Determination of spatial distribution of oxidation products in ultra-high molecular weight polyethylene by staining with sulphur dioxide or hydrochloric acid

The true nature of the browning has been difficult to establish, but it seems to originate from a charge transfer complex between the double bonds and the sulphuric acid. A similar type of coloration develops in oxidised UHMWPE, when it is treated with hot hydrochloric acid. However, in that case the coloration is proportional to the carbonyl concentration and has been concluded to originate from the oxonium ion formed by protonation of ketones. The coloration of both SO2/heat-treated samples and samples treated with hot hydrochloric acid can be used to give a qualitative picture of the spatial distribution of oxidation in UHMWPE. The techniques have been applied to study the heterogeneous oxidation in badly consolidated UHMWPE. It was found that the very good spatial resolution gave information about the heterogeneous oxidation that is not possible to obtain when using other techniques, such as FTIR mapping and imaging chemiluminescence.