Properties of Polypropylene Yarns with a Polytetrafluoroethylene Coating Containing Stabilized Magnetite Particles

Round 1

Reviewer 1 Report

This article is well done but before publication the authors must solve the following problems:

-what is the washing durability of a product made from these yarns knowing that during the life cycle  (in consumption/utilization step), more launderings are needed?

-how do you justify that PP coated with PTFE and magnetite stabilized by sodium stearate, in presence of US has a specific tensile strength higher than the other tested yarns (table 1) but has a higher surface electrical resistance (table 2)?

Author Response

Dear Reviewer! Thank you for the good evaluation of the article and interesting questions. We will try to answer them.

Point 1: what is the washing durability of a product made from these yarns knowing that during the life cycle (in consumption/utilization step), more launderings are needed? 

Response 1:

PP yarn with a PTFE coating, and therefore products made from it, have a very high resistance to washing. Tests have shown that the specific tensile strength of such yarns remains unchanged after 40 washes for 30 minutes each one. Information on yarn resistance to washing added to the manuscript (lines 373-375, in red). A description of the method for assessing the resistance of yarns to washing is given in the "Materials and Methods" section (lines 201-204, in red).

Point 2: how do you justify that PP coated with PTFE and magnetite stabilized by sodium stearate, in presence of US has a specific tensile strength higher than the other tested yarns (table 1) but has a higher surface electrical resistance (table 2)? 

Response 2:

Perhaps there is some misunderstanding on this issue. PP yarn with a coating formed by a US-treated composition of PTFE and magnetite stabilized by sodium stearate has the highest specific tensile strength (658 ± 23 MPa) and the lowest surface electrical resistance (5.7x10⁸ ohm).

Reviewer 2 Report

The revised manuscript can now be published.

Author Response

Dear Reviewer! Thank you for the good evaluation of the article. 

Reviewer 3 Report

Please consider changing the subject to "properties ……."
Figures 1 and 2 are of poor quality and therefore hardly legible.
Figures 1a and 1b should be shown on the same scale for evaluation.

Include an in-depth analysis over the results in Table 1.
Complete the basic data of the TP-4 device.

Author Response

Dear Reviewer! Thank you for your interesting and useful comments and questions. We have made the necessary changes and will try to answer your questions.

Point 1: Please consider changing the subject to "properties ……."

Response 1: In accordance with your recommendations, we have changed the title of the manuscript. Now it is titled "Properties of Polypropylene Yarns with a Polytetrafluoroethylene Coating Containing Stabilized Magnetite Particles" (lines 2-4, in red).

Point 2: Figures 1 and 2 are of poor quality and therefore hardly legible. Figures 1a and 1b should be shown on the same scale for evaluation.

Response 2: We redesigned Figures 1 and 2. We improved their quality and presented them on the same scale. For improved illustrations, see page 6 of manuscripts.

Point 3: Include an in-depth analysis over the results in Table 1.

Response 3: We provide a brief analysis of the results in Table 1, as a very detailed analysis of the mechanical characteristics of PP yarns with PTFE coating containing stabilized magnetite particles is presented in our recent article (Prorokova, N.P.; Vavilova, S.Yu.; Bouznik V.M. Mechanical characteristics of polytetrafluoroethylene coated polypropylene yarns made by new technology. Khimicheskaya Tekhnologiya. 2020, 9,409-417. DOI 10.31044/1684-5811-2020-21-9-409-417). We have added a link to this article in the manuscript (lines 258-259, in red). 

Point 4: Complete the basic data of the PT-4 device.

Response 4: We presented the schematic diagram of the PT-4 apparatus in Fig. 1 (page 4 of the manuscript).

Reviewer 4 Report

Please find below comments:

1) Show mechanical testing data for the yarns.

2) Wash test results should be shown 

3) Some figures, not clear needs improvement 

4) Explain diffrent coating methods and effect of thickness of coating, cite  R. Villanueva et al., Materials Research Express 6, 016307 (2019)

Author Response

Dear Reviewer! In accordance with your comments, we have made the necessary amendments to the manuscript and will try to answer your questions. 

Point 1: Show mechanical testing data for the yarns.

Response 1: A general idea of the influence of the composition and structure of the coating on the mechanical characteristics of the yarn can be obtained from table 1. A very detailed analysis of the mechanical characteristics of PP yarn with a PTFE coating containing stabilized magnetite particles is presented in our recent article (Prorokova, N.P.; Vavilova, S.Yu.; Bouznik V.M. Mechanical characteristics of polytetrafluoroethylene coated polypropylene yarns made by new technology. Khimicheskaya Tekhnologiya. 2020, 9,409-417. DOI 10.31044/1684-5811-2020-21-9-409-417). We have added a link to this article in the manuscript (lines 258-259, in red). 

