Kneading Block Research Articles

The study of numerical simulation and texture of soybean protein based on high moisture extrusion with different screw elements

Extrusion conditions and suitable screw configuration are key factors that affect protein reactivity and thus the properties of the blend. Fully revealing the whole extrusion process using numerical simulation is still a strong challenge due to the complexity of the flow field. In this paper, the flow behavior of protein under the action of kneading block and kneading block-reversing element was further revealed through the equivalent substitution, and the quality attribute of the extruded protein was also investigated. The results demonstrated the fluid pressure inside the barrel presented as a stepped and jagged increasing trend, and higher temperature and lower viscosity can be obtained at the screw root. The outlet pressure loss decreased when kneading block approached the outlet. Since the more complex fluid flow state at the location of the reversing element, more mechanical energy is transformed into internal energy, which amplifies the effect of temperature rise. Compared to the kneading block, the introduction of a reversing element can effectively improve the hardness and texturization of the extruded product, increase the brightness of color, and a better performance can be obtained at the backward reversing element. Overall, the consistency between the numerical simulation and the experimental results provided a research basis for the optimization of screw design combinations, and new theoretical support for the subsequent processing of meat analogs.

A new 2.5‐D twin screw extruder melting model with comparisons to data

AbstractMany polymers are processed and compounded in co‐rotating, fully intermeshing twin screw extruders. A typical compounding process consists of multiple unit operations including feed introduction, solids transport, transitioning from the conveying zone to the kneading block melting zone, melting, a downstream feed zone, a mixing zone, a devolatilization region, and a pressure generating discharge section. This paper will focus on the kneading block melting zone which typically includes a reverse pitch element so the kneaders remain full. Mechanisms for flow and energy input to pellets in kneading elements, including friction heating, pellet compression, energy diffusion, and viscous dissipation to form a melt phase: followed by viscous dissipation in a solid pellet/melt slurry, and heat transfer; are developed and implemented in a novel melting model. The model is validated with extrusion measurements and visualizations using low density polyethylene (LDPE). The predictions of the model are also compared with a classical set of experiments using high density polyethylene (HDPE). This paper describes the physics and engineering concepts that the authors feel are inherent in the melting section of the twin screw extruder where a large pressure peak is calculated using the friction and compression of the polymer pellets. The modeled increase in pellet bulk/surface temperature is due to the inclusion of four energy sources, pellet compression, thermal diffusion, friction energy dissipation, and viscous energy dissipation. This combined thermal dynamics based melting model results in a novel melting protocol. The melting mechanisms are coupled to flow regimes in the kneading blocks as melting progresses. The effects of throughput, Q, and screw rotation speed, N, are also examined.Highlights Novel 2.5D melting model for corotating, intermeshing twin‐screw extruders. Energy for melting; friction, deformation, diffusion, and viscous dissipation. The model helps elucidate mechanisms during melting in a twin‐screw extruder.

Study on the Function of Conveying, Kneading Block and Reversing Elements on the Mixing Efficiency and Dispersion Effect inside the Barrel of an Extruder with Numerical Simulation.

In order to better understand the extrusion process mechanism of plant protein inside a barrel, the parameter changes and flow characteristics of fluids under conveying, kneading block and reversing elements were investigated with numerical simulation. The results showed that the shear rate increased obviously with the increase in pitch; the shear rate value of the reversing element was larger, while that of the kneading block was the opposite. The screw combinations of conveying, kneading blocks and reversing elements all have a certain degree of mixing effect on the particles, and the reduction in pitch can effectively increase the mixing effect of the particles. The conveying element can provide a relatively constant acceleration for the particles, due to the pumping capability and pressure buildup as the pitch increases. The kneading block and the reversing element can increase the leakage flow between the discs and backflow, resulting in an extension of the residence time distribution that facilitates fluid interaction in the barrel and improves the dispersion of the particles. The restraint by the reversing element on the particles is obviously weaker than that of the kneading block and shows a higher particle mixing degree. Overall, the influence of different elements on the flow condition, mixing degree and residence time is significantly different, which improves the process controllability and provides references for potential applications to meet multiple demands.

