Novel Proton Exchange Membranes Based on Sulfonated Poly(acrylonitrile-co-glycidyl methacrylate)/Poly(vinyl chloride) Composite

Round 1

Reviewer 1 Report

The manuscript reported the novel PEMs based on a blend of SPAN, SPGMA or SP(AN-co-GMA) with PVC for DMFCs. The physical-chemical, structural and morphological properties of the resulting membranes are characterized. The findings revealed that the prepared PEMs based on SP(AN-co-GMA)/PVC blends showed lower methanol permeability than that for Nafion membranes. Therefore, these prepared PEMs can be good candidate for DMFC applications.

 

I consider the content of this manuscript will definitely meet the reading interests of the readers of the Sustainability journal. However, there are certain English spelling and grammar issues, and also the discussion and explanation should be further improved. I suggest giving a minor revision and the authors need to clarify some issues or supply some more experimental data to enrich the content. This could be comprehensive and meaningful work after revision.

Detailed comments can be found in the PDF file.

Comments for author File: Comments.pdf

 For grammar issues, it is suggested that the author double-check the small grammar errors in the full text, especially the lack of and redundant use of definite articles.

Author Response

1. For grammar issues, it is suggested that the author double-check the small grammar errors in the full text, especially the lack of and redundant use of definite articles.

Response:

Ok. The manuscript has been revised.

2. For the Keywords, ‘solvent evaporation technique’, ‘methanol permeability’, and ‘blend
   membrane’ should be added in order to attract a broader readership

Response:

‘Solvent evaporation technique’, ‘Methanol permeability’, and ‘Blend
membrane’ have been already added as “Keywords” Page#1, Lines# 33&34.

3. The length of the abstract is too long, which clearly exceeds the requirements of the journal. The number of words and content in the text need to be further refined. ‘Abstract: The abstract should be a total of about 200 words maximum. (https://www.mdpi.com/ journal/sustainability/instructions).

Response:

Fine, the abstract has been shortened to be a total of about 200 words maximum.

4. Page 1, ‘Fuel cells that use proton exchange membranes have made tremendous signs of progress in the previous decade as clean energy candidates. Due to their simplicity and high-power density, PEMFC-powered cars have become increasingly popular [1].’ When introducing the advantages of PEMFC or DMFC, please do not overlook the drawbacks of current fossil fuels. If it were not for these defects and limitations, it would be difficult for fuel cells to embrace the current rapid development. For example, the destruction of the natural environment and damage to human health caused by greenhouse gases, toxic smoke, and dust due to the use of fossil energy is increasingly significant. There is an urgent need to replace traditional fuel vehicles with electric vehicles charged using renewable energy sources, such as hydrogen-based fuel cells [10.3390/en16041653].

Response:

Ok, this valuable information has been added with citing by new reference.  Page#1, Lines# 37-40

The use of fossil fuels results in an increasing amount of greenhouse gas emissions, toxic smoke, and dust that harm human health and the environment. It is urgent to switch over to electric vehicles powered by renewable energy sources, like hydrogen-based fuel cells, in place of conventional fuel vehicles.

 

5. Page 2, ‘A high-water uptake, low methanol uptake, and low methanol crossover should be
   present in the membrane (MCO).’ When the readers read membrane (MCO), they cannot understand what MCO means. This issue should be clarified, and methanol crossover (MCO) should be the correct form [Renewable and Sustainable Energy Reviews 56 (2016): 51-74.]

Response:

Ok. Methanol crossover (MCO) has been mentioned. Page#2, Line #46.

6. Page 2, ‘The most successful membrane is DuPont's Nafion® because of its strong proton
   conductivity and chemical and mechanical stability. At high temperatures (over 800 ° C) and low humidity, the performance of the device suffers significantly (below 30 percent).’
   What is the structure of Nafion to own such good proton conductivity and excellent stability?
   This should be explained better. For example, it is a perfluorosulfonic acid membrane and has a rigid and hydrophobic PTFE backbone, so it has good chemical and mechanical stability. Due to the significant phase separation between the hydrophobic backbone and hydrophilic sulfonic acid groups at the end of the side chain when the membrane is hydrated, Nafion possesses a very high proton conductivity [10.1002/er.4875]. Moreover, the latter sentence is due to DMFC. However, in the Introduction part, DMFC is not very clearly mentioned, but always fuel cells or PEMFC.

Response:

Ok, this valuable information has been added with citing by new reference.  Page#2, Lines# 49-53.

