The effects of environmental conditioning on tensile properties of high performance aramid fibers at near-ambient temperatures

Abstract

Aramid and aramid copolymer fibers are used in a wide variety of military and civilian applications; however, the long-term effects of environmental exposure on tensile properties are still not well understood. The current effort investigates the effect of hygrothermal conditioning on the tensile properties of Kevlar® KM2 ®, Twaron®, and the newly available Russian copolymer, Armos® high performance fibers. Moisture uptake studies show that at room temperature, water diffuses more slowly into the copolymer Armos ® (D = 8.7 × 10-13 cm2/s) compared to the Kevlar® KM2® and Twaron® homopolymers (D = 2.16 × 10-12 cm2/s and D = 1.8 × 10 -12 cm2/s, respectively). Tensile properties have been measured for these aramid fibers that have been conditioned in water at 40°C, 60°C, 80°C, and 100°C for periods of 17 and 34 days. For both aramid and aramid copolymer fibers, hygrothermal conditioning did not significantly change fiber tensile properties below 80°C. At the most extreme condition of 100°C, 34 days, aramid fibers showed significant loss of tensile strength (58% for KM2 and 34% for Twaron®), while a reduction in tensile strength of 13% (Armos®) was observed for aramid copolymer (Armos®) fibers. Conditioned fibers exhibited no significant change in mass as a result of the conditioning procedure and FTIR spectroscopy results did not indicate signs of chemical or thermo-oxidative change due to hygrothermal conditioning. These results suggest that in aramid fibers, the primary mechanism of degradation at temperatures between 80°C and 100 °C is due to the ingress and egress of moisture in the highly ordered core structure of the fiber. The presence of water in the intercrystalline regions of the fiber core enable segmental chain motion that can relax tie molecules, alter crystal orientation, and change apparent crystallite size. Because of differences in molecular architecture and phase morphology, the aramid copolymer, Armos®, is less susceptible to degradation of tensile properties under these conditions.

Combined effects of kink bands and hygrothermal conditioning on tensile strength of polyarylate liquid crystal co-polymer and aramid fibers

“…There are several previous studies on hydrolysis resistance of PPTA fibers against water at elevated 15,16 and relatively low temperatures. 5 As reported in the literature, 15 Kevlar Õ 49 fibers treated in water at 180 C using an autoclave cell for 1 day exhibited a 75% decrease in tenacity. Abu Obaid et al 5 recently studied the degradation in tenacity of Kevlar Õ KM2 fibers after treatment in water at temperatures ranging from 40 C to 100 C for 17 and 34 days, and found the tenacity of these fibers begins to decrease significantly for samples conditioned at 80 C for 17 days and the effect becomes more pronounced at 100 C for 34 days, where the decrease in tenacity was approximately 58%.…”

“…Prior work has documented that equilibrium water uptake in Kevlar fibers is on the order of 5% by weight under ambient conditions at room temperature. 5 Weight change for Vectran due to conditioning was not measurable, due to its very low water uptake. Overall, results indicate there was no thermal oxidation or degradation due to hygrothermal treatments.…”

Comparative Study of the Reinforcement Type Effect on the Thermomechanical Properties and Burning of Epoxy-Based Composites

“…The characteristic absorption bands for each fiber may be observed. The complex FTIR spectra of AF consist of as listed prominent absorption bands 3300 cm −1 (N-H stretching), 1638 cm −1 (C=O stretching, Amid I), 1536 cm −1 (coupled C-N stretching and in-plane N-H bending, Amid II), 1400 cm −1 (primary amine salt), 1306 cm −1 (C-C, C-N group motion and N-H vibrations, Amid III), 1103 cm −1 (C-H in-plane bending), 892 (C-H out of plane), 862 cm −1 (C-H out of plane bending), and 725-844 cm −1 (N-H and aromatic C-H out of plane bending) [51][52][53][54]. For both inorganic fillers, i.e., BF and GF, the most distinct wide absorption band with a maximum at 897 cm −1 was originated from SiO stretching mode [55].…”

Novel lignosulfonate/N,N‐dimethylacrylamide/γ‐methacryloxypropyl trimethoxy silane graft copolymer as a filtration reducer for water‐based drilling fluids

“…High temperature will lead to thermal degradation reaction on the main chain of copolymer molecule, the hydrolysis trend of amide group is more obvious, the adsorption capacity decreases sharply, and the breakage of large molecular weight will eventually lead to the loss of the ability to reduce drilling fluid loss . As shown in Figure , with the increase of aging temperature, the liquid loss of bentonite‐based mud increases gradually.…”