Optimization of Process Parameters for Obtaining Polyethersulfone/Additives Membranes

Round 1

Reviewer 1 Report

This paper talks about the physical properties of the hollow fiber membrane they made with the water permeance as well. 

To better understand the paper. I do have a some questions for the authors. 

1. What is the objective to study this PES/PVP/Clay system? It is not clear to me in the introduction. How does it work for water treatment.
2. I think the paper is lack of the information in the experimental part, for example, what is the MW of the polymers. What is the spin condition for the polymers, what is the bore solutions etc. 
3. I think it is not far to draw any conclusion that how the polymers wiill affect the viscosities if we don`t know the molecular weight of them. 
4. In SEM your fibers are not round, which is hard for to understand the thickness measurements and it will influence the permeance calculation in the end. 
5. In Figure 12, AM-6 the flow increase over the time at 1 bar but not at 2 bar, can author explains that?
6. PVP is water soluble, the authors chose PVP to do water permeance test, how can they confirm that PVP is not washed out over time?
7. There is only pure water flux, how is this related to water treatment.

Author Response

Response to Reviewer 1 Comments

 

The comments suggested by Reviewer 1 were answered in the manuscript in yellow color and by Reviewer 2 were in green color.

 

Point 1.           What is the objective to study this PES/PVP/Clay system? It is not clear to me in the introduction. How does it work for water treatment.

Response 1: Done, a paragraph was included explaining the variables that influence membrane production by phase inversion. (lines 66-79). This work is the first part of a study with several effluents types that we will publish in the future.

Point 2.           I think the paper is lack of the information in the experimental part, for example, what is the MW of the polymers. What is the spin condition for the polymers, what is the bore solutions etc.

Response 2: Done (line 91, 94, 113-114 and 123). The parameters for obtaining the hollow fiber are shown in table 1 (Line 142-146).

 

Point 3.           I think it is not far to draw any conclusion that how the polymers wiill affect the viscosities if we don`t know the molecular weight of them.

Response 3: Really. The mass of were added to the line 105 (PES) and 108 (PVP).

 

Point 4.           In SEM your fibers are not round, which is hard for to understand the thickness measurements and it will influence the permeance calculation in the end.

Response 4: The fibers are not really uniform (SEM), for this reason the thicknesses were calculated by making 20 measurements along the membrane with the aid of image analysis software and averaging these values, as shown in lines 342-345.

Point 5.           In Figure 12, AM-6 the flow increase over the time at 1 bar but not at 2 bar, can author explains that?

Response 5: We really don't have an explanation. This behavior is strange and we will repeat the test. All other samples had an almost constant behavior, only sample 6 that presented this increasing behavior.

Point 6.           PVP is water soluble, the authors chose PVP to do water permeance test, how can they confirm that PVP is not washed out over time?

Response 6: The term "higher concentration of polymers" has been replaced by "higher concentration of PES" (line 358). The high concentration of PES influences the permeability. As for PVP, it is actually soluble in water and does not remain in the final membrane structure. However, PVP can indeed influence the viscosity of the solution before spinning, except that table 2 shows that the high concentration of PES in samples AM3, AM4 and AM5 masked the effect of PVP, that is, PVP did not have influences sample processing.

Point 7.           There is only pure water flux, how is this related to water treatment.

Response 7: This work is the first part of a study with several effluents types that we will publish in the future. But for a better adaptation to the present work, the term "water treatment" was removed of the manuscript title (line 4).

 

Author Response File: Author Response.docx

Reviewer 2 Report

Protection of water and treating wastewater is one of the most important tasks for the inhabitants of the earth. Day by day, newer and more modern ways to solve this problem can be found on several research places.

This work is one of these modern topics, dealing polymeric membrane technology, being the fastest developing procedures for treatment of wastewater. Authors are investigating the polyether sulfone membranes with addition of nanoparticles, by using of clay an another additives, e.g. polyvinylpirrolidone.

The elaboration of the work in point of view of experimentals, mathemathical and analytical methods and by using of model of experiments is impressive and seems to be adequate. The conclusions drawn are correct and the results are well.interpreted.