Nafion is a perfluorosulfonic acid membrane and has a rigid and hydrophobic PTFE backbone, so it has good chemical and mechanical stability. Due to the significant phase separation between the hydrophobic backbone and hydrophilic sulfonic acid groups at the end of the side chain when the membrane is hydrated, Nafion possesses a very high proton conductivity

7. Page 5, for Part 2.5, more details should be provided. For example, 2.5.2, what exactly is the gas atmosphere of TGA? What is the rate of temperature increase? For 2.5.3, what is the shape and size of the sample for testing? For 2.5.4, the morphology and microstructure are mainly for the surface of membrane or the cross-section of membrane should be explained better. For 2.5.8, ‘By the same aforementioned technique, methanol uptake was determined by replacing methanol with water [22].’I consider the order is wrong, the correct order should be replacing water with methanol’, just the opposite as the current description

Response:

-Type of gas atmosphere in TGA (N₂), and the heating rate (10°C/min) has been added Page#5, Line#122.

-Shape and size of the sample for testing in Section (2.5.3) has been added Page#5, Lines 127&128 as follow:

The specimens were 30´10 mm. Measurements carried out at constant speed of cross heads movement 5mm/min.

-The morphology and microstructure have been clearly explained for membranes Page#5, Lines#132:134 as follow:

The morphological features of the polymer particulates and topographic features and cross-section microstructure of the polymer membranes were examined. Samples operated at an acceleration voltage of 20KV. Samples were mounted on stainless steel stubs with double tape, 10-20 nm thick layer of gold was sputtered on the samples.

-For 2.5.8 Section, this sentence has been corrected Page#6, Lines# 164&165.

 

 

8. Page 6, ‘A diffusion glass cell composed of two similar compartments was used in this test. Where, PEM specimen was tightly clamped between these compartments. A and B that were filled with 2M methanol solution and deionized water, respectively.’ Please note that in order to avoid differences in liquid pressure caused by different liquid levels, equal volumes of solution should be used on both sides. Moreover, when taking out 1mL of liquid from B, it is also necessary to take out 1mL of liquid from A, otherwise hydraulic pressure difference will occur, and the measured results are not entirely due to the methanol permeability caused by the membrane material, but also include methanol permeability caused by hydraulic pressure difference as the driving force. In addition, how are the transmission curves and concentrations of methanol obtained? By what technology was used to measure the above parameters? The current text lacks relevant descriptions.

 

Response:

-Indeed, this comment is very important if the liquid compartments are placed in vertical form that generates hydraulic pressure. However, in this experiment, liquid compartments were horizontally placed as indicated.

- Concentrations of methanol was measured using gas chromatography.  Page# 6, Lines# 173.

9. Page 6 and 7, for FTIR part, just for sulfur-based groups, it is very confusing. “SPAN revealed an absorption peak at 1134 cm^-1 due to the symmetric vibration of O=S=O”; “a characteristic absorption band was observed at 1149 cm⁻¹ due to the stretching of the sulphonate groups”; “The absorption band at 1153 cm^-1 due to vibration of the sulphonate groups”. However, the authors also describe “Another characteristic peak appeared at 1153 cm⁻¹due to the typical stretching vibration of C-O-C”. So, at 1153 cm^-1, it should be C-O-C or sulphonate groups is very confusing. Moreover, it is not very possible that at 1149 cm^-1 and 1153 cm^-1 appears two peaks, and both of them are related to sulphonate groups. I suggest the authors double-check for this issue.

Response:

Ok. The reviewer has all right in this comment, and the following sentences has been revised to get rid of this confusion;

-The broad absorption peak at 1149 cm^-1 can be due to overlapping the adsorption bands due to vibration of the sulphonate and C-O-C groups.

-Thus, the overlapped peaks appeared at 1149 cm^-1 can prove sulphonation of poly (AN-co-GMA).

10. For both FTIR and Raman spectra, except assigning each peak to each functional group, the interactions between sulfonated polymer and PVC should be discussed, especially about the shift of peaks. However, this issue is not discussed much. and we agree that the excellent results achieved in terms of ethanol and glucose yields in this study were not adequately emphasized in the conclusion section.

Response:

Ok. The potential interactions between PVC and sulfonated polymers on their blending have been indicated that it is mostly physical blending.

11. For TGA part, to better distinguish each thermal event, I suggest adding the ‘the first derivative of the wt% vs. Temperature’ [10.1016/j.electacta.2019.03.056]. For Table 1, many stage is wrongly assigned. For example, around 100 °C should be related to water loss, and around 250 °C is related to the loss of sulfur-based groups. In Table 1, for example, the first stage of SPAN appears at ‘0-364’ °C, while ‘about 250°C corresponds to the decomposition of sulfonic groups. It means the two stages of ‘water loss’ and ‘sulfonic groups loss is wrongly mixed together in Stage 1. The same applies to other polymers or blends.