Point 2: Wash test results should be shown. 

Response 2: Information on yarn resistance to washing added to the manuscript (lines 373-375, in red). PP yarn with a PTFE coating, and therefore products made from it, have a very high resistance to washing. Tests have shown that the specific tensile strength of such yarns remains unchanged after 40 washes for 30 minutes each one. A description of the method for assessing the resistance of yarns to washing is given in the "Materials and Methods" section (lines 201-204, in red). 

Point 3: Some figures not clear needs improvement. 

Response 3: We redesigned Figures 1 and 2. We improved their quality and presented them on the same scale. For improved illustrations, see page 6 manuscripts. 

Point 4: Explain different coating methods and effect of thickness of coating, cite  R. Villanueva et al., Materials Research Express 6, 016307 (2019) 

Response 4: In the introduction (lines 60-64, in red), we have added a fragment dedicated to various methods of applying thin coatings to fibrous materials. This fragment cites an article by R. Villanueva et al.

Round 2

Reviewer 1 Report

The article "Properties of Polypropylene Yarns with a Polytetrafluoroeth-2 ylene Coating Containing Stabilized Magnetite Particles" is well done and documented and the conclusions are pertinent. For these reasons I agree with the publication in Coatings Journal.

Reviewer 4 Report

Revisions were made.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

1. The title of the publication does not reflect the content of the article.

The article is incoherent and it is difficult to know whether the authors describe a surface coated polypropylene fiber or a PP polymer layer and what was tested: coated fibers or only polymer layers? Moreover, the characteristics of both the fibers and the polymer layers is missing.

2. The authors have written about PP yarn, but nowhere in the text is there a characteristic of this yarn, so it is not known how the particles with a size of 0.3 - 300 µm cover the surface of the fibers with a diameter of 15 µm?
3. The scale is missing in fig. 3
4. What is illustrated in the fig. 4 ? What did the authors want to show in this picture?
5. The graph 6 (coating affected by abrasion 500 times) is missing in fig. 5
6. In the article, I found the research results without their description and explanation:

- What do the numbers in Table 3 mean?

-Please determine the number of bacteria colonies and explain whether the increase of turbidity is caused by the increase in the number of bacteria?

- Why has the strength of PTFE coated and magnetite doped yarns increased even more?

Moreover:

(84-85) at what point was sodium stearate introduced?

(88-89) what was the amount of particles whose diameter was smaller than that of the spinneret?

(90-92) was it only magnetite which passed through the spinnerette?

Author Response

Dear reviewer, thank you for your comments. We have made the necessary changes in the paper to improve it.

Comment 1. The title of the publication does not reflect the content of the article.

The article is incoherent and it is difficult to know whether the authors describe a surface coated polypropylene fiber or a PP polymer layer and what was tested: coated fibers or only polymer layers? Moreover, the characteristics of both the fibers and the polymer layers is missing.

Answer 1. We have changed the title into Polypropylene Yarns with a Polytetrafluoroethylene Coating Containing Stabilized Magnetite Particles.

This paper considers the properties of a polypropylene yarn with a polytetrafluoroethylene coating. The only testing of the coating was that of its resistance to abrasive effects. We have added a short description of the characteristics of the obtained yarns (lines 127-128) and data about the coating thickness (lines 128-129). The characteristics of the PTFE coating were described in detail in one of our earlier works (Prorokova, N.P.; Vavilova, S.Y.; Bouznik, V.M. A novel technique for coating polypropylene yarns with polytetrafluorоethylene. J. FluorineChem.2017, 204, 50 – 58. DOI: 10.1016/j.jfluchem.2017.10.). The reference to this work is provided.

Comment 2. The authors have written about PP yarn, but nowhere in the text is there a characteristic of this yarn, so it is not known how the particles with a size of 0.3 - 300 µm cover the surface of the fibers with a diameter of 15 µm?

Answer 2. As we have stated above, we have added a description of the yarn to the text (lines 127-128). The composition used to make a coating includes stabilized magnetite particles subjected to ultrasonic treatment in advance (fig. 3). The fractions are either nanosized (with the average size of several nanometers) or microsized (with the average size of 15-25 µm). The nanosized fractions of the stabilized magnetite build into the 0.18 µm PTFE coating, while larger particles cannot get attached to the filaments of 15 µm in diameter.

