Overview

All polymers, in addition to the basic plastic, usually contain several, if not a multiplicity, of non-polymeric components in amounts from less than one part per million to several percent. The presence of these substances obviously have an implication in the suitabilities or otherwise of the plastic for applications involving contact with foodstuffs. Thus, although the plastic itself, due to its very high molecular weight, might not contaminate the foodstuff, it is apparent that certain additives, which are usually of relatively low molecular weight, and therefore of higher solubility, will be transferred from the plastic to the foodstuff during storage. This raises questions regarding the toxicity of the additives, the amounts which transfer and the possible implications of this, from the toxicity point of view, as far as the food consumer is concerned.

Non-polymeric components are present in plastics either unavoidably as a result of the process of manufacture, or as the result of deliberate additions to the plastic in order to improve some aspect of ease of manufacture or final polymer properties.

Thus, non-polymeric components can be subdivided into three groups:

• Polymerisation residues,

• Processing aids, and

• End-product additives.

Polymerisation residues cover substances whose presence is to a large extent unavoidable, such as low molecular weight polymers, oligomers, catalyst remnants, and polymerisation solvents. Raw material non-polymerisable impurities, are impurities picked up from plant materials. Processing aids include such substances as thermal antioxidants and heat stabilisers added to prevent decomposition of the polymer during moulding and slip...