Extrudate Swell Research Articles

High-value application of kaolin by wet mixing method in low heat generation and high wear-resistant natural rubber composites

In this study, a silane coupling agent and kaolin, a natural mineral resource, were introduced into the wet mixing process of natural rubber latex, the high wear-resistant and low-generation heat natural rubber composites were prepared. The sputtering, collision, and deposition of coupling agent/fillers/natural rubber latex mixed emulsion onto the roller effectively could break up the filler aggregates, enable fillers to be better infiltrated, distributed, and dispersed in the rubber. The effects of dry/wet mixing processes and the ratio of kaolin to silica on the crosslinking density, filler dispersion, extrusion rheological properties, gas barrier properties, dynamic mechanical properties and thermal stability of NR composites were investigated, and the silanization mechanism was summarized by FTIR and XRD. The experimental results showed that kaolin improved the crosslinking density and failure temperature, reduced the Payne effect, extrusion swell, and rolling resistance. Compared with 60 phr silica-filled natural rubber, the gas barrier property and wear resistance of 60 phr kaolin-filled natural rubber were improved by 64 % and 27 %, respectively, and the rolling resistance was reduced by 57 %. When the ratios of silica to kaolin were both 20:40, the crosslinking density, gas barrier property, and wear resistance of wet mixing were improved by 24 %, 45 %, and 9 %, respectively, compared with dry mixing. This study provided a new method for the high-value application of kaolin in wet mixing and green tires.

Multiphysics modeling and simulation of monolayer flow and die swelling in industrial tube extrusion process

AbstractIn a regular extrusion process for thermoplastic specimen, the material behavior in dies and its rheological properties have a major influence on the mechanical properties and the quality of the extruded product. This study outlines the multiphysical model, which has been adapted to address the specific issues associated with polyamide 12 polymer extrusion. A series of numerical simulations, based on the modeling of material behavior, have been conducted using the computational code Comsol Multiphysics®. These simulations have been applied to the study of polymer melt flows through an industrial extrusion die. The objective of this study is to analyze the influence of the imposed extrusion parameters on the physical field distribution and the material displacement within the die. The die swell at the exit of the extrusion die has been investigated as a function of the imposed pressure. The progression of the polymer flow front inside the extrusion tool and the swelling rates have been analyzed. In particular, the phenomenon of delayed swelling at high pressure has been highlighted at high pressure.Highlights Polymer swelling at industrial extrusion die exit is investigated. Polymer melt extrusion within industrial extrusion tool is numerically simulated. Flow front progression and extrudate swell are analyzed. Effect of extrusion pressure on instabilities and die swell is highlighted.

Influence of various pretreatments on molecular and rheological properties of a linear and a long-chain branched polypropylene

The influence of a mechanical or a thermal pretreatment of a linear (L-PP) and a long-chain branched polypropylene (LCB-PP) in the molten state was studied. The molar mass distributions and the branching structure were determined by high-temperature gel permeation chromatography HT-GPC coupled with laser-light scattering. The samples were extruded through long or short capillaries of various geometries corresponding to a predominant shear or elongational deformation. As a rheological probe, the extrudate swell at low stresses was measured for the differently pretreated samples. For the L-PP, neither molecular nor rheological changes were observed. However, the extrudate swell of the LCB-PP was found to decrease with increasing volume throughput. It was more strongly affected by shear in the capillary than by molecule stretching in the entry region. The smaller extrudate swell was accompanied by a decrease of the high molar mass tail of the LCB-PP, which could be the reason for the decay of swell, in principle. However, a comparable degradation of the high molar mass tail was obtained by a pure thermal treatment that was shown to leave the extrudate swell unchanged. This result and the unaffected branching structures found by high-temperature gel permeation chromatography (HT-GPC) support the hypothesis of a change of the branching topography by the mechanical pretreatment.

