Oxidation of ultra high molecular weight polyethylene (UHMWPE) part 2: Critical examination of the total luminescence intensity (TLI) method for determining hydroperoxides

The validity of the total luminescence intensity (TLI) method for determining the amount of hydroperoxides in a UHMWPE sample has been assessed. Measurements of hydroperoxides with FTIR before and after a TLI run showed that only about 50% of the hydroperoxides were decomposed at 150 °C. It was also found that this value was not constant with ageing time, which means that the TLI value could not be representative of the total number of hydroperoxides in a sample as a function of ageing time. Thermoluminescence was also found to complicate the measurements and could, if care was not taken, give TLI values that were much too high. In addition it was found that the TLI value is actually connected with the build-up of carbonyls rather than the build-up of hydroperoxides. This last finding is consistent with part one of this study, where it was reported that CL from oxidising UHMWPE is a type of activated CL, where carbonyls are the activating species. From all of these results it is concluded that TLI is not a suitable method for determining hydroperoxides in UHMWPE.