Polyethylene terephthalate packaging applications

Many polymers are used in barrier applications, either to keep contents in or contaminants out. Food packaging is an excellent example of such usage. Plastic films and containers of many types are used to package food. Blow moldedbottles often contain numerous layers, each of which provides specific benefits. Polyethylene layers are excellent water barriers, polyvinyl alcohol is a good oxygen barrier, and polyethylene terephthalate impedes the diffusion of carbon dioxide from carbonated drinks. Other barrier applications include toothpaste tubes, diaper backsheets, tarpaulins, and geomembranes, which are used to line containment ponds and landfill pits. 

Polyesters, which are a class of engineering thermoplastics, are found in a wide variety of applications including carbonated drink bottles, fibers for synthetic fabrics, thin films for photographic films and food packaging, injection molded automotive parts, and housings for small appliances. In this chapter, we svill explore the synthesis of this class of polymers. We will also look at the typical properties and end uses for the most common of these resins, polyethylene terephthalate and polybutylene terephthalate, which are commonly known as PET and PBT, respectively. 

Franz, R., Recycled Polyethylene terephthalate) for direct food contact application, FDA submission CTS 71903, Petitioner Buhler A. G, Representative Laboratory Fraunhofer Institute for Process Engineering and Packaging, Freising, Germany, Petition to the FDA, 2000. 

Polyethylene terephthalate (PET) is a copolymer of ethylene glycol with either terephthalic acid or dimethyl terephthalate. PET is used in packaging applications for soft drinks and mineral water, and for the bottles that are collected by curbside or deposit systems. As it does not thermally deform below about 220° C, PET is also used for trays and dishes for microwave and conventional cooking. 

International Life Sciences Institute (2000). Report on Packaging Materials 1. Polyethylene terephthalate (PET) for food packaging applications. ILSI Europe Packaging Material Task Force, Brussels. 

Terephthalic acid and dimethyl terephthalate are used to produce polyester fibers, polyester resins, and polyester film. Terephthalic acid or dimethyl terephthalate is usually reacted with ethylene glycol to give polyethylene terephthalate) but sometimes it is combined with 1,4-butanediol to yield poly (butylene terephthalale). Polyester fibers are used in the textile industry. Films find applications as magnetic tapes, electrical insulation, photographic film, packaging, and polyester bottles. 

Regioselective dialkylation of naphthalene is another reaction of considerable interest as 2,6-dialkylnaphthalenes can be oxidised to naphthalene-2,6-dicarboxylic acid, which is used in the synthesis of the commercially valuable polymer, poly(ethylene naphthalenedicarboxylate) (PEN).22 PEN has properties that are generally superior to those of polyethylene terephthalate) (PET) and has become the polymer of choice for a variety of applications such as in films, industrial fibres, packaging, liquid crystalline polymers, coatings, inks and adhesives. However, the high cost of naphthalenedicarboxylic acid has been a major hindrance to widespread application. 

R. FRANZ, F. BAYER, F. WELLE, Guidance and criteria for safe recycling of post consumer polyethylene terephthalate (PET) into new food packaging applications, EU Report 21155, ISBN 92-894-6776-2, Office for Official Publications of the European Communities, Luxembourg, 2004. 

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. 

Although the possible number of polymers is theoretically limitless, the economics of their production and processing, as well as the physical and chemical properties they have, restrict the number of commercial importance to a few dozen (see Fig. 2.2), and in packaging applications the number of polymers used is even smaller. The polymers most commonly used in packaging are polyolefins, specifically polyethylene and polypropylene. Polystyrene, polyvinyl chloride, and polyethylene terephthalate (PET) are also among the most commonly used packaging polymers. 

Polystyrene films and polyester (polyethylene terephthalate) films are only used in the biaxially stretched form, because unstretched films are very weak and brittle. To a lesser extent this is also true for polypropylene films. Roll-quenched flat film is used for many packaging applications, but below 0°C these films become brittle. Biaxially oriented polypropylene film, on the other hand, is not brittle at a temperature as low as — 50°C and is suitable for packaging frozen foods. 

Isotropic PHB foils possess excellent barrier properties against gas permeation. This is the rationale for potential applications in packaging, especially for food. The substitution of polyethylene terephthalate (PET) for bottle production seems to be especially attractive, considering the volume of PET waste. Another option consists in the modification of paper since paper/poly(HB-c<7-HV) foils are completely biodegradable, unlike paper coated with conventional foils [212]. The simplest apphcation is in containers, plastic bags and foils, commonly produced... 

The major plastic resins used in packaging are high-density polyethylene, low-density and Unear low-density polyethylene, polyethylene terephthalate, polypropylene, polystyrene, and polyvinyl chloride. A variety of plastics are used in lesser quantities nylons or polyamides, polycarbonate, polyethylene naphthalate, polyvinyhdene chloride, ethylene vinyl alcohol, polyvinyl alcohol, polyvinyl acetate, polyacrylonitrile, and more. In many applications, copolymers... 

Consumption of virgin polyethylene terephthalate (PET) resin in the United States and Canada totaled 5110 million pounds in 2000 [3]. Bottles were by far the largest application (Fig. 4.8). Soft drink bottles continue to be the largest use for PET bottles, but other applications (custom bottles) have been growing at a much faster rate for the past several years. According to EPA estimates, soft drink bottles accounted for 49.4% of all PET packaging in U.S. municipal solid waste in 1998, and 53.2% of all PET containers in municipal solid waste [1]. 

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