Comment 3. The scale is missing in fig. 3

Answer 3. The image in Fig. 3 was obtained by the optical microscopy method. The scale is not normally provided for such images. The magnification value is specified in the Figure caption (lines 244-245). We have also added the name of the study method to the figure caption (line 244).

Comment 4. What is illustrated in the fig. 4? What did the authors want to show in this picture?

Answer 4. The paper contains a commentary to Fig. 4 (lines 236-240): “The image obtained by scanning electron microscopy and showing a film with a coating formed by a US-treated composition based on PTFE and magnetite stabilized by sodium stearate (Figure 4) indicates that the coating structure does not contain noticeable foreign inclusions. The magnetite particles are uniformly distributed over the coating.”

Comment 5. The graph 6 (coating affected by abrasion 500 times) is missing in fig. 5

Answer 5. We have corrected the caption to Figure 5.

Comment 6. In the article, I found the research results without their description and explanation:

Question:

- What do the numbers in Table 3 mean?

Answer:

Table 3 characterizes the inhibition of the vital activity of pathogenic microorganisms (in points). Points, according to ASTM E2149 – 10, have the following meanings: 1 point (0.0–0.1%) indicates that there is no antimicrobial effect; 2 points (0.1–90%) – a slight decrease in the number of microorganism colonies, an insufficient antimicrobial effect; 3 points (90–94%) – a significant reduction in the number of microorganism colonies, a good antimicrobial effect; 4 points (95–98%) – a significant reduction in the number of microorganism colonies, a very good antimicrobial effect; and 5 points (99% and higher) – a strong reduction in the number of microorganism colonies, an excellent antimicrobial effect.

For a better understanding we have included this excerpt in the experimental part of the paper (167-175). We have also added data to Table 3.

Question:

-Please determine the number of bacteria colonies and explain whether the increase of turbidity is caused by the increase in the number of bacteria?

Answer:

It is true that the turbidity increase is caused by the larger number of bacterial colonies. It is the principle underlying the nephelometric method of determination of the number of bacterial colonies. We did not determine the absolute number of bacterial colonies. Instead, we used the solution turbidity value to evaluate the relative changes in the number of bacterial colonies. After correction, Table 3 presents the capacity of a PP yarn with a PTFE coating to inhibit the vital activity of pathogenic microorganisms not only in points, but also in percentage terms.

Question:

- Why has the strength of PTFE coated and magnetite doped yarns increased even more?

Answer:

The strength of the PP yarn with a PTFE coating is 643 ± 16 mPa, the strength of the PP yarn with a PTFE coating doped with stabilized magnetite is 658 ± 23 MPa. The strength changes are within the confidence interval. That is why we cannot conclude that the strength has increased. It has remained at the same level.

Question:

 (84-85) at what point was sodium stearate introduced?

Answer:

Sodium stearate was introduced during the synthesis of magnetite after adding an ammonia solution NH₄OH. This fact is mentioned  in the description of the magnetite preparation process.

Question:

 (88-89) what was the amount of particles whose diameter was smaller than that of the spinneret?

Answer:

We do not completely understand the question. Magnetite does not get through the spinnerettes, only the polypropylene melt does. Probably, the term “spinnerette filter” – the name of the tool we used to sift the synthesized magnetite – is misleading. It means that we used a grid protecting the spinnerettes to remove large aggregates of the synthesized magnetite. We have removed the word “spinnerette” from this part of the text.

Question:

 (90-92) was it only magnetite which passed through the spinnerette?

Answer:

As we have mentioned above, the magnetite did not pass through the spinnerette. The spinnerettes were only used to form the PP yarns. The PTFE-based composition containing stabilized magnetite was deposited onto the surface of the PP yarn after it was formed, at the oiling stage (112-114). The process of the PP yarn formation and obtaining of the PTFE coating is described in detail in one of our earlier works (Prorokova, N.P.; Vavilova, S.Y.; Bouznik, V.M. A novel technique for coating polypropylene yarns with polytetrafluorоethylene. J. Fluorine Chem.2017, 204, 50 – 58. DOI: 10.1016/j.jfluchem.2017.10.) A reference to this work is provided in this paper.

Author Response File: Author Response.docx

Reviewer 2 Report

The topic is interesting and innovative. The authors take up an important problem which is the modification of PP fibers. The work requires minor corrections. There are 5 spectra in Fig 5, but there are 6 in the caption. The bibliography lacks works from recent years, the youngest is from 2018. It would be nice to supplement the knowledge overview with the latest discoveries from others. After the revision, the article should be published in this journal.

