Packaging applications plastics

US NFPA, 1995, Guidelines for the safe use of recycled plastics for food packaging applications. Plastics Recycling Task Force. National Food Processors Association. Washington DC Society of Plastics Industry Inc., March 1995. 

K. R. Osborn and W. A. Jenkins, Plastic Films-Technology and Packaging Applications, Technomic Publishing Co., Inc., Lancaster, Pa., 1992. 

Current usage is almost entirely associated with the good adhesion to aluminium. Specific applications include the bonding of aluminium foil to plastics films, as the adhesive layer between aluminium foil and polyethylene in multilayer extrusion-laminated non-lead toothpaste tubes and in coated aluminium foil pouches. Grades have more recently become available for manufacture by blown film processes designed for use in skin packaging applications. Such materials are said to comply with FDA regulations. 

The main fluids of interest with plastics are oxygen and water vapour (for packaging applications) and CO2 (for carbonated drinks applications). Fig. 1.13 and Fig. 1.14 illustrate the type of behaviour exhibited by a range of plastics. In some cases it is necessary to use multiple layers of plastics because no single plastic offers the combination of price, permeation resistance, printability, etc. required for the application. When multi-layers are used, an overall permeation constant for the composite wall may be obtained from... 

Table I shows the chemical composition limits of various aluminum alloys presently used for packaging applications (3). In general, these alloys have good corrosion resistance with most foods. However, almost without exception, processed foods require inside enameled containers to maintain an acceptable shelf life (4, 5). Moreover, when flexible foil packages are used for thermally processed foods, the foil is laminated to plastic materials that protect it from direct contact with the food and also provide heat sealability as well as other physical characteristics (6,7).

Plastics packaging and contained food products are chemically related in four distinct ways. This relationship is based largely on the permeation property of the plastic material. Direct chemical reaction between plastic and product is seldom a problem when inert plastics such as polyethylene are used. However, polyethylene can transmit minute amounts of product to the outside. This paper examines the effect of permeation through the plastic wall and the direct effects of the plastic on the food product. Specific food packaging applications and methods of testing are discussed. 

IX lists the results of some of these experiments, comparing the nitrile materials with polyethylene, the most widely used plastic container material, and poly (vinyl chloride), which is being used for a number of food packaging applications. Note that in all instances there is an order of magnitude difference between the Lopac container and the other two. For flavorants, which are usually present in very low concentrations, this dilute solution test is probably more significant than a standard permeability test which only measures weight losses of the pure ingredient. 

Poly(ethylene terephthalate) (PET) is one of the most extensively recycled polymeric materials. In 1995, 3.5 x 104 tons of PET were recycled in Europe.1 The main reason for the widespread recycling of PET is its extensive use in plastic packaging applications, especially in the beverage industry as plastic bottles. The consistency in terms of volume and availability of postconsumer bottles from sorting facilities and its high material scrap value create an excellent economic environment for PET recycling. 

The above results suggest a potential for utilizing surface fluorinated plastics for modified atmosphere and vacuum packaging applications. If needed, the barrier properties can be improved further by vacuum metalization. Excellent adhesion was found for vacuum-deposited aluminum on this new fluorinated layer, achieving an adhesion index of 10 using the classical cross-hatch method. With this treatment method it was also possible to heat-seal PP or PE onto PET. 

Thermoplastics, which account for 87% of plastics sold, are the most recyclable form of plastics because they can be remelted and reprocessed usually with only minor changes in their properties. Five resins are commonly used in consumer packaging applications. 

VAE, a copolymer of vinyl acetate with minor amounts of ethylene is used as an adhesive for paper, plastics and leather and as a binder for different paints. Shoes, tubes, toys and other articles of daily use also contain VAE polymers. The hydrolysis product of VAE polymers, EVOH, is a thermoplast and can therefore be processed by extrusion and injection moulding and is used as barrier polymer for O2 and CO2 (e.g. in packaging applications). 

Hot blown plastic films usually do not possess sufficient orientation to be heat shrinkable at temperatures below 100°C. For certain shrink packaging applications low temperature shrinkage is essential and can be obtained by biaxial orientation below the melting point. Radiation crosslinking was found to facilitate orientation of these copolymers greatly because of the much greater bubble stability which results from crosslinking. 

The alternative to using a dish is to form the material into a bag and this so-called pouch or sachet method is often used for plastics films. The advantages are that a larger surface area is exposed, leaks through the wax seal are eliminated, and the conditions are more similar to packaging applications. It is less attractive for rubbers because they are not often used in that sort of packaging application and an alternative to heat sealing the pouch would be necessary. 

Polypropylene. Polypropylene (PP) is used in packaging applications as films and in rigid containers. Battery cases could be considered another packaging application. Dead batteries are often collected at the point of sale of new batteries. In the U.S., some states have laws mandating this. Lead, acid, and plastics, particularly PP from battery casings is recovered and recycled (3). Care must be taken to limit worker exposure to lead during this process (44). PP is also recovered from bale wrap and other PP fabrics used for wrapping in the textile industry and from other containers (45). 

Other Plastics. A relatively small amount of poly(vinyl chloride) goes into packaging applications and appears in municipal solid waste (25). 

The physical properties and melt processing of PLA are similar to those of conventional packaging resins. It may thus be used as a commodity resin for general packaging application. In many aspects the basic properties of PLA lie between those of crystal PS and PET [ 14]. When plasticized by its own monomer lactic acid, PLA becomes increasingly flexible so that products that mimic PVC, LDPE, LLDPE, PP, and PS can be prepared [15]. Possible applications are espe-... 

Huber, M., and Franz, R. (1997). Studies on contamination of post-consumer plastics from controlled resources for recycling into food packaging applications. Deutsche lebensmittel-Rundschan 93(10), 328-331. (In Franz, R., and Welle, F. (2003). Recycling packaging materials. Ch. 23. In "Novel Food Packaging Teclmiques" (R. Ahvenainen, ed.), pp. 497-518. Woodhead, CRC Press, Boca Raton, FL). 

One of the first applications of biodegradable materials is based on the cooked, extruded, and expanded starch known from the food and chemical sectors (Fig. 14.23). Starch is cooked with water in the extruder and chemically modified as necessary or mixed with plasticizers, then expanded to a starch foam and dried. The extrudate is ground so that the functional properties thus created can be used in the food/chemicals sector. The foamed, cut, and dried extrudate is the end product for loose-fill packaging applications. The degree of expansion is a measure of the foam texture. It increases strongly with product temperature at the die, helped by a higher specific mechanical energy input. However, both measures increase the water-solubility of the product. 

We are confident that sometimes in the future suitable computational approaches and powerful hardwares will be available to predict D of additives, stabilizers, monomers, dyes and/or plasticizers in polymeric materials used in packaging applications. To evaluate, if such an endeavour may help to reduce the considerable volume and costs of experimental migration testings peformed nowadays, it is necessary to consider also the following aspects. 

---