Response:

As well known, there are many maximum decomposition temperatures for various components and groups in each plain or blend membranes. Therefore, the thermal decomposition has the same slope on each thermogram is considered as a definite decomposition stage.  

12. Except IEC, proton conductivity is also very important parameter. However, it is not measured in the manuscript. For different polymers, it is hard to just compare IEC values to determine the real proton conductivity. For example, the IEC of SPEEK membranes are typically higher than Nafion, but for conductivity, Nafion is still higher [10.1016/j.electacta.2019.03.056]. For efficiency factor, maybe ‘selectivity’ which defines as ‘proton conductivity/methanol permeability’ will make more sense.

Response:

The reviewer has all right in this comment, but unfortunately, the proton conductivity testing was unavailable in our lab. in a performing period of this study.  

13. Since the membranes are designed for DMFC applications, why is there no DMFC single cell test? This is the most intuitive evidence of whether the membrane material is suitable for DMFC applications, but this key result is missing in the last part of the article. Also, how about the chemical stability of the membrane material? Why was it not tested with Fenton's reagent? The thermal stability of many membrane materials is good, but the dual environment of heating + chemical oxidation will lead to rapid degradation of membrane materials. Therefore, the good thermal stability measured by TGA does not mean that the membrane material can exist stably for a long time in the working environment of DMFC without any degradation.

Response:

 The reviewer has all right in this comment, but unfortunately, the chemical stability testing was unavailable in our lab. in a performing period of this study. In the future work, fuel cell performance will measure.

 

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript by Desouky et al. describes the preparation and studying of new PEM membranes as an alternative to expensive Nafion, based on mixture of PVC and other polymers, with sulfonation applied. The work is of some interest but many things need to be improved.

1.     A typo in affiliation (Depart and nt of Chemistry), line 7.

2.     The abstract is too long. Some unimportant details may be shortened, such as detailed description of three stages of membranes preparation.

3.     Line 49. It is not clear, what the term MCO means. Please, include a full meaning.

4.     Full name of KPS needed (line 76).

5.     Lines 101-102. How long did it take for membranes to dry at ambient conditions? Why heating has not been applied? Typically DMF very hard evaporates at ambient conditions, that leaves some doubts on the described method.

6.     The description of TGA measurements of PAN and SPAN (lines 271-274) contradicts to Fig. 6A, where it is shown, that PAN is more resistant to temperature. Please, check this carefully.

7.     Page 21: the thickness of Nafion 117 is 7.2 mm in Table 3. Isn’t it a mistake?

8.     At the Fig. 8a two micrographs at the bottom, P(AN-co-GMA) and the corresponding sulfonated version are shown at different scales (50 and 5 microns). Similar magnification is needed for the correct comparison. The description of SEM results (having 3 Figs) is too brief, even without a reference to Fig. 8c in the text.

9.     To page 25 (IEC results). Could IEC values be recalculated to a proton conductivity? What means that Nafion 117 has the highest IEC? Does it mean that all prepared membranes surpassed Nafion 117 in conductivity? It does not correlate with the highest water uptake of Nafion (Table 7).

10.  Overall, the manuscript presents a number of measured parameters and values with few connections between them. I recommend to improve the work by adding the discussion, to connect each parameter with the others, how structure affect the properties, etc.

Author Response

1. A type in affiliation (Depart and not of Chemistry), line 7.

Response:

 Affiliation is corrected to (Chemistry Department) in the Manuscript, Page#1- Line#9.

2. The abstract is too long. Some unimportant details may be shortened, such as detailed description of three stages of membranes preparation.

Response:

Ok. The abstract has been shortened to be a total of about 200 words maximum.

3. Line 49. It is not clear, what the term MCO means. Please, include a full meaning.

Response:

Ok.  Methanol crossover (MCO) has been written.

4. Full name of KPS needed (line 76).

Response:

Ok. potassium persulphate (KPS) has been mentioned. Page#2- Line#75

5. Lines 101-102. How long did it take for membranes to dry at ambient conditions? Why heating has not been applied? Typically, DMF very hard evaporates at ambient conditions, that leaves some doubts on the described method.

Response:

It is well-known that the film matrix cohesiveness and subsequently its mechanical and barrier properties is highly affected by the solvent evaporation or rate or drying acceleration in case of casting and solvent evaporation technique. Therefore, to avoid brittleness of the resulting membranes, the cast film-forming solution were left to dry at ambient temperature (30±2°C) for about 48 hrs. Drying these membranes at temperature above 40 °C for 4 hrs. led to obtain brittle membranes.

6. The description of TGA measurements of PAN and SPAN (lines 271-274) contradicts to Fig. 6A, where it is shown, that PAN is more resistant to temperature. Please, check this carefully.

