Kinetics for the tensile strength degradation of nylon and kevlar yarns

Abstract

SynopsisThe tensile strength degradation of nylon 66 and Kevlar 29 yarns was studied. at elevated temperatures and over a broad range of relative humidities. The degradation rates for nylon are initially slow but increase rapidly, suggesting the depletion of an inhibitor. Kevlar showed no evidence for similar inhibitor action. The effect of relative humidity on degradation can be very large, especially at values in the 9C-100% range and at elevated temperatures. Degradation is governed by thermal-oxidative and moisture-induced mechanisms. At the very high humidities and elevated temperatures, the moisture-induced degradation predominates. Rate relationships were developed in which contributions from each mechanism were considered. Calculated degradation from these relationships agrees well with observed degradation over a broad range of temperatures and humidities.

Influence of Hydrolytic and Chemical Treatment on the Mechanical Properties of Aramid and Copolyaramid Fibers

“…Several authors have discussed the underlying process of degradation [ 2,3,8,111. Auerbach [ 1 ] proposed a second order process and also considered the additional influence of an inhibitor at the beginning of degradation. He deduced the following equations in an integrated form:…”

Influence of finish treatment on the durability of aramid fibers aged under an alkaline environment

“…Twaron and Technora fibers both contain amide functions that are sensitive to hydrolysis 4,5 ; although, Imuro and Yoshida 6 reported that the dilution of aramid-linkages by ether-linkages as in Technora fibers may contribute to provide the latter with better hydrolytic stability. The mechanism of PPTA hydrolysis has been identified and involves scission of the amide NAC linkage, yielding acid and amine functions 4,5 (Fig. 2).…”

Effect of elevated temperature and humidity on fibers based on 5-amino-2-(p-aminophenyl) benzimidazole (PBIA)

“…Attempts were made to fit the Auerbach [18] and Springer [19] degradation models to this strength data; however, the amount of degradation seen here is so minimal, and the failure distributions are so broad that a meaningful fit could not be obtained. Furthermore, there is no clear trend in the Weibull shape parameters for the strength, strain or modulus for all three materials.…”

“…Molecular spectroscopy was used to characterize chemical changes in the three fibers after ageing to determine what, if any, chemical changes occurred in the polymer. Two likely reactions that could occur in response to the hydrolytic environment are opening of the benzimidazole ring [39] and chain scission [16,18,19] at an amide bond. Schematics for these two potential reactions are presented for the fibers in Fig.…”

“…Significant efforts [12,17] have been focused on examining the long-term stability of polymeric fibers used in body armor, such as PPTA, by investigating detrimental changes in these mechanical properties after exposure to environmental conditions. For PPTA, Auerbach [18] performed an analysis of the chemical kinetics of aramid degradation. This work was performed in the context of predicting aramid and nylon parachute lifetimes, so in addition to temperature and humidity exposure, yarns were tightly knotted to mimic the folding within the parachutes.…”