Barrier Multilayered plastic

Attempts have been made to perform thermal retorting ia a gas barrier flexible pouch or tray. The retort pouch, under development for many years, has a higher surface-to-volume ratio than a can and employs a heat seal rather than a mechanical closure. Similarly, plastic retort trays have higher surface-to-volume ratios and are usually heat seal closed. Plastic cans iatended for microwave reheating are composed of bodies fabricated from multilayer plastic including a high oxygen barrier material, plus double-seam aluminum closures. 

Multilayer fabrication is the simultaneous processing of two to up to at least seven plastics melt streams meeting in a die/mold to produce laminated or multilayer plastic products. Product performances gained are a combination of what each individual plastic provides with a potential of obtaining synergistic gains. Each ply of the laminated structure imparts a desired property such as impermeability or barrier/... 

You are designing a multilayer plastic structure with 4 layers. The total oxygen permeability is required be 30 cm mil/m day atm. Calculate the required thickness of the barrier layer (layer 2) in mil. (Answer x = 2.55 mil)... 

The market for plastic cookware that can be used in the fi-eezer and microwave is set for a big expansion. Most cookware is made up of fiberglass reinforced thermoset resins. High-barrier multilayer containers that have gained popularity in the market are heat retortable, microwaveable, and provide a shelf life of up to two years without refrigeration for a variety of convenience foods. Liquid crystal polymers have also been used to make cookware as they are transparent to microwave, offer high heat resistance, and give an excellent finish. 

LCPs have recently been blow molded into containers by extrusion blow molding, and they have been used in multilayer containers made by coextrusion blow molding [33,34], As in high barrier multilayer films, the LCP provides a thin high barrier layer, and a less costly plastic, such as PET, is used to provide... 

Film or sheet generally function as supports for other materials, as barriers or covers such as packaging, as insulation, or as materials of constmction. The uses depend on the unique combination of properties of the specific resins or plastic materials chosen. When multilayer films or sheets are made, the product properties can be varied to meet almost any need. Further modification of properties can be achieved by use of such additives or modifiers as plasticizers (qv), antistatic agents (qv), fire retardants, sHp agents, uv and thermal stabilizers, dyes (qv) or pigments (qv), and biodegradable activators. 

To enhance water-vapor- or gas-barrier properties, layers of different plastics may be injected together or sequentially. Multilayer injection-molded pieces may be prepared as packaging or for blowing into bottle or jar shapes. 

Thermoform able sheet may be mono- or multilayer with the latter produced by lamination or coextmsion. Multilayers are employed to incorporate high oxygen-barrier materials between stmctural or high water-vapor barrier plastics. Both ethylene vinyl alcohol copolymers and poly(vinyhdene chloride) (less often) are used as high oxygen-barrier interior layers with polystyrene or polypropylene as the stmctural layers, and polyolefin on the exterior for sealing. 

Because high oxygen-barrier plastics are incompatible with other thermoplastics, extmdable adhesives must be extmded between the layers. Scrap can be included within the multilayer stmcture, provided an extmdable adhesive is incorporated. 

More advanced insulations are also under development. These insulations, sometimes called superinsulations, have R that exceed 20 fthh-°F/Btu-m. This can be accomplished with encapsulated fine powders in an evacuated space. Superinsulations have been used commercially in the walls of refrigerators and freezers. The encapsulating film, which is usually plastic film, metallized film, or a combination, provides a barrier to the inward diffusion of air and water that would result in loss of the vacuum. The effective life of such insulations depends on the effectiveness of the encapsulating material. A number of powders, including silica, milled perlite, and calcium silicate powder, have been used as filler in evacuated superinsulations. In general, the smaller the particle size, the more effective and durable the insulation packet. Evacuated multilayer reflective insulations have been used in space applications in past years. 

Another route to protect polymers from oxygen, light and UV is to encapsulate the part with a continuous film of another, more-resistant polymer to provide a barrier to oxygen. This technology is also used for decoration of plastic parts (in mould decoration or IMD, painting, multilayer sheets for thermoforming. ..). There is no protection against heat. 

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). 

One approach to reduce the contaminant levels consists in reusing the wasted plastic as the core of the new material. Residues of pesticides or harmful contaminants may limit recycling of plastics as a result of their potential toxicity. Utilisation of post-consumer plastics for pharmaceutical or food-contact applications is forbidden, and multilayer food packaging materials manufactured using functional barriers are subjected to strict regulations [9, 40, 41]. 

To replace glass, a plastic substrate must offer the properties of glass, i.e. clarity, dimensional stability, thermal stability, barrier, solvent resistance, low coefficient of thermal expansion, and a smooth surface. No plastic film has all these properties so any plastic based substrate will almost certainly be a multilayer composite structure. In addition to choosing the right materials for the different layers, one now has a new set of issues associated with the properties of multilayer structures. These issues include the adhesion of the different layers, the effect of thermal and environmental cycling, and the effect of flexing the structure, not only on specific... 

With the flexibility of the blown film extrusion process, one-step production of wide multilayer films is possible. Incorporating a built-in adhesive layer, PVDF films can be laminated directly onto various thermo and thermoset plastics or primed metal substrates. PVDF films can protect the esthetics of UV sensitive substrates while also providing a thermal, chemical, and abrasion-resistant barrier. Recently, white PVDF films have been commercialized that are of full opacity in the UV range of 290 00 Most recently,... 

In addition to internal or external coatings, barrier enhancers can be incorporated into the plastic as additives. These can include various metal oxides, glass fibre, mica, etc. Incorporating a foil ply between layers of plastic is a further way of obtaining excellent barrier properties, e.g. multilayer laminated tubes, cold formed blisters, and additional overwraps should not be ignored. 

In the last few years, a rapid expansion in the use of high gas barrier plastic structures for food packaging has taken place. These structures include multilayer films, trays, bottles and cups, "bag in the box" and "bag in the barrel" type packages and laminated cartons. 

Laminated tubes are made from multilayer materials that usually contain paper as well as plastic, and often also include aluminum foil as a barrier layer. The preprinted tube bodies are sealed into a cylinder, with the edges of the sleeve overlapped and compressed, squeezing some of the plastic out around the raw edges of the foil and paper to make a good seal. Next the tube is cut to length, and finally the head is molded and assembled to the body. To improve the barrier in the head, a premolded insert of polybutylene terephthalate or urea can be incorporated in the injection mold when the head is formed. 

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