The polymer melt swelling behavior in micro-extrusion process for preparation of continuous carbon fiber reinforced PP prepreg filament

The micro-extrusion process for polymer melt has been increasingly used for the production of high value-added prepreg filaments with applications in the fields of fused deposition modeling (FDM). In this study, the effect of characteristic scale, defined as the gap of die land in an annular micro-extrusion die, on the extrudate swelling behaviour of viscoelastic melt is analyzed through numerical simulations and micro-extrusion experiments. The results show that the swelling behaviour displays an obvious dependence on the characteristic scale. An increase in the characteristic scale reduces the swell ratio and retards the process to reach the equilibrium state. In contrast, a decrease in the characteristic scale results in a larger magnitude of change in velocity field and faster relaxation development of stress field. The location of the maximum velocity layer for the laminar flow gradually deviates from the geometric center of channel toward the wall of mandrel with the increase in the characteristic scale. It is imperative to consider the complicated swelling behavior and remarkable viscoelastic effect simultaneously in micro-extrusion process.

Wet continuous mixing technology and extrusion rheological properties of carbon black/natural rubber composites

AbstractIn order to solve the problems of dust, low mixing efficiency, and poor quality stability in dry mixing and continuous mixing, this study combined the flocculation extrusion technology with continuous mixing technology of carbon black/additives/natural rubber composites. The flocculation of latex was achieved by carbon black itself and the shearing of the twin screw. The continuous mixing was carried out in a double‐rotor continuous mixer, which was composed of functional elements such as the exhaust section and extrusion section. The results showed that the technology promoted the formation of the filler‐rubber network, the sensitivity of viscosity to temperature was weakened, and the rubber was closer to a Newtonian fluid, with less extrusion swell phenomenon and no obvious spiral distortion. Compared with the dry mixing, the tensile strength, rebound rate, and abrasion resistance of the rubber composites prepared by this technology were increased by 11%, 31%, and 9%, respectively, providing theoretical and technical guidance for the green production and continuous production of high‐performance natural rubber composites.Highlights The process is achieved by a twin‐screw extruder and a twin‐rotor continuous mixer. The process promotes the formation of the filler‐rubber network. The sensitivity of viscosity to temperature is weakened, with no spiral distortion. The tensile strength, rebound rate, and abrasion resistance are increased by 11%, 31%, and 9%.

Effects of starch–fatty acid complexes with different fatty acid chain lengths and degrees of saturation on the rheological and 3D printing properties of corn starch

The effect of corn starch-fatty (CS-FA) complexes from varying carbon chain length and degree of unsaturation on the rheological and 3D printing properties of corn CS–FA complex gels. The CS-FA complexes with longer carbon chain lengths and lower saturation enhanced the ability of gels to bind water, promoting the formation of intermolecular hydrogen bonds. The CS-FA complexes inhibit retrogradation and increase the amount of bound water, thereby reducing the structural integrity and transforming the original skeleton structure into a flake-like structure. These changes in gel structure led to lower flow stress and storage modulus for CS-FA gels containing FAs with shorter carbon chain lengths and lower saturation, resulting in reduced “extrusion swelling” of the material and facilitating its extrusion. The decreased “extrusion swelling” of gel improved print line width and printing performance. The CS-FA complex gel-printed product with a 12-carbon chain FA has the greatest printing accuracy, thanks to its moderate G', flow stress, and viscosity. This study provides important information for the CS-FA complexes for the preparation of starch-based 3D printing materials.

Numerical Simulation of Three-Dimensional Free Surface Flows Using the K-BKZ-PSM Integral Constitutive Equation.

This work introduces a novel numerical method designed to address three-dimensional unsteady free surface flows incorporating integral viscoelastic constitutive equations, specifically the K-BKZ-PSM (Kaye-Bernstein, Kearsley, Zapas-Papanastasiou, Scriven, Macosko) model. The new proposed methodology employs a second-order finite difference approach along with the deformation fields method to solve the integral constitutive equation and the marker particle method (known as marker-and-cell) to accurately capture the evolution of the fluid's free surface. The newly developed numerical method has proven its effectiveness in handling complex fluid flow scenarios, including confined flows and extrudate swell simulations of Boger fluids. Furthermore, a new semi-analytical solution for velocity and stress fields is derived, considering fully developed flows of a K-BKZ-PSM fluid in a pipe.

