Determining the swelling behavior, mechanical, and thermal properties of Buna-N O-rings and polymer sheets after exposure to petroleum fuels, synthetic blending components, and pure components

This work explored the swelling behavior, tensile strength, hardness, and thermal properties of various Buna-N polymer sheets and O-rings with 14%, 30% and 40% acrylonitrile (ACN), hydrogenated (HNBR, 50% ACN), or unknown compositions [aerospace (AS) and military specification (MS)] after exposure to pure organic solvents, jet and diesel fuel, and six synthetic blending components (SBCs). Liquid systems with high aromatic composition induced the greatest swellings and losses of hardness and tensile strength, while some liquid systems lacking aromatic compounds induced shrinkage of the polymers. For some polymers, solvent evaporation induced shrinkage and increased hardness values compared to unexposed samples. Acetone-treatment of several samples extracted mass from each, producing materials that were more thermally stable and swelled more when exposed to fuels. These results suggest the removal of acetone-soluble components from the polymer and a possible rearrangement of polymer chains. The AS O-rings behaved similarly to the 14% ACN polymer in terms of swelling, tensile strength, and some differential scanning calorimetry (DSC) thermal features. The MS O-rings only matched the swelling of the 33% ACN O-rings. These data elucidating cause/effect relationships to fuel and polymer composition will help those exploring ways to enhance O-ring swelling induced by SBCs with low aromatic content.