Higher Screw Speed Research Articles

Effect of Processing Conditions on Properties of PET/Clay Nanocomposite Films

Abstract Polyethylene terephthalate (PET) nanocomposite films (with 3 wt.% Cloisite 30B) were prepared by cast extrusion followed by uniaxial stretching, using chill rolls. Two screw profiles with different mixing elements under different screw speeds (N) and feeding rates (Q) were used to prepare PET/clay nanocomposite (PCN) films. Transmission electron microscopy (TEM) and wide angle X-ray diffraction (WAXD) showed that the clay layers were aligned in the machine direction (MD). XRD patterns depicted that the interlayer distance of clay platelets in the state of intercalation is somehow independent of the processing conditions, but the macro-scale characterization, including barrier and mechanical properties, showed that the level of clay layer delamination was affected by processing conditions. The results reveal that the applied strain has stronger effect than residence time on the barrier and mechanical properties. At the highest screw speed (N = 250 min−1), 27% reduction in oxygen permeability and 30% improvement in tensile modulus were obtained for the more severe screw profile.

Preparing iPP/HDPE/CB functionally gradient materials: influence factors of components and processing

In this work, gradient materials with low electrical resistivity were prepared by compounding isotactic polypropylene (iPP)/high density polyethylene (HDPE) blends with carbon black (CB) through extruding and injection molding. Contact angle measurements and morphology measurements showed that the CB particles were selectively located in HDPE phase and the final composites had a gradient structure that the HDPE/CB phase exhibited different morphologies in the skin layer and core layer of the composites under different processing procedures. The main factors influencing the formation of the functional gradient materials (FGM), including screw speed during extruding, iPP types and CB contents were discussed. They affect the phase morphology by shear stress, the restoration of HDPE phase, and the viscosity ratio of polymer blends, respectively. In conclusion, iPP/HDPE/CB FGM could be formed easily in the composites blending with the iPP type with narrow molecular weight distribution (MWD) and higher CB content extruded at higher screw speed. The electrical properties of iPP/HDPE/CB composites were studied and the results showed that screw speed in extrusion significantly influenced the percolation curve and electrical property of the final composites. Copyright © 2011 John Wiley & Sons, Ltd.

Power Requirements for Paddy Rice (Oriza Sativa L.) Grain Handling with Augers

The objective of this study was to determine the effects of auger size, screw rotational speed, and transport angle on the specific and net power requirements for handling paddy rice grain with auger conveyors. The experiments were conducted at three auger sizes of 15.5, 20, and 25 cm; five screw speeds of 200, 300, 400, 500, and 600 rpm; and four transport angles of 0, 10, 20, and 30. Based on the results obtained, paddy rice grain conveyed by the augers required more power in higher screw speeds, transport angles, and auger sizes. In addition, the specific power requirement statistically increased with screw rotational speed and transport angle, while these values decreased as auger size increased. The average net power requirement was obtained as 104.31 W varying from 31.10 to 237.36 W, while the average specific power requirement was calculated as 84.88 W s/kg m ranging from 33.61 to 228.21 W s/kg m.

Scaling-up a Reactive Extrusion Operation: A One-dimensional Simulation Analysis

Abstract The peroxide-initiated degradation of polypropylene is simulated by means of a one-dimensional (1D) reactive extrusion (REX) model. Two scale-up rules, namely, constant thermal time and specific energy consumption (SEC) are evaluated for co-rotating intermeshing twin screw extruders (COITSEs) of various sizes. The weight-average molecular weight (Mw) and the polydispersity index (PDI) are selected as the evaluation parameters for testing the scale-up procedures being analyzed. The results for the simulated operating conditions show that when the REX operation is scaled-up under constant thermal time, very good agreement is obtained between the Mw and PDI of the larger extruders and the values of these parameters corresponding to the reference extruder. For the constant SEC approach, more significant variations are observed for both of the aforementioned parameters. In the case of the constant thermal time scale-up approach, the effect of operating conditions of the reference extruder on the scaled-up operation is further analyzed. For a constant screw speed, when the reference mass throughput increases the predicted time of extrusion increases. Regarding the temperature of reaction, the higher increase of this parameter corresponds, in general terms, to the lower mass throughputs and higher screw speeds specified for the reference extruder.

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.

Effects of extrusion conditions on system parameters and physical properties of a chickpea flour-based snack

Abstract Response surface methodology (RSM) was used to study the effects of feed moisture content (16–18%), screw speed (250–320 rpm), and barrel temperature (150–170 °C) on extruder system parameters (product temperature, die pressure, motor torque, specific mechanical energy, SME) and physical properties (expansion, bulk density, hardness) of a chickpea flour-based snack. Second-order polynomials were used to model the extruder responses and product properties as a function of process variables. Product temperature and die pressure were affected by all three process variables, while motor torque and SME were only influenced by screw speed and barrel temperature. All three variables affected product responses significantly. Desirable products, characterized by high expansion ratio and low bulk density and hardness, were obtained at low feed moisture, high screw speed and medium to high barrel temperature. It was demonstrated that chickpeas can be used to produce nutritious snacks with desirable expansion and texture properties.

