Coextrusion Process Research Articles

The numerical study of the coextrusion process of polymer melts in the cable head

The process of coextrusion consists in a simultaneous creation of all necessary insulating layers of different polymers in the channel of a special forming tool. The main focus of this study is the analysis of technological, geometrical and rheological characteristics on the values of the layer’s thickness. In this paper are considered three geometries of cable head on the three–dimensional and two–dimensional representation. The mathematical models of separate and joint flow of polymer melts have been implemented by the finite element method in Ansys software package. The velocity fields, temperature, pressure in the cross–sections of the channel and by the length have been obtained. The influence of some thickness characteristics of insulation layers has been identified.

Establishment of a Molding Procedure to Facilitate Formulation Development for Co-extrudates.

Co-extrusion offers a number of advantages over conventional manufacturing techniques. However, the setup of a co-extrusion line is cost- and time-intense and formulation development is challenging. This work introduces a novel procedure to test the applicability of a co-extruded reservoir-type system at an early product development stage. We propose vacuum compression molding (VCM), a fast procedure that requires only small material amounts, for the manufacturing of cylindrical reservoir-type system. To this end, the commercially available co-extruded product NuvaRing® and variations thereof were used as test systems. All VCM systems showed a homogeneous skin thickness that adhered well to the core, thereby providing a precise core/skin interface. As drug release is a key criterion for pharmaceutical products, a modified in vitro dissolution method was set up to test the VCM systems. The drug release from the VCM systems was in the same order of magnitude as the corresponding co-extruded strands and followed the same release kinetics. Moreover, the VCM systems were capable of indicating the relative effect of formulation-related modifications on drug release. Overall, this shows that this system is a powerful tool that facilitates formulation tailoring and co-extrusion process setup at the earliest stage.

Robocasting of carbon-alumina core-shell composites using co-extrusion

PurposeThis study aims to achieve the fabrication of three-dimensional core-shell filament-based lattice structures by means of robocasting combined with co-extrusion. For core and shell materials, colloidal gels composed of submicron carbon and alumina powders were developed, respectively. Simultaneously, the co-extrusion process was also studied by numerical simulation to investigate the feed pressure-dependent wall thickness.Design/methodology/approachSignificant differences in the rheological behavior of the carbon and alumina gels were observed because of differences of the particle morphology and surface chemistry of the carbon and alumina powders. Precise control over the cross-sectional diameter of the core and shell green state elements was achieved by alteration of the feed pressures used during co-extrusion.FindingsAfter subsequent thermal treatment in an oxidizing atmosphere (e.g. air), in which the carbon core was oxidized and burned out, lattice structures formed of hollow filaments of predetermined wall thickness were manufactured; additionally, C-Al2O3 core-shell filament lattice structures could be derived after firing in an argon atmosphere.Originality/valueGreen lattice truss structures with carbon core and alumina shell filaments were successfully manufactured by robotically controlled co-extrusion. As feedstocks carbon and alumina gels with significantly different rheological properties were prepared. During co-extrusion, the core paste exhibited a much higher viscosity than the shell paste, which benefited the co-extrusion process. Simultaneously, the core and shell diameters were exactly controlled by core and shell feed pressures and studied by numerical simulation. The experimentally and numerically derived filament wall thickness showed qualitative agreement with each other; with decreasing core pressure during co-extrusion, the wall thickness increased.

Modeling and numerical simulation of multiflux die in the multilayer co-extrusion process

It is of great importance to understand the stretching and folding mechanism in the multiflux co-extrusion die to get uniform multilayer distribution at the end of die lip in the multilayer co-extrusion processes. In this work, to understand the mechanism of the layer distribution, modeling and numerical simulation were carried out for three-dimensional flow analysis in the multilayer co-extrusion die. The multilayer flow fields were numerically visualized and analyzed on the arbitrary cross-section of the multiflux die. In addition, numerical results for the multiflux die characteristics were obtained for non-Newtonian fluids in terms of power-law index for the cross model, which will be useful for the optimal design of screw and die, simultaneously, in the multilayer co-extrusion process.

The numerical study of the influence of rheological parameters stratified flows characteristics in cable dies

Today the process of coextrusion is the most technological in the cable production with cross-linked polyethylene, composed of two or more layers of polymeric insulation. Since the covering technology is a simultaneous imposition of all necessary layers (two semiconducting shields on the insulation and conductor and one - on insulation), the main focus of this study is the analysis of significance of various factors influence on stratified flows characteristics. This paper has considered the flow of two abnormally viscous liquids in the cable head. The problem has been solved through a three-dimensional statement by applying the finite element method in the Ansys software package. The influence has been estimated by varying the rheological properties of materials to create all necessary layers thickness.

