Effects of stress and sulfur dioxide on Spectra®

Abstract

Polymers are often subjected to aggressive environments where mechanical and chemical mechanisms may act synergistically to degrade the polymers. This research focused on the effects of stress and sulfur dioxide (SO2) environments on ultrahigh molecular weight polyethylene (UHMWPE) fibers (Spectra®). Spectra® yarn specimens were exposed to stress, SO2, and/or near ultraviolet (UV) light environments. Degradation, a decrease in tensile properties, was measured by tensile testing specimens immediately after exposure to the stress/environment conditions. Creep lifetime degradation of Spectra® single fiber specimens was also measured in SO2 and/or near UV light environments. The Spectra® fibers were found to degrade due to the applied stress. This was evidenced by a decrease in the ultimate strength subsequent to an applied creep load and the short creep lifetimes. No chemical degradation was observed, nor were any mechanical–chemical synergisms observed due to the SO2 and/or near UV light environments. The creep lifetimes of the Spectra® fibers, however, increased slightly in environments of SO2 and/or near UV light. The degradation of the Spectra® fibers is consistent with their fibrillar morphology and was attributed to chain scission of the interfibrillar tie chains due to the applied creep load. Since no degradation of the Spectra® was observed in the SO2 and/or near UV light environments, it was concluded that it is relatively insensitive to environmental attack from SO2 and/or near UV light. The increase in the creep lifetimes of the Spectra® fibers suggests that the SO2 and/or near UV light does affect the Spectra® fibers. Based on this and the work of other researchers, it is hypothesized that the SO2 and/or near UV light are, to a limited extent, capable of crosslinking or branching linear polyethylene molecules. Such crosslinking or branching appears to be minimal, altering only the creep lifetimes and leaving the other tensile properties largely unaffected.