Study on Crystallization Behaviors and Properties of F-III Fibers during Hot Drawing in Supercritical Carbon Dioxide.

Xiaoma Ding,Mengmeng Qiao,Zhifeng Hu,Muhuo Yu,Haijuan Kong

doi:10.3390/polym11050856

Xiaoma Ding, Mengmeng Qiao + Show 3 more

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https://doi.org/10.3390/polym11050856

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Abstract

In order to obtain F-III fibers with high mechanical properties, pristine F-III fibers were hot drawn at the temperature of 250 °C, pressure of 14 MPa, tension of 6 g·d−1, and different times, which were 15 min, 30 min, 45 min, 60 min, 75 min, 90 min, and 105 min, respectively, in supercritical carbon dioxide (Sc-CO2) in this article. All the samples, including the pristine and treated F-III fibers, were characterized by a mechanical performance tester, wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), and thermogravimetric analysis (TGA). The results showed that the thermal stability of F-III fibers was enhanced to some extent, and the tensile strength and modulus of F-III fibers had great changes as the extension of treatment time during hot drawing in Sc-CO2, although the treatment temperature was lower than the glass transition temperature (Tg) of F-III fibers. Accordingly, the phase fraction, orientation factor fc of the (110) crystal plane, fibril length lf, and misorientation angle Bφ of all the samples were also investigated. Fortunately, the hot drawing in Sc-CO2 was successfully applied to the preparation of F-III fibers with high mechanical properties.

Highlights

Aramid fibers (AFs) have been widely used in bulletproof products, building materials, special protective clothing, electronic equipment, and other application fields owing to their super tensile strength, high elastic modulus, good impact resistance, great thermal stability, and excellent insulation property [1,2,3,4]
Compared with the pristine fibers, the crystallinity of F-III fibers increased by 47.0%, and the orientation factor of the (110) crystal plane increased by 22.4% at 90 min after hot drawing, which were obtained by Wide Angle X-ray Scattering (WAXS)
The small-angle X-ray scattering (SAXS) showed that the fibril length of F-III fibers increased by 18.8%, and the misorientation angle decreased by 57.9% when the treatment time was 90 min compared with the pristine fibers

Summary

Introduction

Aramid fibers (AFs) have been widely used in bulletproof products, building materials, special protective clothing, electronic equipment, and other application fields owing to their super tensile strength, high elastic modulus, good impact resistance, great thermal stability, and excellent insulation property [1,2,3,4]. Compared with the current industrialized "para" AFs (such as Kelvar, Twaron, and Technora fibers) and "meta" AFs (such as Nomex and Conex fibers), the F-III fiber has shown higher tensile strength and modulus due to the more complex molecular structure. Due to the excellent mechanical properties, F-III fibers are specially used in the military bulletproofing field [5]

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