Knowledge of the history of plastics provides useful background to their identification. Mossman (1988) and Braun (1986) provide simple tests for identifying plastics primarily based on solubility, heating and flame tests although additives for plastics are likely to modify test results (Gächter and Müller, 1985). The identification of additives in many instances can be carried out using methods described elsewhere in this chapter, however some additives are extremely difficult to identify directly and can only be inferred by the modification of properties from pure polymer or by sophisticated instrumental analytical techniques.
The increased complexity of polymeric materials has made their positive identification correspondingly more difficult. Lebeaux (1989) has published a book known as the Resinkit that contains fifty samples of common plastics along with simple tests for identifying unknown plastics and comparing them to standards. This kit is helpful for observing the range of physico-mechanical properties of commercial polymers. Urbanski et al. (1977) provides more advanced methods for identifying plastics. Though some methods require sample amounts that may prohibit their use in conservation, the use of silicon carbide sampling of materials for examination by Fourier Transform Infra Red (FTIR) spectroscopy, as described by Martin (1988), is virtually non-destructive. FTIR microscopy is now becoming more generally available. Spectroscopic methods are further discussed by King (1992). Blank (1988) provides some simple tests relevant to conservation issues to help identify classes of polymers in order to determine proper consolidants and storage methods. Further information on the characterization of polymers is given by Campbell and White (1989) and by Hunt and James (1992). The identification of polymers used as coatings and media, adhesives and consolidants is discussed in section 4.8 below.
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