Preparation and Self-Healing Application of Isocyanate Prepolymer Microcapsules
Round 1
Reviewer 1 Report
In the submitted manuscript entitled: Preparation and self-healing application of isocyanate prepolymer microcapsules, facile and efficient method for preparing isocyanate prepolymer microcapsules is presented for self-healing application. In addition, the corrosion resistance of the coating has been tested.
The manuscript is written well, is clear, and sufficiently supported by sources in the literature.
I have some comments and recommendations.
- The epoxy resin used in the self-healing testing should be described in the section materials
- did the samples not burn due to the electron beam? Before SEM analysis, have not been samples coated (e.g., by gold)?
- Statement in lines 129 – 133 does not belong to the section "Characterization." Please, move it to section 2.3. Preparation of microcapsules, if it belongs to this section. If not, please, remove it.
- In line 143 (section 2.5. Evaluation of self-healing performance), the epoxy resin AB component is mentioned for the first time. The description of this material is missing (please provide information about epoxy resin into the "Materials" section, as noted in comment 1.)
- The authors mentioned that particles sizes become uniform when the GA dosage is 7.5wt%. Optical microscope images support this notice; however, SEM image (Figure 3 (e)) does not support this notice. From the reader's point of view, it seems as the difference in microparticles sizes has widened. Why is that so?
- Could you please provide the average diameters and standard deviations of the microparticles sizes? Statistical data gives the reader a better idea of the particle size than just the size from-to.
- Figure 6. - why is the magnification different in figure 6a than 6b and 6c?
Thank you.
Author Response
Response to Reviewer 1 Comments
Referee: 1
Firstly, thank you for your valuable question which make a huge improvement to the quality of my paper. Here, I would like to express my sincere thanks to you for your hard work and careful reading.
Although personal research level is limited. every question you raise that I actually try my best to solve. The specific response details are as follows：
Point 1: The epoxy resin used in the self-healing testing should be described in the section materials.
Response 1: I am sorry for my negligence that I did not mention this in the article and thank you for your careful reading. It has been described in the manuscript.
Point 2: did the samples not burn due to the electron beam? Before SEM analysis, have not been samples coated (e.g., by gold)?
Response 2: The question is very proffeional, your research on polymer materials must be excellent.
The samples didn’t burn due to the electron beam. And the microcapsule samples were not sprayed with gold before SEM analysis.
Point 3: Statement in lines 129 – 133 does not belong to the section "Characterization." Please, move it to section 2.3. Preparation of microcapsules, if it belongs to this section. If not, please, remove it.
Response 3: Sincerely thank you for your suggestion! It has been removed in the manuscript.
Point 4: In line 143 (section 2.5. Evaluation of self-healing performance), the epoxy resin AB component is mentioned for the first time. The description of this material is missing (please provide information about epoxy resin into the "Materials" section, as noted in comment 1.)
Response 4: I am sorry for my negligence that I did not provide the information about the epoxy resin AB component. And I have added the information about epoxy resins in the section on "Materials". Sincerely thank you for your careful reading.
Point 5: The authors mentioned that particles sizes become uniform when the GA dosage is 7.5wt%. Optical microscope images support this notice; however, SEM image (Figure 3 (e)) does not support this notice. From the reader's point of view, it seems as the difference in microparticles sizes has widened. Why is that so?
Response 5: Sincerely thank you for your careful reading, and I have seriously considered this question you raised.
The particle size of microcapsules can be affected by many factors, such as mixing rate, emulsifier concentration, BDO content, core-to-wall mass ratio, etc. When I saied that the particle size became uniform, I didn’t mean that all microcapsules had the same particle size, but that the percentage of microcapsules with the same and suitable particle size increased, so we could still see microcapsules with a small difference in particle size in Figure 3(e).
Point 6: Could you please provide the average diameters and standard deviations of the microparticles sizes? Statistical data gives the reader a better idea of the particle size than just the size from-to.
Response 6: Sincerely thank you for your suggestion which is very helpful to improve the quality of my article. And I have added the average particle size of the microcapsules in the manuscript. The average particle size of the microcapsules under optimal preparation conditions is about 124.39 μm.
Point 7: Figure 6. - why is the magnification different in figure 6a than 6b and 6c?
Response 7: Thanks for your careful checks. We used different magnifications because we wanted to increase the persuasiveness of the manuscript by magnifying the cracks in the blank control group, which is more convenient for observation and favorably illustrates the lack of repair effect of the coating without microcapsules.
We will deeply study the relevant properties of the self-healing coatings in the next research. Thank you for your professional review work and sincere thanks again!
Kind regards,
Xiaode Guo
Reviewer 2 Report
The manuscript with the title of "Preparation and Self-healing Application of Isocyanate Prepolymer Microcapsules" has great potential for accepting in this journal. The suggestions, issues and questions for increasing the rate of this manuscript are as following:
- The first sentence of abstract section is not necessary. It is better to remove that.
- In some cases, the authors used the active sentences. Be modified and used the passive sentences.
