Mechanical and Thermal Properties of Waterborne Polyurethane Coating Modified through One-Step Cellulose Nanocrystals/Graphene Materials Sols Method
, Shuqin Zhang 2, Haiming Zhang 1, Suilang Zhao 1, Jilei Zhang 4 and Benhua Fei 2,*Round 1
Reviewer 1 Report
Dear authors,
Results of article are interesting and usable mainly for wood-flooring industry.
Reviewer has only small comments and suggestions:
Introduction:
L38-39: Please, rewrite this sentence – using of waterborne coatings is increasing not only in China and reasons are low health and environmentally impact – please also add reference.
But decision of government in your country is clever…
L43-45: Add some relevant reference.
L61-62: Add some relevant reference.
L62-63: This sentence in this form is in opposite to sentence in L39-40. I advise you to add …in some applications…. And add also relevant reference.
Materials and methods:
L88 : Please define more clear this coating also with details of composition – it is crucial in this article.
Suggestion: important can be also colour stability of newly prepared coating for wood floors under visible light in the interior conditions – authors can test coating on wood using Xenotest with windows glass filter. Only short test is necessary (in hundreds of hours) because colour and chemical changes of surface layers of coatings are very fast mainly during initial periods of aging.
Conclusions.
L265 reviewer advise to add: hardness was increased from 5H to 6H….
With Best Regards
Author Response
1. Introduction: L38-39: Please, rewrite this sentence – using of waterborne coatings is increasing not only in China and reasons are low health and environmentally impact – please also add reference. But decision of government in your country is clever…
Answer: That's a good advice，and thanks. The sentence has been modified by “Waterborne coatings recently have been increasingly used in the worldwide wood industry because of low health and environmentally impact.” The below references have been also added. Aqdas N.; Khalid, M.Z.; Mohammad, Z. Recent trends in environmentally friendly water-borne polyurethane coatings: A review. Korean Journal of Chemical Engineering, 2015, 33(2):1-13. Doi. 10.1007/s11814-015-0241-5. Jinyue Dai, Songqi Ma, Xiaoqing Liu. Synthesis of bio-based unsaturated polyester resins and their application in waterborne UV-curable coatings[J]. Progress in Organic Coatings, 2015, 78:49-54.
2. L43-45: Add some relevant reference.
Answer: The relevant references have been added. Thanks for your suggestions.
3. L61-62: Add some relevant reference.
Answer: The relevant references have been added. Thanks for your suggestions.
4. L62-63: This sentence in this form is in opposite to sentence in L39-40. I advise you to add …in some applications…. And add also relevant reference.
Answer: The previous sentence is not accurate, and it has been modified according to your suggestion. Thanks, and the relevant references have been added.
Materials and methods:
5. L88 : Please define more clear this coating also with details of composition – it is crucial in this article.
Answer: The coating used in the experiment was provided by cooperative research institute, not synthesized by our research group. The scientific papers published by cooperative research institute have been added here to support our research. This is a very valuable suggestion. Thanks a lot.
6. Suggestion: important can be also colour stability of newly prepared coating for wood floors under visible light in the interior conditions – authors can test coating on wood using Xenotest with windows glass filter. Only short test is necessary (in hundreds of hours) because colour and chemical changes of surface layers of coatings are very fast mainly during initial periods of aging.
Answer: It is a excellence suggestion. For colour stability and durability properties, these dates are meaningful and necessary for studying wooden products, relevant properties are being tested, we will collate and analyze these data, and the results will be published in our next scientific paper. Conclusions.
7. L265 reviewer advise to add: hardness was increased from 5H to 6h….
Answer: The previous sentence is not accurate, and it has been modified according to your suggestion. Thanks With Best Regards Submission Date 29 November 2019 Date of this review 11 Dec 2019 10:35:37
Author Response File: 
Author Response.doc
Reviewer 2 Report
Dear authors, I have few suggestions, how to improve quality of your article:
The Introduction part should have more background. What is Heat conduction coefficient please? Methodology of thermal properties measurements should be more precise, see for example here: https://www.hindawi.com/journals/amse/2019/2303720/ Are results statistically significant? Please add at least error bars in the graphs. Thermal conductivity, 4.5% increase, what is the measurement accuracy of Isomet? Is 4.5% statistically significant? Discussion about thermal stability and thermal conductivity should be more precise. What about thermal diffusivity? Line 266 - Findings can help wood flooring industries to improve... more discussion is needed. "Improve thermal conductivity", this is not scientific statement, thermal conductivity can increase/decrease/enhance... thermal properties can be improved.
