Multilayer Food Packages

A layer in a multilayer packaging structure that acts to retard, limit, or prevent migration of components from package layers exterior to it, into the package contents is called a functional barrier. This barrier may or may not be the food contact material itself. For example, in a multilayer structure containing an inner layer of aluminum, the aluminum can be expected to be an excellent barrier to any possible migrants from all layers from the outside of the package up to the aluminum. 

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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... 

Film Applications Grilon CF 6S is particularly suitable for boil-in-bag applications. Grilon CR 9 is suitable for multilayer food packaging films for dry, nonfatty food packaging. Grilon CR 9 HV is a superior product for extreme-draw, thermoforming fiims.P i... 

Regulatory Approval Grilon CR 6S is FDA-listed for direct contact with foodstuff containing less than 8% alcohol. Grilon CR 9 and CR 9 HV may be used in multilayer food packaging without direct contact with foodstuff... 

Uses and applications multilayer food packaging, boil in bag, automotive fuel components. 

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. 

Results are presented of a study in which confocal microRaman spectroscopy was used to determine the structure of the individual polymers present in a series of multilayer food packaging films. 8 refs. 

The commercial polymeric films (Table I) that are used as the outside layer of multilayered materials for thermoprocessed food packaging are poly(ethylene terephthalate), polyiminocaproyl, or polypropylene. The other five films listed in Table I or polypropylene are used for the food-contacting layer. 

Multilayered materials can be readily formed using thermoforming including food packaging that may involve inclusion of layers of ethylene-vinyl alcohol copolymers, PS, polyolefins, and/or copolymers of vinylene dichloride and vinyl chloride. Microwavable food trays from (crystallized) PET are manufactured using thermoforming. 

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. 

Copolymers of ethylene and norbomene exhibit excellent transparency, high moisture barrier, high strength and stiffness, and low shrinkage. In comparison to poly(ethylene) (PE) and polypropylene) (PP), they show a very low gas permeability. They are used for blister packaging in pharmacy applications and for flexible films for food packaging. Multilayer films consisting of PP outer layers and a cyclic olefin copolymer are in use. 

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). 

Plastics can be placed into two main categories, thermoplastic and thermoset. Thermoset plastics are irreversibly formed into a permanent shape often by applying heat. Thermosets caimot be softened and remoulded on heating and have few applications in food packaging, except for the iimer linings used for can coatings and many adhesives, as used, for example, in multilayer materials. A limited range of food contact materials is made from thermosets, predominantly melamine resins and unsaturated polyesters used in tableware and utensils. 

There are two polymers used in a maj ority ofhigh barrier food packages copolymers containing polyvinylidene chloride (Saran ) and ethylene-vinyl alcohol copolymer (Eval, Selar-OH ). Packages in which either polyvinylidene chloride or ethylene-vinyl alcohol copolymer (EvOH) provide the barrier are invariably multilayer since neither of these materials offers the properties required to make a good monolayer structure. There are advantages and disadvantages associated with each of these materials, and the... 

Retortable food packages using EvOH as the oxygen barrier are multilayer structures which are formed by coextrusion. The number of different layers in a the structure can vary a representative five-layer structure is shown in Figure 3. Often one or more layers are added to reuse scrap and regrind in the package. There is a wide range of possible combinations of layer thicknesses which can be used in this type of structure. 

A similar situation does not presently exist for multilayer retortable food packages. In our initial study of LEP and PEP food packages we found that there are very few experimental studies on water permeation in polymers. The studies which we did find were usually limited to low temperature, far removed from retort conditions. The effect of water activity on transport and sorption behavior has not received much attention especially for water-sensitive polymers such as EvOH. In EvOH-type systems the problem is especially acute because EvOH exhibits case II sorption at moderate humidities and its effective glass transition is depressed below storage temperatures at high humidities. Thus, modelling the transport in this type of material is very complex and does not lend itself to analysis with existing models. 

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. 

Because of their carcinogenicity, amines have to be monitored. For example, primary aromatic amines (PAAs) are substances that can be transferred from food packaging materials into foodstuffs. In the production of multilayer plastic materials it is common to use reactive adhesive mixtures containing aromatic isocyanate monomers. In cases of incomplete curing, residues of the aromatic isocyanates react with water to produce PAAs. Some of these amines, including... 

A novel organic (chitosan) and inorganic (tetraethyl orthosilicate) composite membrane has been prepared, which is pH sensitive and drug permeable [258]. The latter possibly involved in ionic interactions. By plasma source ion implantation technique, the adhesion between linear low-density polyethylene and chitosan could be improved [259]. Such bilayer films showed 10 times lower oxygen permeability, a property of use in food packaging applications. These multilayer films were easily recyclable. 

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