Improved Optimization of a Coextrusion Die with a Complex Geometry Using the Coupling Inverse Design Method.

The main challenge in a polymer coextrusion process is to have a good die design prior to the process, which can minimize the geometric errors that are caused by extrusion swell and interface motion. For this purpose, a coupling method of optimization and inverse design for a coextrusion die was studied for a medical striped catheter. In the study, the main material was thermoplastic polyurethane (TPU), and the auxiliary material was TPU filled with 30 wt% barium sulfate. An overall optimization design method was used to optimize the geometry of the extrusion die channel for the striped catheter, which had a complex geometry. In the global optimization process, the local inverse design method was used to design the inlet of the auxiliary material. The non-linear programming by quadratic Lagrangian (NLPQL) algorithm was used to obtain the optimal geometric solution of the coextrusion die runner. The experimental verification results showed that the coupling method for coextrusion die design improved the design efficiency of the coextrusion die remarkably. The value of the objective function, which was used to measure the geometric error of the product, was reduced by 72.3% compared with the initial die design.

Research on improved gas‐assisted extrusion of plastic sheets based on time–temperature equivalence principle

AbstractBased on the time–temperature equivalence principle, the relationship between the melt relaxation time (MRT) and melt heating temperature (MHT) in an improved gas‐assisted extrusion (GAE) of a polypropylene (PP) sheet was investigated by numerical simulations. In the simulations, the MRT was varied and the inherent properties of the MHT were controlled using experimental methods. With an increase in MRT, the velocity in all directions, pressure drop, and shear rate of the melt increased; however, increasing the MRT does not always yield a positive effect on the GAE process of the melt. For instance, the melt velocity increased vertically at the die exit with MRT, resulting in an outward extrudate swell. In addition, the extruded product was intact when the melt was heated to 220°C, which verified the principle of time–temperature equivalence.

Experimental and numerical investigation of extrudate swell of polylactic acid via extrusion-based additive manufacturing process

Extrudate swell is a rheological phenomenon of polymers that occurs after the extrusion die exit due to relaxation of the residual molecular stress. This phenomenon is essential to ensure the accuracy and stability of components manufactured by Extrusion-based additive manufacturing (EAM) process. Extrudate swell can be affected by multiple factors including material properties and processing parameters that can be coupled and it is difficult to fully understand their effects, especially in absence of accurate online measurement devices. In this study, the extrudate swell was investigated experimentally as a function of the extrusion rate, melt temperature and nozzle diameter for polylactic acid (PLA) material. The Computational fluid dynamics (CFD) and level set method (LS) in COMSOL Multiphysics were used to simulate the polymer flow out of the extrusion nozzle. The simulation results matched well with experimental results and showed that the swell rate decreases with increasing temperature and nozzle diameter and decreasing extrusion rate. These results can be used to optimize the parameters of EAM processes.

Transverse mixing zone under dispersion in porous media: Effects of medium heterogeneity and fluid rheology

The addition of an environmental remediation modifier—polymer solution—to a Newtonian fluid expands the distribution of remediation agents injected in situ into saturated aquifers (affecting plume velocity and deformation), enhancing remediation efficiency. However, the effect of the flow properties of the polymer solution on the macroscopic transverse dispersion remains poorly understood. In this work, a transparent thin-layer two-dimensional sandbox was constructed to simulate the aquifer, and the transverse distribution range of colored solute—permanganate solution and viscous shear-thinning fluid (permanganate solution + xanthan gum)—was captured in real-time by a camera device during transport in porous media. The boundary dispersion coefficient was obtained by fitting a breakthrough curve of the boundary concentration, while the overall plume dispersion coefficient was determined via image moment analysis. The effects of fluid rheology and heterogeneity on the transverse mixing of the plume were analyzed, and the mechanism of viscoelasticity-induced transverse dispersion and mixing enhancement was summarized. The results indicated that the anisotropic stress generated by polymer fluid deformation at high water velocity increased the fluctuation and transverse distribution of the plume, while higher-viscosity polymers increased the initial extrusion swelling and additional compressive stress, covering a larger area. Xanthan gum enhanced the transverse distribution of the plume mainly through initial injection-extrusion expansion effect, viscoelastic stability of the post-injection part, and streamline crossing attributed to elastic turbulence. This study also verified that the shear-thinning fluid enhanced the effect of transverse dispersion and mixing under heterogeneous conditions, providing insights applicable to groundwater remediation.

