Rigid Plastic

Rigid plastic packaging consumes around 6 million tonnes of plastic per year in Western Europe alone. This figure is even higher in the US with a value in excess of US$6.5 billion. It includes bottles, jars, tubs, buckets, pails and larger items such as pallets and drums.

Many polymer types are used in plastic packaging from the primary polymers such as low density polyethylene, high density polyethylene, polystyrene, polyvinyl chloride and polypropylene, with polyethylene terephthalate (PET) now also taking a major role, to high barrier polymers. The latter are used in much smaller quantities, but provide vital protection in packaging, either for the polymer or for the packaging contents. Barrier polymers include polyamide, ethylene-vinyl alcohol copolymer and thermoplastic epoxies. These are applied as additional layers in multilayer constructions using a variety of processes. Silicon oxide and carbon have also been used as barrier coatings, and can be applied in different ways. Fluorination of HDPE is used to improve the solvent barrier properties of this polymer.

Plastic containers can be manufactured using the spectrum of processes available to the plastics industry: extrusion and co-extrusion; thermoforming; injection molding and multimaterial injection molding, with in-mold labellings: injection blow molding; and injection-stretch blow moulding. These processing methods are described briefly in the review with an overview of each type accompanied by a discussion of forthcoming developments.

Many requirements are placed on packaging materials. They must withstand handling and abuse. They must also protect their contents and not affect them. For example, some food containers must withstand freezer to oven use and not alter the taste or chemical content of the food. Special grades of PET have been developed for such applications. Different materials and material combinations are used to obtain the ideal packaging product. The properties of the different polymers and polymer grades related to packaging applications are discussed here.

One of the key challenges this century has been to find an adequate way of packaging beer in plastic. Issues include the need to limit gas diffusion and to design a product that is acceptable to beer drinkers. Carbonated drinks have also proven difficult to package in plastic. PET bottles can be formed which address many of the issues, but further developments are still required.