Degradation of aramid fibers under alkaline and neutral conditions: Relations between the chemical characteristics and mechanical properties

Abstract

Aramid fibers are high-performance materials that have been used in various applications such as heat and cut protection, composites, rubber reinforcement, ropes and cables, and fabrics; today their use is proposed in geotextiles for alkaline ground reinforcement, and they have been used in cables for marine applications for a few years. However, there is a lack of experience with the long-term behavior of aramid fibers in wet and alkaline environments. Aging studies were therefore performed on Twaron 1000 fibers under different conditions (sea water, deionized water, pH 9, and pH 11). Hydrolytic degradation was evaluated with Fourier transform infrared and viscosimetry measurements, which were correlated with tensile test measurements. The tensile strength followed a logarithmic evolution with the aging time, whereas the modulus remained constant. A linear relation between the tensile strength and the reduced viscosity of the hydrolytically aged fibers is highlighted. Aging indicators are proposed that allow the hydrolytic degradation to be quantified.

Crystallite size evolution of aramid fibres aged in alkaline environments

“…The corresponding chromatograms are shown in Figure 10. The M w evolutions are consistent with the viscosity measurements from a previous study [21]. The degradation is significantly higher at pH11 than at pH9.…”

“…A previous study has shown that in moderate alkaline environments (pH9 and pH11) the chemical degradation of Twaron 1000 fibres can be fitted by Springer et al's equation 1, using one decay function at pH9 and two decay functions at pH11 [21]. We assumed thus that the degradation may be attributed to one degradation process at pH9 and two degradation processes at pH11.…”

“…Single fibres were tested to failure using a Zwick 1474 tensile testing machine with a 5N load cell and a rate of extension of 10%/min, at 20°C. These tests are described in more details elsewhere[19][20][21].Size Exclusion ChromatographySize exclusion chromatography was performed by dissolving the sample in concentrated H 2 SO 4 (1 mg/mL) and separating this using a modified Zorbax column (250 x 6.2 mm) and concentrated H 2 SO 4 as the mobile phase (0.1 mL/min). A UV detector operating at 340 nm was used.…”

Degradation of Technora aramid fibres in alkaline and neutral environments

“…After extraction of the finish with deionised water at ambient temperature, FTIR analyses of the isolated finish enable the peak located at w2923 cm À1 to be attributed to the finish. As Technora fibres contain PPTA sequences similar to Twaron fibres, the spectra display some peaks related to the amide functions in common [10]: the peak located at w1639 cm À1 is related to the C]O vibration and the peak at w1306 cm À1 is related to the C-N, N-H and C-C combined vibrations. The peaks related to the amide functions of PPTA and 3-4 0 -POP-T sequences are not clearly separated.…”

Humid Ageing of Organic Matrix Composites

“…Styrene cured unsaturated polyesters are, by far, the most important composite matrices undergoing hydrolysis. Among other polymers in which problems of hydrolytic ageing have been observed, one can cite: polyamides, including aromatic ones (for instance, Kevlar) [122], anhydride cured epoxies, polyurethanes based on polyesters, vinyl esters, polyvinyl acetate used as low profile additive in polyester sheet molding compounds or bulk molding compounds, etc. There is not, to our knowledge a theoretical tool able to predict the hydrolysis rate of a given group in a given polymer.…”