Co-extrusion processes

Charge Air Cooling Duct on 2004 Ford Super Duty F-Series Truck is produced from soft and hard durometer Hytrel (TPEE) grades in sequential co-extrusion process. Three plastic pieces replace seven metal pieces. 

In the refrigeration laminate application, as with many advanced HIPS design challenges, the polymer chemist trades one important property for another. Here, the desired gloss is sacrificed to provide toughness and chemical resistance. The co-extrusion process allows the fabricator to meet the gloss... 

Materials made by a co-extrusion process for coating glass, copper, or titanium wire with lead [30] have been proposed as a substitute for the lead grid. The diameter of... 

Co-extrusion processes. Liquid core and shell materials are pumped through concentric orifices, with the core material flowing in the central orifice, and the shell material flowing through the outer annulus. A compound drop forms that is composed of a droplet of core fluid encased in a layer of shell fluid. 

FIGURE 5.88 Schematic of a co-extrusion process of microencapsulation being developed at Southwest Research Institute (SWRI) using machine vision-based control system that allows inflight capsule inspection. The desired capsule size and sphericity are obtained by manipulation of process input variables, such as flow rate, temperature, vibrational frequency, and amplitude via a feedback control loop. (After Franjione, J. and Vasishtha, N. 1995. Technology Today, Southwest Research Institute Publications.)... 

Institute (San Antonio, Texas) allows inflight capsule inspection, while the process input variables including flow rate, temperature, vibrational frequency and amplitude are manipulated via a feedback control loop to obtain desired capsule size and sphericity [207]. Due to the involvement of so many factors and their complex interrelationships, co-extrusion processes are designed and operating conditions determined usually on a case-by-case basis. 

Recent efforts by Arora et al. have led to the development of DE based liber actuators [262]. These actuators are essentially miniaturized tube actuators. In their work, prestrain was applied by both uniaxial elongation as well as inflation. These actuators may be of interest for artificial muscle applications since they mimic the fibular nature of natural muscle however, unUke natural muscle, their method of actuation is through elongation and the maximum strains reported were limited to 7% in the axial direction. Cameron et al. have performed similar work on co-extruded tube DE actuators [263]. Their co-extrusion process presents a fast, easy, scalable method to produce small diameter tubes, or hoUow fibers, for use as DE actuators that would make these actuators very amenable to mass manufacturing. Strains, thus far, are limited to approximately 2%. 

Co-extrusion processing using thermoplastic binder systems for ceramic bodies has been described by Van Hoy [Hoy 98]. The major binder component used in this study was ethylene vinyl acetate, and methoxypoly-ethylene glycol was used as a plasticizer. Feedstocks of alumina, a piezoelectric ceramic powder and carbon black were repeatedly co-extruded to form an array of fine M -shaped structures. With this method the size of the alumina M shapes could be reduced by a factor of 915. In this example the use of solvent-based binders would have been problematical because of drying of the feedstocks and extrudates during the co-extrusion process and during handling. 

Poulon-Quintin used the co-extrusion process to fabricate bi-phase oxide ceramic filament structures [Pou 04]. For these investigations commercial AI2O3 and Zr02 feedstocks from the University of Warwick were used. The polymer binder system in these feedstocks was based on low molecular weight polyethylene and a small amount of polyethyleneglycol. 

The oxygen permeability in general decreases by 50 percent in polyamide matrix on nano-clay incorporation. Clay-polyamide nanocomposites can be used for packaging of processed meats, cheese, confectionery, cereals and boil-in-the-bag foods also for extrusion-coating applications in association with paperboard for fruit juice and dairy products, together with co-extrusion processes for the manufacture of beer and carbonated drink bottles (www.tifac.org). The nanocomposite packaging enhances the shelf life of many types of food. 

The co-extrusion process was developed by Southwest Research Institute in the United States, and has found a number of commercial applications. A dual fluid stream of liquid core and shell materials is pumped through concentric tubes and forms droplets under the influence of vibration (Fig. 1.14). The shell is then hardened by chemical crosslinkings, cooling, or solvent evaporation. Different types of extrusion nozzles have been developed in order to optimize the process [103]. 

Texture manufactured by the co-extrusion process (Process 3) is quite uniform and it offers good friction values in combination with fine grained mineral materials. The texture is evenly distributed over the surface, but their friction resistance cannot be varied or at least only to a small extent. The problem of stress eraek resistance must be considered as with the other textures. Sinee the geomembranes are usually textured throughout the whole surfaee, two textured areas must be welded for each hot wedge weld seam. For the individual co-extruded textures as well as for impinged or laminated textures proof must be provided showing that this is possible without any loss of quality in the properties of the weld seams (Sect. 10.3). 

Lankhorst Pure Composites produces and sells PURE . This product is made of different grades of polypropylene that are combined using a co-extrusion process. The core is a highly oriented, high modulus PP tape which is skinned with a specially formulated PP that allows welding of the tapes together. Parts are usually made from semifinished products in the form of fabrics and are found in antiballistic applications as well as automotive, construction and consumer products, such as suitcases and sporting apparel. 

Extruding can produce soft or rigid items, which can be compact or cellular in form. For producing hollow articles, a special tool is required and this process is called extrusion blow moulding. Profiles that require an aesthetic appearance are made by the co-extrusion process which uses two extruders and a specially shaped die. 

Most PVC is recycled via a co-extrusion process in which it becomes the inner layer of sewerage pipes and window Irames, the outer layer being virgin PVC to comply with building regulations. To meet the requirements for the extrusion process it is important to remove all trace amounts of solid contaminants, hence prior to extrusion the melt is usually filtered. Further stabilizers and HCl scavengers are usually also added to prevent polymer degradation. 

Figure 8.27 (a) Cross-section of a/our-Iager microtube made in a one-step co-extrusion process [59], The inner layer is 90% nickel + YSZ and the outer layer is YSZ with the two Intermediate anode layers containing 30 and 60% nickel, respectively. This was made into a cell by painting a ISM cathode ink on the outside, then connecting with wires, (b) Improvement in performance of the co-extruded multilayer cell compared with an extruded YSZ electrolyte-supported SOFC. 

For a more economical fabrication of microtubular SOFC with more reliability and flexibility in quality control, an advanced dry-jet wet extrusion technique, that is, a phase inversion-based co-extrusion process, followed by co-sintering and reduction processes was employed to fabricate a novel electroly te/anode dual-layer hollow fiber. Using the co-extrusion technique, one of the layers has to be thick in order to provide mechanical strength to the fiber, and in this design, the anode is chosen to be the thick layer due to the much lower ohmic losses (as shown in Figure 11.16). Use of co-extrusion has many advantages over conventional dry-jet wet extrusion methods such as simplified fabrication and better control over the manbrane structure. Furthermore, the risk of defects formation can be reduced and at the same time greater adhesion between the layers can be achieved. 

The dual-layer hoUow-fiber precursors were prepared by a phase inversion-based co-extrusion technique. Prior to the co-extrusion, both spinning suspensions were degassed while stirring at room temperature to fully remove the air trapped inside the suspensions. Both spinning suspensions were then loaded into two stainless steel containers and forced simultaneously through a triple-orifice spinneret. The co-extrusion process is represented schematically in Figure 11.17. 

FIGURE 11.17 Schematic diagram of the phase inversion-based co-extrusion process of the dual-layer hollow-fiber precursor. 

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