Overview

The reader is referred to Sections 3.18.1 and 3.18.2, which are also relevant to the discussion of additives.

The numerous and diverse applications of polyethylene (PE) would not be possible without the development of suitable additives. Additives are used for the preservation of some properties (stabilisation against the action of heat, oxygen, light, and so on), to facilitate the processing of different items, and/or for the modification of some properties for special purposes. Usually, the first two objectives must be considered and fulfilled concomitantly, and therefore complex systems of additives (antioxidants, light stabiliser mixtures, or complex formulations) are used. As PE degradation may occur at every stage, it is advisable to add some kind of stabilisation as early as possible, even in the polymerisation process, or to add the antioxidant before the polymer comes into contact with air. In drying, palletising, or processing operations the masterbatches are preferred as powder or as master fluff. Crosslinking agents are applied in phlegmatised form, pre-blended with mineral fillers or extender oil and sometimes with stabilisers. Such mixtures facilitate peroxide handling. Some additives used in PE formulations may play a multiple role sometimes they can even have a negative effect. For example, many pigments act as photostabilisers, the protective action against light being fulfilled by the coloured pigments, while white pigments such as the anatase form of titanium dioxide act as photosensitisers. The choice of a suitable additive for a particular use is very important, as it involves knowledge of the behaviour of...