Multilayer coextrusion

Approximately 252 million dollars in counterfeit U.S. currency is recovered each year. While this is a small percentage of the 540 billion U.S. dollars that are assumed to circulate worldwide, there is clearly a need for more sophisticated security features. A possible solution is to use multilayer coextrusion technology to create an optical polymer substrate for U.S. currency. 

Multilayer coextrusion technology is used to create an optical polymer substrate for U.S. currency. The final product specifications of the optical currency are listed below ... 

Ramanathan, R., Shanker, R., Rehg, T., Jons, S., Headley, S., and Schrenk, W.J., Wave Pattern Instability in Multilayer Coextrusion - An Experimental Investigation, SPE ANTEC Tech. Papers, 42, 224 (1996)... 

Extrusion. Sheet, film, and profiled articles are made by extrusion (20). The resin is melted and forced through a die plate or head. Variations include multilayer and blown film applications. In multilayer coextrusions, different combinations of plastics are separately but concurrently extruded to form layered sheet or film. In the packaging industry, specialty resins such as high barrier ethylene—vinyl alcohol copolymers are combined with heat- and impact-resistant thermoplastics for food packages. The properties of each resin layer are additive, as opposed to the "averaging of property" in blends. Multilayers are also used for blow-molded containers, films, and sheet products (see also Film AND sheeting materials). 

With sheet or pipe, multilayer coextrusion can be used. Solid outer-solid core coextmsion can place an ABS grade on the outside that has special attributes such as color, dullness, chemical resistance, static dissipation, or fire-retardancy over a core ABS that is less expensive or even regrind. 

Du et al. [67] investigated effects of layered architecture and blend morphology on the SM behavior using thermoplastic PU and PCL. The PU/PCL ratios set were 75/25,50/50, and 25/75, respectively. The layered structure was achieved by a special multilayer coextrusion technique. The layer thickness varied with the composition ratio whereby keeping the number of layers and the overall thickness of the multilayer film as constants. of PCL served as 70 °C) during shape... 

The multilayer coextrusion blow molding technology can be used for a wide variety of containers made from LCP and other thermoplastics. Figure 11.36 shows a multilayer bottle and tray made from LCP and PET by coextrusion blow molding. Figure 11.37 shows high barrier bottles made with LCP and PET. 

With sheet or pipe, multilayer coextrusion can be used. Solid outer-solid core coextrusion can place an ABS grade on the outside that has special attributes such as color, dullness, chemical resistance, static dissipation, or fire-retardancy over a core ABS that is less expensive or even regrind. Composites can be created in which the core optimizes desired physical properties such as modulus, whereas the outer layer optimizes surface considerations not inherent in the core material. Solid outer-foam core can provide composites with significant reductions in specific gravity (0.7). Dry blowing agents can be dusted onto the pellets or liquid agents injected into the first transition section of the extruder. 

Multilayer coextrusion of thermoplastic film and sheet has developed into an important plastic fabrication process, providing large growth opportunities for the plastics industry. Coextruded multilayer plastics are challenging such traditional materials as metals, glass, paper, and textiles. 

Flat Dies (Slit Dies). Flat dies, also called slit dies because the orifice is a wide rectangular opening, are used in chill-roll, cast-film coextrusion. These dies are used almost exclusively for multilayer coextrusion with sheet thickness >254 /um, as well as in coextrusion coating processes (2), where a multilayer web is extrusion-coated onto a substrate such as paperboard, aluminum foil, plastic foam, or textiles. 

Some years of experience also clearly show that a sound policy must necessarily combine several approaches, whereas in the field only well defined and realistic objectives must be selected. This work describes the mechanical recycling of PVC bottles and/or pipes to non-pressure coextruded three-layer pipes. In a first step the material (bottles or pipes) must be regenerated and in the second step, re-used. The coextrusion process also describes the modification of the production equipment required by multilayer coextrusion. 

Multilayer coextrusion has been widely used, studied and understood in the domain of synthetic polymers for its effect on the viscosity of polymers, die geometry, layer distribution, encapsulation, and interfacial instabilities, influencing the quality and functionality of the multilayer products. Despite the number and diversity of studies on multilayer flow and stability, only some articles report the use of biopolyester in coextrusion processes. Different stratified structures were processed by coextrusion and studied. But very few studies have been carried out with PHA. Most of these are based on the association between PHA e.g. PHBV, and plasticized starch. Applications of such PHA-based multilayers as commodities are primarily limited by PHA cost and have been until now by PHA availability, and thus attention is being focused on products with plastics constituting only a minor part, such as paper coatings like the plastic film moisture barrier in food and drink cartons and in sanitary napkins. 

