An 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.
The melting process of polypropylene inside a twin‐screw extruder at several axial locations upstream and along the first restrictive zone of the screw was measured and shown in a diagram. The onset of melting takes place in partially filled conveying elements, then melting develops quickly as the latter become fully filled, and is completed well before flow through the kneading block. Turbidity and birefringence are sensitive to the unmolten PP solid content and so were used to take the quantitative measurements.
Extrusion is the most important polymer processing operation. This paper focuses on obtaining an analytical solution for describing transient polymer movement and heat and mass transfer in the zone ...of polymer melting delay. The coupled nonlinear partial differential equations describing the phenomenon have been decoupled using the perturbation method and solved analytically using Eigenfunction expansion technique. The results obtained revealed that the Reynolds number and Eckert number have significant effects on the velocies, polymer temperature and mass flow rate.
The stability of free-standing nanobubbles is a long-standing controversial problem due to the Laplace pressure catastrophe at the nanoscale. In most industrial circumstances, a large quantity of ...surfactants is required as stabilisers or emulsifiers to generate stable bubbles or foams. However, when surfactants exceed a certain level, they can adversely affect living organisms and pose environmental risks. Towards biomedical use, we investigated nanobubble generation through a mini-extruder in amino acid solutions. Herein, we considered glycine (having two acid dissociation constants, i.e. pKa values) and lysine (having three pKa values) as two model amino acids, conducting experiments with various concentrations (0.1 M, 0.5 M and 1 M), along with different pH values (above, equal to, and below the isoelectric points of each amino acids; 5.97 for glycine and 9.74 for lysine). Our results showcased the proof of concept that amino acids can stabilise nanobubbles in bulk for a few days. We achieved remarkable products of nanobubbles via nanopores by extrusion, with reproducible size distribution and stability. We also compared the extrusion protocol with the commonly used ultrasound method. It turned out that extrusion generated samples with smaller sizes and higher concentrations than sonication. This study provides a reliable protocol for generating small-scale nanobubbles for biomedical use, showing great potential in drug delivery for medical treatment.
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Breakup (dispersion) and distribution of nanoparticles are the chief hurdles towards taking advantage of nanoparticles in polymer nanocomposites for reinforcement, flame retardancy, conductivity, ...chromaticity, and other properties. Microscopy is often used to quantify mixing, but it has a limited field of view, does not average over bulk samples, and fails to address nano-particle hierarchical structures. Ultra-small-angle X-ray scattering (USAXS) can provide a macroscopic statistical average of nanoscale dispersion (breakup) and emergent hierarchical structure, as well as the distribution on the nanoscale. Here, this work compares several common mixer geometries for carbon black-polystyrene nanocomposites. Two twin-screw extruder geometries, typical for industrial processing of melt blends, are compared with a laboratory-scale single screw extruder and a Banbury mixer. It is found that for a given mixer, nanoscale distribution increases following a van der Waals function using accumulated strain as an analogue for temperature while macroscopic distribution/dispersion, using microscopy, does not follow this dependency. Breakup and aggregation in dispersive mixing follow expected behavior on the nanoscale. Across these drastically different mixing geometries an unexpected dependency is observed for nanoscale distributive mixing (both nano and macroscopic) as a function of accumulated strain that may reflect a transition from distributive turbulent to dispersive laminar mixing as the mixing gap is reduced.
This study considered numerical applications of smoothed particle hydrodynamics (SPH) to non‐Newtonian flow in filled or partially filled conveying elements of twin‐screw extruders (TSEs). The ...algorithms were validated by using a plane Poiseuille flow. Two geometrical configurations with different gap were investigated. A large sound speed was used to prevent particles penetrating the wall boundary of the complex geometry. The velocity field and flow rate of Newtonian flow and non‐Newtonian flow (power law) in filled model and partially filled model were analyzed. The distribution of particles in partially filled conveying element in one rotation is introduced. The rheological properties of material take important effect on the flow in fully filled and partially filled cases. For the fully filled cases, the screw–barrel clearance takes important effect on the flow due to the leakage flow reducing the flow rate. For the partially filled case, the clearance affects the non‐Newtonian flow by changing the rheological properties of the fluid. The effect of clearance on Newtonian flow is very limited due to no back pressure in the partially filled case. This work prepared a groundwork for the accurate analysis of real extrusion by SPH.
Distributions of particles in the half filled conveying element.
To reduce the degradation of polylactic acid (PLA) during processing, which reduces the molecular weight of PLA and its properties, prior studies have recommended low processing temperatures. In ...contrast, this work investigated the impact of four factors affecting shear heating (extruder type, screw configuration, screw speed, and feed rate) on the degradation of PLA. The polylactic acid was processed using a quad screw extruder (QSE) and a comparable twin screw extruder (TSE), two screw configurations, higher screw speeds, and several feed rates. The processed PLA was characterized by its rheological, thermal, and material composition properties. In both screw configurations, the QSE (which has a greater free volume) produced 3–4 °C increases in melt temperature when the screw speed was increased from 400 rpm to 1000 rpm, whereas the temperature rise was 24–25 °C in the TSE. PLA processed at low screw speeds, however, exhibited greater reductions in molecular weight—i.e., 9% in the QSE and 7% in the TSE. Screw configurations with fewer kneading blocks, and higher feed rates in the QSE, reduced degradation of PLA. At lower processing temperatures, it was found that an increase in melt temperature and shear rate did not significantly contribute to the degradation of PLA. Reducing the residence time during processing minimized the degradation of PLA in a molten state.