The following should be corrected:

1. The Abstract is not enough clear and concrete. It shows unnecessary details instead of presenting factually the research work.
2. The Conclusion is very long, without presenting the scope and limitations of the results obtained.
3. The English in some places is circumstantial and difficult to understand.

Author Response

Response to Reviewer 2 Comments

 

The comments suggested by Reviewer 1 were answered in the manuscript in yellow color and by Reviewer 2 were in green color.

 

Point 1.     The Abstract is not enough clear and concrete. It shows unnecessary details instead of presenting factually the research work.

Response 1: The abstract has been changed to improve understanding for the reader. The changes can be seen on lines 16 and 24-28

 

Point 2.     The Conclusion is very long, without presenting the scope and limitations of the results obtained.

Response 2: The conclusion was reduced and the scope and limitations of the membranes were added. The changes can be seen in lines 401, 404-409 and 414.

 

Point 3.     The English in some places is circumstantial and difficult to understand.

Response 3: English was correct and improved.

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

1. I guess what I am asking in the previous review is what is the objective of study the PES/PVP/Clay system. The author claims that the clay is cheap and PVP is well studied. Not sure this is a scientific reason that the author want to do this experiments. 

2. I am still not clear that how the PVP influence the viscosity from your table. 

3. In the abstract, the authors would like to find the best composition for the HF spin, I did not see it in the conclusion.

4. I dont know how to do a contact angle test and viscosity test without knowing the concentration of the additives in the the solvent. 

5. Authors prepare 9 solutions and only get 7 SEM of them and 4 water permeance of them, I will recommend to complete all the test. 

Author Response

Response to Reviewer 1 Comments

 

The comments suggested by Reviewer 1 were answered in the manuscript in yellow color and by Reviewer 2 were in light blue color.

 

Point 1. I guess what I am asking in the previous review is what is the objective of study the PES/PVP/Clay system. The author claims that the clay is cheap and PVP is well studied. Not sure this is a scientific reason that the author want to do this experiments.

Response 1: Done. Information was added on lines 59-69. The use of planning was to optimize the choice of processing parameters, where the PVP would control viscosity and expedite precipitation, and in the case of clay, it would be to improve the properties of the membranes, both in terms of morphology and hydrophilicity and mechanical strength.

 

Point 2. I am still not clear that how the PVP influence the viscosity from your table.

Response 2: Done. Information was added on lines 255-257. According to the literature, PVP acts as a viscosifier, however this effect was not very pronounced when compared to the effects of the concentration of PES and Clay. However, it facilitates the processing of the hollow fiber membrane, speeding up the precipitation.

 

Point 3. In the abstract, the authors would like to find the best composition for the HF spin, I did not see it in the conclusion.

Response 3: Done. The information was added on the conclusion (lines 409-410).

 

Point 4. I dont know how to do a contact angle test and viscosity test without knowing the concentration of the additives in the the solvent.

Response 4: The solvent concentration was added to the methodology (lines 135-137)

 

Point 5. Authors prepare 9 solutions and only get 7 SEM of them and 4 water permeance of them, I will recommend to complete all the test.

Response 5: Analyzes were added, as can be seen in Figures 11 and 12. For flow measurements, samples AM3, AM4 and AM5 did not obtain flow. The explanation can be seen in lines 375-377

Author Response File: Author Response.docx

Reviewer 2 Report

396 "showed great potential for application in the effluents treatment ??? não tirou do título???.  This is a mistake.

Author Response

Response to Reviewer 2 Comments

 

The comments suggested by Reviewer 1 were answered in the manuscript in yellow color and by Reviewer 2 were in green color.

 

Point 1.     396 "showed great potential for application in the effluents treatment ??? não tirou do título???.  This is a mistake.

Response 1: The sentence has been removed from the text

Author Response File: Author Response.docx

Round 3

Reviewer 1 Report

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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

Water, as one of the basic requirements in all of the Earth for sustainable development, is one of the most important basic conditions in our world. Thus, the conservation and creation of water resources is our fundamental task. Any research that puts this at the forefront is essential and gets the most attention. This work is also related to this topic and presents an excellent research, noting its weaknesses and mistakes, as well.

