TABLE OF CONTENTS A very popular method of estimating antioxidants in polymer extracts is by coupling or oxidising them to form coloured products and measuring the result ing absorbance in the visible region of the spectrum. This technique is not particularly specific for individual antioxidants, but is specific for phenolic antioxidants in general (also amine antioxidants), and hence can often be applied without interference from other types of polymer additives.
Meyer [77] described a quantitative method for estimating hydroxy toluene (BHT) involving a colour-forming reaction with 2,6-dichloro- p-benzoquinone-4-chloramine. Glavind [78] and Blois [79] have devised methods for estimating total antioxidants, irrespective of type, by coupling them with the free radical ?, ? ?-diphenyl- ?-picrylhydrazyl. The decrease in absorption of the reagent solution upon mixing with the polymer extract is related to the amount of antioxidant present.
Stafford [69] has described a procedure for the determination of Ionol (2,6-di- tert-butyl- p-cresol), in polyolefins, involving refluxing the polymer with cyclohexane for 30 minutes followed by oxidation in potassium hydroxide-saturated isopropanol to produce a colour which is evaluated spectroscopically.
An early British Standard method for estimating the total phenolic antioxidant content of PE involves a preliminary extraction of the polymer with hot toluene to extract the additive, followed by addition of ethanol to precipitate any dissolved polymer, then coupling the extract with diazotised sulfanilic acid to produce a colour which can be compared with standards by visible...
