Coextrusion Process

In previous studies, it was presumed that a GI POP fabricated by this process would have a refractive index distribution with a tail at the core/cladding boundary, not as steep as that prepared by the conventional batch process [50]. Therefore, the bandwidth of the GI POF obtained by dopant diffusion coextrusion would be inferior to that obtained by the batch process. However, contrary to this expectation, a GI POF without any tail prepared by the process was reported in 2007 [57]. If low-molecular-weight molecules diffuse in a radial direction, their diffusion can be expressed by Fick s diffusion equation 

C is the concentration of low-weight molecules, t is the diffusion time, r is the distance from the fiber center, and D is the mutual diffusion coefficient of 

Recent Studies of Low-Loss and Low-Dispersion Polymer Materials 

With various improvements in the fabrication process enabling the avoidance of contaminants and the formation of Gl profiles, low-loss and high-bandwidth POFs have become leading candidates for short-distance networks (e.g.. 

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Strength they are of interest as a streteh film for meat packaging and for cling-wrap purposes. Some EVA is used in coextrusion processes for the manufacture of laminated film. 

Schematic illustrations showing coextrusion process to fabricate FMs (a) initial feedrod formation, (b) coextrusion, (c) lamination, and (d) hot-pressing. 

In the last 10 years, significant advances in fibrous monolithic ceramics have been achieved. A variety of materials in the form of either oxide or nonoxide ceramic for cell and cell boundary have been investigated [1], As a result of these efforts, FMs are now commercially available from the ACR company [28], These FMs are fabricated by a coextrusion process. In addition, the green fiber composite can then be wound, woven, or braided into the shape of the desired component. The applications of these FMs involve solid hot gas containment tubes, rocket nozzles, body armor plates, and so forth. Such commercialization of FMs itself proves that these ceramic composites are the most promising structural components at elevated temperatures. 

The flat film and sheet coextrusion analyses mentioned earlier can be easily extended to the treatments of the wire coating and film blowing coextrusion processes. 

In chapter 7, section 7.2.8 an example of permeation through a functional barrier is described. Three-layered coextruded PET films were produced in which the core layer (P) was contaminated with chlorobenzene and the outer barrier layers (B) were made with virgin material. During the coextrusion process a partial contamination of the virgin layer occurred. The symmetrical structure of this film leads to a simplified treatment of it as a two layer laminate with the thickness d = a + b = 160 + 40 = 200 pm. For the modeling of this problem with numerical mathematics all parameters given in Section 7.2.8 are used. 

Very fine aluminum pigments display a very grayish silver effect if they do not have a chance to orient themselves parallel to the surface, as is often the case in injection-molded parts. They are preferably applied in film and coextrusion processes because of their very high opacity, ability to orient, and reflectivity of light. 

Centrifugal extrusion encapsulation, or coaxial extrusion processing, is a liquid coextrusion process that uses an assembly of cylindrical nozzles consisting of concentric orifices located at the outer circumference of a rotating cylinder (Figure 24.3). 

The single-layer coextrusion process based on the use of low-volatility UV absorbers has been adopted for thin-walled sheet and profile manufacture, both in Europe and worldwide. Coextrusion coating using PC is important also from the point of view of recycling, because single-polymer systems increasingly are being required. 

Good gas and odour barrier. Good moisture value when dry, but as moisture is absorbed, moisture barrier properties reduce. Relatively expensive. Usually used as a central ply in coextrusion processes. Replacing foil layer in some laminated tubes. Good barrier to certain flavours peppermint, spearmint, etc. 

U.S. Pat No. 6,827,995 [53] discloses a single coextrusion process of making a WPG as a hollow profile comprising a weatherable outer layer made of a first polymeric material, a core layer made of a thermoplastic polymeric foamed composition including a wood component, and an inner layer made of a third thermoplastic material. The first and second polymeric materials are PVC or acrylonitrile-styrene-acrylic polymer or a combination thereof. The third polymeric material is PVC. 