New 2.5‐Dtwin screw extruder model for the feed section of a co‐rotating twin screw extruder with comparisons to data

AbstractMany polymers are processed and compounded in co‐rotating, fully intermeshing twin screw (TS) extruders. The typical compounding process consists of multiple unit operations including feed introduction, conveying solids away from the feed zone, transitioning from the conveying zone to the kneading block (KB) melting zone, melting, a downstream feed zone, a downstream mixing zone, a devolatilization region, and a pressure generating discharge section. This paper will focus on the first of these unit operations, the conveying of pellets in a partially filled screw leading to compaction and pressure generation in the full screw channel prior to the KB melting zone. Mechanisms for pellet conveying, for heating the polymer pellets, and for developing pressure at the end of the solids conveying screw elements are first presented for low‐density polyethylene (LDPE). The predictions of the model are also compared with a classical set of experiments on high‐density polyethylene (HDPE). The model is then tested using published characteristics of a polyamide‐type polymer. This paper focuses on the physics and engineering concepts that are inherent in the feed section of the TS extruder where the pressure is calculated using the friction of the polymer pellets. The effects of throughput,Q, at a constant rotation speed,N, are examined. Low and highQ/Nratios have significantly different axial pressure profiles.

Modeling melt conveying and power consumption of co‐rotating twin‐screw extruder kneading blocks: Part B. Prediction models

AbstractIntermeshing co‐rotating twin‐screw extruders are very versatile because their screw configurations can be tailored both to the application and to the properties of the materials used. Finding the best screw configuration is one of the main purposes of twin‐screw extrusion modeling, and requires models that accurately predict conveying and power consumption. The better the process can be predicted, the better the requirements of the final product can be met. We present novel prediction models of the conveying and power‐consumption behaviors of intermeshing co‐rotating twin‐screw extruder kneading blocks for Newtonian fluids. These are based on numerical simulations and therefore consider the complex three dimensional (3D) geometry of this element type without the need for common simplifications. Our models are thus capable of including all leakage flows and gap influences, which are usually ignored, for example, by the flat‐plate model. Since our models are derived by symbolic regression based on genetic programming, they consist of algebraic functions and are low‐threshold. They can be used to calculate various process parameters for individual kneading blocks or entire screw configurations, as illustrated by a use case.

Continuous film casting of polycarbonate/single‐walled carbon nanotubes composites with ultrasound‐assisted twin‐screw extruder: Effect of screw configuration

AbstractPolymer films are widely used in various industries, and incorporation of nanofillers into polymer films can give much more versatility in their applications. Polymer/carbon nanotubes (CNTs) composite films with good electrical conductivity can easily find applications in anti‐static or electrostatic discharge (ESD) protection. In the present study, efforts were devoted to investigate novel ultrasound‐assisted twin‐screw extrusion technology on improving the dispersion and distribution of single‐walled carbon nanotubes (SWNTs) in polycarbonate (PC) composites films via extrusion process. As a key processing parameter, effect of screw configuration on the performance of the composite films were systematically studied. Electrical, rheological, morphological and mechanical properties were characterized to illustrate the processing‐structure–property relationship during continuous film casting of PC/SWNTs composites with ultrasound‐assisted twin‐screw extruder. Results indicated that the screw configuration containing more kneading blocks led to better SWNTs dispersion and distribution, while the effect of ultrasound was more prominent in screw design with less kneading blocks.

On-Line Optical Monitoring of the Mixing Performance in Co-Rotating Twin-Screw Extruders.