Fuel filtration properties and mechanism of a novel fibrous filter produced by a melt-process

A porous filter comprised of polypropylene (PP)/polyamide 6 (PA6) micro-/nano-fibers has been produced from a novel melt-based plastics co-extrusion and exfoliation process technology for the separation of microscale water droplets from diesel fuel. The filter media have a mean pore size of 11µm, a porosity greater than 85%, a surface area of more than 12x the value for an electrospun medium, tough mechanical properties, and a contact angle of 124°, all of which make the co-extruded filter a superior fuel filter. An improvement in water-separation from diesel fuel feed stream from 62–85% water-removal was achieved by the co-extruded and exfoliated PP/PA6 fibrous media in comparison to a commercial fuel filter under identical test conditions and pressure drop. The fuel/water separation mechanism was identified as a capture-coalescence-release process. It has been found that the highest performance fuel filter required small pore sizes and large surface area for droplet capture, due to the hydrophobic nature of materials required for successful droplet release, and a high porosity for minimizing flow resistance. In addition to the proof of concept water separation demonstration, studies into (a) the effect of increasing the barrier substrates thickness and (b) surface corona treatment to alter the hydrophilicity of media surfaces on the filtration efficiency co-extruded, exfoliated filters are reported.

Polymeric Nanofiber/Antifungal Formulations Using a Novel Co-extrusion Approach.

We report the successful implementation of a novel melt co-extrusion process to fabricate ca. 1μm diameter fibers of poly(caprolactone) (PCL) containing the antifungal compound clotrimazole in concentrations between 4 and 8wt%. The process involves co-extrusion of a clotrimazole-loaded PCL along with poly(ethylene oxide) (PEO) as a co-feed, with subsequent removal of PEO to isolate PCL-clotrimazole fibers. In vitro tests of the clotrimazole-containing fibers against the fungus Aspergillus fumigatus, Candida albicans, and Trichophyton mentagrophytes strains demonstrated good antifungal activity which was maintained for more than 3weeks. An in vivo study using a mouse model showed the lowest tissue fungal burden for PCL-clotrimazole when compared to a PCL-only patch and untreated controls. Comparative studies were conducted with clotrimazole-containing PCL fibers fabricated by electrospinning. Our data showed that the co-extruded, clotrimazole-containing fibers maintain activity for longer times vs. electrospun samples. This, coupled with the much higher throughput of the co-extrusion process vs. electrospinning, renders this new approach very attractive for the fabrication of drug-releasing polymer fibers.

Triple‐shape‐memory polymer films created by forced‐assembly multilayer coextrusion

ABSTRACTTriple‐shape‐memory polymers are capable of memorizing two temporary shapes and sequentially recovering from the first temporary shape to the second temporary shape and eventually to the permanent shape upon exposure to a stimulus. In this study, unique three‐component, multilayered films with an ATBTA configuration [where A is polyurethane (PU), B is ethylene vinyl acetate (EVA), and T is poly(vinyl acetate) (PVAc)] were produced as a triple‐shape‐memory material via a forced‐assembly multilayer film coextrusion process from PU, EVA, and PVAc. The two well‐separated thermal transitions of the PU–EVA–PVAc film, the melting temperature of EVA and the glass‐transition temperature of PVAc, allow for the fixing of the two temporary shapes. The cyclic thermomechanical testing results confirm that the 257‐layered PU–EVA–PVAc films possessed outstanding triple‐shape‐memory performance in terms of the shape fixity and shape‐recovery ratios. This approach allowed greater design flexibility and simultaneous adjustment of the mechanical and shape‐memory properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44405.

LINEAR STABILITY ANALYSIS AND CFD SIMULATION OF DOUBLE-LAYER RAYLEIGH-BÉNARD CONVECTION

Abstract Natural convection in superimposed layers of fluids heated from below is commonly observed in many industrial and natural situations, such as crystal growth, co-extrusion processes and atmospheric flow. The stability analysis of this system reveals a complex dynamic behavior, including the potential multiplicity of stationary states and occurrence of periodic regimes. In this study, a linear stability analysis (LSA) was performed to determine the onset of natural convection as a function of imposed boundary conditions, geometrical configuration and specific perturbations. To investigate the effects of the non-linear terms neglected in LSA, a direct simulation of the full nonlinear problem was performed using computational fluid dynamics (CFD) techniques. The numerical simulation results show an excellent agreement with the LSA results near the onset of convection and an increase in the deviation as the Rayleigh number increases above the critical value.