Influence of processing window and weight ratio on the morphology of the extruded and drawn PET/PP blends

AbstractTo obtain polyethylene terephthalate (PET)/polypropylene (PP) microfibrillar composite (MFC) with good mechanical properties, a high content of PET fibrils in the drawn strand (i.e. PET droplets in the extrudate) is preferred. However, a phase inversion (from PP matrix to PET matrix) takes place when the concentration of the PET reaches 40 wt% at the screw speed of 40 rpm (rounds per minute). This “PP domains in PET matrix” phase structure is the undesired phase structure for preparing MFC. However, the desired phase structure of “PET droplets in PP matrix” can be regained by adopting a low screw speed (20 rpm) during extrusion of the PET/PP (40/60); if a higher screw speed is adopted (80 rpm), then a suitable amount of PP grafted maleic anhydride (PP‐g‐MA) should be incorporated. The PET/PP blends which demonstrate the desired “PET droplets in PP matrix” phase structure were stretched into strands, and PET/PP MFC was prepared. The MFC with high content of PET microfibrils as the reinforcement exhibits superior tensile properties than the neat PP. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

The Effect of Processing on Fiber Dispersion, Fiber Length, and Thermal Degradation of Bleached Sulfite Cellulose Fiber Polypropylene Composites

The goal of this study is to examine how the extrusion process affects the dispersion, length, and thermal degradation of cellulose fibers (CF) in polypropylene (PP) composites. Bleached sulfite CF are pelletized and then compounded (20 and 30wt%) in a co-rotating twin screw extruder. The pelletizing process of CF is found to cause extensive fiber breakage. The fiber length is decreased from an initial 1.7 to 0.8 mm. The results show that higher screw speed, higher fiber content, and two extrusions not only increase the shear energy, resulting in improved fiber dispersion but also cause fiber breakage and thermal degradation. The composite's mechanical properties are not improved with better fiber dispersion and the reason for this might be the extensive fiber breakage and thermal degradation. Moreover, it is found that the PP polymer is also slightly degraded during the compounding process.

Residence time distribution of a pharmaceutical grade polymer melt in a single screw extrusion process

The residence time distribution (RTD) of a flowing polymer through a single screw extruder was studied. This extruder allows injecting supercritical carbon dioxide (scCO 2) used as physical foaming agent. The tested material is Eudragit E100, a pharmaceutical polymer. RTD was measured at various operating conditions and a model describing RTD has been developed. High screw speed or high temperature implies short residence time, but these parameters do not have the same effect on polymer flow. In the flow rate range studied, scCO 2 has no significant influence. A mathematical model consisting of a plug flow reactor in series with a continuous stirred tank reactor (CSTR) cross-flowing with a dead volume fitted well the experimental data.

Ultrasonic diagnosis of the single screw behavior during extrusion—A case study

AbstractUltrasonic diagnostic method of screw behavior during extrusion has been designed, developed, and carried out on a 63.5‐mm single screw extruder, equipped with either a basic conveying screw or a mixing screw. It was found that the screw behavior depends on the screw speed and the die pressure. Whereas initially at low speed, the screw centered by the hydrodynamic forces rotates smoothly in the axial position, at higher screw speeds and high die pressures the screw starts vibrating. Thus, (1) the screw tip vibrated with the amplitude of 10–210 μm as the screw speed varied from 5 to 100 revolutions per minute; (2) the screw vibrations in the vertical and horizontal directions were asymmetrical; (3) the vibration pattern repeated itself at every two revolutions; (4) the vibrations originated in the poorly aligned engagement in the gearbox sleeve when the screw was pushed deeply into it by backpressure; (5) once pushed in the screw oscillated at any screw speed or die pressure. POLYM. ENG. SCI., 2009. Published by the Society of Plastics Engineers

Evaluation of ingredient effects on extruded starch-based foams using a supersaturated split-plot design

The aim of this study was to use a supersaturated split-plot design to identify the significant effects of ten ingredients, each at two levels, and two levels of screw speed on selected properties of starch-based packaging foams. Supersaturated designs are special types of fractional factorial designs that allow for evaluating many factors with a minimal amount of experimental material. Rice starch foams were prepared with a twin-screw extruder. The ingredients used were α-cellulose (fiber), potato starch, poly(lactic acid), polystyrene, glycerol, sodium chloride, talc, sodium bicarbonate, citric acid and moisture content of the feed. The properties studied were radial expansion ratio, unit density, bulk spring index, bulk compressibility and Young's modulus. The results showed that the ingredients identified to have significant effects on the properties were the high levels of talc, citric acid, moisture content and the low level of fiber. Low screw speed was found to have greater effect on the properties of the foams than did the high screw speed. It was concluded that the supersaturated split-plot design was successful in identifying the significant ingredients and screw speed that should be used to further investigate the extrusion of starch-based packaging foams.