Author Response
Comments and Suggestions for Authors
Dear authors, I have few suggestions, how to improve quality of your article: The Introduction part should have more background. What is Heat conduction coefficient please? Methodology of thermal properties measurements should be more precise, see for example here: https://www.hindawi.com/journals/amse/2019/2303720/ Are results statistically significant? Please add at least error bars in the graphs. Thermal conductivity, 4.5% increase, what is the measurement accuracy of Isomet? Is 4.5% statistically significant? Discussion about thermal stability and thermal conductivity should be more precise. What about thermal diffusivity? Line 266 - Findings can help wood flooring industries to improve... more discussion is needed. "Improve thermal conductivity", this is not scientific statement, thermal conductivity can increase/decrease/enhance... thermal properties can be improved.
Answer: First of all, thank you very much for your advices and guidance. We have learned a lot from your example and improved our understanding of thermal conductivity. We have revised our article according to your suggestions. All the inaccurate description mentioned have been modified and references added, such as definition and accuracy of thermal conductivity, discussion of thermal conductivity, etc., please see the detailed in the revised version. Thanks again for your excellent suggestions and helps.
Author Response File: Author Response.doc
Round 2
Reviewer 2 Report
Authors improved the manuscript. I suggest to accept it.
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
All my detailed comments are in the attachment.
Comments for author File: Comments.docx
Author Response
Dear Editor and Reviewers: I am pleased to resubmit for the revised version of manuscript entitled “Mechanical and thermal properties of waterborne polyurethane coating modified by cellulose nanocrystals/graphene sols through one-step method”. Thank you for reading our manuscript and reviewing it. Those comments are all valuable and very helpful for revising and improving our paper. We have revised our manuscript carefully and have made correction which we hope meet with approval. So we have sent the revised manuscript and have highlighted changes by using the track mode. The main corrections in the paper and the responds to the reviewers’ comments are as following:
Responds to the reviewers’ comments:
Reviewer 1 Comments:
1. Abstract: The quality of English written language in the abstract is not acceptable, which is especially valid for the first half of the abstract. Please write the abstract once again in such a way that it will be understandable and of an acceptable quality. In the other parts of the paper the quality of English written language is batter, but still needs improvements, in some parts quite a lot and in some other parts of the paper less.
Answer: Ok. The manuscript was rewritten and edited by a native English speaker. The new abstract is “Due to the growing needs of thermal management in modern multifunctional coatings for wood applications, developing advanced composite coatings with both excellent mechanical and thermal properties is highly desirable. The recent development of waterborne wood coatings suggests a promisingthermosetting material with many advantages, including very low volatile organiccontents (VOCs), hardness, and fast curing. In this work, the cellulose nanocrystals/graphene (CNC/Gr) sols have been prepared by one-step method and used as thermally conductive and reinforced modifier for preparing of the high thermal conductivity waterbornepolyurethane (WPU) coatings. The influence of thermal and mechanical properties such as thermal conductivity, abrasion resistance and adhesion on the modified coatings was analyzed and studied. The results showed that the hardness and abrasion resistance of the WPU coatingswere all increased in some degree when CNC/Gr sols were added. The adhesion of the coatings remained at the highest grade (level 1) with different additions of CNC/Gr sols. Comparing with the hardness of the control coating sample (5 H), the hardness of modified coatings was all increased to 6 H. The best abrasion resistanceofmodifiedcoatingwas obtained (0.023g/100r)when the addition of Gr was 3%.The thermal conductivity slightly increased with the adidition of CNC/Gr sols”.
2. L 50: The expression “waterborne UV-cured coatings” is used in the first sentence. I suggest that you replace it with the same term that is used as a keyword: “waterborne UV-cured coatings”. I suggest that you raplace “waterborne” with “waterborne” everywhere in the paper..