Author Response

Dear reviewer, thank you for such positive commentary. We have corrected the paper in accordance with your remarks.

Comment 1. There are 5 spectra in Fig 5, but there are 6 in the caption.

Answer 1. We have changed the caption to Figure 5.

Comment 2.. The bibliography lacks works from recent years, the youngest is from 2018. It would be nice to supplement the knowledge overview with the latest discoveries from others.

Answer 2. We have added references to several papers published in 2018-2020 – [6], [7], [10], [11], [12], [13], [14] – to the list of references.

Author Response File: Author Response.docx

Reviewer 3 Report

Dear Authors,
After reading carefully your manuscript I am sorry to communicate you that in my opinion it does not fulfill the minimum standards of a scientific publication therefore, I had to recommend its rejection.
Here you will find my specific comments which in case of possibility by the editor to revise and resubmit must be carefully taken into account.  

General comments:

The English and the writing are quite poor, an extensive editing is needed.

I do not really like expressions like “for + -ing form” I would substitute with “to+infinitive”

Troughtout the paper the authors should avoid personal way of expressing concept such as “we did that” but instead use an impersonal phrase such as “this was done”

Comments on the sections.

The Introduction section is my opinion not well structured and some points are missing.

First of all, the state of the art is very poor and some further points need to be discussed. Also looking at the bibliography analyzed I need to point out that it quite poor and self-referential: only 23 sources have been reported and 11 of them are by the same authors. Thus the state of the art needs to be significantly enlarged consulting many more works done by other research groups. Also it needs to be taken into account that the sources used are quite old and therefore the may be updated.

Regarding the macrotopic of producing textiles for health application with antimicrobial properties the authors provided a discussion on the usage of metallic nanoparticles used either as surface finishes of as core materials. On the other hand, many different strategies have been proposed and reviewd in the last years such as the usage of chitosan microcapsules or chitosan based polymeric functionalizations. Also, bio-functional textiles have been proven to effectively impart biocidal activities to fabrics. This is just to give an example about the fact that the authors should discuss the benefit of their approach with respect to the many others proposed in literature over the recent years.

Regarding the possibility of introducing the nanoparticles in the bulk the authors claim that this, as solution is quite complicated, however a more detailed literature review should be proposed to better sustain such a claim.

In the final part of the introduction the present work is described. The way this part is written is however should be smoothed, the introduction ends in a very sharp which is in my opinion not the best way to end a section of a scientific paper.

Materials and methods

Line77: probably the Cyrillic alphabet should be avoided

Line 135: The author should justify the choice of the investigate spectral region and why the range above 1600 was not measured.

Reagarding the testing of antibacterial properties it need to be specified if a standard test according to international norms was used or not.

Overall the writing of the methodology section is very poor. More subsections should be employed so that the reader could best follow the kind of experiments done alongside with the purpose of each test.

Results and discussions:

Lines 182-190: The justification behind the choice of particular materials shoud be avoided in this point.

The authors talked in the introduction and methododlogy section about the use of nanoparticles, hoewever, looking at the size reported in line 191-196 were well above the nanoscale.

Figure 1-2 is the unit on x-axis a microkilometer ? are you sure ?

Table 1 and relative discussion:
Some more exhaustive comments needs to be carried out to better asses the effect of each element affecting the mechanical properties, please also report here also the particle size

Figure 3-4 as for figure 1 and 2 the three picture/graph need to be merge in a single figure

Table 3: I am missing the results about the biocidal activity on candida albicans. Also not clear which magnetite particles were used. It is needed to report the results of all particles ( non stabilized, with sodium sterate and with ultrasound) to obtain a reliable data set to be discussed. I also would like to see data on the effect of the sole PTFE coating on antimicrobial activity.

Generally this section does not fulfill the minimum requirement of a scientific publication. It is just repeating the scope of the experiment and reporting some the results without providing sufficient explanation of why such trends were observed.

Also no idea about the coating thickeness and/or Fiber to coating weight ratio is given.

Author Response

Dear reviewer, thank you for your thorough analysis of our paper. We have introduced a number of changes to the paper in accordance with your remarks. However, we cannot agree with some of your comments as they are, probably, based on your own preferences rather than rules.

General comments:

The English and the writing are quite poor, an extensive editing is needed.

