Analysis of Polymer Extraction Liquids Containing More Than One Migrant

Analysis of Polymer Extraction Liquids Containing More Than One Migrant 

Polymer formulations usually include one or more compounds such as antioxidants, secondary antioxidants, antistatic additives, light stabilisers, lubricants, plasticisers, stabilisers, slip and antiblock agents. In addition, the polymer and hence the extractant liquid might contain other substances not deliberately added such as unreacted monomers, residual polymerisation solvents and catalysts. The result is that practical extractants from such plastics can contain very low concentrations of several very different types of substances which may or may not mutually interfere with each other during these subsequent analyses and one or more of which it may be necessary to determine. 

The problem resolves itself into three stages. Firstly, the additives must be extracted from the extraction liquid in the form of an extract which is suitable for subsequent analysis. Frequently, extraction with diethyl ether or another low boiling organic solvent will achieve the required separation, certainly in the case of the aqueous and simple hydrocarbon polymer extractants. In addition to isolating the additives in the form of a suitable extract, this process will achieve a useful concentration factor of up to 100 fold in the level of additives present in the extract. Secondly, it is usually necessary to separate in this extract the additive or additives which it is required to determine from those for which analysis is not required, in order to avoid any analytical interference effects. Techniques such as thin-layer or column chromatography are particularly useful in this respect and are discussed in further detail next. 

If it is required to ascertain the extent to which such hydrolysis of the additive has occured then, again, chromatographic techniques are amenable to the determination in the extractant of both the unchanged additive (RC0N(CH2CH20H)2) and its hydrolysis product (RCOOH). 

Finally, having extracted total additives from the extraction liquid and, if necessary, separated these into individual fractions by chromatography it is necessary to apply appropriate analytical techniques of sufficient sensitivity to the determination of the individnal additives. 

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