A dual-layer urethane acrylate UV-cured coating is widely used to protect optical fibres because of its well-balanced mechanical properties, weathering resistance and rapid curing. The long-term mechanical behaviour of fibre coatings is important for the reliability of optical fibres. Long-term exposure of UV-cured polyether urethane acrylate films was carried out in dry air and in water at elevated temperatures. Tensile testing was performed to reveal changes in mechanical properties and dynamic mechanical analysis to determine both the glass transition temperature and the crosslink density. The equilibrium swelling allowed assessment of the crosslink density. Tensile testing and strip force measurements were performed on virgin and aged optical fibres. Initially the fracture strengths of the secondary coatings increased under all ageing conditions indicating post-curing reactions and the possible loss of uncrosslinked species. Ageing under wet conditions led at a later stage to hydrolytic degradation of the network and to a decrease in the fracture stress. The equilibrium swelling and equilibrium modulus measurements showed good correlation with the changes in strength. The primary coatings showed a decrease in mechanical strength after only 2-4 weeks under all conditions.
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