Improved tension-compression performance of Mg-Al-Zn alloy processed by co-extrusion

Mg-3Al-1Zn round ingots were divided into several pieces and then cobbled together to introduce specific interfaces before direct extrusion. The microstructure, texture and mechanical response of the magnesium alloys processed by conventional extrusion and co-extrusion with introducing various interfaces were examined. The results indicated that the prewired various interfaces played important role on the microstructure evolution and texture modification of magnesium alloys during extrusion, and consequently influenced the tension-compression performance of the extruded alloys. Co-extrusion process by introducing appropriate interfaces during extrusion was suggested as a sample and effective method to enhance the comprehensive mechanical properties of Mg-Al-Zn alloys.

As40S59Se1/As2S3 step index fiber for 1–5 μm supercontinuum generation

A high-purity As40S59Se1/As2S3 core/cladding step-index fiber for supercontinuum generation was fabricated in this study. The glass rods were obtained by using a relatively effective and inexpensive method of modified physical and chemical purification. Then, the multi-material fiber preform was fabricated through a modified laboratory using one-step co-extrusion process. Moreover, the fiber preform with a Polyether Sulfone (PES) polymer was drawn with a core diameter of ~22μm. The core/cladding ratio of the fiber was approximately 1:17, and the minimum loss was approximately 1dB/m between 4 and 6μm. By pumping a 13cm-long fiber with different laser powers and another two different lengths (20cm and 50cm, respectively) of fiber at 4.8μm, a supercontinuum covering 1–5μm could be recorded in all fibers. This study attained a 1–5μm supercontinuum that covered the second atmospheric window. Result of this study can be a promising reference in the production of mid-infrared light source.

Influence of processing conditions on the properties of alginate solutions and wet edible calcium alginate coatings

Two alginates with different viscosities (ƞ-low and ƞ-high) were used to study the effects of processing conditions (pH, addition of sodium chloride, addition of CaCl2, mixing speed, mixing temperature, gelation time, gelation temperature) on the viscosity of sodium alginate solutions and the properties of wet calcium alginate films. No differences in the monomeric fractions proportion (M/R ratio) between alginates were observed. ƞ-high presented higher values of estimated average length of G- and MG-blocks than ƞ-low alginate. The viscosity of the alginate solution was increased in the presence of calcium traces. The impact of CaCl2 addition on alginate viscosity was much stronger for ƞ-low alginate. However, no improvement of the mechanical properties was observed. The presence of NaCl in alginate solutions also increased the viscosity and had a negative impact on the puncture properties of calcium alginate films. On the contrary, the use of high mixing speeds resulted in less viscous sodium alginate solutions and stronger films. Finally, the use of neutral pH values and refrigeration temperatures during the co-extrusion process would be advisable in order to prevent a detrimental effect on the mechanical properties of alginate films.

Co-extrusion of a Mg/Al composite billet: A computational study validated by experiments

A coupled finite element analysis in conjunction with experiments was used to investigate hot co-extrusion of a novel composite Mg AZ80/Al 1100 billet assembly. To validate the computational model, results from both radiography, and metallography were used.It is demonstrated that the billet configuration proposed in this study results in a uniform composite rod, with no indication of cracks, tears, wavy interface surfaces or voids. The computational model is first validated by the experiments and then used to thoroughly study the thermo-mechanical fields that develop during the co-extrusion process. The interplay of the thermal and mechanical fields during the process is examined for different initial temperatures, die angle and ram velocity. It is demonstrated that using the proposed billet assembly, constant compressive radial stress develops across the magnesium core, leading to sound-proportional flow conditions.

Protein and Bacterial Antifouling Behavior of Melt-Coextruded Nanofiber Mats.

