highly porous and expanded snack products with high dietary fibre and protein contents were obtained from barley flour and WPI when water content of mass was 17%, screw speed 500 rpm and temperature of section 6 and die 130 °C. Barley flour alone or with PD resulted in hard and non‐expanded extrudates. Expansion of extrudates was statistically significantly increased with decreasing water content of the mass and increasing screw speed in all trials.

Influence of Thermomechanical History on Chemical and Rheological Behavior of Bitumen

It is well-known that asphaltene content plays an important role in determining the high viscosity of bitumen. This paper presents an experimental study of the specific effects of extrusion operating conditions on the physical and chemical properties of bitumen. Five bitumen samples were prepared by twin screw extrusion with different operating conditions (feed rate Q and screw speed N). Physical properties were studied by rheological measurements. Viscosity values were measured by steady state flow tests. Chemical changes in the bitumen structure were followed in the infrared region with attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy by measuring the evolution of the bands areas at 1700 cm–1 (C═O), 1030 cm–1 (S═O), and 1600 cm–1 (aromatic C═C) and the bands between 900 and 730 cm–1 attributed to aromatic C—H. An increase in feed rate Q induces a decrease in the Newtonian viscosity, as a result of a decrease in the asphaltene volume fraction. The characterization by ATR confirms that the decrease in feed rate entails the creation of C═O functional groups and the increase in sulfoxide (S═O) functional groups and C═C bonds, accompanied by a decrease in the C—H aromatic bonds. These results indicate a structure that is more oxidized and more aggregated at low feed rate, certainly as the result of an increase in the residence time into the extruder. The increase in screw speed also induces decreases in the viscosity and the volume fraction of asphaltenes, until a point after which the situation reverses. This change may be explained by the appearance of new peaks between 1200 and 1050 cm–1, attributed to C═S bonds, and between 640 and 540 cm–1, for S—S bonds. A competition between shear rate and residence time takes place. The thermomechanical history has, thus, a great influence on the chemical and rheological behavior of pure bitumen, and the chemical changes observed show that the asphaltene volume fraction is not the unique parameter that explains the variations in viscosity.

Effects of Extrusion Process Variables on Quality Properties of Wheat-Ginseng Extrudates

The present study investigated the effects of extrusion process variables (feed moisture, screw speed, and barrel temperature) on the physical [expansion ratio, water absorption index (WAI), and water solubility index (WSI)], pasting, and thermal properties of wheat-ginseng extrudates (WGE). A wheat flour-ginseng powder (GP) blend (10% GP, w/w) was extruded in a twin-screw extruder (L/D ratio of 25:1) with full factorial combinations of feed moisture (25, 30, and 35%), screw speed (200 and 300 rpm), and zone 5 barrel temperature (110, 120, 130, and 140°C). The expansion ratios of WGE were significantly increased with decreasing feed moisture, decreasing screw speed, and increasing barrel temperature. Increasing feed moisture significantly increased WAI values of WGE and significantly decreased WSI values of WGE. However, an increase in either screw speed or barrel temperature caused a significant decrease in WAI values of WGE and a significant increase in WSI values of WGE. Rapid visco analyzer peak viscosity values of WGE were significantly affected by changes in extrusion process variables studied, indicating that the degree of starch degradation and/or gelatinization in WGE is a very important factor associated with their peak viscosity. WAI values of WGE were positively correlated (r = 0.88, p ≤ 0.001) with peak viscosity values of WGE samples, whereas WSI values of WGE samples were negatively correlated (r = 0.82, p ≤ 0.001). Increasing feed moisture resulted in an increase in values of transition peak temperature (Tp) of WGE, whereas increasing screw speed and barrel temperature each led to a decrease in Tp values of WGE, determined by differential scanning calorimetry.