The use of real-time techniques to evaluate the global mixing performance of co-rotating twin-screw extruders is well consolidated, but much less is reported on the specific contribution of individual screw zones. This work uses on-line flow turbidity and birefringence to ascertain the mixing performance of kneading blocks with different geometries. For this purpose, one of the barrel segments of the extruder was modified in order to incorporate four sampling devices and slit dies containing optical windows were attached to them. The experiments consisted in reaching steady extrusion and then adding a small amount of tracer. Upon opening each sampling device, material was laterally detoured from the local screw channel, and its turbidity and birefringence were measured by the optical detector. Residence time distribution curves (RTD) were obtained at various axial positions along three different kneading blocks and under a range of screw speeds. It is hypothesized that K, a parameter related to the area under each RTD curve, is a good indicator of dispersive mixing, whereas variance can be used to assess distributive mixing. The experimental data confirmed that these mixing indices are sensitive to changes in processing conditions, and that they translate the expected behavior of each kneading block geometry.

Machine learning assisted optimization of blending process of polyphenylene sulfide with elastomer using high speed twin screw extruder

Random forest regression was applied to optimize the melt-blending process of polyphenylene sulfide (PPS) with poly(ethylene-glycidyl methacrylate-methyl acrylate) (E-GMA-MA) elastomer to improve the Charpy impact strength. A training dataset was constructed using four elastomers with different GMA and MA contents by varying the elastomer content up to 20 wt% and the screw rotation speed of the extruder up to 5000 rpm at a fixed barrel temperature of 300 °C. Besides the controlled parameters, the following measured parameters were incorporated into the descriptors for the regression: motor torque, polymer pressure, and polymer temperatures monitored by infrared-ray thermometers installed at four positions (T1 to T4) as well as the melt viscosity and elastomer particle diameter of the product. The regression without prior knowledge revealed that the polymer temperature T1 just after the first kneading block is an important parameter next to the elastomer content. High impact strength required high elastomer content and T1 below 320 °C. The polymer temperature T1 was much higher than the barrel temperature and increased with the screw speed due to the heat of shear. The overheating caused thermal degradation, leading to a decrease in the melt viscosity and an increase in the particle diameter at high screw speed. We thus reduced the barrel temperature to keep T1 around 310 °C. This increased the impact strength from 58.6 kJ m−2 as the maximum in the training dataset to 65.3 and 69.0 kJ m−2 at elastomer contents of 20 and 30 wt%, respectively.

Fiber Length Distribution in Twin-Screw Extrusion of Fiber-Reinforced Polymer Composites: A Comparison between Shear and Extensional Mixing

Abstract New extensional mixing elements (EME) for twin-screw extrusion were applied to compound glass fibers (GF), carbon fibers (CF) or polyethylene terephthalate fibers (PETF) reinforced polymer composites with polymer matrix of polypropylene (PP) or polyethylene oxide (PEO) and the resulting fiber degradation upon processing was evaluated and compared with compounding via shear flow-dominated kneading blocks (KB). Composites structures were characterized in terms of fiber length and distribution, and cumulative length ratio, at five locations along the mixing zone. Although significant fiber breakage was achieved for both configurations, it was markedly lower in composites processed using the EME, because whereas the high shear stress kneading motion in the KB degrades fibers significantly, fiber breakup is significantly minimized by the alignment induced by the EME prior to flow in the high-stress regions.

Effect of Mixing Elements on Granule Formation in Hot Melt Twin Screw Granulation

Twin screw granulation (TSG) has been applied to wet granulation, although its application in melt granulation has been more limited. This work explores potential advantages of hot melt granulation using twin screw extrusion. Four main operating and formulation parameters were investigated: screw speed, number of mixing elements, temperature, and binder percentage. Combinations of these factors were then studied to determine their impact on the quantity and characteristics of granules within the desired size range of 125 – 1000 µm. A screening design of experiments (DOE) study was used with each factor set at three levels, to investigate individual factor effects and interactions. Two types of mixing elements were studied: kneading block (KB) and chaotic elements. The type and number of mixing elements were found to be paramount in contributing to the quantity and characteristics of granules formed. Results obtained agreed with previous findings in literature on the influence of different screw elements on the characteristics of granules formed by twin screw granulation. Additionally, the study revealed the unique impact which different mixer elements have on both granule production and characteristics. Depending on the specific need or use of granules in required applications, the granulation process can be effectively designed to meet the end product quality and outcome.