U.S. Pat. No. 6,844,040 [54] discloses a coextrusion process of making reinforced WPC structural members comprising hollow profiles formed from a thermoplastic-cellulose fiber composite material and reinforcing sections bonded to the hollow profile. 

Cast coextrusion Processed meats, cheese PET/EVOH/EVA... 

Density of the core material can negatively affect some encapsulation processes. For example, increasing differences in shell and core material density for a coextrusion process may result in incomplete encapsulation of the core material, or off-centered cores. Density can also be a concern with emulsion-based processes, as a stable suspension is typically required during the formation of a shell or matrix. Density modification can be used to balance the core and shell systems to improve encapsulation efficiency. 

Film Processing Methods Extrusion, coextrusion, and Saran F- lacquer solution films. Multilayer Extrusion Saran resins are used in combination with a myriad of other polymers in flexible and rigid multilayer products. Multilayer cast and blown film coextrusion processes for Saran can be used with all polyethylenes, polypropylenes, and nylons. 

Mueller, C., Topolkaraev, V., Soerens, D., Hiltner, A., and Baer, E., Breathable Polymer Films Produced by the Microlayer Coextrusion Process, J. Appl. Polym. Sci. 78, 816 (2000). 

A tie layer or coextrudable adhesive has the function of improving interfacial forces between dissimilar polymers in the Coextrusion process. The layer is used in cases where resins coextruded are so incompatible that effectively no bond develops between them, or where the bond between two polymers is so limited as to be impracticable (see Compatibility). A typical coextruded film stractuie may consist of five layers of the basic form sealant layer/adhesive tie/barrier/adhesive tie/outer layer. The tie layers will generally be only a few microns thick. 

Body materials that have been used include polypropylene, high density-polyethylene, or low-density polyethylene mixed with the bonding agent. The barrier material generally used is nylon, which may be either on the inside of the container or on the outside. Some of the advantages claimed for the coextrusion process are excellent aroma barrier, surface gloss, surface priming, scratch resistance (with the nylon on the outside), and chemical resistance and barrier to hydrocarbons (with the nylon on the inside). 

The recycled polymer can be used in new frames making up the core layer (two-thirds by weight) while virgin PVC forms an external layer in a coextrusion process. These profiles perform just as well as those from the virgin polymer and, after another 10 years of service, are ready for another recycling loop [259, 263]. 

This surface treatment allows low cost blow-molded PE bottles to be used for paint, paint thinner, lighter fluid, polishes, cleaning solvents, cosmetics, toiletries, etc, and higher cost resins or coextrusion processes are not always necessary. For floorination to be effective, the parison temperature must be greater than 195°C. 

The coextrusion process is used to combine multiple materials into a single film (see Coextrusion). Both blown films and cast films may be coextruded in three, five, seven, or more layers. The combination of multiple materials in a single film allows a cost-eflective means of combining the performance properties of several polymers in a single film. One example would be the coextrusion of a... 

The basic coextrusion process consists of the generation of two or more melt streams and their confluence while in the melt phase. The number of separate extrusion systems is determined by the number of polymer types. This is typically 2, but occasionally 3 and exceptionally up to 10. Each polymer type to be incorporated in the structure is separately melted, pressimized, and (optionally) filtered in parallel extrusion systems before flowing into the coextrusion hardware. The optimum method of bringing the separate melts together depends primarily on their respective flow behaviors. The melt layers must remain distinct but well bonded in the process from the point(s) of confluence through to sohdification. There are basically two hardware configurations in use for common polymers the multi-manifold die and the injector block. Combinations of the two are also possible for complex structures (8,9). 

New processing techniques offer another way to recycle PVC scrap. One example is the production of window frames by coextrusion. The regenerated PVC is used in core whereas virgin resin is used as the skin. In this process only 1/3 of new material is necessary to obtain the same properties as a window frame from 100% virgin PVC. The coextrusion process is also feasible for the production of pipes where the inside and the outside layers are made out of a new resin and the old material is used for the thick middle layer. ... 

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