Synthesis of Silane Functionalized Graphene Oxide and Its Application in Anti-Corrosion Waterborne Polyurethane Composite Coatings
Round 1
Reviewer 1 Report
This manuscript recommned the accept after minor versions.
The author seems to have experimented and discussed very sincerely.
-minor opinion
In the Fig.11, all line shape is same. In the case ter gray version, reader will confuse. so the line type is correct with various line shape(dot, short line, et al)
Author Response
Dear Reviewer,
Thank you for your comments, below is our response to the comment.
1. Response to comment: In Fig. 11, all line shape is same, the reader will confuse once the paper is published in ter gray version.
Response: The line type have been revised with different line shape to identify clearly.
Thanks for all the help.
Reviewer 2 Report
This paper describes fabrication of graphene oxide and reactive microsphere containing waterborne polyurethane coating and its characterization on steel surfaces including corrosion performance. All in all, the paper has points of interest but the authors are required to do the following revisions before their paper may be accepted for publication:
Several English language problems exists. The paper much be edited professionally, otherwise the quality of the paper will decline. What type of PU are you using? Polyester, polyether or other? Please indicate and also present FTIR of the pure polymer in Figure 2 and discuss. Please present in situ EDX Si elemental map of the best performing coating by SEM imaging its surface and cross section and discuss Si dispersion within the coating in connection with GO. Why there are (a) and (b) in Figure 6 caption what are the differences? More info is needed for Figure 9 caption. Figure 12 caption a, b, c please explain in caption. In the introduction section please also cite other important works that combine graphene and other fillers such as silica nanoparticle aggregates that create superior non-wetting coatings that can resist abrasion damage such as Journal of Colloid and Interface Science Volume 519, 1 June 2018, Pages 285-295. Please change your conclusions and itemize each conclusion separately and clearly in relation to the 13 figures discussed in the paper.
Author Response
Dear Reviewer,
Thank you for your comments, below is our response to the comment
1.Response to comment: Several English language problems exists, the paper must be edited professionally.
Response: I have made great efforts to revise the English problems in order to meet with approval.
2.Response to comment: What type of waterborne polyurethane are used and present FTIR of the waterborne polyurethane.
Response: The waterborne polyurethane belongs to polyether, and it is confirmed by FTIR spectra.
3.Response to comment: Present in situ EDX Si elemental map of the 0.5% PVSQ-GO/WPU coating by SEM imaging its surface and cross section and discuss Si dispersion within the coating in connection with GO.
Response: The in situ EDX Si elemental map images of the 0.5% PVSQ-GO/WPU coating specimen for its surface and cross section show that PVSQ-GO composite exhibit good dispersion in coating matrix and good compatibility between PVSQ-GO composite and waterborne polyurethane.
4.Response to comment: Why there are (a) and (b) in Figure 6 caption, what are the differences?
Response: Fig.6a and Fig.6b represent the adhesion strength and hardness of as-prepared coating specimens, respectively.
5.Response to comment: More info is needed for Figure 9 caption
Response: I have supplemented the meaning of each equivalent electrical circuits in the paper.
6.Response to comment: Figure 12 caption a, b, c please explain in caption.
Response: I have supplemented explanation for Fig.12 caption.
7.Response to comment: In the introduction section please also cite other important works that combine graphene and other fillers such as silica nanoparticle aggregates that create superior non-wetting coatings that can resist abrasion damage.
Response: I have cited literature which involving wear resistance that combine graphene and other silica nanoparticle in the introduction section.
8.Response to comment: Change the conclusions and itemize each conclusion separately and clearly in relation to the 13 figures discussed in the paper.
Response: I have revised the conclusion section and itemize each conclusion separately.
Thank you for your valuable comments.
Reviewer 3 Report
Good paper.
Author Response
Dear Reviewer,
Thank you for your comments, below is our response to the comment.
1.Response to comment: Good paper
Response: Thank you for your review and praise.
Thanks for all the help.