Morphology optimization of poly(ethylene terephthalate)/polyamide blends compatibilized via extension-dominated twin-screw extrusion

Abstract Poly(ethylene terephthalate) (PET) and polyamide (PA) are immiscible polymers, which requires the use of compatibilizers to stabilize the morphology and achieve acceptable property levels. Therefore, controlling the degree of dispersion, especially the size of the disperse PA droplets in the PET matrix is of paramount importance. This study aims to improve the mixing, i.e., minimize PA droplet size, in immiscible and compatibilized PET/PA and PET/Nylon-MXD6 (MXD6) blends by resorting to extension-dominated mixing in twin-screw extrusion (TSE). MXD6 is an aromatic polyamide similar in polarity to PET, so it is expected that it will blend more effectively than is the case with aliphatic nylon-6 and PET. Two screw configurations are used, a benchmark shear-dominated screw with kneading blocks (KBs) in an aggressive configuration, and an extension-dominated screw configuration with static mixers with hyperbolic C–D channels, recently developed by our group, in place of the KBs. The results show that the use of extensional mixing elements (EMEs) in place of KBs results in a significant decrease of both average and maximum droplet size for all blends, and up to more than one order of magnitude between the most extreme cases of the KB-processed immiscible blend and EME-processed compatibilized blends.

How Does the Dissimilarity of Screw Geometry Impact Twin-screw Melt Granulation?

Using a model formulation of 80% gabapentin and 20% hydroxypropyl cellulose (KlucelTM), we investigate how differences in the geometry of mixing elements in the Leistritz Nano-16 and Micro-18 extruders affect granulation mechanisms and the properties of the resulting granules. Two extruders, Leistritz Nano-16 and Micro-18, commonly used in development and manufacturing, respectively, were used. The kneading blocks of the Nano-16 extruder are less efficient in dispersive mixing than the kneading blocks of the Micro-18 due to the thinner discs (2.5 mm wide) of the Nano-16. Therefore, our model formulation could be granulated only under a higher degree of fill (DF) by enhancing the axial compaction and heating of the barrel. In contrast, the thicker (5 mm wide) kneading blocks of the Micro-18 extruder provide efficient dispersive mixing that enables granulation without axial compaction and barrel heating. The higher specific mechanical energy (SME) achieved at higher screw speeds and lower feed rates led to more granulation. Because of the difference in granulation mechanisms between the two extruders, critical processing parameters also differed. Tabletability and degradant content of granules correlated positively with DF for the Nano-16 but with SME for the Micro-18 extruder.

Online optical monitoring of polymer melting in a twin‐screw extruder

AbstractAn experimental setup containing a sliding online optical device is used to monitor in real‐time the melting process of a commercial polypropylene in a corotating intermeshing twin‐screw extruder. Turbidity and birefringence are measured at several axial locations upstream and along the first restrictive zone of the screw, where melting develops. The experiments are performed using different set barrel temperatures, extruder feed rates, and screw speeds, to generate distinct flow histories and, accordingly, changes in the onset and rate of melting of the polymer. The local flow conditions are characterized in terms of residence time distribution and data equivalent to axial pressure profiles. Turbidity and birefringence are sensitive to changes in the operating conditions providing a coherent description of melting. The onset of melting seems to take place in partially filled conveying elements, and then melting develops quickly as the latter become fully filled, and is completed well before flow through the kneading block.