Response:

Indeed, there is a mistake in defining each thermogram belonging for each polymer in Fig. 6A. This has been corrected on the Figure. Page#17.

 

7. Page 21: the thickness of Nafion 117 is 7.2 mm in Table 3. Isn’t it a mistake?

Response:

Ok. It is mis-written. It has been corrected as follow:” Thickness of Nafion 117 is 7.2 mil (183 mm).

8. At the Fig. 8a two micrographs at the bottom, P(AN-co-GMA) and the corresponding sulfonated version are shown at different scales (50 and 5 microns). Similar magnification is needed for the correct comparison. The description of SEM results (having 3 Figs) is too brief, even without a reference to Fig. 8c in the text.

Response:

Figure 8a has been changed, whereas the corresponding micrographs for sulfonated form has been shown at the same magnification power. Page#23.  In addition, the SEM micrograph for cross-section of the polyblend membrane has been interpreted. Page#22, Lines#349-356.

Ditto, the micrograph of cross-section of the polyblend membrane Fig 8c exhibited more dense and compact structure comparing with its corresponding for pristine PVC membrane that is characterized with loose structure. The changes can be explained on the basis of the inclusion the sulphonated polymer particulates as a filler in the porous PVC matrix. This explanation can be also confirmed from the SEM micrograph for polyblend membrane surface that revealed non-porous structure with even surface for this membrane on contrary for its corresponding for pristine PVC membrane [48].

Figure 8a. SEM micrographs of homo-and co-polymers and their sulfonated forms.

9. To page 25 (IEC results). Could IEC values be recalculated to a proton conductivity? What means that Nafion 117 has the highest IEC? Does it mean that all prepared membranes surpassed Nafion 117 in conductivity? It does not correlate with the highest water uptake of Nafion (Table 7).

Response:

 The reviewer has all right in this comment, but unfortunately, the proton conductivity testing was unavailable in our lab. in a performing period of this study.

10. Overall, the manuscript presents a number of measured parameters and values with few connections between them. I recommend to improve the work by adding the discussion, to connect each parameter with the others, how structure affect the properties, etc.

Response:

Ok. some improvements have been already done in the discussion section of the manuscript that serve in achieving this aim.

Author Response File: Author Response.docx

Reviewer 3 Report

The authors investigated various polymers that can be potentially used as membrane for DMFCs. The properties of various membranes have been comprehensively characterized and studied. The authors found that when sulfonated polymers are inserted into the PVC matrix, these membrane outperforms Nafion 117 membrane, except the ion exchange capacity, which should be improved in further works. The work is very helpful, but there are several critical issues that must be addressed before the consideration. Please see comments below.

1.      Introduction should be significantly improved. The current status of the research in the field should be introduced, and the bottleneck or issues that existed should be pointed out. Therefore, the intention of this work can be proposed and the novelty of this work should be highlighted.

2.      All figures should be referred or cited in the text. Figure 1 and 2 are not. Please revise.

3.      Why figure 5B doesn’t show the XRD results of the other PVC blends?

4.      The discussions from Line 271-273 are so weird and seem incorrect. Similarly, on line 275, it should not be 300℃ for PGMA with 55% weight loss from Figure 6B. In addition, we cannot see the plot at 700℃ in Figure 6B, which is mentioned on line 277.

5.      I would like recommending to merge Table 1 and 2.

6.      Why the first Column and last Column in Table 3 are identical?

7.      Why the magnifications of SEM images in Figure 8a are so varied? In addition, the figures are not arranged like Figure 8a/8b/8c like this. The labels of samples in Figure 8a are also different compared to Figure 8b and 8c.

8.      Where is Section 3.9?

9.      The most critical issue is that the authors only presented the results of the tests, without any analysis. How does these properties impact the PEM performance is not addressed.

1.   The Figure 9 has a low quality, which should be replot.

The English is fine.

Author Response

1. Introduction should be significantly improved. The current status of the research in the field should be introduced, and the bottleneck or issues that existed should be pointed out. Therefore, the intention of this work can be proposed and the novelty of this work should be highlighted.

Response:

Fine, Introduction has been improved and the novelty is highlighted in the manuscript. Page#2, lines#59-63.

These novel proton-conducting polymer blend membranes based on SPAN/PVC, SPGMA/PVC and SP(AN-co-GMA)/PVC have been prepared for the first time and their structural and functional properties have been characterized. Moreover, the impact of AN: GMA monomeric ratios has been studied.

2. All figures should be referred or cited in the text. Figure 1 and 2 are not. Please revise.

Response:

Ok. Fig.1 and 2 was have been referred in the manuscript. Page#2, line #79 and Page#4, lines #88-89.