1.The manuscript should be revised in English language. There are several rather complicated sentences.

2.In the Introduction more informations and literature data are needed supporting the object and plan of the research.

3. Describe please the composition of the „clay”. The structure of polymers – primarily the PES – should be presented.
4. Table 1.: the units (% and °) should be added to the top line.
5. Table 6.: missing SI units of diameter and thickness. Are these diameter and thickness average values of the membranes? Please, mark the deviations of diameters and thicknesses.
6. The abbreviations are unneccessary in the titles (85, 135).
7. In Conclusion a scope and limitation should be added to the practical use of the procedure.

 

In summary: This is an excellent research project and an excellent elaboration and discussion of the experimentals and their theoretical evaluation. I can suggest the acceptation with minor revision.

Author Response

Response to Reviewer 1 Comments

 

The comments suggested by Reviewer 1 were answered in the manuscript in yellow color and by Reviewer 2 were in green color.

 

Point 1. The manuscript should be revised in English language. There are several rather complicated sentences.

Response 1: The review was done.

 

Point 2. In the Introduction more informations and literature data are needed supporting the object and plan of the research.

Response 2: Informations were added in the introduction to give more focus to the research objective.

 

Point 3. Describe please the composition of the „clay”. The structure of polymers – primarily the PES – should be presented.

Response 3: Done. It was explained in the text, lines 95-101

 

Point 4. Table 1.: the units (% and °) should be added to the top line.

Response 4: Done.

 

Point 5. Table 6.: missing SI units of diameter and thickness. Are these diameter and thickness average values of the membranes? Please, mark the deviations of diameters and thicknesses.

Response 5: SI units were placed.  Yes, they are the average values and their deviations have been added.

 

Point 6. The abbreviations are unneccessary in the titles (85, 135).

Response 6: Done. Abbreviations have been removed.

 

Point 7. In Conclusion a scope and limitation should be added to the practical use of the procedure.

Response 7: Done. This comment was included in line 381-386.

Author Response File: Author Response.pdf

Reviewer 2 Report

 

General comments：

In this manuscript, the authors present a study of a statistic method to optimize the additives in membrane fabrication. However, the method and novelty were not well discussed. The manuscript needs to strength how the initial parameters are given to the software and why? What’s their priority?  Does the modelling came after the experiment result or guided the experiment? The manuscript may of great value to the membrane scientist. The reviewer would like to recommend its major revision.

 

1.     Line 46-48:

 “Most of the membranes used are polymeric due to the low cost and ease of manufacture.

However, they have some limitations that may restrict their use, such as instability at high

temperatures and low selectivity [10,11]. Among the available polymers for membranes production, polyethersulfone (PES) is one of the most widely used due to its good mechanical strength, thermal stability and fast precipitation.”

Question: PES is still a polymeric membrane. Here, the statements are in conflict with each other.

2.     Use of PVP to optimize the pore size and hydrophilicity is actually not new. The author should focus more in the novelty of their work instead focus on other well-known knowledge.  

 

3.      The reader would like to know more about the clay material, such as the size (interlayer distance), dispersion or other parameters.

4.     Figure 10 shows the structure of the hollow fiber which are not clear. Why the fibers are asymmetrical (thickness distribution)? It’s better to provide high magnification.

5.     How to calculate the thickness in Table 6 for the asymmetrical thickness? All the values in Table 6 are invalid without unit.

6.     Figure 11.

Why the flux is increasing at 1.0 bar along with the testing but stale at 2 bar for sample 6?

Did the membrane damage?

Again, should keep the membrane code consistent in the text and figures. AM 6 means sample 6?

7. The caption is too simple and the information is not enough. Please help to improve.

 

Author Response

Response to Reviewer 2 Comments

 

The comments suggested by Reviewer 1 were answered in the manuscript in yellow color and by Reviewer 2 were in green color.

 

Point 1.     Line 46-48:

 “Most of the membranes used are polymeric due to the low cost and ease of manufacture. However, they have some limitations that may restrict their use, such as instability at high temperatures and low selectivity [10,11]. Among the available polymers for membranes production, polyethersulfone (PES) is one of the most widely used due to its good mechanical strength, thermal stability and fast precipitation.”

