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Cross-linked polyethylene consists of a resin in which a substantial proportion of the chains are chemically bound together to form an insoluble network. The aim of cross-linking is to prevent the slippage of noncrystalline chain segments past one another. Cross-linking aids dimensional stability at temperatures in excess of the crystalline melting point and reduces creep and stress cracking. The properties relevant to the typical end use of such a material principally depend upon the proportion of the sample making up the network and the concentration of cross-linking sites that bind neighboring chains together. Gel content analysis addresses the first of these concerns, and swelling in hot solvent the second. For

mostcommercialpurposesthesetestsareusedtoensurethatsufficientcrosslinkinghasoccurredfortheendproducttomeetitsservicerequirements

1.GelContentAnalysis Thegoalofgelcontentanalysis(GCA)istoascertainwhatproportionofacrosslinkedsampleisboundintoaninsolublenetwork.Thisisdeterminedbyextractingaspecimeninahotsolventforaspecifiedperiodoftimeandmeasuring itsweightloss.Suchtestsareoftenusedtodeterminewhetherthecross-linking reactionhasoccurreduniformlythroughoutthesample.Theyarealsoused routinelyduringthedevelopmentofnewproductgradesandprocessingconditions.Astandardprocedurewherebythismeasurementcanbemadeisfound inASTMMethodD2765.Variationsonthisprocedureaboundinthescientific literature.