Poly ethylene terephthalate Moulding Materials

In 1997 it was estimated that global production of PET was about 16.7 X 10 t.p.a., of which 12 million tonnes was used in textiles, 2 million tonnes for audio and video film (with a small quantity for technical mouldings) and 3 million tonnes for packaging, particularly bottles. The tremendous growth in the bottles market from zero in the late 1970s to 1.5 million tonnes in the USA alone in 1998 is, in consumption terms, one of the most spectacular examples of growth in plastics materials in recent times and will be considered later in this section. 

The moulding of Amite PETP must be carried out with dried material and because of the free-flowing nature of the melt, restricted nozzles should be used 

Crystalline, opaque, mouldings are produced by using a mould temperature of about 130°C and grades containing crystallisation accelerators . The crystalline grades retain their shape up to temperatures near to and therefore for many applications may be used above r . 

A further substantial development, although not on the scale of the bottle and film markets, had been the use of thermoformed PET sheet for menu trays. The high heat distortion temperature of 220°C allows these products to be used in both traditional and microwave ovens. 

As with many other plastics materials being manufactured in a large number of countries statistics for capacity and usage are subject to considerable uncertainty. One estimate was that in 1997 capacity for making container grades was about 6 000 000 t.p.a. with consumption at about 4 000 000 t.p.a. 

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Table 25.7 Some properties of poly(ethylene terephthalate) moulding material ( Amite ) (ASTM Test Methods unless otherwise stated.)...

Substantial quantities of UPVC are also used for blow moulded containers for such diverse materials as consumable liquids such as fruit squashes, liquids for household use such as detergents and disinfectants, cosmetics and toiletries, and pharmaceuticals. For most of these applications UPVC is in competition with at least one other polymer, particularly poly(ethylene) terephthalate (Chapter 25), polyethylene (Chapter 10), polypropylene (Chapter 11) and, to a small extent, the nitrile resins (Chapter 15). The net result is that in recent years there has been some replacement of PPVC in these areas, in part because of problems of waste disposal. 

In the late 1970s several developments occurred causing renewed interest in poly(ethylene terephthalate) as a plastics material. These included the development of a new mouldable grade by ICI (Melinar) and the development of a blow moulding technique to produce biaxially oriented PET bottles. In addition there appeared a glass-fibre filled, ionomer nucleated, dibenzoate plasticised material by Du Pont (Rynite) (see Chapter 26). 

Glass-filled, toughened poly(ethylene terephthalate) (PET) resins can be readily moulded into highly impact-resistant structural parts for appliances and automotive components. The PET-based compounds are also suitable for construction (e.g. as structural members), equipment housings (e.g. printer and copier parts), agricultural applications (e.g. mower and tractor engine covers), materials handling (e.g. pallets and ttays), furniture (e.g. office chair bases), as well as electrical and electronic applications. 

Polyester polymers are materials which exhibit various chemistries but all contain ester linkages in the polymer chain. They have attained industrial importance as moulded materials, fibres, packaging film and as structural materials which are reinforced with fibres and fillers. Chemists, John Rex Whinfield and James Tennant Dickson, employees of the Calico Printer s Association of Manchester, patented polyethylene terephthalate in 1941, after advancing the early research of Wallace Carothers. Poly (ethylene terephthalate) is the basis of polyester fibres and fizzy drinks botdes. The first polyester fibre known as Terylene was also developed in 1941. 

The versatility of polymers, already commented on, must be taken to apply not only to these materials as a class, but also to many of its individual members. Poly(ethylene terephthalate) (PET), for instance, is used not only as a textile fibre but also as a packaging material in the form of both film and bottles. Poly(vinyl chloride) (PVC) is used not only as a rigid material for making mouldings but also, in plasticised form, for making flexible tubing and artificial leather. 

The major commercial interest continues to be centred on poly(ethylene terephthalate) 2GT and its use in fibres, films, and as a moulding material. Poly(tetramethylene terephthalate) 4GT has, however, found use recently as a moulding compound, and the lower members of the aliphatic series continue to find use in urethane technology. 

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