Enhanced Dispersion and Mechanical Behavior of Polypropylene Composites Compounded Using Extension-Dominated Extrusion

Abstract The process of dispersing filler in polymer matrix is vital to the behavior of polymer composites. The current study involves understanding the extent of dispersion of filler by only varying the nature of mixing during the process. Identical polymer composite materials are processed via two different kinds of mixing sections on the screw in a twin-screw extruder, differing in the type and amount of stress they impose on the filler agglomerate. An aggressive (900) Kneading Block (KB) mixing section is compared with recently developed Extensional Mixing Elements (EMEs), which impart extension dominated mixing while KB imparts shear dominated mixing. Various EME geometries of different levels of aggressiveness were computationally studied and validated. Composites obtained from KB are compared with composites processed using five different EME geometries. Three composites of Polypropylene (PP) filled with carbon black, graphene nano platelets and carbon nanotubes were studied independently. Composites processed through EMEs display about an order of magnitude better dispersion of filler agglomerate over the composites processed through KB. In addition, enhanced modulus and yield stress is observed for composites processed through EMEs. An improvement of 63% to 266% in the strain achieved for EME processed composites is seen under biaxial film stretching.

Study of Mechanical and Moisture Absorption Behavior of Epoxy/Cloisite-15A Nanocomposites Processed Using Twin Screw Extruder

Abstract This paper presents the effect of process parameters of twin screw extruder and addition of Cloisite-15A on mechanical, thermal and moisture barrier properties of epoxy/Cloisite-15A nanocomposites. Four lobed kneading blocks were used the in shearing zone of the extruder, based on their effectiveness in dispersing nanofillers in epoxy. Screw speeds from 100 min−1 to 400 min−1, number of passes up to 15, temperature from 5°C to 80°C and Cloisite-15A contents from 1 wt.% to 2.5 wt.% were considered for designing the L12 Orthogonal Array. Improvements in tensile strength, compression strength, flexural strength, impact strength, hardness and moisture diffusivity in the nanocomposites were 11.89%, 20.06%, 27.73%, 37.26%, 25.48% and 56.22% respectively, when compared to neat epoxy. The improvements were achieved for screw speed of 400 min–1, 5 passes through the extruder, processing temperature of 5°C and 2 wt.% of Cloisite-15A. Dispersion of Cloisite-15A in epoxy was studied by XRD, SEM and TEM. Thermal stability and moisture barrier properties were superior in the nanocomposites.

The role of the screw profile on granular structure and mixing efficiency of a high-dose hydrophobic drug formulation during twin screw wet granulation.

This study aimed at systematically investigating the role of distributive comb mixing element (GLC) and neutral dispersive mixing kneading block element (K90) on the structure and physical properties of granules containing high-dose of poorly water-soluble drug. Albendazole was used as the model drug at 50wt% drug loading. Lactose monohydrate and microcrystalline cellulose were used as diluent, and 3 w/v% hydroxypropyl cellulose aqueous solution was used as binder liquid. It was found that the use of GLC element resulted in formation of granules with higher internal porosity, more homogeneous binder distribution, smaller particle size, superior compaction properties and tabletability while K90 kneading element produced relatively larger and denser granules with less homogeneous binder distribution where binder was mainly concentrated in larger granules. The use of downstream GLC element was shown to result in an approximately 8% and 57% reduction in the D50 for 0.2 and 0.3 liquid-to-solid ratios, demonstrating a significantly higher sensitivity of granule size to screw profile at higher liquid-to-solid ratios. The axial mixing efficiency was assessed by measuring the residence time distribution of the granulation process with screw profiles containing K90 and GLC elements. It was found that granules had longer mean residence time and broader residence time distribution within GLC element due to enhanced backmixing and axial dispersion processes. The continuous "fragmentation-reagglomeration" cycle was proposed to be the main advantage of distributive GLC element in granulation of hydrophobic powders.

Effect of screw profile and processing conditions on physical transformation and chemical degradation of gabapentin during twin-screw melt granulation

Twin-screw melt granulation (TSMG) was applied to process a powder blend consisting of 80% gabapentin (GABA) and 20% hydroxypropyl cellulose. The effect of screw profile and processing conditions on the process-induced transformation and chemical degradation of gabapentin was studied. When a neutral kneading block was used, gabapentin underwent polymorphic transformation. A forward kneading block in combination with processing under torque conditions was required to minimize chemical degradation and to inhibit polymorphic transformation of gabapentin. Both the size of the extruded granules and gabapentin degradant level correlated positively with the specific rate, the ratio between feed rate and screw speed. At higher specific rate, the barrel was filled to a greater extent. The material packing and compressive forces were enhanced, as proven by the increased rupturing of CAMES® sensor beads and GABA crystal size reduction. This resulted in more interaction between the powder particles and facilitated granule growth. Simultaneously, this also resulted in higher degradant level. To attain adequate tabletability, the specific rate must reach a threshold value. The development of an optimum TSMG process requires balancing processing parameters based on the physical and chemical stability of GABA as well as its tabletability.