3. Why figure 5B doesn’t show the XRD results of the other PVC blends?

Response:

Indeed, XRD patterns for the other polymer blend membranes have been included in Fig.5b. Page#15.

 Figure 5. XRD Patterns of homo-and co-polymers and their sulfonated derivatives (A) and PVC and its blend with sulfonated copolymer (B).

4. The discussions from Line 271-273 are so weird and seem incorrect. Similarly, on line 275, it should not be 300℃ for PGMA with 55% weight loss from Figure 6B. In addition, we cannot see the plot at 700℃ in Figure 6B, which is mentioned on line 277.

Response:

Thermal stability of sulphonated polymers is high thermally stable than un sulphonated one which was obviously shown in Fig.6.

5. I would like recommending to merge Table 1 and 2.

Response:

Ok. Table1&2 have been merged. Page#19.

6. Why the first column and last column in Table 3 are identical?

Response:

Ok. It is mis-written. Table 3 has been edited. Page#21.

7. Why the magnifications of SEM images in Figure 8a are so varied? In addition, the figures are not arranged like Figure 8a/8b/8c like this. The labels of samples in Figure 8a are also different compared to Figure 8b and 8c.

Response:

The reviewer has all right in this comment. Figure 8a was changed whereas, the SEM micrographs with same magnification power have been presented with using identical labels in all Fig. 8a, b, and c. Page#23.

 

Figure 8a. SEM micrographs of homo-and co-polymers and their sulfonated forms.

 

8. Where is Section 3.9?

Response:

Fine, section 3.9 is belonging to methanol permeability section. This has been corrected. Page#27.

 

9. The most critical issue is that the authors only presented the results of the tests, without any analysis. How does these properties impact the PEM performance is not addressed?

Response:

Fine, all the characterized structural and functional properties of PEMs are highly related with their performance and this was indicated in the discussion section. However, the real assessment by employing the resulting PEMs in DMFC will be subject of the part#2 of this research work which will be prepared in the near future.

10. The Figure 9 has a low quality, which should be replot.

Response:

Ok. Figure 9 has been improved.  Page#28.

Author Response File: Author Response.pdf

Reviewer 4 Report

Reviewer's comments- See the attachment.

Comments for author File: Comments.pdf

Author Response

Ok. All editing comments have been done and highlighted with a red color.

Author Response File: Author Response.docx

Reviewer 5 Report

This work developed a novel proton exchange membranes (PEMs) based on a blend of sulfonated polyacrylonitrile, sulfonated polyglycidyl methacrylate or sulfonated poly(acrylonitrile-co-glycidyl methacrylate)/polyvinyl chloride  for direct methanol fuel cells. This is a very interesting subject in the clean energy technology. However, a few of recommendations/comments which should be addressed before acceptance for publication in this journal.

 

The English language must be proofread carefully and missing words are found in the manuscript.

Line 49: MCO and CO are not defined.

Many short terms should be defined and spelled in full terms in the first time mention in the Introduction section. Lack of literature review relevant to this study in the Introduction section. How a polymer blend and composite membrane can improve the device performance? The problem statement of the study is not clear. There have been many sulfonated membranes developed for fuel cells in the literatures. KPS should be defined in full.

Sample preparation procedures for characterization should be explained in detail. Author should include the relevant schematic diagrams/photos such as IEC measurement, methanol permeability, etc. The method to measure methanol concentration should be explained as well. There are no explanation of influences of morphology, roughness and wettability as well as other parameters on fuel cell performance in Introduction section and discussion section. Suggesting the author to describe an ideal PEM in the Introduction section. How to increase the IEC? Hydrophilic or hydrophobic is preferable? What is the value of roughness for Nafion?

Author should proofread the whole manuscript carefully. 

Author Response

The English language must be proofread carefully and missing words are found in the manuscript.

Response:

Ok. The manuscript has been entirely revised.

Line 49: MCO and CO are not defined.

Response:

Fine. It has been mentioned as, methanol crossover (MCO)

Many short terms should be defined and spelled in full terms in the first-time mention in the Introduction section. Lack of literature review relevant to this study in the Introduction section.

Response:

Ok. Introduction section has been completely revised with considering these notes.

 How a polymer blend and composite membrane can improve the device performance? The problem statement of the study is not clear. There have been many sulfonated membranes developed for fuel cells in the literatures.

Response:

As well-known, the fuel cell performance is highly affected by the efficiency of PEM as one of the most important components of PEMFCs. Therefore, the development of cost-effective and efficient PEMs remains a corner stone and the importance of formation of polymer blends and composites has been mentioned in the introduction section and in result and discussion section for the prepared sulphonated polymers-PVC blend membranes.