Question: PES is still a polymeric membrane. Here, the statements are in conflict with each other.

Response 1: The text was changed in order to eliminate existing conflicts.

 

Point 2.     Use of PVP to optimize the pore size and hydrophilicity is actually not new. The author should focus more in the novelty of their work instead focus on other well-known knowledge. 

Response 2: The novelty of the work is the use of clay to solve the limitations of PES, as well as the use of experimental design to assess the influence of membranes components on the response variables considered, seeking to optimize the process.

 

Point 3.     The reader would like to know more about the clay material, such as the size (interlayer distance), dispersion or other parameters.

Response 3: Done. It was explained in the text, lines 95-101

 

Point 4.     Figure 10 shows the structure of the hollow fiber which are not clear. Why the fibers are asymmetrical (thickness distribution)? It’s better to provide high magnification.

Response 4: Done. Hollow fiber membranes are asymmetric as they coexist micro and macropores along the thickness of the membrane. They can be better viewed at the higher magnification (Fig.10b).

 

Point 5.     How to calculate the thickness in Table 6 for the asymmetrical thickness? All the values in Table 6 are invalid without unit.

Response 5: The thickness was estimated according to the outer and inner diameter media. Thickness = outer diameter – inner diameter. SI units were placed

 

 

Point 6.     Figure 11. Why the flux is increasing at 1.0 bar along with the testing but stale at 2 bar for sample 6?

Did the membrane damage?

Again, should keep the membrane code consistent in the text and figures. AM 6 means sample 6?

Response 6: Flow measurement tests were performed some times to confirm the results. In fact, the tests performed for AM6 showed the same flow behavior, in which the membranes were not damaged. Initially, with 1.0 bar, it was noticed that the flow tends to increase over time, while with 2.0 bar the flow was stable more quickly.

AM 6 means sample 6, the Figure 11 was changed to keep the membrane code consistent with the text.

 

Point 7.  The caption is too simple and the information is not enough. Please help to improve.

Response 7: Done. The captions have been reformulated.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The author did not answer the reviewer's question properly (question 4 to 6).  There are still major problem in the data analysis.

 

Point 4.     Figure 10 shows the structure of the hollow fiber which are not clear. Why the fibers are asymmetrical (thickness distribution)? It’s better to provide high magnification.

Response 4: Done. Hollow fiber membranes are asymmetric as they coexist micro and macropores along the thickness of the membrane. They can be better viewed at the higher magnification (Fig.10b).

--------------Comment 4: I have studied hollowfiber before. A good hollowfiber membrane should have symmetrical strucure in thickness. I understand that the pore structure is asymmetric for phase inversion underreview in high maginification. Form your SEM in Figure 11b, it is quite difficult to determine the thickness. 

 

Point 5.     How to calculate the thickness in Table 6 for the asymmetrical thickness? All the values in Table 6 are invalid without unit.

Response 5: The thickness was estimated according to the outer and inner diameter media. Thickness = outer diameter – inner diameter. SI units were placed

------Comment 5: Firstly, In Point 4，it is difficult to determine the thickness,and the distribution should not that uniform as your data distribution is quite small. Secondly, the thickness calculation method is incorrect, should be half of the (outer diameter-inner diameter). The author should be careful in data analysis to avoid obvious errors when you prepare your manuscript before submission. 

 

 

Point 6.     Figure 11. Why the flux is increasing at 1.0 bar along with the testing but stale at 2 bar for sample 6?

Did the membrane damage?

Again, should keep the membrane code consistent in the text and figures. AM 6 means sample 6?

Response 6: Flow measurement tests were performed some times to confirm the results. In fact, the tests performed for AM6 showed the same flow behavior, in which the membranes were not damaged. Initially, with 1.0 bar, it was noticed that the flow tends to increase over time, while with 2.0 bar the flow was stable more quickly.

AM 6 means sample 6, the Figure 11 was changed to keep the membrane code consistent with the text.        

Comment 6: you did not answer my question. I understand the result but you should provide the reason why it happen.