Effects of stress and sulfur dioxide on Spectra (R)

Polymers are often subjected to aggressive environments where mechanical an d chemical mechanisms may act synergistically to degrade the polymers. This research focused on the effects of stress and sulfur dioxide (SO2) environ ments on ultrahigh molecular weight poly ethylene (UHMWPE) fibers (Spectra( R)). Spectra(R) yam specimens were exposed to stress, SO2, and/or near ultr aviolet (UV) light environments. Degradation, a decrease in tensile propert ies, was measured by tensile testing specimens immediately after exposure t o the stress/environment conditions. Creep lifetime degradation of Spectra( R) single fiber specimens was also measured in SO2 and/or near UV light env ironments. The Spectra(R) fibers were found to degrade due to the applied s tress. This was evidenced by a decrease in the ultimate strength subsequent to an applied creep load and the short creep lifetimes. No chemical degrad ation was observed, nor were any mechanical-chemical synergisms observed du e to the SO2 and/or near UV light environments. The creep lifetimes of the Spectra(R) fibers, however, increased slightly in environments of SO2 and/o r near UV light. The degradation of the Spectra(R) fibers is consistent wit h their fibrillar morphology and was attributed to chain scission of the in terfibrillar tie chains due to the applied creep load. Since no degradation of the Spectra(R) was observed in the SO2 and/or near UV light environment s, it was concluded that it is relatively insensitive to environmental atta ck from SO2 and/or near UV light. The increase in the creep lifetimes of th e Spectra fibers suggests that the SO2 and/or near UV light does affect the Spectra(R) 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, ca pable of crosslinking or branching linear polyethylene molecules. Such cros slinking or branching appears to be minimal, altering only the creep lifeti mes and leaving the other tensile properties largely unaffected. (C) 2000 E lsevier Science Ltd. All rights reserved.