Degradation studies of crosslinked polyethylene. 1, Aged in air

Silane crosslinking of polyethylene, carried out by grafting an organofunctional silane (vinyltrimethoxysilane) onto polyethylene and by subsequent moisture crosslinking in hot water using a tin catalyst, has been widely used in industrial applications because of its advantages in terms of low cost and easy processing. This study focused on the degradation processes which occurred in the material after air ageing in an oven; temperatures ranged from 90 to 220°C, while ageing times ranged from 2h to 500h. Significant structural changes were observed according to the different ageing conditions (below and above the melting region of the material), since the carbonyl group concentration increased substantially during ageing above the melting region and the silicone containing groups were also affected by the degradation. These structural changes affected the mechanical and thermal properties of the material, which was annealed at lower ageing temperatures (up to 155°C) and highly degraded at higher temperatures, when C-C crosslinks formed. Experimental design software was used in order to optimise the number of experimental trials and to model the results obtained; its analysis contributed to the interpretation of the results.