I do not really like expressions like “for + -ing form” I would substitute with “to+infinitive”

Troughtout the paper the authors should avoid personal way of expressing concept such as “we did that” but instead use an impersonal phrase such as “this was done”

Answer. We have rephrased parts of the text substituting the for + ing forms for other expressions. However, an English language specialist has confirmed that our paper is written in accordance with the rules of the English language. In particular, since the editorial board’s guidelines for the authors do not contain any recommendations to use impersonal forms instead of personal expressions, the authors have the right to choose either of the ways to express their ideas. And in our previous paper published in the “Coatings” journal, we also used some “we”-forms.

Comments on the sections.

The Introduction section is my opinion not well structured and some points are missing.

First of all, the state of the art is very poor and some further points need to be discussed. Also looking at the bibliography analyzed I need to point out that it quite poor and self-referential: only 23 sources have been reported and 11 of them are by the same authors. Thus the state of the art needs to be significantly enlarged consulting many more works done by other research groups. Also it needs to be taken into account that the sources used are quite old and therefore the may be updated.

Answer.

We have added 8 references; 7 of them were published in 2018-2020.

Regarding the macrotopic of producing textiles for health application with antimicrobial properties the authors provided a discussion on the usage of metallic nanoparticles used either as surface finishes of as core materials. On the other hand, many different strategies have been proposed and reviewd in the last years such as the usage of chitosan microcapsules or chitosan based polymeric functionalizations. Also, bio-functional textiles have been proven to effectively impart biocidal activities to fabrics. This is just to give an example about the fact that the authors should discuss the benefit of their approach with respect to the many others proposed in literature over the recent years.

Answer.

We would like to draw your attention to the fact that the paper does not focus on providing fabrics, often made from cellulose, with antimicrobial properties, although quite a lot of works have been published on this subject. Our paper focuses on providing polypropylene fibers and non-woven materials with biocidal properties in the process of their melt-spinning. These are two conceptually different research directions. They are even related to different branches of industry: the first one – to the textile industry, the second one – to the chemical one (production of chemical fibers). These processes are based on absolutely different regularities. Natural and synthetic fibers possess completely different properties. And it seems unreasonable to discuss strategies of producing fabrics for medical purposes in the Introduction to our paper. It is also important to note that neither chitosan, nor its derivatives can be used to modify polypropylene fibers during their melt-spinning. We compare the approach proposed by us with the strategies of filling polymers with fillers stabilized by a variety of methods. Making coatings on freshly spun yarns is our “know-how”, that is why the references on this subject include only our publications.

Regarding the possibility of introducing the nanoparticles in the bulk the authors claim that this, as solution is quite complicated, however a more detailed literature review should be proposed to better sustain such a claim.

Answer.

We have stated that it is rather difficult to stabilize metal-containing nanoparticles by introducing them into a polyolefin matrix during the synthesis procedure. The Introduction contains 4 references to our works in this subject field. This is an innovation, and there are no other works on this problem. However, we have extended the Introduction section related to the introduction of nanofillers into polymers ((lines 35-45).

In the final part of the introduction the present work is described. The way this part is written is however should be smoothed, the introduction ends in a very sharp which is in my opinion not the best way to end a section of a scientific paper.

Answer.

We respect your point of view but cannot agree with it because the remark is rather general. In our opinion, the most important thing is that the Introduction fulfills its functions.

Materials and methods

Line77: probably the Cyrillic alphabet should be avoided

Answer.

This has been corrected by the journal editors.

Line 135: The author should justify the choice of the investigate spectral region and why the range above 1600 was not measured.

Answer.

This region contains the reflection bands characteristic of PTFE and PP (line 147).

Reagarding the testing of antibacterial properties it need to be specified if a standard test according to international norms was used or not.

Answer.

The description of the test of the antibacterial properties contains a reference to the standard international test (ASTME 2149 - 10 Standard Test Method for Determining the Antimicrobial Activity of Immobilized Antimicrobial Agents Under Dynamic Contact Conditions. USA, 2001).

Overall the writing of the methodology section is very poor. More subsections should be employed so that the reader could best follow the kind of experiments done alongside with the purpose of each test.

Answer.

The guidelines for the authors do not contain such requirements, which means the authors can choose how to structure their writing in the methods sections.

Results and discussions:

Lines 182-190: The justification behind the choice of particular materials shoud be avoided in this point.

Answer.

This justification of the choice of the materials is given for a better understanding of the paper that considers the effect of a certain metal oxide possessing biocidal properties (magnetite) stabilized with a certain thermally stable surfactant (sodium stearate) on the properties of the polypropylene yarn.

The authors talked in the introduction and methododlogy section about the use of nanoparticles, hoewever, looking at the size reported in line 191-196 were well above the nanoscale.

Answer.

