MWCNT–Polyimide Fiber-Reinforced Composite for High-Temperature Tribological Applications

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript “MWCNT-polyimide fiber reinforced composite for high-temperature tribological applications” addresses an actual problem related to design of high-performance polymer based composites reinforced with PI fibers for tribological applications at high temperatures. The developed composites comprised of PI matrix with hybrid of polyimide fibers (PIF) grafted with multi-walled carbon nanotubes (MWCNTs). It is shown that in contrast to neat PI, the mechanical properties of the PIF-based composites were enlarged. In addition, the onset of decomposition temperature for the MWCNT-PIF-based composite was increased by 14.5℃, while the wear rate at elevated temperature of 300℃ was decreased by 34.5%. The grafting mechanism was simulated with the use of Dmol3 software. It was found out that the benzene ring and the hydroxyl group of diene-acceptor (DA) donated electrons to the oxygen atom in the nitrogen-containing five-membered ring of PIF. In addition, the straight chains structures exhibited higher reactivity than branched chain structure.

 The state of the art is deeply analyzed, with the number of cited references of 51.

Not all the required experimental details are described.

The Result section misses some important parts, firstly about experimental evidences of wear mechanisms.

There is no separate Discussion section; however, all the results are immediately interpreted in the brief Results section.

The Conclusion is very brief and lacks important, relevant information.

 The manuscript falls within the scope of the journal of coatings. Regardless of some important new results, the manuscript does not look like a comprehensive completed study. It requires major revision. Authors are welcome to address the following aspects.

Page 1, line 33. “recent years, people have developed hybrid fiber materials with improved overall performance through hydrothermal and coating methods”. Who are those “people”?

Page 2. The Materials and Methods section misses the important detailed information on the equipment used for tribological tests. The same is related to atomic force microscopy (mentioned in Page 3, line 84) as well as TGA analyzer (mentioned in Page 4, line 115) and nanoindentor (mentioned in Page 5). In fact, this section is too brief and must be expanded.

The manuscript lacks information of structure of the composites, with due characterization of fibers’ distribution and interphase boundaries. It is of importance to explain the mechanical properties.

 

Section 3.4 describes results of tribological tests. Every result is immediately interpreted with literature data. However, important experimental evidences on wear track surfaces’ characterization are missing. It is not correct for the paper, that is entitled “…composite for high-temperature tribological applications”. Why should a reader believe the numerous literature based interpretations instead of observing the real experimental evidences that illustrate the high temperature wear mechanisms? Thus, the tribolocal part of the manuscript must be expanded with more relevant experimental details. The current volume of the manuscript of 9 pages quite allowed to make the description more comprehensive.

Comments on the Quality of English Language

Minor language revision is required.

Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors

Authors talk about MWCNT-polyimide fiber reinforced composite for high-temperature application. The work shows some significant improvement in mechanical and tribological properties. Following are my review comments: 

1. It will be helpful if authors discuss application (in more detail) and specifications of analogous commercial product. 

2. Figure 1 c and d - same scale on SEM image will help compare better. 

3. It is suggested to show some characterization evidence to prove that the interaction between PIF and MWCNT is chemical and not just physical.

4. It will help if the current PI and it's composite properties are compared with commercial products.

5. TGA shows improvement in decomposition temperature of 14 degree C. How significant it is since the decomposition temperature is already > 500 degree C.

6. Overall, the incorporation of nanotechnology seems to have helped better the performance properties and it would be beneficial if authors cite 1) relevant Nano incorporated PI review articles, example: https://doi.org/10.3390/mi14030616 and 2) review articles that talk about how nanotechnology advancements are leading the evolution of advanced diverse polymeric products, example:  https://doi.org/10.3390/coatings13091569

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

The paper deals with the MWCNT-polyimide fiber reinforced composite for high-temperature tribological applications. 

According to the reviewer, the paper is worth publishing at Coatings Journal, 

but some corrections are needed and then the paper can be accepted for publication in the journal.

While the authors have made considerable research effort, 

the presentation of the paper and the results must be proved. 

Additionally make the following corrections to the manuscript:

 

Comment 1

The authors should give more details for the using equipment (SEM, AFM, TGA, nanoindentation tests, a pin-on-disk equipment: model, type) and the conditions of the tests.

The authors should insert (add) a Figure with the typical sample (for measurement of COF and wear). 

The authors should give more details for the tests (ISO or ASTM?). 

 

Comment 2

The authors should comment the ref. [29] in the paper.

 

Comment 3

The authors should give more details for the Table 1 (in PI/PIF-MWCNTs the composition of the composites PIF-MWCNTs is 10%).

It should be clarified in this percentage what is the percentage of PIF and what is the percentage of MWCNTs. 

 

Comment 4

Major problem

Figure 5 (or a new figure) should be improved by adding more results, such as Figure 5c and 5d for the PI and PI/PIF cases (for comparison with the PI/PIF-MWCNTs) at the room temperature and the 300oC.

 

Comment 5

The authors did not mention (in the Section 3.4 Tribological property) the wear rate at 300℃ decreased by 34.5% (how this value occurs).

In contrast, the value of 34.5% is only reported in the abstract and the Conclusions.

 

Comment 6

The authors performed a considerable number of experiments to characterize the properties of the materials they are concerned with.

The introduction is accompanied by the citation of many relevant bibliographic references and this can be characterized as positive.

Perhaps for the improve the quality of the publication, a section with discussion could be inserted, so as to highlight the feasibility of using these materials especially at high temperatures.

Author Response

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Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript has been improved. Most of the reviewer's remarks have been taken into account. Unfortunately, the conclusions have not been corrected. They are too brief for the results of comprehensive studies reported in the manuscript. However, it is up to the author, to ignore some of the reviewer's remarks. Clearly formulated statements help the reader to get the key ideas. In addition, I do hope, that you will take a habit to separate results from discussion one day.

Reviewer 3 Report

Comments and Suggestions for Authors

Accept in present form