Effect of screw configuration on the dispersion of nanofillers in thermoset polymers

Abstract This paper deals with the study of screw configuration for dispersing nanofillers in thermoset polymers using an intermesh co-rotating twin screw extruder. The influence of kneading elements on the dispersion of nanoclay in epoxy was examined using 10 different screw configurations. Nanoclay was dispersed in epoxy at a barrel temperature of 5°C and a screw speed of 100 rpm. The combination of right hand kneading block and three/four lobed kneading blocks resulted in uniform dispersion of nanofiller. Positive staggered angle with right hand kneading elements yielded uniform dispersion of the nanofiller. Mechanical properties of epoxy nanocomposites processed with these configurations were better than those of neat epoxy. Excessive shear was associated with four lobed kneading block (4KB)/4KB configuration and hence degradation of polymers leading to shorter chains, whereas inadequate shearing in neutral kneading block (NKB)/NKB configuration led to agglomerations. These observations were evidenced by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

Effect of extrusion conditions on the physico-chemical properties and in vitro protein digestibility of canola meal

Canola meal has potential as a high protein food ingredient. The extrusion-induced changes in color, pH, extractable protein and in vitro protein digestibility of canola meal under different extrusion conditions was assessed. The extrusion barrel moisture (24%, 30% or 36%) and screw kneading block length (0, 30 or 60mm) were used as independent process parameters. Extrusion at high barrel moisture (36%) favored protein aggregation resulting in lower extractable protein compared to extrusion at the lowest barrel moisture (24%). At lower barrel moisture contents (24% and 30%), a longer kneading block length increased extractable protein but this was not the case at 36% barrel moisture. Canola protein digestibility was improved upon extrusion at 30% barrel moisture but there was no significant change at lower (24%) or higher (36%) barrel moisture. The kneading block length of the screw had no significant effect on the canola protein digestibility within the same barrel moisture level. The relationship between the physico-chemical parameters and in vitro digestibility was examined. This study highlighted the complex interplay of extrusion processing variables that affect protein degradation and the interaction of components, with consequent effects on protein digestibility.

Agglomerate size evolution in modular twin‐screw extruder: Modeling and validation with CaCO3/LLDPE compounding experiments

ABSTRACTThe screw combination of twin‐screw extruder affects the filler size in inorganic filler‐reinforced polymeric compounds. This article tried to conveniently and precisely model the agglomerate size evolution in modular co‐rotating twin‐screw extruder. The break‐up process of agglomerate was analyzed to obtain the relationship between average deagglomerating energy (M) and agglomerate size, the result presented a mathematic relationship between M and agglomerate size. Numerical simulation study was conducted to consider the effect of kneading blocks (KB) or flight elements (FE) number on dispersion capacity of screw combination. The average deagglomerating energy, calculated based on POLYFLOW simulation, was introduced as major parameter to evaluate the dispersion capacity, which presented a proportional relationship to the KB or FE number. The model was developed by combining the agglomerate break‐up process and simulation results. In validation, CaCO3/linear low‐density polyethylene (LLDPE) compounds were prepared by modular co‐rotating twin‐screw extruder with different screw combinations. The optical image analysis showed that CaCO3 agglomerate size decreased with the KB or FE number rising, while it achieved minimum when the KB number was 4. The model was in accordance with the experimental results, and proved to be valid for KB and FE combinations in preparing CaCO3/LLDPE compounds. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45535.