The significance of variation in extrusion speeds and temperatures on a PEO/PCL blend based matrix for oral drug delivery

The body of work described in this research paper outlines the use of PEO/PCL blends in the production of monolithic matrices for oral drug delivery. Several batches of matrix material were prepared with carvedilol used as the active pharmaceutical ingredient. The matrices were prepared using various extrusion parameters to investigate the effect of screw speed and barrel temperature on the properties of the drug delivery devices. The resultant extrudate was characterised using steady state parallel plate rheometry, differential scanning calorimetry (DSC) and dissolution testing. Higher screw speeds were observed to result in slightly lower matrix melt viscosity when compared with matrices compounded using lower screw speeds. Dissolution testing showed that the incorporation of the hydrophobic PCL polymer into a PEO matrix results in a retarded drug release profile.

Visualization study on the dynamic mixing quality during single-screw extrusion

An empirical method was developed to study the dynamic mixing characteristics of a single-screw extrusion process. The method basically involved a modified version of the visible extruder developed by Wong et al. (Plast Rubb Comp Proc Appl 26:78, 1997). Digitized films of the molten polymer web emerging from the slit flow cells attached to the “windows” of the visible extruder’s barrel were captured in bitmap file format. Subsequent statistical analysis (largely variance) on the pixel intensity of the cropped films had made quantification of mixing quality possible. The higher the average variance of the pixel intensity, the poorer the mixing quality. The focus of this investigation was on the effects of temperature and screw speed. For the selected single-flighted conventional screw, it was found that, in general, the higher the screw speed, the shorter the residence time and, hence, poorer mixing quality. High screw speed also generated erratic average variance data. The results suggested that a critical screw speed for optimized mixing might have been present. For the equipment used in the current project, this critical screw speed lied between 50 and 80 rpm. However, unlike screw speed, melt temperature alone appeared to have relatively little effect on the mixing quality during extrusion.

Influence of processing conditions on the morphological and mechanical properties of compatibilized PP/LCP blends

AbstractThe main aim of this work is to study the influence of the application of different processing conditions on the morphological and mechanical properties of thermoplastic/LCP blends, in which the viscosity ratios are inferior to unity and decrease with increasing temperature. The way the microstructure evolves along the extruder determines the final morphology and thus, the mechanical performance of the systems. In the present case, the mechanical properties are related with the degree of fibrillation in the final composites. The best degree of fibrillation was obtained for low screw speeds and temperatures and for intermediate outputs. The use of high screw speeds and processing temperatures results in a decrease of the viscosity ratio, in the former case via an increase in the viscous dissipation, at the regions of higher shear rates (kneading‐elements). The application of a lower processing temperature is advantageous for deformation, break‐up, and fibrillar formation because of the higher viscosity ratios and higher shear stresses involved. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

A New Calculation Model and Optimization Method for Maddock Mixers in Single Screw Plasticising Technology

Abstract A homogenous melt is the prerequisite to achieve the demanded product quality in single screw plasticising technology. At higher screw speeds and mass flow rates solid particles can occur in the melt. Dispersive mixing elements are often used to improve the melt quality. Calculation models are necessary for designing mixing elements in the right way. A new model for the often used fluted mixing sections like axial and spiral Maddock-elements and Z-elements is presented in this paper. The calculation model is reduced to a single pair of inlet and outlet flute, connected by the shearing gap. Especially in spiral Maddock mixers the longitudinal flow in the flutes is a combined pressure and drag flow but in axial Maddock mixers pure pressure flow occurs. In the shearing gap a combined pressure and drag flow can occur. The leakage flow through the flight clearance is also considered. Geometry functions are introduced for considering the rectangular or circular segment shaped cross section of the flutes. The viscosity is shear rate and temperature dependent, the channel height as well as the channel width can vary along the mixing element. The model allows the calculation of the longitudinal pressure profile in the inlet and outlet flutes, the total pressure drop and the shear stress distribution in the shearing gap. Mixing sections sometimes show a too high pressure consumption and insufficient shearing efficiency. Therefore a geometry optimization method for axial Maddock mixing heads is presented in this paper.

