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.
•Transport of a molten-salt lignin mixture is possible in a twin screw extruder.•Hydrodynamics of the molten salt-lignin mixture in the extruder were determined.•Limited char formation was found when ...using short residence times.•Molecular changes in the lignin structure e.g. demethoxylation were observed.•Findings may be used to effectively feed lignin to (hydro)-pyrolysis units.
Thermochemical conversions of waste lignocellulosic biomasses such as kraft lignin are highly relevant for the production of biobased chemicals and fuels. Of the many available thermochemical technologies, pyrolysis and (pressured) hydropyrolysis are promising pathways to produce liquids from biomass. However, pressurization and continuous feeding of solids into pyrolysis reactors operated at elevated temperatures and pressures is a practical challenge. In this study, we report the use of a molten salt (ZnCl2:NaCl:KCl with a molar composition of 60:20:20) in combination with a twin-screw extruder to pressurize and transport a molten salt-lignin mixture. The effect of different operating parameters such as the residence time (determined by residence time distribution (RTD) analysis) in the extruder and the mass ratio of lignin to salt was studied in detail at a fixed operating temperature of 230 °C. The mass of recovered lignin was up to 92 % at optimized conditions (35 s residence time, lignin to salt ratio of 1 to 10), the remainder being char. It was found that lower residence times and lower amounts of lignin in the feed have a positive effect on the amount of recoverable lignin. The extrusion process also affects the molecular structure of the lignin. 2D-NMR HSQC analysis of the modified lignin before and after processing showed a strong reduction in the intensity of peaks in the oxygenated aliphatic region, indicating demethoxylation during the extrusion process, supported by elemental analyses. The findings may be used to feed lignin effectively to pyrolysis or hydropyrolysis units.
Display omitted
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.
This paper deals with the construction and validation of a new, very simple purely mechanical rheometer, which is assembled from a syringe and a steel spring. This rheometer does not require any ...expensive measuring equipment and yet can measure the viscosities of common Newtonian and non-Newtonian liquids with satisfactory results. By determining the temporary position of the piston, the force applied by the spring and the piston velocity can be ascertained and the viscosity of a given sample of Newtonian liquid can be calculated with repeatability of better than 2%. When measuring non-Newtonian and viscoelastic liquids, a camera is used to record the time course of the moving piston and the swelling ratio. Preliminary tests conducted on power-law liquids demonstrate reproducibility of rheological parameters even for very high viscosity liquids. A new correction to inlet effects is also derived as a function of Reynolds number.
•Construction and experimental verification of a mechanical rheometer is presented.•Rheometer is made from a syringe and driven by a steel spring.•Viscosity is evaluated from the video recording of the piston position.•Construction of the rheometer is very simple, cheap, and sterilizable.•Rheometer is validated by comparing the measured results with the viscosity of water.
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.
Display omitted
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.
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.
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.
PDF
