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Study of the Acid Generation in Aqueous Environments from Copolymer Fibers based on 5-amino-2-(p-aminophenyl)-benzimidazole



Amanda L. Forster, Guillaume Messin, Kirk D. Rice, Michael A. Riley, Stephanie S. Watson


In a communication to the ballistic vest community released in January 2006, there was an allegation by a competing fiber manufacturer that copolymer fibers based on 5-amino-2-(p-aminophenyl)-benzimidazole can release hydrochloric acid, which could potentially be detrimental to other fibers that might come in contact with these materials, or hazardous to an officer's health. Despite the fact that these allegations came from a competing manufacturer, due to recent issues with degradation of another fiber in field use, it was determined that an effort should be made to investigate this issue to determine if it was an officer safety issue. This study investigates the evolution of acid in aqueous environments from these fibers, reviews the available literature on the fibers, and provides an analysis of the chemical structure of these fibers to serve as the basis for future studies. It was determined that there is some truth to the allegations, two of the fiber samples studied emitted a sufficient amount of acid to drop the pH of an aqueous solution from approximately pH 6.0 to approximately pH 3.0 in less than ten days. Further studies of chlorine ion emission from these fibers indicated that hydrochloric acid may not be the species responsible for this pH reduction. Future studies are proposed to better elucidate the species responsible for this pH reduction and examine the effect of vapor moisture on the pH reduction of the fibers, as well as the effect of water vapor on the chemical and physical properties of these fibers.
NIST Interagency/Internal Report (NISTIR) - 7592
Report Number


acid evolution, ballistic fibers, ballistic materials, body armor, fiber, infrared analysis, polymer, weapons and protective systems


Forster, A. , Messin, G. , Rice, K. , Riley, M. and Watson, S. (2009), Study of the Acid Generation in Aqueous Environments from Copolymer Fibers based on 5-amino-2-(p-aminophenyl)-benzimidazole, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed May 21, 2024)


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Created September 1, 2009, Updated February 19, 2017