It is essential to understand the degradation rate and failure modes of armor constituent materials to enhance their reliability during their service period. Armor materials when exposed to humidified or oxidative environments, degradation in the polymeric chain is expected to cause major alterations in microstructural characteristics of its constituent components. As a result, tensile strength and modulus are considerably compromised and this leads to a significant loss in ballistic performance of body armors. Thus, an investigative study into hydrolytic aging and its effect on the mechanical properties of armor materials holds crucial importance which may act detrimental to the service life of soft armors. In this present work, PPTA yarns are considered for hydrolytic aging study due to their quick susceptibility to hydrolysis and reduction in mechanical strength upon humidity exposure. The humidified condition has been generated by exposing yarns into the humidity chamber controlled to 80oC and 85%RH i.e. the maximum limit of temperature and humidity a body armor can face. Tensile tests are performed on the yarns extracted at different times over 70 days of the total exposure period to determine breaking tenacity, modulus, and elongation at break as a function of time. The ballistic limit has been evaluated with the help of Cunniff relation and tensile parameters to determine the bullet penetration resistance of hydrolytically aged fibers. ATR-FTIR analyses of aged fibers reveal the presence of a new absorption band ascribed to the combination of amine N-H stretching and carboxylic acid O-H stretching at 3300 cm-1 due to the hydrolysis of the key amide linkage. Time-dependent microstructural changes confirm the major crystalline and inter-crystalline link breakage which may be primarily responsible for the mechanical and ballistic performance degradation.

It is essential to understand the degradation rate and failure modes of armor constituent materials to enhance their reliability during their service period. Armor materials when exposed to humidified or oxidative environments, degradation in the polymeric chain is expected to cause major alterations in microstructural characteristics of its constituent components. As a result, tensile strength and modulus are considerably compromised and this leads to a significant loss in ballistic performance of body armors. Thus, an investigative study into hydrolytic aging and its effect on the mechanical properties of armor materials holds crucial importance which may act detrimental to the service life of soft armors. In this present work, PPTA yarns are considered for hydrolytic aging study due to their quick susceptibility to hydrolysis and reduction in mechanical strength upon humidity exposure. The humidified condition has been generated by exposing yarns into the humidity chamber controlled to 80^o^C and 85%RH i.e. the maximum limit of temperature and humidity a body armor can face. Tensile tests are performed on the yarns extracted at different times over 70 days of the total exposure period to determine breaking tenacity, modulus, and elongation at break as a function of time. The ballistic limit has been evaluated with the help of Cunniff relation and tensile parameters to determine the bullet penetration resistance of hydrolytically aged fibers. ATR-FTIR analyses of aged fibers reveal the presence of a new absorption band ascribed to the combination of amine N-H stretching and carboxylic acid O-H stretching at 3300 cm-1 due to the hydrolysis of the key amide linkage. Time-dependent microstructural changes confirm the major crystalline and inter-crystalline link breakage which may be primarily responsible for the mechanical and ballistic performance degradation.

Influence of hydrolytic aging on the microstructural characteristics, mechanical and ballistic performance of PPTA fibers used in soft body armor

ACS Spring 2022

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