Answer: Ok, the “water-based” was replaced with “waterborne” everywhere in the paper.
3. L 58-59: “Those difficulties include incomplete dispersion and poor adhesion”: this sentence is a bit unclear – poor adhesion of what to what? I guess the film to the substrate, but this is not clear from the sentence. Please make it more clear what adhesion did you have in minds.
Answer: The sentence “Those difficulties include incomplete dispersion and poor adhesion” was changed to “Those difficulties include incomplete dispersion of nanoparticles in the polymer matrix and poor adhesion between cured coatings and wood substrates.”
4. L 59-61: “To address these issues, directly incorporating organic nanoparticle materials into aqueous media for creating a stronger coating has be regarded as one of the most promising strategies [13].” In what sense the word “stronger” is used in this sentence? Please explain, write the sentence in a more understandable way.
Answer: Ok. To further improve the durability and upgrade the functionality of wood products, several inorganic additives (fillers) can be used to obtain an excellent desired property of the waterborne coatings, such as Al2O3 [3-4], SiO2 [5-6], TiO2 [7], ZnO [8-9], CaCO3 [10], Cr2O3 [11-12], etc. However, the above nano-fillers encounter their difficulties in term of incorporation of inorganic nanoparticles in those organic polymer matrix. Those difficulties include incomplete dispersion of nanoparticles in the polymer matrix and poor adhesion between cured coatings and wood substrates. To address these issues, directly incorporating organic nanoparticle materials into aqueous media for creating a better properties coating has been regarded as one of the most promising strategies [13].
5. L 76: The abbreviation CNF is here used for the first time in the paper. Please write it also with whole words.
Answer: Ok. Cellulose nanofibril (CNF)... L 80-85: Here it is described what you have done. Graphene is mentioned for the first time in the Introduction here, in the last paragraph, and so also the thermal conductivity.
6. Please add into the introduction a text, supported by literature sources (references) why did you decide to combine graphene with CNC! Justify the selection of graphene! Similarly, explain in the introduction (text, references), why the high thermal conductivity was one of your key target properties of this work!
Answer: Ok. The literatures were added. Waterborne wood coatings have some dominant environmental and operational characteristics, they have being mainly used in building industrial fields. However, their further applications are limited by some default properties, including water resistance, hardness, wear resistance and stability against strong mechanical forces are poor, and their thermal conductivity needs to be improved in special requirements (such as for heating floor using) [1-2, 8]. Graphene (Gr) has emerged as a revolutionary functional material due to its amazing high thermal conductivity properties (above 3000 W·m·K−1) [33]. Tang et al. [34] found that adding graphene materials into epoxy resin resulted in epoxy resin having its thermal conductivity enhancement factor up to 1900% and yielding greater stability at a high temperature. However, the large specific surface area of graphene-based carbon nanomaterials tends to agglomerate them together when dispersed into other materials as property enhancement agents, thereby causing lower performance of these nanomaterials as property-enhancement agents. Carrasco et al. [35] reported that cellulose nanocrystals as a stabilizer are very efficient for graphite exfoliation through tip sonication and stabilization, resulting in graphene flakes dispersed in aqueous media at a high concentration up to 1 mg/ml.
7. L 95-96: “Basswood (Tilia) veneers measured 100mm long×100mm wide×10mm thick and the tin were obtained from Dehua New Material Co., Ltd., China”: what does it mean “and the tin” in this sentence? And please provide information about the orientation of the samples (longitudinal? radial? tangential?)
Answer: Sorry about the mistake. Basswood (Tilia) samples measured 100mm long×100mm wide×10mm thick obtaining from longitudinal, tangential and radial directions, respectively and were obtained from Dehua New Material Co., Ltd., China. L 108: “PH” should be written as “pH” Answer: Thanks, the PH was replaced with pH.
8. L 102-109: (Section 2.2): how do you actually know that from MCC you obtained CNC?
Answer: From the TEM images (Figure 5) we could distinguish the CNC and Gr as the same morphology as our former work and other published references.