This study employs machine learning algorithms to analyze the bead foam extrusion process and to assess the impact of processing parameters, specifically focusing on their effects on bead foam ...density and melt pressure in under water granulation (UWG) for polylactic acid (PLA). These interrelated parameters, influenced by processing parameters such as temperature, screw speed, and blowing agent, possess challenges for traditional empirical methods to capture. The key factors that significantly impact the prediction of melt pressure in UWG are blowing agent, injector pressure, temperature in B‐extruder and die size. Likewise, essential parameters for predicting bead foam density comprise blowing agent, injector pressure, temperature in B‐extruder, die plate temperature, melt temperature in B‐extruder, and melt pressure in B‐extruder. Machine learning (ML) models were employed to forecast bead foam density and melt pressure in UWG using various processing parameters in PLA bead foam extrusion. The random forest model achieved a high coefficient of determination R2 score of 0.96 for predicting melt pressure in UWG. Additionally, the decision tree model demonstrated effective predictions for bead density, with the R2 score: 0.81. These ML models can be applied to diverse materials, leading to more sustainable, efficient processes for bead foam extrusion.
Comparison of True and Predicted melt pressure.
The continuous development of plasticizing conveying methods and devices has been carried out to meet the needs of the polymer processing industry. As compared to the conventional ...shear-flow-dominated plasticizing and conveying techniques, a new method for processing polymers based on elongational flow was proposed. This new method and the related devices such as vane extruders, eccentric rotor extruders and so on, exhibited multiple advantages including shorter processing time, higher mixing effectiveness, improved product performance and better adaptability to various material systems. The development of new techniques in the field of polymer material processing has opened up a broad space for the development of new plastic products, improved product performance and reduced processing costs. In this review, recent advances concerning the processing techniques based on elongational flow are summarized, and the broad applications in polymer processing as well as some future opportunities and challenges in this vibrant area are elucidated in detail.
Breakup (dispersion) and distribution of nanoparticles are the chief hurdles towards taking advantage of nanoparticles in polymer nanocomposites for reinforcement, flame retardancy, conductivity, ...chromaticity, and other properties. Microscopy is often used to quantify mixing, but it has a limited field of view, does not average over bulk samples, and fails to address nano-particle hierarchical structures. Ultra-small-angle X-ray scattering (USAXS) can provide a macroscopic statistical average of nanoscale dispersion (breakup) and emergent hierarchical structure, as well as the distribution on the nanoscale. This work compares several common mixer geometries for carbon black-polystyrene nanocomposites. Two twin-screw extruder geometries, typical for industrial processing of melt blends, are compared with a laboratory-scale single screw extruder and a Banbury mixer. It is found that for a given mixer, nanoscale distribution increases following a van der Waals function using accumulated strain as an analogue for temperature while macroscopic distribution/dispersion, using microscopy, does not follow this dependency. Breakup and aggregation in dispersive mixing follow expected behavior on the nanoscale. Across these drastically different mixing geometries an unexpected dependency is observed for nanoscale distributive mixing (both nano and macroscopic) as a function of accumulated strain that may reflect a transition from distributive turbulent to dispersive laminar mixing as the mixing gap is reduced.
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•Nanoparticle dispersion/distribution is controlled by mixing geometry and accumulated strain.•Nanocomposites of carbon black in polystyrene studied using twin and single screw extruders and a Banbury mixer.•Small-angle X-ray scattering (virial/Van der Waals model) and SEM characterized mixing.•Dispersive/breakup may arise in narrow gap/laminar flow; distributive mixing in wider gap/turbulent flow.•Mixing changes in carbon black hierarchical structure are described.
Aiming at the problem of difficult to remove high‐carbon α‐olefin in polyethylene, the influences of operation conditions and devolatilization additives on the devolatilization of LLDPE/1‐octene ...system in an exhaust twin‐screw extruder are studied by headspace gas chromatography. The results showed that the devolatilization efficiency increases with the devolatilization temperature and vacuum. With the screw rotational speed, the content of liquid additives and the gas velocity of gas additives increasing, the devolatilization efficiency first increases and then decreases. The devolatilization difficulty of different grades of polyethylene varies due to the difference of the viscosities. When the volatile content is high, the effect of devolatilization additives is anhydrous ethanol > surfactant > water > nitrogen. When the volatile content is low, the effect of nitrogen on devolatilization is obviously better than anhydrous ethanol and water. Finally, a novel devolatilization process is proposed, that is, an evacuation system (vacuum degree 0.08–0.1 MPa) is set up in each stage of the devolatilization section, the anhydrous ethanol is introduced in the first stage, and high‐purity nitrogen is introduced in the second, third, and fourth stages, which can ultimately reduce the VOC content of LLDPE products to less than the target value of 50 ppm.
Highlights
The devolatilization process is used to remove high carbon α‐olefins from LLDPE.
Each additive has an optimal injection value.
Ethanol is the most effective in the foam‐dominated devolatilization stage.
Nitrogen is the most effective in the diffusion‐dominated devolatilization stage.
A new additive‐enhanced twin‐screw extruder devolatilization process is proposed.
Extrusion devolatilization mechanism diagram.
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