- The last paragraph of introduction section is too long. Be summarized and mentioned only the main novelties.
- In the sections of 2.2 and 2.3, the atmosphere of synthesis process be mentioned. Are the authors used the nitrogen atmosphere? The related explanations be added in these sections.
- The core content of synthesized microcapsules be calculated and added. The calculation of this parameter has been reported in the literature with the title of " Microcapsulated epoxy resin with nanosilica-urea formaldehyde composite shell. Journal of Applied Polymer Science, Vol. 137, No. 16, 48580, 2020. DOI: 10.1002/app.48580".
- For increasing the rate of manuscript, it is recommended that the shell thickness of synthesized microcapsules be added in the results and discussion section.
Author Response
Response to Reviewer 2 Comments
Referee: 2
First of all, thank you for taking time out of your busy schedule to read my article. You have given me a lot of professional questions. These questions not only improve the overall score of my article, but also lead me to comprehend new knowledge points and scientific research skills, which are of great help to my future scientific research. Sincerely thank you again.
Point 1: The first sentence of abstract section is not necessary. It is better to remove that.
Response 1: Sincerely thank you for your careful reading and suggestion. It has been removed in the manuscript.
Point 2: In some cases, the authors used the active sentences. Be modified and used the passive sentences.
Response 2: I am really sorry for the lack of consistency in morphology, and I will correct all grammatical errors in the manuscript. Thank you for your careful reading.
Point 3: The last paragraph of introduction section is too long. Be summarized and mentioned only the main novelties.
Response 3: I think this suggestion is very professional, and it has greatly improved the logic of my article. Thank you very much! And we have modified in the manuscript.
Our main innovation is the preparation of isocyanate prepolymer microcapsules with high repair efficiency, which is different from the traditional microcapsule of monomer repair agent, the curing speed of the prepolymer healing agent is faster, and there are a large number of soft segment structures in the formed polyurea, and the formed repair area have elasticity and toughness, which can reduce the probability of secondary damage.
Point 4: In the sections of 2.2 and 2.3, the atmosphere of synthesis process be mentioned. Are the authors used the nitrogen atmosphere? The related explanations be added in these sections.
Response 4: I am sorry for my negligence that I did not provide the information about the atmosphere of synthesis process. And I have added the information about it in the section of 2.2.
It is very important to blow nitrogen into the isocyanate prepolymer, because the isocyanate groups would react with water in the air to form polymers. So we used a nitrogen atmosphere when synthesizing the prepolymer.
I didn’t use nitrogen atmosphere when preparing microcapsules, because in the oil-in-water (O/W) system, Bayer L-75 and BDO were used to react chain extension. The reaction process was controllable and greatly improved the reaction rate of the inter-facial polymerization to form a membrane, which could protect the core material from the water phase and reduce the loss of core material during the preparation of microcapsules.
Point 5: The core content of synthesized microcapsules be calculated and added. The calculation of this parameter has been reported in the literature with the title of " Microcapsulated epoxy resin with nanosilica-urea formaldehyde composite shell. Journal of Applied Polymer Science, Vol. 137, No. 16, 48580, 2020. DOI: 10.1002/app.48580".
Response 5: Thank you for your direction which is very helpful to improve the persuasiveness of my article! The calculation method and results of the core content have been supplemented in sections 2.4 and 3.4 respectively.
The core content of the microcapsule has a greater impact on its repair efficiency. The core contents of the prepared microcapsule samples were 31.56%, 40.88% and 32.13% when the GA concentrations were 5wt%, 7.5wt% and 12.5wt%, respectively. This was be-cause the emulsifier increased the stability of the emulsion, and more emulsion films coated the surface of the oil droplets, so the core content of the microcapsules was in-creased. However, when the concentration of emulsifier increased to 12.5wt%, the emul-sion formed was too viscous, so that not only was it more difficult to disperse the emul-sion, but also the emulsion filmed on the surface of the oil droplets was very thick, and it was difficult for the synthetic wall material to be deposited on the surface of the oil drop-lets, thus it was hard to effectively encapsulate the core material.
Point 6: For increasing the rate of manuscript, it is recommended that the shell thickness of synthesized microcapsules be added in the results and discussion section.
Response 6: Your research on microcapsules must be excellent. The suggestion is very professional.
We have done some tests on this in previous research, but the effect is not very satisfactory. The prepolymer formed by isocyanate-terminated polyetheramine D2000 has a higher viscosity, and part of the core material adheres to the shell after the microcapsule is broken, which is not conducive to testing the thickness of the shell. Then we tested the thickness of the hollow shell, the result is shown in the figure below, the thickness is approximately 14.3μm, and it is impossible to compare the thickness of the wall material under various parameters. After comprehensive consideration, we did not write this part of the test in the manuscript.
We will deeply study the relevant properties of the self-healing coatings in the next research. Thank you for your professional review work and sincere thanks again!
Please don’t hesitate to contact us if you have any questions.
Kind regards,
Xiaode Guo
Author Response File: 
Author Response.pdf
