Examining impact of vapor-induced crosslinking duration on dynamic mechanical and static mechanical characteristics of silane-water crosslinked polyethylene compound

Silane-crosslinked polyethylene (Si-XLPE) compounds are widely used cable insulation materials, cured by water as the crosslinking inducer. Herein, an attempt was made to evaluate the alterations of dynamic mechanical and static mechanical properties of Si-XLPE by increasing the water vapor-triggered crosslinking duration. The criterion for determining the progress of crosslinking was based on an industrially-used method (hot set test), and results indicated 16 h of vapor exposure as an appropriate duration for approaching maximum attainable crosslinking extent. Progress in crosslinking during this period was confirmed by FTIR spectroscopy. DMA was employed to assess the variations of dynamic mechanical behavior. Extending the crosslinking duration affected the storage modulus noticeably, and decreased it due to adverse effect of crosslinking on crystallinity. DSC confirmed the diminishment of crystallinity owing to the extended crosslinking time. Furthermore, prolonged vapor exposure period impacted β and γ transitions due to the influence of formed crosslinks on the mobility of chains. Tensile testing was carried out to ascertain the static mechanical characteristics of crosslinked samples. Findings demonstrated that tensile strength at yield increased below 5%, and tensile stress at break grew around 17%. Besides, elongation and Young's modulus experienced nonmonotonic changes due to the lengthened crosslinking period.