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Effect of Moisture on Copolymer Fibers based on 5-amino-2-(p-aminophenyl)-benzimidazole



Guillaume Messin, Stephanie S. Watson, Amanda L. Forster, John R. Sieber


In recent years, there has been concern in the soft body armor community 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. In an effort to examine this issue, a study was designed to investigate the generation of acid in different environments from these fibers. During the first phase of the study, fibers were exposed to water and pH decreases were observed. While submerged into deionized water, two of the fiber samples studied released a sufficient amount of acid to drop the pH of the solution from approximately pH 6.0 to approximately pH 3.0 in less than ten days. Further ion-selective electrode studies of chloride ion released from these fibers indicated that hydrochloric acid may not be the species responsible for this pH reduction. In a second phase of the investigation, fibers were exposed to water vapor in an elevated temperature environment. While the pH reduction generated by the water vapor exposure was substantially lower than observed in the submersion phase of the study, a reduction in the yarn tensile strength of some of the fibers was observed during this phase of the study. In a third phase, fibers were exposed to an elevated temperature and low relative humidity. Almost no pH reduction or strength reduction were observed. Molecular spectroscopy was also performed to better understand the effect of elevated temperature and moisture environments on these fibers.
Polymer Degradation and Stability


Acid generation, body armor, copolymer fibers, degradation, moisture, 5-amino-2-(p-aminophenyl)-benzimidazole


Messin, G. , Watson, S. , Forster, A. and Sieber, J. (2011), Effect of Moisture on Copolymer Fibers based on 5-amino-2-(p-aminophenyl)-benzimidazole, Polymer Degradation and Stability, [online],,2011.07.008, (Accessed May 26, 2024)


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Created October 4, 2011, Updated September 9, 2019