KPS should be defined in full.

Response:

Full name of KPS (Potassium persulphate) has been mentioned. Page#2, Line#73.

 

Sample preparation procedures for characterization should be explained in detail. Author should include the relevant schematic diagrams/photos such as IEC measurement, methanol permeability, etc.

Response:

That can be more interesting. However, as well-known, the authors are committed with a definite number of figures that is allowable.

 

 The method to measure methanol concentration should be explained as well.

Response:

Concentrations of methanol was measured by gas chromatography in Page#6, Line#178.

There are no explanation of influences of morphology, roughness and wettability as well as other parameters on fuel cell performance in Introduction section and discussion section.

Response:

1. These explanations have been done.

Suggesting the author to describe an ideal PEM in the Introduction section.

Response:

Describing the ideal PEM has been done in the introduction section.

 How to increase the IEC?

Response:

By increasing an ion conducting groups as sulphonic group.

 Hydrophilic or hydrophobic is preferable?

Response:

The hydrophilic/hydrophobic structure with significance of phase separation between the hydrophobic backbone and hydrophilic sulfonic acid groups at the end of the side chain when the membrane is hydrated.

What is the value of roughness for Nafion?

Response:

Roughness value of Nafion is 0.09 µm and it has been mentioned in Table 3. Page#25

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

1. At the following query:

“10. Overall, the manuscript presents a number of measured parameters and values with few connections between them. I recommend to improve the work by adding the discussion, to connect each parameter with the others, how structure affect the properties, etc.”

The authors replied:

“Ok. some improvements have been already done in the discussion section of the manuscript that serve in achieving this aim.”

This is not enough, and the discussion section is not found in the latest version of the manuscript. It still represents a number of measured characteristics with few connections between them. This is the main thing necessary to accept the manuscript. Section 3 (Results) may be called “Results and discussion”. Do Raman spectra confirm FTIR results of complex formation between two matrices? Is it follows from XRD data that the degree of crystallinity rises after sulfonation? Can the degree of crystallinity be calculated from these spectra? Can be the higher thermal stability of sulfonated membranes be the result of their higher crystallinity? What mechanical properties are better for membranes for the work in fuel cells – with larger elongation at break or not, and how sulfonation and variation of the content (additive to PVC) affects the mechanical properties? If this can be explained, then you can predict, how to prepare membranes with optimal properties in future works. Why the roughness of complex membrane rises triple vs pure PVC membrane? Is it good or not for the work in fuel cell? Why PVC have roughness 12 times larger than Nafion? How roughness measurements correlate with SEM results? What follows from the reducing of the contact angle for complex membranes, and how it correlates with degree of crystallinity (XRD data)? These and other questions need to be discussed in details. The conclusion is also too short and does not reveal the essence of the whole work.

2. The title of Table 6 is not correct (it is not contact angle data).

3. To 2.5.3. section: what were the relative humidity of air conditions during mechanical measurements? Was RH nearly equal for all studied samples? It is very important for mechanical data.

4. To the section 2.4. Why different solvents THF and DMF were used to form polymer mixtures? I had some doubts that membranes may be dried at ambient temperature because of using DMF. Now it is clear that it is possible due to THF, but still requires a long time (48 h). Why not choose THF for both components? It will evaporate more quickly.

Author Response

 

Reviewer#2

1. Overall, the manuscript presents a number of measured parameters and values with few connections between them. I recommend to improve the work by adding the discussion, to connect each parameter with the others, how structure affect the properties, etc.”

The authors replied:

“Ok. some improvements have been already done in the discussion section of the manuscript that serve in achieving this aim.”

This is not enough, and the discussion section is not found in the latest version of the manuscript. It still represents a number of measured characteristics with few connections between them. This is the main thing necessary to accept the manuscript. Section 3 (Results) may be called “Results and discussion”. Do Raman spectra confirm FTIR results of complex formation between two matrices? Is it follows from XRD data that the degree of crystallinity rises after sulfonation? Can the degree of crystallinity be calculated from these spectra? Can be the higher thermal stability of sulfonated membranes be the result of their higher crystallinity? What mechanical properties are better for membranes for the work in fuel cells – with larger elongation at break or not, and how sulfonation and variation of the content (additive to PVC) affects the mechanical properties? If this can be explained, then you can predict, how to prepare membranes with optimal properties in future works. Why the roughness of complex membrane rises triple vs pure PVC membrane? Is it good or not for the work in fuel cell? Why PVC have roughness 12 times larger than Nafion? How roughness measurements correlate with SEM results? What follows from the reducing of the contact angle for complex membranes, and how it correlates with degree of crystallinity (XRD data)? These and other questions need to be discussed in details. The conclusion is also too short and does not reveal the essence of the whole work.