Effects of online pretreatment of plant ingredients on processing responses and physical properties in extruded fish feed

A feed processing study, using a 4×2×2 design, was conducted to evaluate the influence of plant ingredient (soybean meal, rapeseed meal, field peas and faba beans), pretreatment of the mash (water addition of 400g/kg total moisture to the plant meal fraction of the mash for 45min at 45°C) and conditions applied during the extrusion process (screw speed of 325 or 225rpm) on quality of fish feeds. Pretreatment of the plant ingredients increased the extrusion temperature (P<0.001) and the steam pressure in the barrel (P<0.05) and reduced the specific mechanical energy (P<0.05), resulting in a decrease (P<0.01) in hardness in the diets subjected to the pretreatment. Pretreatment of the feed also resulted in a decrease in bulk density (P<0.01) that was lowest for the rapeseed meal diet (P<0.01). There was an effect of plant ingredient on temperature in the extruder (P<0.05), but only in the third section, while no effect was observed on pressure. Diets with field peas and faba beans resulted in increased (P<0.05) pellet hardness. Increased screw speed reduced both pellet hardness (P<0.05) and bulk density (P<0.001). In conclusion, the novel pretreatment method can be implemented online in an extrusion line, if desired, for nutritional purposes. However for regular ingredients it does not affect physical quality.

Extrusion parameters related to starch/chitosan active films properties

SummaryDespite the increased use of extrusion technology in the production of biodegradable films, a better understanding of its effects on the several biopolymers is required. Therefore, the influence of extrusion temperature (120, 130 and 140 °C) and screw speed (25, 35 and 45 r.p.m.) on the properties of an active film formulated with starch, chitosan and oregano essential oil was investigated. Mechanical and barrier properties, apparent opacity and blow‐up ratio (BUR) of films were determined. The increase in screw speed had a positive effect on BUR and water vapour permeability (WVP) and a negative effect on opacity, tensile strength and elongation at break of the films. Low die temperatures resulted in decreased tensile strength, elongation at break, Young’s modulus and WVP of the films. Sorption isotherms of films were directly influenced by the extrusion conditions and films produced at 130 °C and 35 r.p.m. were less hydrophilic.

Morphology Evolution in PC/PE Blends with and without Compatibilization During Twin-Screw Extrusion

The morphology evolution in polycarbonate/polyethylene (PC/PE) blends with and without compatibilization in a twin-screw extruder was studied using a scanning electron microscope (SEM). The effects of screw speed and compatibilizer on the morphology of PC/PE blend during the extrusion were discussed in detail. It was found that the shape and size of the dispersed phase in the uncompatibilized PC/PE blend are both influenced by the screw speed. The evolution of dispersed phase morphology can be affected by increasing screw speed, and the dispersed particle size decreases with the increasing of the screw speed. As a compatibilizer, the addition of the (ethylene-methyl acrylate-glycidyl methacrylate) copolymer (E-MA-GMA) could accelerate the breakup of the PC dispersed phase and decrease the dispersed particle size. The dispersed droplet size in the PC/PE blend with compatibilization was hard to change at different positions along the screw axis with a higher screw speed. Along with the addition of the compatibilizer, the dispersed particle size was slightly influenced by the screw speed.

Improvements of the Tensile Properties of Recycled High Density Polyethylene (HDPE) by the Use of Carbonized Olive Solid Waste

Recycling of plastic poses several concerns to manufacturers. The most important concern is the unpredictable of their mechanical properties (modulus of elasticity, tensile strength and ductility). Olive solid waste, an abundant material usually thrown into land causing harms to environment was mixed with HDPE plastic and used as a filling material. The mixture was fed to a house made extruder operating at different speed and temperature. Two carbon particle sizes range (less than 150 µm and 180–250 µm) were used. The effect of carbon contents from 0 to 10% wt/wt and operating conditions were tested on the mechanical properties of the recycled HDPE plastic. It was found that up to 5% wt/wt carbon of less than 150 µm resulted in a noticeable improvement of modulus of elasticity and tensile strength. The optimum value of modulus at carbon particle size 180–250 µm was found at 2.5 olive solid carbon content. Increasing screw speed was found to increase tensile modulus and strength of used plastic. This was related to melt viscosity and reduction in particle size. An increase in processing temperature was found to improve tensile properties up to certain point where degradation of polymeric matrix begins to occur and therefore tensile properties deteriorate.