Radiation processing of polyethylene

The structure-property relationships of low density polyethylenes and ethylene-vinyl acetate copolymers used in film forming processes, particularly extrusion coating and heavy-duty film, are discussed together with the influence these structural parameters have on crosslinking by high energy radiation. Films were irradiated with doses ranging from those sufficient for sterilization (2.5 Mrad) to those sufficient to develop optimum physical properties (approximately 15 Mrads). The tensile strength, elongation, stiffness, tear strength and density were the physical properties least affected by crosslinking, whereas the impact strength showed the expected dramatic improvement. The density and n-heptane extractables content were unaffected over the dose range 0 to 15 Mrads and since density and MVTR are directly related, it is thought that MVTR also remains constant. Most importantly, the heat sealability of these materials was unaffected or enhanced after irradiation. This is attributed to the unique structural characteristics of the resins. This applies especially to the USI heavy duty films which showed enhanced sealability even after exposure to 15 Mrads of radiation. Crosslinking expands the applications for heavy duty polyethylene film and can result in significant cost savings when compared with non-crosslinked film employed in the same application. (author)