New insights in the peroxide crosslinking mechanism of polyethylene

In general the peroxide crosslinking mechanism of polyethylene is believed to be quite simple. However, different structural parameters may have a great influence. In this work the effect of pendant vinyl groups and long chain branching are discussed. The network formed is denser than what can be expected which is explained by the presence of trapped entanglements, i.e. physical crosslinking points. It turned out that the trapped entanglements constitute the major part of all the crosslinking points formed, about 60%. A higher 'quality' network is formed in the vinyl containing material due to the extra number of crosslinking points generated by the reaction of the vinyl groups. That network gives also a smaller deviation from a linear response when tested with different loads as the physical crosslinking points present are more permanent, i.e. there is less chain slippage under load. In contrast, an increased number of long chain branches gives more intramolecular crosslinking points, resulting in a less efficient network.