9. Table 1: It is a kind of strange. Does “/g” means that there was 98 (or 10) (units) of the substance per gram of something, or that you had in the mixture 98 (or 10) grams of the substance. There is a remark “1” (31) but the explanation of this remark 1 does not appear anywhere. And also this 1%, 2% and 3% “ratio to the MCC weight” is a bit confusing – strange. The best would be that in Table 1 you just simply write down the composition in grams for all three substances (the acid, MCC and Gr).
Answer: Microcrystalline cellulose (MCC) powder and graphene (1 %, 2 %, and 3 %, ratio to the MCC weight) were hydrolyzed by sulfuric acid (analytical reagent, mass fraction 64 %), respectively (Table 1). Table 1. Preparation of CNC/Gr compound solution by one-step method (Unit: gram, g) H2SO4 MCC Gr 98 10 0.1 98 10 0.2 98 10 0.3
10. L 115-116: “CNC/Gr/2K-WPU coating containing from 3 g 2K-WPU solution and 0.09 g different levels of pre-prepared CNC/Gr compound solution…” This is not at all understandable. Please write the sentence so that it will be more clear!
Answer: The CNC/Gr/2K-WPU coating was prepared by magnetic stirring 2K-WPU coating and CNC/Gr compound solution at 25 ℃ for 20 min. The weight ratio of 2K-WPU coating to CNC/Gr compound solution was 100 : 3.
11. L117-118: “were coated onto tin plates (120 mm long × 50 mm wide × 2 mm thick) using a glass rod…” This is not understandable. How were they coated “using a glass rod”? It sounds strange and unusual.
Answer: Sorry the mistake. The coating was coated by a paint film fabricator.
12. L118-120: I do not uinderstand. In this paper the “UV-cured waterborne coating” is discussed. But you say: “…and dried under controlled conditions (25 ℃ and 50 % of relative humidity) during 1 week according to the Chinese standard of GB/T1727-1992.”. So wher do we have the process of UV-curing? Please explain!
Answer: The coating used in this paper is two-component waterborne polyurethane coating (2K-WPU). Sorry about the misleading, we already changed the discuss in the introduction part.
13. L120: All standards, including this one (GB/T1727-1992” should be cited as references in the list of references!
Answer: Ok, the standards have been added in the reference list. GB/T1727-92 General preparation of paint film; Standardization Administration of the People`s Republic of China: Beijing, China, 1992; pp. 318-326. (In Chinese). GB/T 6739-2006 Paints and varnishes-Determination of film hardness by pencil test; Standardization Administration of the People`s Republic of China: Beijing, China, 2006; pp. 425-428. (In Chinese). GB/T1768-2006 Paints and varnishes-Determination of abrasion resistance by rotary rubber grinding wheel method; Standardization Administration of the People`s Republic of China: Beijing, China, 2006; pp. 429-433. (In Chinese). GB/T4893.4-2013 Test of surface coatings of furniture-Part 4: Determination of adhesion-Cross cut; Standardization Administration of the People`s Republic of China: Beijing, China, 2013; pp. 1-9. (In Chinese). GB/T 11048-2018 Textiles-Physiological effects-Measurement of thermal and wate-vapour resistance under steady-state conditions (sweating guarded-hotplate test), MOD; Standardization Administration of the People’s Republic of China: Beijing, China, 2018; pp. 1–16. (In Chinese).
14. L 130-142: The title of this section is “CNC/Gr compound solution”. But you are mentioning also, for instance, Raman spectra of modified coatings. It is not clear what the mentioned characterisation methods are about. Only to measure properties of the solution or of the coating, or of both? For instance, it is not clear FT-IR spectra of what were recorded, etc. Please rewrite this part to become more clear.
Answer: The absorbance values of CNC/Gr compound solution were measured on a Lambda 950 ultraviolet spectrophotometer (PE, US). The wavelength scanning range of absorbance was 200-800 nm. The FT-IR spectra was recorded on a VERTEX 80V spectrometer (Bruker, Germany) over the scan range of 400-4000 cm−1. The dried CNC/Gr compound solution (1 part in weight) was mixed to potassium bromide (KBr) (100 parts in weight). The transmission mode was selected.
15. L146-157: I am somehow not convinced that from the spectrum in Fig. 2 it is so obvious that graphene was successfully grafted to cellulose. But I have to admit that I have not written the references 52 and 53. If the authors are so very convinced about this, they should add more explanations, might be also from or on the basis of the mentioned references.