Antifouling surfaces are important for biomedical devices to prevent secondary infections and mitigate the effects of the foreign body response. Herein, we describe melt-coextruded poly(ε-caprolactone) (PCL) nanofiber mats grafted with antifouling polymers. Nonwoven PCL fiber mats are produced using a multilayered melt coextrusion process followed by high-pressure hydroentanglement to yield porous patches. The resulting fiber mats show submicrometer cross-sectional fiber dimensions and yield pore sizes that were nearly uniform, with a mean pore size of 1.6 ± 0.9 μm. Several antifouling polymers, including hydrophilic, zwitterionic, and amphipathic molecules, are grafted to the surface of the mats using a two-step procedure that includes photochemistry followed by the copper-catalyzed azide-alkyne cycloaddition reaction. Fiber mats are evaluated using separate adsorption tests for serum proteins and E. coli. The results indicate that poly(oligo(ethylene glycol) methyl ether methacrylate)-co-(trifluoroethyl methacrylate) (poly(OEGMEMA-co-TFEMA)) grafted mats exhibit approximately 85% less protein adhesion and 97% less E. coli adsorption when compared to unmodified PCL fibermats. In dynamic antifouling testing, the amphiphilic fluorous polymer surface shows the highest flux and highest rejection value of foulants. The work presented within has implications on the high-throughput production of antifouling microporous patches for medical applications.

Kinetics of thin polymer film rupture: Model experiments for a better understanding of layer breakups in the multilayer coextrusion process

We show that the kinetics of bursting of a thin film embedded in another polymer matrix can be well described by a simple equation balancing the viscous and capillary forces. The role of viscosity, interfacial tension and thickness of the layers under static conditions was investigated by adapting a simple model experiment initially designed to study the dewetting of a thin polymer film on another polymer substrate. Kinetics was correlated to instabilities occurring during multilayer coextrusion leading to the break-up of layers below a critical nanometric thickness. The results suggest that shear and elongation forces during the process actually stabilize the layers. Understanding these instabilities is of great interest since this innovative process showed potential to design at an industrial scale macromolecular materials displaying new macroscopic properties, due to interfacial and confinement effects. However, instabilities leading to the breaking of these nanometric layers will alter final properties (optical, gas barrier …).

Characterization and Properties of Reactive Poly (Lactic Acid)/Ethylene–Vinyl Alcohol Copolymer Blends with Chain-Extender

A hydrophilic copolymer, ethylene–vinyl alcohol (EVOH), was incorporated into the poly(lactic acid) (PLA) matrix to improve the barrier property of PLA through twin-screw extrusion rather than the typical coextrusion process. A chain extender, poly[(ethylene)-co-(methyl acrylate)-co-(glycidyl methacrylate)] (PEMG), was used to reduce the probability of the thermal degradation of PLA during melt compounding. Biaxial stretching was used to enhance the microstructure and barrier property of PLA-PEMG/EVOH films. Experimentally, PEMG considerably reduced the probability of the thermal degradation of the PLA-PEMG sample. Biaxial stretching increased the tensile strength and decreased the value of elongation at break of the PLA-PEMG/EVOH80 (PLA/EVOH 100/80) film. Because of the efficient blending of PLA/EVOH in the twin-screw extruder, the dispersion of EVOH in the PLA matrix revealed homogeneous dispersion with a domain size of 1–5 μm. EVOH effectively improved the water vapour transmission rate (WVTR) of PLA through melt blending. Blending PLA-PEMG with EVOH substantially decreased the WVTR from 250 cc—20 μm/m2-day-atm for neat PLA to approximately 65 cc—20 μm/m2-day-atm for the PLA-PEMG/EVOH80 film, a decrease of approximately 74 % compared with neat PLA. Moreover, the WVTR decreased further from 65 cc—20 μm/m2-day-atm for the unstretched PLA-PEMG/EVOH80 film to 6.3 cc—20 μm/m2-day-atm for the film stretched at a stretch ratio of 3.5 × 3.5 and at 100 %/s, a decrease of approximately 90 % compared with neat PLA.

Low weight steel-magnesium composites achieved by powder compaction

Low weight steel-magnesium composites with various volume fractions of Mg were achieved by a multi-step co-extrusion process. Hollow tubes filed with Mg powders were extruded, annealed, cut and restacked in hollow tubes before subsequent extrusion. This way, fully dense composites with various architectures and length scales were achieved. Microstructure observations revealed that both phases undergo an axisymmetric deformation in the early stage of the process. At higher extrusion ratio, Mg/Fe interfaces become wavy and irregular which is attributed to a strong crystallographic texture. In the as-extruded states, the composites exhibit peculiar elastic to plastic transition with an unusually high strain hardening. Tensile tests performed after annealing prove that this behavior is directly linked to large internal stresses.