Reviewer 4 Report
The authors present a study on the anti-corrosion waterborne polyurethane coating containing silane functionalized graphene oxide (PVSQ-GO). The motivation for this study was not strongly supported by the introduction. The synthesized PVSQ-GO was characterized with appropriate analytic tools and the experimental results are clearly presented. However, each result was not discussed enough to persuade potential readers. In addition, the manuscript requires extensive editing of English. After English editing and significant revision of the manuscript, it could be considered for publication in Coatings.
- Clarify how graphene contributes to the anti-corrosion property. I presume the most important feature is its impermeability (especially in the case of CVD-grown graphene) to gas or moisture. If so, adding reduced GO or GO sheets to coating materials would be also beneficial for providing a tortuous pathway. But the mechanisms or backgrounds for these improvements were not clearly written.
- What excellent properties and unique effects drove the authors to choose PSQ for the modification of GO (line 78-81)? I also wonder if this modification performs better than GO sheets modified with 2-(3,4-epoxycyclohexyl)ethyl triethoxysilane (C. Zhang et al, Coatings 2019, 9, 46). This previous work seems highly related to the current one, but it was missing in the references.
- The authors argue that PVSQ-GO has better dispersion stability in water than pristine GO. However, PVSQ-GO is more hydrophobic than GO (Figure 3a and 3b). In addition, it is more likely that PVSQ-GO sheets were aggregated. Figure 2b shows the 2theta angle close to graphite after modification with PVSQ. This implies that graphene oxides were aggregated or even reduced chemically, either of which leads to poor dispersion. Taking photographs is a simple but rather inaccurate way to compare dispersion of each material. Instead, comparing the relative change in UV-Vis light absorption of each solution before and after settling for 24 hours will be a more quantitative way.
- The thermal stability of PVSQ-GO seems exaggerated. There are many inorganic components and its content is supposedly more than 18 wt%, the Si content in PVSQ-GO (Figure 2f). If PVSQ is non-flammable, this good thermal stability makes sense. But I do not think Si-O-C alone is strong enough to resist at the temperature up to 800 degrees C.
- Please explain why PVSQ-GO was dispersed well in polyurethane than pristine GO. Is the PU hydrophobic enough to have good affinity to PVSQ-GO?
- There is no explanation of how high adhesion strength was achieved after incorporating 0.5 wt% of PVSQ-GO. How does the surface chemistry of the steel affect the adhesion to polyurethane containing GO?
- Incorporating 0.5 wt% of pristine GO into WPU shows poor performance in Figure 7. It seems adding GO to WPU is not a good strategy for anti-corrosion. Then why don’t we put PVSQ particles only instead of PVSQ+GO hybrid materials? If the hydrophilicity of GO is the problem, would it be better to chemically or thermally reduce PVSQ-GO for anti-corrosion?
- It is hard to compare the performance of each material in Figure 8. I highly recommend the authors put the same scale for the y-axis of each figure. Another possible way is to compare them measured on the same day (1d, 5d, 10d, 20d, and 30d) like Figure 9 and 10 in a previous study (C. Zhang et al, Coatings 2019, 9, 46)
- The abstract needs significant editing. See the following statements as examples.
- What does the well anti-corrosion abilities (line 22) mean? Shouldn’t it be good anti-corrosion abilities?
- I cannot understand the meaning of “improves availably” (Line 21).
- (Line 16) I do not think all the 5 digits in 18.623 are significant numbers. In addition, it was only an average thickness of a single PVSQ-GO sheet or agglomerate. Thus, it cannot be representative of the thickness of PVSQ-GO.
- The rules for abbreviations may differ among various journals, but there are many wrong definitions of abbreviations. First, I believe they should be defined at first appearance except the abstract. On the other hand, TMEVS, APS, MPS, rGO were not defined at all. POSS and OCP were defined more than once through the manuscript. Many words including PSQ, OI, PVB, CVD, and CNT were once defined but do not appear in the rest of the manuscript.
- (Line 46) ‘Doping’ does not seem a proper word.
- (Line 112) The 320 mesh is not a proper way to describe the dimension of graphene oxide powder. Please provide its lateral dimension in micrometers at least.
- (Figure 3) (e1) and (f1) seem awkward. Same for Fig. 4 and 5.
- (Line 249-250) Please consider the significant digits in both 2.652 nm and 18.623 nm.
