History of the Irradiation Cross-Linking of Polyethylene

The formation of covalent C-C bonds or cross-links between the long chains in polyethylene (PE) by means of high energy irradiation was first deduced from changes in the stress-strain curves of the PE samples after irradiations in vacuo in the heavy water pile of the Argonne National Laboratory near Chicago in the academic year 1947-48. These cross-links can be produced in the solid sample at room temperature without change of shape of the sample. Such irradiated PE samples have a “memory effect” which has led to a large-scale application of the irradiation of PE to make heat shrinkable films and tubing.