The composition used to make a coating includes stabilized magnetite particles pre-treated by ultrasound (Fig. 3). The fractions are either nanosized (with the average size of several nanometers) or microsized (with the average size of 15-25 µm). The nanosized fractions of the stabilized magnetite build into the 0.18 µm PTFE coating structure, while larger particles cannot get attached to the filaments of 15 µm in diameter.

Figure 1-2 is the unit on x-axis a microkilometer ? are you sure ?

Answer.

Thank you for drawing our attention to this misprint. A micrometer (10^-6 m) is meant. We have corrected the paper.

Table 1 and relative discussion:

Some more exhaustive comments needs to be carried out to better asses the effect of each element affecting the mechanical properties, please also report here also the particle size

Answer.

The aim of the work was to find out the effect of magnetite on the properties of the coated yarn. We did not study the complex regularities reflecting the effects of the other components of the composition in this work. As it is stated in the paper, we used magnetite particles stabilized by sodium stearate and pretreated by ultrasound to prepare the composition. We did not determine the sizes of the particles embedded in the PTFE coating either.

Figure 3-4 as for figure 1 and 2 the three picture/graph need to be merge in a single figure

Answer.

Figures 3 and 4 are separated because the images in them were obtained by different methods. Figure 2 is also given separately from Figure 1 to make it easier to understand that we used stabilized magnetite particles pre-treated by ultrasound during the experiment (Fig. 2). Fig. 1 shows data about the effect of magnetite stabilization with sodium stearate on the magnetite particle sizes.

Table 3: I am missing the results about the biocidal activity on candida albicans. Also not clear which magnetite particles were used. It is needed to report the results of all particles (non stabilized, with sodium sterate and with ultrasound) to obtain a reliable data set to be discussed. I also would like to see data on the effect of the sole PTFE coating on antimicrobial activity.

Answer.

Table 3 has been extended to include data about the ability of the coated yarns to inhibit the vital activity of Candida albicans and effect of the PTFE coating on the biological activity of the PTFE yarns. In the experiment, we used stabilized magnetite particles pre-treated by ultrasound. We have provided an additional explanation to the paper (lines 271-272). We considered it unreasonable to perform a long microbiological experiment with unstabilized magnetite particles and stabilized particles without preliminary ultrasonic treatment because it is well known that the antimicrobial activity of microsized particles is much lower than that of nanosized ones.

Conclusions

Generally this section does not fulfill the minimum requirement of a scientific publication. It is just repeating the scope of the experiment and reporting some the results without providing sufficient explanation of why such trends were observed.

Answer.

We cannot agree with your opinion that it is necessary to repeat the explanation of the obtained results in the Conclusions. We describe the main result of the study – obtaining of a polypropylene yarn with unique properties – in the Conclusions.

Also no idea about the coating thickeness and/or Fiber to coating weight ratio is given.

Answer.

We have added data about the coating thickness to the text (122-123). Since the coating is rather thin (0.18 µm), the ratio of the fiber weight to that of the coating is not informative and is not given in the work. The characteristics of the PTFE coating were described in detail in one of our earlier works (Prorokova, N.P.; Vavilova, S.Y.; Bouznik, V.M. A novel technique for coating polypropylene yarns with polytetrafluorоethylene. J. FluorineChem.2017, 204, 50 – 58. DOI: 10.1016/j.jfluchem.2017.10.). The reference to this work is provided.

Author Response File: Author Response.docx

Reviewer 4 Report

The manuscript describes a method of coating polypropylene yarns with PTFE and magnetite nanoparticles. The work is interesting and new, but the manuscript suffers from the following issues:

1) Ultra sonic bath (and tip sonication) is a standard technique to treat nanoparticle or composite solutions or dispersion. It is well known that ultra sonic bath will separate particle agglomerations. Hence, there is no need to have 4 figures to prove that ultra sonic bath results in smaller nanoparticles. In addition, The units on the figures 1 and 2 do not make sense (what is microK? Should it be microm?). Furthermore, Figure 3 does not give that much info. Why is not the SEM of the respective samples presented?

2) Antimicrobial activity does not mean bacteriocidal per se, it can also be bactreristatic. In the manuscript it is not clear if the authors mean bacteriocidal or bacteriostatic (even if they call it biocidal). In the Experimental Methods section, there is no description of the experiment performed to assess antimicrobial activity. In Table 2, it is not clear what are the numbers presented.

3) The FTIR spectrum in Figure 5 seems to present the smoothed version of the spectra. This is shown from the scale structure of the lines. See for example in the region 1050-100 cm-1. One cannot present a smoothed spectrum without saying that it has smoothed.