- (Line 263) Shouldn’t it be good dispersion rather than well dispersion?
- (Figure 8) The inset of Fig. 8b is too small to see.
Author Response
Dear Reviewer,
Thank you for your comments, below is our response to the comment
1.Response to comment: Clarify how graphene contributes to the anti-corrosion property in the mechanisms or backgrounds
Response: I have clarified how graphene contributes to the anti-corrosion property in the mechanisms and introduction section. It is mainly owing to the impermeability of graphene to small molecule and it will provide a tortuous pathway for corrosion medium penetration.
2.Response to comment: What excellent properties and unique effects drove the authors to choose PSQ for the modification of GO (Line 78-81)? I also wonder if this modification performs better than GO sheets modified with 2-(3, 4-epoxycyclohexyl) ethyl triethoxysilane (C. Zhang et al, Coatings2019, 9, 46). This previous work seems highly related to the current one, but it was missing in the references.
Response: PVSQ microspheres possess the organic functional group of double bond which will improve the compatibility with organic matrix. On the other hand, as organic-inorganic hybrid material, PVSQ microspheres show hydrophobicity. It is potential for PVSQ to be applied in the modification of graphene and anti-corrosion waterborne polyurethane. The coating matrix used in Zhang’s work is epoxy resin, GO was modified with 2-(3, 4-epoxycyclohexyl) ethyl triethoxysilane which containing epoxy group. Modified graphene oxide participates in the curing process of the coating, so it will disperse better in epoxy matrix. Because the materials used and perspective of consideration are different, it is difficult to compare them together.
3.Response to comment: The authors argue that PVSQ-GO has better dispersion stability in water than pristine GO. However, PVSQ-GO is more hydrophobic than GO (Figure 3a and 3b). In addition, it is more likely that PVSQ-GO sheets were aggregated. Figure 2b shows the 2theta angle close to graphite after modification with PVSQ. This implies that graphene oxides were aggregated or even reduced chemically, either of which leads to poor dispersion. Taking photographs is a simple but rather inaccurate way to compare dispersion of each material. Instead, comparing the relative change in UV-Vis light absorption of each solution before and after settling for 24 hours will be a more quantitative way.
5.Response: There still exist few uncrosslinked hydroxyl groups of PVSQ microspheres on GO surface. Hydrogen bonds form between hydroxyl groups and water molecules, so that PVSQ-GO has better dispersion stability in water. Taking photographs can qualitatively determine dispersion of material from a macro perspective although it is inaccurate. I agree UV-Vis light absorption method is a more quantitative way.
4.Response to comment: The thermal stability of PVSQ-GO seems exaggerated. There are many inorganic components and its content is supposedly more than 18 wt%, the Si content in PVSQ-GO (Figure 2f). If PVSQ is non-flammable, this good thermal stability makes sense. But ‘I’ do not think Si-O-C alone is strong enough to resist at the temperature up to 800 degrees C.
Response: The TG curves was based on measured result. PVSQ microspheres have excellent heat resistance, on the other hand, Si-O-C bonds also contribute partly.
5.Response to comment: Explain why PVSQ-GO was dispersed well in polyurethane than pristine GO. Is the PU hydrophobic enough to have good affinity to PVSQ-GO?
Response: The PVSQ-GO composite was dispersed well in waterborne polyurethane than pristine GO which could be ascribed to the double bonds in PVSQ, the double bonds will improve the compatibility between PVSQ-GO and organic coating matrix.
6.Response to comment: There is no explanation of how high adhesion strength was achieved after incorporating 0.5 wt% of PVSQ-GO. How does the surface chemistry of the steel affect the adhesion to polyurethane containing GO?
Response: The well-dispersed PVSQ-GO reduced void spacing in the coating matrix and enhanced the coating density, so that it will improve the adhesion strength of coating system. If there are chemical bonds formation in the interface between coating system and steel substrate, the adhesion will increase. Unfortunately, the chemical bonds at the interface is not easy to characterize, so we just infer whether there are chemical bonds based on the results of the test adhesion strength.