Experimental and Numerical Investigation of the Die Swell in 3D Printing Processes

Fused deposition modelling is one of the most widely used additive manufacturing techniques and the diffusion of 3D printers has increased in popularity even further in recent times. Since high precision is required in 3D printing, a good control over the extrusion process is necessary. In this regard, a crucial phenomenon to be accounted for is the die or extrudate swell, i.e., the enlargement of the cross-section of the strand when coming out of the printer nozzle. While this phenomenon has been studied in large scale extruders, it has not yet been investigated in depth for 3D printing processes. In this work, the die swell phenomenon observed in a printed PLA filament is studied by experiments and fluid dynamic simulations. A novel, easy-to-use, accurate and fast procedure for measuring the value of the die swell ratio during the printing process is developed, accounting for typical errors related to a non-constant strand diameter and possible oscillations of the filament with respect to the extrusion direction. As the printing velocity is increased, a linearly increasing swelling ratio is observed at low printing speeds. The trend flattens at moderate speed values. A sudden increase is found at high printing velocities. The swelling ratio measured with the proposed technique is compared with the results of multi-mode viscoelastic simulations at different temperatures. A fair agreement between the experimental measurements and the numerical predictions is found for printing velocities that are typically employed in commercial 3D printers, supporting the reliability of the developed procedure.

Heavy oil recovery in blind-ends during chemical flooding: Pore scale study using microfluidic experiments

The blind-end is a typical tiny structure widely distributed in reservoir rock. In this work, we used the microfluidics to observe the fluid flow phenomenon in blind-ends at pore scale. A microfluidic chip that contains four blind-ends with different widths was designed. The microfluidic chip is initially saturated with light oil or heavy oil. Then, deionized water, sodium oleate solution, or hydrolytic polyacrylamide solution is selected to inject into the microfluidic chip to displace the oil in blind-ends. We recorded the blind-end snapshots at different experiment conditions and then analyzed the variation of oil saturation quantitatively. Moreover, we explained the oil displacement mechanism in blind-ends with the perspective of micro force. The results demonstrated that the oil in wide blind-end is more easily displaced than the narrow blind-end due to higher shear force and lower capillary force. Heavy oil in blind-end is more difficult to displace from the blind-end due to higher viscous force and elastic force. Polymer flooding is more effective to light oil due to the extrusion swell effect. The reduction of capillary force caused by surfactant is beneficial to recover more oil from the blind-end. This work presents detailed oil displacement mechanism of blind-ends and can be a method to screen more effective chemicals for blind-end oil.

Control of extrudate swell and instabilities using a rotating roller die

• The moving walls (rotating rollers) provide a flexible mean to control die swell and instabilities • The smooth convergent geometry of the rotating die prevents volume instabilities normally related to entrance effect. However very large stresses on the melt are generated in the stationary mode so much so that surface roughness instabilities, not usually reported with polystyrene, appear on the extrudate surface. • This surface roughness resembles sharkskin but the mechanism leading to it is different to that leading to sharkskin. • This observation is a first as PS is reported to never exhibit surface roughness. • The rotating die is a versatile tool to produce sheet of various thicknesses as the gap can be changed by moving the rollers up and down. • The experimental data presented are underpinned by simple theoretical considerations, showing the importance of the wall shear stress and the changes in extension at the die exit. Thermoplastics extruded from dies will always swell and above a critical flow rate display instabilities (sharkskin, stick-spurt or gross melt fracture). Prior research has shown that the best way to suppress these instabilities is to reduce the entry converging angle using a smooth convergence and induce permanent wall slip. In this research we go a step further by allowing the walls to move using a rotating roller die. Thus both extrudate swell and flow instabilities become controllable. This paper presents data to support this claim. The practical benefits are important as stable operation at higher flow rates become permissible. Also, by providing extra control variables, this device becomes a useful tool to help unravel the causes of the various instabilities that arise in polymer melt die extrusion. A first from this research, using this roller die geometry we were able to tease out surface roughness instability with polystyrene hitherto not reported.

