Mechanical Properties Evolution and Damage Mechanism of Kevlar Fiber under Ozone Exposure in Near-Space Simulation

Round 1

Reviewer 1 Report

Dear Authors

This manuscript is focused on the elongation at break of Kevlar fiber was decreasing obviously and the elastic modulus was increasing after ozone exposure. The tensile strength of fiber decreased gradually with the increase of ozone concentration and exposure time. With the increase of ozone exposure time, the surface morphology of Kevlar fiber gradually roughened and even peeled off and the content of oxygen in the surface layer increased.

The following suggestion and comments should be taken:

1. The overall English needs to be improved. Please seek guidance from a native English speaker if possible ("the" "a", commas, plural form and others could be corrected).
2. The authors could insert more numerical data into the Abstract for enhancement of the manuscript.
3. The introduction section needs enhancement 1-3 sentences about potential applications of fiber. Please cite (1) Effect of Relative Humidity on Adsorption Breakthrough of CO₂ on Activated Carbon FibersMaterials 2017, 10(11), 1296; https://doi.org/10.3390/ma10111296 (2) Materials 2021, 14(9), 2448; https://doi.org/10.3390/ma14092448 (3) Nanomaterials 2021, 11(8), 2080; https://doi.org/10.3390/nano11082080
4. Figure 5. Please correct this image for better quality.
5. Figure 6. Please correct this image for better quality.
6. Could the authors include the standard deviation of the methods?
7. Figure 10. Please correct this image for better quality.
8. In conclusions. Please add some information about the potential applications of this material in the conclusions.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

This is a very well-structured and written manuscript, pleasant to read, on the degradation of Kevlar fiber in zone atmosphere. The authors carefully determine the alteration of the mechanical properties which they successfully relate to the changes in the morphology and the chemical composition at the surface of the fiber. They clearly highlight an oxidation at the surface of the fiber which, no doubt, is responsible for the alteration of the mechanical properties, and they propose a quite relevant oxidation mechanism.

If we understand why the fracture properties (i.e. ultimate elongation and stress at break) decrease throughout oxidation, in contrast, it is not clear at all why the Young's modulus is increasing. Is it due to a change in the crystal structure or to an increase in the crystallinity ratio at the surface of the fiber? Could the authors discuss this result and argue their point of view? It is a pity that X-ray diffraction measurements were not carried out…

I found a few typos that need to be corrected.

• Page 2, Line 54, the sentence must start with a capital letter: “Envelope”
• Page 5, Lines 166 and 167, the unit is “MPa” and not “Mpa”
• Page 5, Line 168, please remove the capital letter: “ozone”
• Figures 5 and 6, titles of the y-axis, the unit is “MPa” and not “Mpa”
• Figures 6, titles of the y-axis, please replace “Stress” by “Strength”

Page 6, Line 207, the notation “ph” needs to defined before being used.

Author Response

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Reviewer 3 Report

1) can the authors report on whether or not the manufactured kevlar fibers have a sizing or coating on them?

2) I do not understand the purpose of adhering the fiber to kraft/cowhide paper. Why did the authors not use a clamp that holds a fiber? R8 mm is not defined; is this where the adhesive was placed?

3) Figure 8: The figure shows that the peak intensities are decreasing, but it's unclear whether peak ratios are changing. The authors should plot difference spectra of the difference in 1000 h versus 0 h, etc to demonstrate these changes.

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

• Page 3, Why the Kevlar fibers were not used for the studies in the form of yarn or fabric and the monofilaments were used and fixed using acrylic adhesive?
• It is recommended to report the effect of ozone treatment on wettability of the fibers using contact angle measurement.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

I recommend this manuscript for publication.

Reviewer 3 Report

The authors have addressed my concerns and I have no additional comments.