이축 스크루 압출기내 유동의 수치 해석과 혼합 성능 분석

We analyzed the non-Newtonian and non-isothermal flow in the melt conveying zone in co-rotating and counter-rotating screw extruder system with the commercial code, STAR-CD, and compared the mixing performance with respect to screw speed and rotating direction. The viscosity of fluid was described by power-law model. The dynamics of mixing was studied numerically by tracking the motion of particles in a twin screw extruder system. The extent of mixing was characterized in terms of the residence time distribution and average strain. The results showed that high screw speed decreases the residence time but increases the shear rate. Therefore higher screw speed increases the strain and has better mixing performance. Counter-rotating screw extruder system and co-rotating screw extruder has the similar shear rate with the same screw speed in spite of different rotating direction. However, the counter-rotating screw has good mixing performance, which is resulted from longer residence time than that of co-rotating screw extruder.

RingExtruder boosts output without degradation

In addition to its CX range of twin screw extruders, Centruy Inc. offers its 3+ RingExtruder through a joint venture with Blach Verfahrentechnik GmbH. The design consists of 12 closely intermeshing co-rotating screws and is claimed to offer a unique alternative for increasing throughput without excessive shear or heat generation. The company adds that rather than relying on high screw speeds the 3+ RingExtruder can achieve higher throughput through increased torque and greater free volume. Century adds that melt flow analysis undertaken on samples produced on the 3+ show no appreciable material degradation. A series of RingExtruders ranging from 30-120 mm are available to meet most throughput requirements. The RingExtruder’s screws may be removed from the front or the back of the machine. This is a short news story only. Visit www.addcomp.com for the latest additives and compounding industry news

TEM Series looks to wood-plastic composites

NFM Welding Engineers manufactures the TEM Series of co-rotating, intermeshing compounding twin-screw extrusion systems. The company says that this offers a high torque-per-free volume and high screw speed. The TEM Series can process a wide variety of plastics compounds including wood-plastic composite materials, such as PVC, polyethylene and polypropylene, in combination with most woods including pine, maple and oak. NFM adds that the system requires no pre-drying or pre-mixing, saving capital equipment costs, plant space and maintenance. End product can either be directly extruded or pelletized for direct feed to a single screw system. The TEM Series is available in models from 26–240 mm. This is a short news story only. Visit www.addcomp.com for the latest additives and compounding industry news

Extrusion Processing of Rice‐Based Breakfast Cereals Enhanced with Tocopherol from a Chinese Medical Plant

ABSTRACTBrown rice flour was mixed with a Chinese medical plant (Euryale ferox Salisb.) and processed to make ready‐to‐eat breakfast cereals using twin‐screw extrusion. Levels of 15 and 20% feed moisture in flour, and 200 and 250 rpm screw speed were set, and the physicochemical properties and content of α‐, β‐, γ‐, and δ‐tocopherols were determined. The data showed that 15% feed moisture gave a low bulk density and water absorption index but a high expansion ratio and water solubility index. High screw speed (250 rpm) produced a result similar to that of 15% feed moisture. A sample with 85% brown rice flour with 15% E. ferox Salisb. retained the highest content of α‐, β‐, γ‐, and δ‐tocopherols (125, 6, 78, and 9 μg/g), respectively. The optimum extrusion conditions determined were 15% E. ferox Salisb. mixed with brown rice at 15% feed moisture and at 250 rpm screw speed.

Study of poly(ethylene terephthalate)/polypropylene microfibrillar composites. I. Morphological development in melt extrusion

Poly(ethylene terephthalate)/polypropylene (PET/PP) blends of different compositions were extruded through a 2-mm capillary die using a corotating twin-screw extruder. The extrudates were cryogenically fractured and examined using scanning electron microscopy. The viscosity ratio of the constituent polymers alone was found to be unsuitable for explaining the polymer blend morphology. At a PET concentration of 20%, the extrudate consists of three regions. The skin layer, which is about 10 μm thick, has a lower concentration of the dispersed PET phase than the overall concentration. The intermediate region, which is about 400 μm thick, has profuse PET fibers and some small PET particles. The central region, which is approximately 800 μm in diameter, mainly contains PET particles that are generally bigger. A low barrel temperature, low die temperature, and fast cooling rate helped to retain the fibers near the extrudate skin. Meanwhile, the variation of the barrel temperature, die temperature, and cooling media did not produce a significant affect on the PET particle size distribution in the central region of the extrudate. A high screw speed and a high postextrusion drawing speed were very effective in producing fibers in the extrudates through elongation of particles. At a PET concentration of 30%, coalescence of the PET phase was prevalent, leading to the formation of PET platelets near the extrudate skin and irregular PET networks in the central region of the extrudate. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1743–1752, 2003