Evolution of interfacial formation and configuration control of bicomponent fiber during full spinning process

As a result of the limitation of bicomponent spinning in which it is difficult to obtain the interface evolution of the fiber forming process and guarantee performance stability, numerical simulation was carried out to investigate the effect of cooling, melt viscosity, and inlet flow rate on the interface throughout the process. The results showed that the position deviation of the interface only occurred inside the orifice and the interface distortion continued until after extrusion, with the maximum deformation occurring during extrusion swelling. Based on sufficient multifield data obtained from the simulation, it was demonstrated that the interfacial curvature was governed only by the viscosity difference between individual components, and the position of the interface was determined by the mechanical energy of the bicomponent melt. Moreover, the curvature and the position of the interface can be adjusted indirectly by changing the viscosity ratio, which can be regulated by the flow ratio, bringing guidance for the full process control of the bicomponent fiber preparation.

Rheological characterization of complex fluids through a table-top 3D printer

3D printing is changing the way we conceive, design, and build 3D objects in mechanical, biomedical, aerospace, construction, automotive and maritime industries. In the current work, the nonlinear rheological behaviour of polymer melts is measured through a table-top 3D printer (3D RheoPrinter) that, smartly modified, allows inline investigation of viscosity, extrudate swell and melt fracture. By using a piezoresistive mini-transducer, the innovative system is designed to be applicable to all Fused Deposition Modelling (FDM) 3D printers by a simple and cost-effective modification of a state-of-art nozzle. The measurements of the nonlinear rheological behaviour are compared with traditional, rotational rheology. Two biodegradable polymers, i.e. polylactic acid and polycaprolactone, are investigated as model systems to test the 3D RheoPrinter. The results of the shear viscosity and the first normal stress difference coefficient, as function of shear rate, show a good agreement between the 3D RheoPrinter and rotational rheometer with an error of about 6% for a confidence interval of 96%. Moreover, the 3D RheoPrinter can still be used as 3D printer. In the last part of this work, it is presented a printing test for building 3D structures in which the results show controllable resolution by means of the measured rheological information such as the extrudate swell. The vision of this work is that an inline rheological characterization, possible with the developed 3D RheoPrinter, can enable automatic process optimization and quality assurance to the 3D printing community. The social and scientific impacts of this work are maximized by the cost-efficiency and simplicity of the design that makes it within reach of the general public. The 3D RheoPrinter opens for a rheological experimentation to a broad audience and it offers important insights to bring FDM to the next level of resolution.

Non-traditional types of milk powder in baby food technology

The need to develop products for infant nutrition is urgent. Cow’s milk is the basis for making porridge. The number of children suffering from allergies to cow’s milk protein is 2-7.5%. The aim of the work is to study the kinetics of extrudate swelling in different types of milk, their influence on the rheological properties of porridges and their ability to digest. The degree of swelling of the extrudate in mares’ milk is 12.5% higher than in cow’s milk, and in goat’s and sheep’s milk - 4% and 19% lower, respectively. The vicosity of mares’ milk porridge is 50% lower than the viscosity of «Malyshka» porridge. The viscosity of goat’s milk porridge is also 40% lower than the viscosity of «Malyshka» porridge. The lowest digestibility of proteins is observed in «Malyshka» porridge, in which 31% less amino acids accumulate in 3 hours of hydrolysis compared to goat milk porridge. In porridge based on mare and sheep milk, 51% and 78% more amino acids are released compared to the control. It is proved that the development of new milk-flour porridges for feeding children aged 6 months to 1 year is relevant. It is established that the degree of swelling of corn extrudate depends on the chemical composition of milk. It has been found that goat’s and sheep’s’ milk porridge retains a high viscosity, which is also explained by the chemical composition of milk, namely the high content of fat and protein. Studies of the digestion process indicate that the developed cereals are digested with a similar intensity, which is higher than the digestion of porridge «Malyshka». Key words: baby food, extrudates, mares’ milk, milk powder, goat’s and sheep’s milk.

