The effect of the processing steps on the oxidative stability of polyethylene tubing crosslinked by irradiation

Abstract

Some chemical and mechanical properties of intermediate products obtained in the production of PE heat shrinkable tubes were studied, seeking correlations between the composition and the properties. Different PE granulates were mixed with antioxidant (amine or phenol derivative), flame retardant agent and, for some samples, with elastomer. The compounds were extruded to tubes, which were then crosslinked by electron beam irradiation and subsequently extended to twice the original diameter.In the course of the production phases, the themooxidative stability decreased compared to that of compounded granulate. The greatest decrease was caused by the irradiation. The aromatic amine seems to be the more effective antioxidant at similar compositions than the phenol derivative and it shows a better resistance against irradiation. The oxidative stability of the finished shrinkable tubes was not affected by the quality of commercial granulate (initial polyethylene).Mechanical properties changed slightly upon ageing, and the introduction of the elastomer did not alter the tensile strength and elongation at break. The remaining stability of the end-product was more than enough to bear the stress of shrinking in use, and the good tensile strength of the material did not decrease upon thermal ageing either.During extrusion of the granulated compound no significant change took place in the distribution and molar mass averages. Irradiation produced more than 50 % insoluble fraction, and the themooxidative properties of the crosslinked sample changed significantly compared to the original PE and to the compound prepared from it.