Improving UV Resistance of High Strength Fibers

Abstract

High strength fibers such as Zylon®, Kevlar®, and Vectran® are characterized by their high strength to weight ratio. They are used to produce high performance products such as cables and ropes, preforms for composites, bulletproof vests, cut resistance articles, firefighter gear, airbags for passenger cars, and tendons for giant scientific balloons. This work starts with a discussion on the properties and uses of the above mentioned high strength fibers followed by a critical review of the published research in the area of UV degradation of textile structures made from different polymeric materials as well as high strength fibers. The physiochemical aspects of polymer photo degradation, the factors affecting polymer photo degradation, the experimental aspects of photo degradation, and the photo degradation of some commonly used polymers have been discussed. It was found in literature that high strength fibers degrade upon exposure to high energy UV radiation. This represents a serious impediment to the use of high strength fibers in a number of end uses where their high strength to weight ratio could be very advantageous. Finally a discussion on photo stabilization of polymers is also provided.

The overall goals of this research were to investigate options for the creation of techniques to improve the resistance of high strength fibers to UV and establish a better understanding of the mechanism of the UV instability for high strength fibers. In this work it has been shown that unprotected Zylon® and Vectran® yarns lose more than 70% of their strength after six days of UV exposure in an Atlas weatherometer, while Kevlar&$174; yarn loses more than 15% of its strength. From our work, the results of the effect of UV exposure time on the strength loss of high strength fibers, and the mechanism of strength loss for Zylon® yarn as a result of UV degradation have been reported. Characterizing techniques like X-ray diffraction, ATR-FTIR spectrophotometry, molecular weight measurements, and SEM micrographs have been used to understand the photo chemical phenomena taking place when this yarn is exposed to high energy UV radiation using an artificial light source.

Keywords: Ultraviolet degradation, ultraviolet resistance, high strength fibers, chemical coatings, sheathings.