The separation angle of the free surface of a viscous fluid at a straight edge

We rework some of the die-swell singularity analysis for Stokes flow, originally by Ramalingam (Ramalingam, 1994 Fiber spinning and rheology of liquid-crystalline polymers, PhD thesis, Massachusetts Institute of Technology) in appendix A of his PhD thesis, in an attempt to demonstrate that for capillary numbers in the range $(0,\infty )$ the curvature may enter into the normal stress balance on the free surface and lead to separation angles exceeding $180^{\circ }$ and infinite curvature at the separation point. The singular coefficients in the asymptotic solution and the free surface shape in a neighbourhood of the separation point cannot be determined by a local analysis of the Michael type (Michael, Mathematika, vol. 5, 1958, pp. 82–84) but must be found from matching with the solution valid away from the die edge. The numerical method that we use in the truncated die-swell domain is a boundary element method incorporating the singular solution near the separation point. Although there is some variation in the extrudate swell ratios at different capillary numbers reported in the numerical literature, our results for capillary numbers $Ca$ from $1$ to $1000$ are within the range of values published in earlier papers. The computed separation angles at different values of $Ca$ agree well with the range of separation angles to be found in experimental and numerical papers. The separation angle appears to converge to a value different from $180^{\circ }$ as $Ca$ increases, leading us to conclude that the case of zero surface tension ( $Ca=\infty$ , with corresponding separation angle of $180^{\circ }$ ), is a singular limit.

Effect of rubber reinforcement with filler on extrusion flow and extrudate swell

Abstract The extrusion process of silica rubber through a chemical reaction is unstable, and the flow mechanism in the extruder is still unclear. In this study, styrene-butadiene rubber (SBR) has been chosen as the matrix and the reinforcing effects of two different kinds of fillers, silica and titanium dioxide, have been investigated on SBR. Additionally, the effect of the properties of the SBR/filler composites on extrudate swelling has been examined. The reinforcing effect of the filler was confirmed by dynamic viscoelasticity, and the swell ratio was measured using a capillary rheometer. The results suggest that titanium dioxide has no reinforcing effect, as there is no interaction between titanium dioxide and the molecular structure of SBR. In contrast, there was a significant interaction between silica and SBR. It was found that the bound rubber, which is an SBR gel with restricted molecular chains, causes a reduction in the swell ratio, and this reduction effect is larger than that caused by filling the filler in the matrix. Furthermore, it was observed that this bound rubber deforms during flow and affects the extrudate swell phenomenon.

Numerical Study of Residual Stresses Due to External Cooling in Extruded Polymer Profiles

AbstractProfile extrusion is a production technique to make polymer profiles and hollow tubes. At a certain distance after the die exit the polymer extrudate is guided into a cooling chamber, where the polymer is cooled extensively to set the part dimensions. Uniform cooling in the cooling chamber is required to avoid warpage and twisting of the extrudate due to differential shrinkage. The effect of extrudate cooling on the shape of the extrudate and the residual stresses in the final extrudate product are numerically studied. Two different cases are studied: a 2D axisymmetric problem of a viscoelastic fluid exiting an annular die and a 3D problem of a hollow square shaped die. The extrudate is extensively cooled from a distance from the die exit. Extrudate cooling is modeled by subjecting the extrudate to heat loss via convection. For the Nusselt number Nu is fixed to 1 to represent the part of the extrudate in between the die exit and the entrance of the cooling chamber. For the Nusselt number is varied to mimic different cooling speeds. The Weissenberg number Wi, the Nusselt number and are varied in this work. Results show that for high values of Wi a significant skin‐effect of high residual stresses appear near the extrudate edges for high Nusselt numbers and small values of . It is also shown that for high Weissenberg numbers the shape of the extrudate is significantly altered due to extrudate swell, when the extrudate is cooled slower. For fast cooling and small values of , the polymer does not have time to relax and the elastic stresses are “frozen in.” This leads to less extrudate swell but large residual stresses near the extrudate edges.