4) The description of the electrical characterization is not complete. What is an IESN-1 apparatus? It is not clear how the electrical characterization is performed.

For all the above reasons, I would propose to reject the publication of the manuscript as it is. The manuscript has to be clear as to the experimental methods used as well as the results presented in a clear manner and resubmitted. 

Author Response

Dear reviewer, thank you for the analysis of our paper. We will try to answer all of your questions and make the necessary corrections.

Point 1a) Ultra sonic bath (and tip sonication) is a standard technique to treat nanoparticle or composite solutions or dispersion. It is well known that ultra sonic bath will separate particle agglomerations. Hence, there is no need to have 4 figures to prove that ultra sonic bath results in smaller nanoparticles.

Response 1a). The main method that we used to prevent the formation of large nanoparticle agglomerations was their processing with a thermally stable surfactant – sodium stearate that played the role of a magnetite particle stabilizer even when the coating was deposited onto the hot surface of a freshly formed yarn. Ultrasonic treatment was only a supplementary method that helped make the aggregates even smaller. That is why we consider it reasonable to include 3 graphs in the paper: one (Fig. 1a) showing the sizes of unstabilized magnetite particles, the second one (Fig. 1b) – the sizes of the particles stabilized by sodium stearate, and the third (Fig. 2) for the particles stabilized and additionally subjected to ultrasonic treatment. Figure 3 gives an idea of how uniform the composition used for making the coating was. Figure 4 indicates that the coating is continuous. It shows that the magnetite nanoparticles are built into the structure of the fluoroplastic coating.

Point 1b). In addition, The units on the figures 1 and 2 do not make sense (what is microK? Should it be microm?). Furthermore, Figure 3 does not give that much info.

Response 1b). We apologize for having overlooked this. The sizes of the particles on the graphs must be given in micrometers (µm) (10^-6 m). We have made the necessary corrections in Figures 1 and 2.

Point 1c). Why is not the SEM of the respective samples presented?

Response 1c). We considered it unreasonable to show SEM images of the powdered magnetite as we were only interested in determining the size of the magnetite particles, which could be done based on Fig. 1-2.

Point 2a) Antimicrobial activity does not mean bacteriocidal per se, it can also be bactreristatic. In the manuscript it is not clear if the authors mean bacteriocidal or bacteriostatic (even if they call it biocidal).

Response 2a). Thank you for this valuable remark. It is true that we cannot claim that the coating kills microorganisms. It may simply inhibit growth of microorganisms. That is why we replaced the ambiguous term “biocidal activity” with “antimicrobial activity” or with “inhibition of microorganism activity” (in red).

Point 2b). In the Experimental Methods section, there is no description of the experiment performed to assess antimicrobial activity.

Response 2b). Lines 166-182 contain a brief description of the experiment on determining the antimicrobial activity. We did not think it necessary to include a more detailed description of the experiment as the work has a reference to the known international standard ASTM E2149 that we used to evaluate the antimicrobial activity.

Point 2c). In Table 2, it is not clear what are the numbers presented.

Response 2c).  Table 2 provides the values of the surface electrical resistance of the PTFE-coated polypropylene yarn. However, this part of the paper focuses on the antimicrobial properties. So, we suppose that your question might be about Table 3. If we are right, then in Table 3 the antimicrobial properties of the coated yarns are characterized by 2 figures – the denominator shows the percentage reduction in the microbial contamination of the test-objects relative to the reference object (physiological solution), the numerator represents its evaluation in points. The evaluation in points was carried out in accordance with the ASTM E2149 international standard. It is described in the Experimental part (lines 175-182).

Point 3. The FTIR spectrum in Figure 5 seems to present the smoothed version of the spectra. This is shown from the scale structure of the lines. See for example in the region 1050-100 cm-1. One cannot present a smoothed spectrum without saying that it has smoothed.

Response 3. The FTIR spectra in Figure 5 were not smoothed or corrected in any other way. They are shown as they were obtained by an «Avatar ESP 360» spectrometer produced by the «Nicollet» company by the multiple attenuated total reflectance method.

Point 4. The description of the electrical characterization is not complete. What is an IESN-1 apparatus? It is not clear how the electrical characterization is performed.

 Response 4. We tried to provide a more detailed description of the procedure of determining the yarn electric characteristics (lines 159-164 in red). In the IESN-1 apparatus, as in any other instrument for measuring electrical resistance, the measurements are made by a teraohmmeter. The distinguishing feature of this apparatus is that the yarn is closely wound in one layer onto the sensor before measurements. The sensor with a yarn wound onto it is mounted onto a dielectric support and is connected to the teraohmmeter. The measurements of the electrical resistance were made in accordance with ГОСТ 19806-74 (GOST 19806-74. Chemical threads. Method of electric resistance determination).