Special polymer blends can be realized using the coextrusion technique. Using two or more extruders, the individual melt streams are put together in a multilayered arrangement, and polymer systems of two up to five clearly visible layers can be produced. Using the special multilayer coextrusion technique, polymer systems of two or three different polymers with a parallel arrangement of up to several thousands of very thin layers are possible see Section 9.3 in Part II. 

The technique of multilayer coextrusion can he used to produce two-dimensional continuous layers of different polymers via the process of forced assembly [1]. Microlayer coextrusion combines two or more polymeric materials into layered configurations that can be used to produce new architectures with improved mechanical, electrical, barrier, and adhesive properties. Layered composites comprising up to 8000 continuous layers can be successfully produced, with the thicknesses of individual layers ranging from several microns down to a few nanometers [1,8]. Multilayered materials with such small layer thicknesses in the range of a few tens of nanometers can be otherwise only obtained by the copolymerization of polymers into block copolymers (see Chapter 3, Block Copolymers ). 

Two routes were explored to fabricate organic superlattices a modified spin casting procedure and multilayer coextrusion. Spin casting was selected as a relatively quick, low tech way to select the most promising photoresponsive polymer. 

After the desired number of multiplication elements, a sheeting section is placed in the flow field. The sheeting section is designed to vertically compress and horizontally stretch the multilayered structure to produce a sheet or film. The molten film exits the multilayer coextrusion line and enters a chill roll take-up device. The water-cooled steel rollers freeze the multilayered structure, preventing it from deforming. 

We have modified the generalized multilayer coextrusion process to meet the requirements of this project and to improve the performance of the process. The... 

Attention has been paid to the possible use of multilayer coextrusion of engineering resins for dual ovenable containers, as multilayer packaging could increase shelf stability and thus eliminate the need for freezing or refrigeration. One multilayer combination in commercial use is a sheet of Lexan polycarbonate sandwiched between layers of Ultem polyetherimide. Thermoformed trays of this material are reported to have better break resistance at lower temperatures and higher stiffness at temperatures up to 232°C, as compared to CPET. They are also insert, compatible with polyester lidding materials, and have lower oxygen permeability than PET materials. 

Figure4.18 Multilayer coextrusion simulations using the commercial software POLYFLOW (a) 5-layer 2D coextrusion and (b) 2-layer 3D coextrusion in a coat-hanger die [16]. In both cases, there is a simultaneous determination of the unknown a priori interfaces.

Coextrusion seems the best option, because it offers the advantages of being a one-step, continuous, and versatile process [11]. Multilayer coextrusion has been widely used in the past decades to combine the properties of two or more polymers in one single multilayered structure. However, some problems inherent to the multiphasic nature of the flow are likely to occur during coextrusion operations ... 

Multilayer coextrusion is a process in which two or more polymers are extmded and joined together in a feedblock or die to form a single stmcture with multiple layers. This paper will discuss techniques for measuring experimental rheology data for monolayer and multilayer stmctures and how that data can be used for determining the processability of multilayer coextmded stmctures. 

A multilayer coextrusion die was used to create polypropylene (PP) / organoclay nanocomposites and to study the stress effects on clay dispersion. Nanocomposites contained 5 wt% maleic anhydride grafted PP compafibilizer and 1-5 wt% organoclay. Nanocomposite layers were extruded opposite talc fill PS before being separated. Individual PP nanoconposite layers were tested for improvements in mechanical, thermal and barrier properties and were compared to theoretical predictions in order to determine an aspect ratio for the organoclay. Aspect ratios from theory were compared to those measured directly through TEM. A PP nanocomposite / elastomer system was also considered. 

The goal of this research is to create PP nanocomposite noatmals using multilayer coextrusion technology. These multilayers will then be sq arated into distinct, individual layers and material and thermal properties for each layer will be measured. These results, along with TEM micrographs, will allow us to assess the effectiveness of qjplying shear stress in a slit die to achieve dispersion in PP nanocomposites. 

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