Answer: Thank you. Yes, the FT-IR analysis is not enough for confirming graphene grafted to the surface on the CNC. We changed the analysis to “... however, whether the graphene could be successfully grafted to the surface of CNC to form a chemical bond, it is not enough to analyze from the FT-IR spectra alone. We need to further test and analyze.”
16. L157: “The quality of copper cooling plate”?? Probably “the quantity”, the mass?
Answer: Yes, m is the quality of copper cooling plate (kg) in the formula.
17. Figure 1: I think that the type of the graph is not properly selected. Because the straight lines, connecting the points do not tell anything. It would be better to present the data in the form of bars. And also the title is not correct. Absorbance of graphene? Probably of the graphene containing solutions?
Answer: Ok, it`s a good suggestion. The figure 1 has been changed to the form of bars and the X axis has been changed to “Gr containing solutions”. Figure 1. Absorbance of graphene with different addition levels at 660 nm
18. L177-183: “The potential of the stylus method to determine any fluctuations of surface quality of raw and 207 overlaid composites was evaluated in this study.” I do not agree! You have not analysed the potential of the stylus method in this paper! You just used this method to get the results which were then compared and analysed! Please correct the conclusions.
Answer: Sorry, we don`t understand the meanting of this comment.
19. Figure 2: The title is not correct- There is a spectrum in Fig. 2 and not “preparation” shown
Answer: Ok, the title of fig. 2 has been change to “Figure 2. FT-IR spectra of CNC/Gr solution by one-step method”.
20. L237-238: “Fig. 6 also showed the hardness of UV-cured waterborne nanocomposite coatings with and without CNC/Gr,…” Please see my comment about UV curing somewhere above. Were your coatings UV-cured or not? From the description in the experimental section does not seem like.
Answer: Ok, sorry about the mistake, the coating that we used in this study is waterborn polyurethane coating. The description in the experimental section was also changed.
21. L257-260: Here you say “Presence of CNC/Gr and theirs proper dispersion within the organic nanocomposite coatings introduce the right hydrophobic/hydrophilic balance, which could have created strong interfaces between the filler and the matrix [45].” But in the Lines 240-243 you say: “This was because Gr was simple dispersed but not covalently bonded to or within the continuous phase, resulting in no increase of hardness [42].” Please explain this contrast!
Answer: Yes, whether the graphene could be successfully grafted to the surface of CNC to form a chemical bond, it is not enough to analyze from the FT-IR spectra alone. But from figure 5 we could see that graphene (hydrophobic) could evenly disperse in the network structure of CNC (hydrophilic) sol, which mightbe result in the better interface between the Gr/CNC and WPU coating. However, in the TEM image (fig. 5) it also could be seen that there were still more Gr plates separated in the solution, not on the surface of CNC, which could result in the lower hardness.
22. L313-314: “This study plays a certain role in improving the thermal conductivity of the floor and promoting the transformation and upgrading of household products.” Here, the floor is mentioned for the first time in the paper. I asked you to write a background (the reasons) of your thermal conductivity studies. So, it looks like that you had in minds the coatings that should be used for wooden floorings? Can you tell about this something in the Introduction Section?
Answer: OK. Waterborne wood coatings have some dominant environmental and operational characteristics, they have being mainly used in building industrial fields. However, their further applications are limited by some default properties, including water resistance, hardness, wear resistance and stability against strong mechanical forces are poor, and their thermal conductivity needs to be improved in special requirements (such as for heating floor using) [1-2, 8]. Graphene (Gr) has emerged as a revolutionary functional material due to its amazing high thermal conductivity properties (above 3000 W·m·K−1) [33]. Tang et al. [34] found that adding graphene materials into epoxy resin resulted in epoxy resin having its thermal conductivity enhancement factor up to 1900% and yielding greater stability at a high temperature. However, the large specific surface area of graphene-based carbon nanomaterials tends to agglomerate them together when dispersed into other materials as property enhancement agents, thereby causing lower performance of these nanomaterials as property-enhancement agents. Carrasco et al. [35] reported that cellulose nanocrystals as a stabilizer are very efficient for graphite exfoliation through tip sonication and stabilization, resulting in graphene flakes dispersed in aqueous media at a high concentration up to 1 mg/ml. In our former research, we have successfully developed the wood composite by impregnating graphene/phenol-formaldehyde resin for heating floor [36]. In this work, the main aim is to further improve the thermal conductivity and mechanical properties of the heating floor....
