HPSEC Analysis of Ester-Based Polyurethane Rubber Materials

Abstract : The work described in this report contributes to a larger study conducted by the U.S. Army Tank-automotive and Armaments Command (TACOM) at Picatinny Arsenal, NJ, to evaluate the environmental and operational stability of candidate commercial polyester-polyurethane rubber materials for possible fuel bladder and containment applications. High-performance size-exclusion chromatography (HPSEC) techniques are employed to analyze and help understand the effects of accelerated environmental exposure on the average molecular weights (MW) and molecular weight distributions (MWD) of the rubber in selected test specimens. A special test method and sample preparation procedures to extract and isolate the soluble polymer in test specimens from coating, interlayer, fabric, and carbon reinforcement components are described. HPSEC separates polymer molecules according to their relative "sizes" in solution and therefore is very useful in studying rubber reversion and estimating the extent of polymer degradation due to chain scission processes. Exposure to elevated temperature and moisture content (percent relative humidity) accelerate sample degradation. As the aging time and severity of aging conditions increase, gel formed during the early stages of exposure disappears and the MW of soluble materials continues to decrease. The chemical mechanism for polymer chain degradation and possible cause and consequences of the gelation effect are discussed.