Hydrolytic Stability of Polyurethane-Coated Fabrics Used for Collapsible Fuel Storage Containers

Collapsible fuel tanks fabricated from urethane-coated nylon fabric were first introduced by the military during the Vietnam conflict. Their performance then and until recently, particularly in any humid tropic environment, has been less than satisfactory. These urethane-based coatings were extremely susceptible to ultraviolet and hydrolytic degradation. Hydrolysis is a chemical reaction with water that chemically and structurally breaks down the urethane coating, resulting in cracking or extreme softening of the urethane polymer. Hydrolysis can be quite rapid in certain urethane systems. In this report, the hydrolytic stability of several currently manufactured urethane-coated fabrics used in collapsible fuel storage containers is investigated. We immerse these fabrics in water held at an elevated temperature of 180 F 81 C. The mechanical strengths were evaluated over several immersion times to assess the degree of hydrolysis occurring for each urethane-coated fabric. We also used Fourier transform infrared spectroscopy to follow the chemical changes occurring at the coated fabric surface. The results show that the coated fabrics available from Reliance and the Cooley TR 3186 and TR 3219 products performed very poorly in our testing. The Reliance fabric fell apart after only 42 days of water immersion, while the two Cooley fabrics fell apart after 70 days. The three materials available from Seaman performed very well, exhibiting minimal hydrolysis.