Round 2

Reviewer 1 Report

As Figure 5 shows, the spectra of all the films subjected to abrasion have bands characteristic of PTFE. 
The authors concluded that even after intensive abrasion, the films retain their fluoroplastic coating, but it cannot be concluded from this that the magnetite nanoparticles also remain on the surface after this.

Author Response

Dear reviewer, thank you for such an important remark.

Point. As Figure 5 shows, the spectra of all the films subjected to abrasion have bands characteristic of PTFE. The authors concluded that even after intensive abrasion, the films retain their fluoroplastic coating, but it cannot be concluded from this that the magnetite nanoparticles also remain on the surface after this.

Response. The paper is based on the idea that nanosized magnetite particles build into the structure of a fluoroplastic coating during its formation. As Figure 4 shows, the coating is continuous, i.e. the magnetite particles are really built into the coating structure and are its part. This fact is also confirmed by the PP yarn with a PTFE coating retaining its extremely high chemical stability after the introduction of a small magnetite amount into the coating structure, which indicates that the coating structure is rather dense. The paper contains an explanation (lines 314-315 in red): Figure 4 shows that the magnetite particles are built into the coating structure and make up its integral part. Thus, it can be concluded that even after intensive abrasion, the films still have a fluoroplastic coating doped with stabilized magnetite (line 316 in red).

Reviewer 3 Report

Given the scarce improvements from the previous version I keep recommending the rejection of the manuscript

Author Response

Response. Dear reviewer, we believe that we addressed your remarks in our previous letter. We are very sorry that we could not discuss them with you.

Reviewer 4 Report

The authors have improved some points on the manuscript and have clarified others. However, still, the antimicrobial activity is poorly described. The mention of the international standard ASTM E2149 to evaluate the antimicrobial activity is not enough. The experimental procedure should be at least briefly described, so the reader known how it was performed without having to search elsewhere. The authors have to describe the experimental procedure they followed. In addition, Table 3 (the authors are right, this is what I meant) is still inadequately described.

The authors have to clarify also this part, before the publication of the manuscript.

The authors have improved some points on the manuscript and have clarified others. However, still, the antimicrobial activity is poorly described. The mention of the international standard ASTM E2149 to evaluate the antimicrobial activity is not enough. The experimental procedure should be at least briefly described, so the reader known how it was performed without having to search elsewhere. The authors have to describe the experimental procedure they followed. In addition, Table 3 (the authors are right, this is what I meant) is still inadequately described.

The authors have to clarify also this part, before the publication of the manuscript.

Author Response

Dear reviewer, we have corrected the paper according to your remarks.

Point 1

The authors have improved some points on the manuscript and have clarified others. However, still, the antimicrobial activity is poorly described. The mention of the international standard ASTM E2149 to evaluate the antimicrobial activity is not enough. The experimental procedure should be at least briefly described, so the reader known how it was performed without having to search elsewhere. The authors have to describe the experimental procedure they followed.

Response 1

We have added a description of the experiment to the paper (lines 174-180, in red): “A standard yarn sample was placed into a physiological solution containing a certain number of microbial colonies in the form of a suspension. We kept the vials at room temperature for 24 hours shaking them all the time. The number of the microbial colonies that the solution contained was determined by the changes in the solution transmission coefficient (the reference sample was assumed to have a 100% transmission coefficient) that was obtained by measuring the solution turbidity depending on the number of the colonies it contains.”

Point 2

In addition, Table 3 (the authors are right, this is what I meant) is still inadequately described.

Response 2

We have extended the discussion of Table 3 (lines 293-296, 299-300, in red):” Table 3 shows that the formation of a PTFE coating with high anti-adhesion characteristics provides the PP yarn with weak antimicrobial properties. The introduction of magnetite nanoparticles into the coating structure significantly strengthens the yarn antimicrobial activity. The coated yarns considerably reduce the number of pathogenic bacterial communities, i.e., the yarns with a PTFE coating containing magnetite particles exhibit excellent antibacterial activity against Escherichia coli - a type of gram-negative bacteria - and Staphylococcus aureus - a type of gram-positive bacteria. The yarn also produces a satisfactory inhibiting effect on the activity of the Candida albicans microfungi.”

Round 3

Reviewer 4 Report

The authors have addressed all points.

Author Response

Thank you