A rubber can be defined as a polymeric material which, above its glass transition temperature, can be stretched repeatedly to at least twice its original length and, on release of the stress, rapidly returns to its original length. These properties are brought about by a combination of the chemical structure of the polymer backbone and the vulcanisation process which results in the formation of a lightly crosslinked three-dimensional matrix.

Thermoplastic rubbers also fall within the scope of this review report. These are a group of polymers that are similar to vulcanised rubbers in resilience and rapid recovery, but can be repeatedly softened by heating (i.e., are thermoplastic) to enable processing, and regain their elastomeric character on cooling to room temperature. There is also a sub-set of materials named thermoplastic vulcanisates (TPVs) in which the rubber phase within the material is crosslinked, but this is done at the polymerisation stage, and these materials do not undergo a vulcanisation step.

In contrast to plastics, rubbers are rarely used in the packaging of food products. Examples where they are found include: the use of rubber seals in flip top stoppers on beer bottles, rubber seals used in some jar tops (e.g., paste containers), and the seal that is present in the ends of food cans. However, in the processing of food, there are a number of situations where significant contact of the food with rubber products can occur. This is due to the fact that the unique properties of rubber lead to it...