Co-extrusion process to produce Al–Mg eutectic clad magnesium products at elevated temperatures

A novel and effective method to co-extrude metallic alloys is described using a direct extrusion method. This co-extrusion method was used to experimentally produce Al–Mg eutectic clad rods of magnesium using a laboratory scale extruder at the University of Waterloo. In addition a mathematical model of the co-extrusion process using DEFORM 2D was developed to gain insight and a scientific understanding of the material flow and metallurgical reactions that occurred between the aluminum and magnesium during the co-extrusion process. The co-extrusion method involved, filling a feeder pocket of the extrusion die with a disc of one material (Al), whereas the billet material had a different composition (magnesium). As the ram pushes the billet into the die, it punches through the disc and the resulting extrudate is clad in a eutectic alloy of the disc and billet material. An added benefit to this process is that with the choice of the correct material compositions and process conditions, the extrusion loads can be substantially lowered as a eutectic composition is formed between the billet and disc materials such that the interface becomes molten at the extrusion temperatures while the parent billet and disc remain solid. This greatly aids in the formation of a high quality interface with respect to bonding between the eutectic clad layer and core material of the extrudate. Subsequent extrusions done using the die with an already punched disc in the feeder pocket (a donut) were also able to be clad and showed significantly lower loads (∼30% difference in peak load) during extrusion as compared to billet materials that were extruded with an empty die feeder pocket. In this research, extrusion trials were performed with a magnesium billet and aluminum disc at 350°C (below the Al–Mg eutectic point) and 450°C (about the Al–Mg eutectic point). At 350°C, no significant cladding of the aluminum on the core Mg alloy occurred, but at 450°C, the co-extrusion process was successful with an Al–Mg eutectic clad rod of magnesium being produced. Subsequent co-extrusion trials were also done using the Al-donut in the feeder pocket of the die and also resulted in significantly lower loads and an Al–Mg eutectic clad extrudate. The integrity of the interface was examined and deemed to be of high quality based on visual and microscopic examinations. Both the Finite Element Method (FEM) simulation using DEFORM 2D and extrusion load measurements showed a significant drop in extrusion pressure using this co-extrusion process.

Microstructure and physical–chemical properties of chicken collagen

Abstract The global consumption of sausages has increased immensely over the last few years, while bovine collagen has become scarce. Thus, collagen from alternative sources is being considered for application in the food industry. Therefore, chicken skin and bone collagen were characterized and compared with the bovine telopeptide-poor collagen aiming at the feasibility of producing pure, co-extruded chicken sausages. Hence, the chemical composition, microstructure and rheological properties of the different collagen samples were examined and SDS-PAGE, mass spectroscopy, and ζ-potential analysis were conducted. Weak bands in the SDS-PAGE gel indicated only partial maceration of chicken bone collagen, whereas chicken skin and telopeptide-poor collagen revealed distinct bands indicating collagen type I and III. This was also verified by mass spectroscopy. Large fragments were visible in optical microscopy for chicken bone collagen, whereas chicken skin collagen revealed a delicate network. Moreover, the highest dynamic consistency index, at 14146 Pa sn*, was determined for chicken bone collagen, followed by chicken skin and telopeptide-poor collagen at 606 and 320 Pa sn*, respectively. By contrast, the intrinsic viscosity was the highest for telopeptide-poor collagen (3.16–3.26 L/g), whereas chicken bone collagen exhibited the lowest value at 0.13 L/g, suggesting poor swelling behavior. Moreover, telopeptide-poor collagen featured the highest dynamic power law factor, suggesting the least crosslinks, serving a negative standard rather than an actual chicken collagen analog. Finally, chicken skin collagen displayed the most suitable source of collagen for the co-extrusion process compared to the well established bovine hide split collagen.

Mechanical behaviour of multi-layer half-cells of microtubular solid oxide fuel cells fabricated by the co-extrusion process

Multi-layer micro-tubes consisting of four anode layers of NiO and YSZ mixture, and an electrolyte layer, YSZ, were fabricated by co-extrusion. The die designed in this study is able to extrude 5 layers around a sacrificial core, which eliminates the difficulties from the use of mandrel in processing tubes. Scanning electron microscopy (SEM) results revealed that this technique can be used for the successful fabrication of multi-layer microtubes with good bonding between the layers. 3-point bending was used to evaluate the mechanical properties of these co-extruded multi-layer samples. Moreover, thermal shock resistance of the tubes was investigated by water quenching from an elevated temperature. The results were compared with those obtained for conventionally extruded single layer samples. The co-extruded samples were found to have the highest average strength and also the highest weibull modulus and reliability. It was also found that multi-layer anode can significantly improve thermal shock resistance.