Polyamide food packaging

Table 10 contains some selected permeabiUty data including diffusion and solubiUty coefficients for flavors in polymers used in food packaging. Generally, vinyUdene chloride copolymers and glassy polymers such as polyamides and EVOH are good barriers to flavor and aroma permeation whereas the polyolefins are poor barriers. Comparison to Table 5 shows that the large molecule diffusion coefficients are 1000 or more times lower than the small molecule coefficients. The solubiUty coefficients are as much as one million times higher. Equation 7 shows how to estimate the time to reach steady-state permeation t if the diffusion coefficient and thickness of a film are known. 

Boil in the bag food packaging is usually a laminate of LLDPE and polyamide 6. Adhesive lamination is normally used to bond these materials together. 

Examples of the use of nanostructured materials for packaging applications have been given in Chaudhry et al. (2008) and references therein. One of the first market entries into the food packaging arena was polymer composites containing clay nanoparticles (montmorillonite). The natural nanolayer structure of the clay particles impart improved barrier properties to the clay-polymer composite material. Some of the polymers which have been used in these composites for production of packaging bottles and films include polyamides, polyethylene vinyl acetate, epoxy resins, nylons, and polyethylene terephthalate. 

Figure 15.12), presumably due to a good degree of miscibility. These commercial PA-6/amorphous polyamide blends have been developed particularly for applications in flexible food packaging markets and hence captively produced as films. 

This copolymer is also widely used as a blending compound with olefin homopolymers as well as with polyamides, polyesters, and polycarbonate to improve impact strength and toughness and either to increase heat seal response or to promote adhesion. EMA is also used in soft blow-molded articles such as squeeze toys, tubing, disposable medical gloves, and foamed sheet. EMA copolymers and ethylene ethyl acrylate (EEA) copolymer containing up to 8% ethyl acrylate are approved by the FDA for food packaging. 

Steam-solvent distillation using diethyl ether has been used to remove and analyse for odour and taint from additives in food packaging films. Another technique that has been used is vacuum/thermal extraction. This procedure has been applied to polyamides and fluorocarbon polymers. The procedure is used for the direct isolation or release of volatile components from a polymeric matrix and may involve the combined use of vacuum and heat, as for example in the mass spectrometer direct insertion probe or during dry vacuum distillation. Alternatively, the volatiles may be swept from the heated sample by a flow of inert gas for concentration by freeze trapping and/or collection on to a solid adsorbent prior to thermal or solvent desorption for GC or mass spectrometric (MS) examination. 

Plastics that are most often used as food packaging materials include polyolefines, polyesteres, polyvinyl chloride, polyvinyli-dene chloride, polystyrene, polyamide, various resins and so on. For example, the world plastic demand in 2011 was dominated by polyethylene, including low density polyethylene (PE-LD), linear low density polyethylene (PE-LLD, 17%) and high density polyethylene (PE-HD, 12%), polypropylene (PP, 19%), polyvinyl chloride (PVC, 11%), polystyrene solid (PS) and expandable (PS-E, 7.5%), polyethylene terephthalate (PET, 6.5%), polyurethane (PUR, 7%) and other plastic types (20%). An overview of the main types of polymeric packaging materials is given in Table 12.73. 

The diffusion of small molecules into polymeric materials is important for many areas of application, for example, food packaging or protective clothing. Polyamides absorb small molecules such as water and alcohols, and this process is accompanied by a change of the melting and glass-transition temperatures [67] and also has a strong influence on their mechanical [68] and electrical [69]... 

Demertzis and co-workers [48] carried out an in-depth study of the influence of gamma irradiation on the formation of solvent extractable radiolysis prodncts of flexible films and sheeting for food packaging. The packaging, which was made from PE, PP, polyethylene terephthalate (PET), PS, polyvinylchloride (PVC) and polyamide (PA), was subjected to Co irradiation at a dose of 44.0 kGy. Separation and identification of extracted compormds were carried out using GC-MS and compositional changes in the radiolysis prodncts quantified by calibration using MS detector response. 

Indeed, simple monomers, snch as styrene, ethylene, propylene, hexene, vinyl chloride, acrylonitrile and caprolactam, nsnally do occur in the corresponding polymers. In addition to unreacted monomer, any non-polymerisable impnrities in the original monomer feed to the polymerisation conld occur in the final prodnct. Thns, styrene monomers can contain low concentrations of numerous saturated and nnsatnrated hydrocarbons, ethyl benzene being particnlarly prevelent and these, particnlarly the saturated compounds which do not polymerise, will occur in the finished polymer and have implications in the nse of the polymer food packaging. It is not nnknown for compounds as toxic as benzene to occnr at very low concentrations, nsnally less than 10 parts per million in styrene monomer, and this could, therefore, also occur in the polymer. For foodgrades of polystyrene, the monomer content is nsnally nowadays limited to 0.2% maximum. Acrylonitrile monomer may be fonnd in amonnts up to 0.1 % in finished polymer, whilst negligible amounts of monomer are fonnd in polyamide and polymethyl-1-pentene. With thermosets, phenol and formaldelyde are likely to be found even in the most carefully manufactured grades. 

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