 

Response:

Ok. some improvements have been done in the discussion section of the manuscript to connect between all measured characteristics as follow:

1. On the other hand, the FTIR spectrum of PVC with sulfonated polymers revealed slight shift for adsorption band of C-Cl from 634 to 622 cm -1and decreasing in its intensity which can be attributed to reduction of PVC proportion in the composites. Furthermore, a new absorption peaks appeared at 1199 and 3443 cm-1 due to the stretching of the sul-phonate and hydroxyl groups, respectively, in addition to the adsorption peak at 1700 cm-1 belonging to C=O group. However, there is no new peaks appeared as a result to the chemical reaction and hence this prove that just physical combination occurred between the two polymeric substances, Page#7- Line#210-217.
2. Raman spectral analysis is a complementary technique to infrared spectroscopy which enabled the identification of characteristic vibrational bands of molecular structures, Page#10- Line#224-226.

The Raman spectrum of PVC exhibited a strong peak at 637 cm^-1 corresponding to the C-Cl bonds [14, 15]. In addition, Raman spectra of composites of sulfonated polymers with PVC showed a slight shift of C-CL bond, in addition to appearance of absorption peaks at 1700 cm^-1 due to C=O group present in SPAN, SPGMA and SP(AN-co-GMA), which prove the combination of the two polymeric substances, Page#10- Lines#240-244.

 

3. Crystallinity degree of such blends was estimated and the results were tabulated in Figure 5c. The percentage of crystallinity of different samples is calculated by the following equa-tion:

% Crystallinity = A _Crystalline × 100 / A _Total

Where, A _crystalline represents the area of the crystalline regions, and A _Total represents the total area under the peak.

This can be confirmed by crystallinity degree of such composites presented in Figure 5c. From this figure, it is noticed that PVC is amorphous while the sulfonated co-polymers were semi-crystalline. Hence, an incorporation of sulfonated co-polymers into PVC matrix led to increasing the crystallinity degree of the resulting composites. However, this increase was more pronounced in case of SPGMA/PVC than SPAN/PVC. Hence, the increase of crystallinity degree in SP(AN-co-GMA)/PVC composite was associated with increasing the GMA proportion in SP(AN-co-GMA), Page#12- Lines#273-280 and Fig 5c Page#15.

Figure 5c. Crystallinity percentage of PVC and its blend with sulfonated copolymer

 

 

4. These data showed that the weight loss percentages at different temperatures for such composite are less than that of pristine PVC, confirming its higher thermal stability, Page#15- Lines#312-314.

As mentioned above, the higher thermal stability of composite membrane can be attributed to increase of its crystallinity degree owing to incorporation of partially crystalline co-polymer into the PVC matrix, Page#16- Lines#318-320.

 

5. This drastic drop in the mechanical strength of PVC when incorporating sulfonated homo- or co-polymers can be explained on the basis that the sulfonated polymers particulates might act as stress concentrators resulting in early failure of the membrane. Whereas, the more pronounced decline in the tensile strength of SPGMA/PVC and SP(AN-co-GMA)/PVC composites-based membranes compared with those based on SPAN/PVC composite may be attributed to the changes in structural and conformational properties of these sulfonated polymers that define the extent of compatibility between sulfonated polymers and PVC and subsequently the dispersion of these modified poly-mers with PVC matrix. Since SPGMA and SP (AN-co-GMA) have higher crystallinity and thermal stability, in addition to more irregularities in their shape comparing with SPAN (as indicated from XRD, TGA, and SEM) which could result to weak interfacial interaction with PVC matrix and poor dispersion reducing the interfacial shear strength thereby reducing the strength of composite membranes. On the other hand, the positive effect of in-corporation of SPGMA in PVC matrix on elongation at break can be attributed to the microstructural features of SPGMA and their distribution into SPGMA/PVC composite matrix, where the longitudinal orientation of SPGMA fibers that have shown from SEM ex-amination (Fig. 8a) can lead to fiber-related energy dissipation mechanisms like fi-ber-matrix debonding, fiber pullout, and fiber breakage restricting the deformation of matrix during tensile loading which resulted in loss of elongation, Page#20- Lines#348-360.
6. Ditto, the micrograph of cross-section of the composite membrane Fig 8c exhibited more dense and compact structure comparing with its corresponding for pristine PVC mem-brane that is characterized with loose structure. The changes can be explained on the basis of the inclusion the sulfonated polymer particulates as a filler in the porous PVC matrix. This explanation can be also confirmed from the SEM micrograph for composite mem-brane surface that revealed non-porous structure with even surface for this membrane on contrary for its corresponding for pristine PVC membrane, Page#21- Lines#387-394.
7. The increase of surface roughness for SPGMA/PVC and SP(AN-co-GMA)/PVC compo-site-based membranes was ascribed to the irregular shape and greater size of these hy-drophilic sulfonated homo- or co-polymers filler within PVC matrix resulting their poor dispersion within the membrane matrix. On the contrary, SPAN particulates can be high-ly dispersed within PVC matrix filling its pores resulting a dense structure and less sur-face pores. This could prevent the methanol diffusion within the composite membrane matrix. Notwithstanding, no positive correlation was noticed between membrane rough-ness and transmission rate as indicated from methanol permeability test (discussed be-low), Page#24- Lines#409-417.
8. This decline in the methanol permeability of the SPAN/PVC composite-based membrane can be attributed to the dense and compact structure of the composite matrix that was previously proven from the SEM examination. In addition to the high hydrophilicity of composite membrane surface that hinders the adsorption of methanol and therefore reduced its cross-over. Compared to SPAN/PVC composite-based membranes with dense structure, SP(AN-co-GMA)/PVC and SGMA/PVC composite-based membranes in despite of their higher surface roughness or pore density exhibited lower methanol permeability, as they led to transport of methanol molecule more complicated through the torturous path owing to the presence of the sulfonated polymers filler particulates, Page#26- Lines#476-484.

