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Microstructural Changes of Aramid Fiber Due to Reaction with Toluene 2,4-diisocyanate under Tension in scCO2

1,*, 1 and 2,*
1
School of Materials Engineering, Shanghai University of Engineering Science, Shanghai 201620, China
2
State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Material Science and Engineering, Donghua University, Shanghai 201620, China
*
Authors to whom correspondence should be addressed.
Polymers 2019, 11(7), 1110; https://doi.org/10.3390/polym11071110
Received: 23 May 2019 / Revised: 11 June 2019 / Accepted: 20 June 2019 / Published: 1 July 2019
(This article belongs to the Special Issue Supercritical Fluid Processing of Polymers)
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Abstract

High modulus aramid fiber, such as Kevlar 49, is conventionally prepared by the heat annealing of high strength aramid fiber under a suitable tension at high temperature, especially higher than 500 °C. This enables the mobility of a rigid molecule chain to be rearranged into a more perfect crystalline or orientation structure under tension. However, annealing decreases the tensile strength, since the thermal degradation of the molecular chain at high temperature cannot be avoided. Kevlar 49 fibers treated in supercritical carbon dioxide (scCO2) under tension could improve their mechanical properties at a low temperature. The effects of the tension on the mechanical properties and structure of the Kevlar 49 fibers were studied by mechanical testing, wide-angle and small-angle X-ray scattering (WAXS, SAXS), and scanning electron microscopy (SEM). The results show that the mechanical properties, crystallinity and orientation of the fiber can be improved when the tension is less than 0.6 cN/dtex, which may be due to the increasing of the mobility of a rigid segment with the help of the plasticization of scCO2 and re-arrangement of macromolecular chain into crystalline and orientation structure under tension. What’s more, the amorphous region also was enhanced by crosslinking reaction of toluene 2,4-diisocyanate (TDI) with the chain end groups of the macromolecules in the amorphous regions. However, a decrease of tenacity was found when the tension was higher than 0.6 cN/dtex, which is because the tension was so high that the microfibril was broken. The results indicated that treating the Kevlar 49 fiber in scCO2 under a suitable tension with TDI as a crosslink agent can simultaneously improve both the tenacity and modulus of the fiber. View Full-Text
Keywords: mechanical properties; tension; crystallinity; microfibril mechanical properties; tension; crystallinity; microfibril
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Kong, H.; Xu, Q.; Yu, M. Microstructural Changes of Aramid Fiber Due to Reaction with Toluene 2,4-diisocyanate under Tension in scCO2. Polymers 2019, 11, 1110.

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