Stabilization of peroxide crosslinked polyethylene

Abstract

In peroxide crosslinked low density polyethylene for wire and cable applications there is a critical balance between the additives. Normally dicumyl peroxide is applied as the crosslinking agent and stabilizers are needed towards thermo-oxidative degradation as described by existing specifications. In addition, the phenomenon known as premature crosslinking, referred to as “scorch”, demands that a certain amount of a phenolic stabilizer deactivates radicals formed during the extrusion step. The aim of this study was to correlate the structure of different phenolic compounds to their capability to react with radicals formed during the extrusion, which would give information in design of new compounds for which scorch properties are of importance. This work shows that the less hindered the phenol is, the more it can contribute to the improvement of the scorch behavior. On the other hand, a good stabilizing effect can only be achieved with hindered phenols together with a secondary stabilizer. Since there is a limit to the absolute amount of additives in LDPE also the molar weight of the additives as well as the number of active groups are crucial for the overall performance of the cable compound. The balance between the different additives to achieve a technically reliable solution is discussed.