In addition to the higher efficiency of these developed composite-based membranes compared to Nafion, they are cost-effective. Therefore, they can be considered promising candidates for DMFC applications, Page#26- Lines#489-491.

9. In this research work, novel proton exchange membranes based on sulfonated poly-acrylonitrile, sulfonated polyglycidyl methacrylate, or sulfonated poly (acrylo-ni-trile-co-glycidyl methacrylate)/poly (vinyl chloride) composites were successfully de-veloped using physical combining and casting with solvent evaporation technique for DMFCs application. The structural and functional properties of the developed compo-sites-based membranes were characterized using FTIR, XRD, SEM, TGA, hydrophilicity, water and methanol uptake, methanol permeability, and IEC measurements. Overall, the most desirable peculiars for PEMs such as IEC, water uptake, methanol permeability, and thermal stability were proper, especially with incorporating sulfonated copolymers into the PVC matrix. The IEC was 0.48 meq/g for SP(AN-co-GMA) (1:2)/PVC composite-based membranes. Moreover, it was found that these composite-based PEMs outperform Nafi-on® by their lower methanol permeability (8.710-7cm2/sec) and lower cost. However, their low mechanical strength and IEC in comparison to Nafion®117 should be improved in future research by optimizing design of composite materials through precise tuning of sulfonation and incorporation process to achieve better mechanical, thermal and chemical stability and therefore increased PEM fuel cell performance, Page#26- Lines#506-521.

 

 

2. The title of Table 6 is not correct (it is not contact angle data).

Response:

Indeed, there is a mistake in title of Table .6 and it has been corrected, Page#27- Line 442.

Table 6. water and Methanol uptake on the surface of pristine PVC and polyblend membranes.

 

 

3. To 2.5.3. section: what were the relative humidity of air conditions during mechanical measurements? Was RH nearly equal for all studied samples? It is very important for mechanical data.

Response:

 Prepared membranes were preserved well before mechanical measurement at ambient temperature and RH was determined (70%).  

4. To the section 2.4. Why different solvents THF and DMF were used to form polymer mixtures? I had some doubts that membranes may be dried at ambient temperature because of using DMF. Now it is clear that it is possible due to THF, but still requires a long time (48 h). Why not choose THF for both components? It will evaporate more quickly.

Response:

Different solvents of THF and DMF was used to form polymer mixtures as:

THF is the best solvent to dissolve PVC polymer, on the other hand sulphonated polymers dissolve better in DMF rather than THF.

 

 

Author Response File: Author Response.pdf

Reviewer 3 Report

This is a revised version and the authors have addressed all the comments from previous reviewers. The manuscript is in good shape now.

Author Response

Thanks alot

Reviewer 5 Report

The author has improved and addressed all the comments. The current form of manuscript is recommended to be accepted for publication in this journal.

Author Response

Thanks alot

Round 3

Reviewer 2 Report

New version of the manuscript is much better. It can be accepted after adding the information about RH regulation in 2.5.3 section during mechanical tests (see a detailed description in a pdf-file).

Comments for author File: Comments.pdf

Author Response

Thanks a lot,

Information about RH regulation in 2.5.3 section during mechanical tests was added in the Manuscript as follow:

Dried membranes were manually removed from the petri dishes and conditioned in a humidity chamber at 25 ± 2 ^o C, and 50 ± 2% relative humidity in an environmental chamber before further mechanical testing.