7.Response to comment: Incorporating 0.5 wt% of pristine GO into WPU shows poor performance in Fig. 7. It seems adding GO to WPU is not a good strategy for anti-corrosion. Then why don’t we put PVSQ particles only instead of PVSQ+GO hybrid materials? If the hydrophilicity of GO is the problem, would it be better to chemically or thermally reduce PVSQ-GO for anti-corrosion?
Response: In this study, graphene is the subject of research, rather than PVSQ. What we want to explore is whether graphene oxide can improve the corrosion resistance of the coating after modification, so we just chose PVSQ+GO hybrid materials. In fact, PVSQ particles can be also chosen to explore the synergistic effect of GO and PVSQ. Chemically or thermally reduce PVSQ-GO will cause agglomerate, and thus it is difficult to disperse in organic matrix.
8.Response to comment: It is hard to compare the performance of each material in Fig. 8, ‘I’ highly recommend the authors put the same scale for the y-axis of each figure or compare them measured on the same day
Response: I have tried to put the same scale for the y-axis of each figure in Fig.8 in order to compare easily, but in fact, the lines will overlap and occupy a small portion of the figure because of the difference in values. When the impedance spectra of the same coating are plotted on a graph, the variation trend of impedance with the prolongation of immersion time can be clearly observed.
1.Response to comment: What does the well anti-corrosion abilities (Line 22) mean? Shouldn’t it be good anti-corrosion abilities?
Response: It's a false statement, and it should be good anti-corrosion abilities.
2.Response to comment: ‘I’ cannot understand the meaning of “improves availably” (Line 21).
Response: The statement of “improves availably” has been revised with “improves effectively”.
3.Response to comment: ‘I’ do not think all the 5 digits in 18.623 are significant numbers. In addition, it was only an average thickness of a single PVSQ-GO sheet or agglomerate. Thus, it cannot be representative of the thickness of PVSQ-GO.
Response: Yes, I agree with your opinion, it was only an average thickness of a single PVSQ-GO sheet that was measured by AFM. I looked for three areas in AFM image, the thickness put in the manuscript was representational.
4.Response to comment: Abbreviations should be defined at first appearance except the abstract. Moreover, TMEVS, APS, MPS, rGO were not defined at all. POSS and OCP were defined more than once through the manuscript. Many words including PSQ, OI, PVB, CVD, and CNT were once defined but do not appear in the rest of the manuscript.
Response: I have revised the abbreviations used in the manuscript.
5.Response to comment: ‘Doping’ does not seem a proper word (Line 46).
Response: I have changed the statement of ‘Doping’ into ‘Adding’.
6.Response to comment: The 320 mesh is not a proper way to describe the dimension of graphene oxide powder. Please provide its lateral dimension in micrometers at least (Line 112).
Response: The 320 mesh may not a proper way to describe the dimension of graphene oxide powder, but it has appeared in some literature. The lateral dimension of graphene oxide is about 0.5-5um.
7.Response to comment: Fig. 3e1 and f1 seem awkward. Same for Fig. 4 and 5.
Response: I made a slight adjustment to Fig. 3 e1 and f1. Fig.4 and Fig.5 were put to display surface and section morphology of coatings at different amplification ratios.
8.Response to comment: Consider the significant digits in both 2.652 nm and 18.623 nm (Line 249-250).
Response: ‘18.623nm’ has been revised with ’18.62nm’ to make the significant digits consistent.
9.Response to comment: Shouldn’t it be good dispersion rather than well dispersion (Line 263)?
Response: Yes, it should be good dispersion, not well dispersion.
10.Response to comment: The inset of Fig. 8b is too small to see.
Response: I have enlarged the inset of Fig. 8b in order to be seen clearly.
Thank you for your valuable comments.
Round 2
Reviewer 2 Report
The authors have revised their manuscript extensively taking into account the comments of the reviewers carefully. This reviewer has found the revised version much improved and has no technical or scientific issues with it. It may be acceptable for publication in Coatings without further alteration.
Reviewer 4 Report
The authors addressed every issue that I concerned. There are still some unusual numberings such as 'Fig.4e1' but I don't think it hurts the value of this study. I would suggest the publication of this paper in Coatings.
