Multilayer barrier packages

Formed multilayer barrier packages, eg, trays, bowls, and cans from coextruded PP/PVDC/ PP, are being developed for soups and entrees that can be stored at ambient temperatures and heated to serving temperature in a microwave oven. Coextrusions of high performance, high temperature polymers, such as polyether-imide and polysulfone, for dual-oven containers capable of withstanding conventional bake-oven temperatures of 204-232°C are being tested. 

Packaging and multilayer barrier films produced from COC materials exhibit improved moisture and thermal resistance. Thus, they are suitable for... 

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]. 

EVOH have superior gas barrier properties.80 89 They are often used as the internal layer in multilayer food packaging films, blow molded rigid containers, gasoline tanks for automobiles for a variety of purposes, etc. EVOH can be fabricated by the usual melt processing methods. The barrier properties of films decrease in the presence of moisture, so multilayer with protective polypropylene (especially biaxially oriented material), low-density polyethylene, nylons, or other moisture barrier films provides films or products that are useful even with liquids. The... 

Flexible PVC film is often used for packaging food products, particularly fresh red meat. The oxygen permeability of PVC film is well suited to maintain the necessary oxygen requirements of the meat, to preserve its red color and appearance of freshness. PVC films also provide good toughness and resilience. PVC is also used to wrap fresh fruits and vegetables. Almost all poultry producers in the U.S. once used PVC stretch films for chilled, tray-packed poultry parts. However, multilayer barrier films have made considerable inroads in this market. PVC is also used for a variety of other food and nonfood packaging applications, as illustrated in Table 4.8. 

An oxygen-sensitive product is packaged in a multilayer barrier pouch containing an inner EVOH layer, tie layers on either side of the EVOH, and outer layers of PR The total thickness of the PP in the film is 3 mils. Does it matter whether the structure is ... 

MAJOR APPLICATIONS Homopolymer and copolymers—usually with vinyl chloride (VC), or methyl acrylate (MA)—used in solvent-based or latex barrier coatings on cellophane, paperboard, plastic film, and rigid food containers. Films of copolymer used as household cling wrap. Also used with other polymers in multilayer barrier films or containers mostly in packaging applications. Also used in fibers and adhesives. 

There are other biomaterials with great potential in food packaging applications which are directly extracted from biomass, such as proteins (gluten, zein, etc.) and polysaccharide (i.e., chitosan). Some proteins and polysaccharides have excellent barriers under dry conditions, comparable to EVOH. However, under humid conditions these deteriorate to a much larger extent than EVOH. On the other hand, thermoplastic biopolymers such as PLA or PCL are not as strongly affected by moisture but have lower barriers than the benchmark PET. Research should therefore aim to diminish the water sensitivity of proteins and polysaccharides and to enhance the gas barrier of thermoplastic biopolyesters to make them suitable for monolayer and multilayer food packaging applications. 

Thermoforming is used to form products from multilayer sheets. Thick-gauge products include PVC-polymethyl methacrylate sanitary structures and polymethyl methacrylate- and fluoropolymer-capped ABS exterior transportation components. An example of a family of thin-gauge products is PS-ethylene vinyl alcohol-polyolefin barrier packaging. Heating and stretching of multilayer sheets often require trial and error to minimize interlayer delamination, excessive barrier film thinning, and incomplete replication of the mold cavity. 

In order to meet the military performance specification, a foil laminate structure is currently used in the MRE food pouch. However, current research is investigating alternative multilayer polymeric packaging structures. [4, 5] Ethylene co-vinyl alcohol (EVOH) is one polymer that is being researched. EVOH is a crystalline, random copolymer of ethylene and vinyl alcohol. EVOH is known to be a superior barrier to oxygen however the barrier properties of EVOH diminish as the humidity increases. Also, the hydrophilic nature of the material becomes a problem with retort packaging applications because the process requires water and steam for sterilization. EVOH resins absorb moisture as a function of humidity and temperature, decreasing the barrier properties of the resin during the retort process. 

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. 

Films, sheets and plates for packaging and thermoforming, barrier layers of multilayer films... 

This technique is used for packaging and industrial multilayer films, often of hybrid nature associating a thermoplastic with paper, cardboard, aluminium foil... Some applications are, for example, barrier films, anti-adherent films, credit cards, wallpapers. .. 

No amount of sterilization wiU prevent or even slow autooxidation, and there are only two defenses removal of O2 and addition of inhibitors. Oxygen barriers in food packaging are a major topic in the engineering of polymer films. The barrier properties of various polymers are very important in food applications, and many of these are multilayer polymers that have a thin layer of an impermeable polymer (such as polyacrylonitrile and ionic polymers) on a cheaper but O2-permeable polymer such as a polyolefin, which gives mechanical strength to the fikn. 

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