Thesis Details

Thesis Title: An Analysis of Thermo-oxidative and Hydrolytic Degradation of Uncoated Polyester and Nylon 6,6 Air Bag Fabrics and Yarns
Thesis Author: A. Hardy Sullivan
Abstract: An estimated forty-one million air bag units will be sold annually by 1996. Currently, nylon 6,6 is the dominant fiber type with over ninety-five percent of the air bag fiber market. Polyester has been introduced as an alternative fiber type and could provide cost savings if shown to meet end-use requirements. Passenger vehicles may be exposed to an infinite number of environmental conditions, requiring air bags to function in the most extreme conditions. In addition, the air bag may be required to function several years after its actual installation. In determining whether a material is suited for long-term demands, empirical studies measuring each material's reliability and performance are needed. This research was designed to evaluate the performance of uncoated nylon 6,6 and polyester (calendered and uncalendered) air bag fabrics. A variety of fabric, yarn, and polymer properties were analyzed following up to 17 weeks of exposure to combinations of 60 and 85°C with 45 and 90 % relative humidity. An air bag module assembler reported the maximum temperature it recorded in a passenger-side module was 75°C with low relative humidity. In addition, fabrics were tested after 28 weeks of real-time aging at South Florida Test Service. The effects of folds and pressure on air bag fabrics after 8.5 weeks of 85°C and 90% RH were also evaluated. Seventeen weeks of exposure to 60°C and 45 or 90 % RH did not affect the morphological or physical properties of nylon 6,6, uncalendered polyester, or calendered polyester yarns and fabrics. Similarly, no changes in grab tensile strength or elongation were detected following 28 weeks of aging at SFTS in Miami, FL under real-time conditions. Generally speaking, changes in nylon 6,6 fabric properties were influenced more by humidity than by temperature. When exposed to an environment with high humidity.nylon 6,6's moisture content increased,-swelling the yams enough to influence properties such as tongue tear strength, fabric stiffness, and air permeability at low air pressure. Hydrolytic and thermo-oxidative degradation of polyester yams and fabrics were detected after 8.5 weeks of exposure to 85°C. Grab tensile, bursting, and tongue tear strengths decreased substantially after 17 weeks at 85°C and 90% RH. In addition to reductions in fabric strength and elongation, microstructural properties were analyzed. The sustainable advantages over time of calendered fabric over uncalendered fabric were that the fabric was thinner and stronger in most cases due to the fabrics greater weight per unit area. The disadvantages of calendered fabric were it was heavier than uncalendered fabric, added an additional process, resulted in a fabric with slightly lower strength and elongation, and did not have lower permeability than uncalendered fabric at high air pressure. After 8.5 weeks of 85°C and 90% RH, no significant changes in fabric grab strength or elongation were attributed to the application of 3 pounds per square inch on folded samples.