We appreciate for Editor and Reviewers’ warm work earnestly, and hope that the correction will meet with approval. Once again, thank you very much for your comments and suggestions.
Yours sincerely,
Feng Yang and Yan Wu
Author Response File: Author Response.docx
Reviewer 2 Report
Unacceptable. Even the language in the abstract cannot be interpreted.
Author Response
Reviewer 2 Comments:
Unacceptable. Even the language in the abstract cannot be interpreted.
Answer: Thanks. The manuscript was rewritten and edited by a native English speaker.
We appreciate for Editor and Reviewers’ warm work earnestly, and hope that the correction will meet with approval. Once again, thank you very much for your comments and suggestions.
Yours sincerely,
Feng Yang and Yan Wu
Author Response File: Author Response.doc
Reviewer 3 Report
My comments to the Authors
Abstract: Written English language should be corrected and improved.
Line 38: it is not true. The pencil hardness increased from 5H to 6 H when content of Gr increased from 0 to 1 percent. The hardness is the same when the additive concentration is 1, 2 and 3 percent according to Figure 6.
Line 39. It is not clear. The abrasion resistance of the coating was the best. Comparing to what, the best of what or the best when the Gr additive proportion was….?
INTRODUCTION
in the Introduction you are talking about water-based UV-cured coatings and you have formulated a coating that is not UV-curable
MATERIALS AND METHODS
This section lacks sufficient details to allow other scientists to repeat the study. What was the composition (formulation) of 2K-WPU?
How the coatings were applied to wooden samples? On how many samples did you measure the adhesion, how many samples did you use for hardness measuring and how many for abrasion resistance?
Veneer is thin layer of wood usually thinner than 3 mm so I recommend using the term wood sample since your wood sample was 10 mm thick. Coating thickness of 60 µm is thickness of wet coating or dry coating?
The methods of measuring surface hardness, adhesion and abrasion resistance should be briefly described in order to make the results understandable.
Why do you mention the standard for gloss measurement when the results of gloss measurement are not mentioned in the paper.
RESULTS AND DISCUSSION
Line 237: This sentence is not clear. Why UV-cured waterborne coating? Your coating is not curing by UV radiation.
Line 240: The results in Figure 6 are the average of how many measurements?
Line 255: This is not clearly explained and is not visible from Figure 7.
CONCLUSIONS
Line 312: The pencil hardness was increased to 6H compared to what. Adhesion did not change comparing to what? What is your basis for comparison. The reader should be able to answer the question: relative to what?
Author Response
Reviewer 3 Comments:
1. Abstract: Written English language should be corrected and improved.
Answer: Ok. The manuscript was rewritten and edited by a native English speaker.
2. Line 38: it is not true. The pencil hardness increased from 5H to 6 H when content of Gr increased from 0 to 1 percent. The hardness is the same when the additive concentration is 1, 2 and 3 percent according to Figure 6.
Answer: Yes, 3 repeats were performed for each test.
3. Line 39. It is not clear. The abrasion resistance of the coating was the best. Comparing to what, the best of what or the best when the Gr additive proportion was….?
Answer: The best abrasion resistance of modified coating was obtained (0.023g/100r) when the addition of Gr was 3%.
INTRODUCTION
4. in the Introduction you are talking about water-based UV-cured coatings and you have formulated a coating that is not UV-curable
Answer: The coating used in this paper is two-component waterborne polyurethane coating (2K-WPU). Sorry about the misleading, we already changed the discuss in the introduction part.
MATERIALS AND METHODS
5. This section lacks sufficient details to allow other scientists to repeat the study. What was the composition (formulation) of 2K-WPU?
Answer: Two-component waterborne polyurethane coating (2K-WPU) was from Institute of chemical industry of forest products, Chinese Academy of Forestry (CAF). The ratio of hardener to resin is 3.5:10.
6. How the coatings were applied to wooden samples? On how many samples did you measure the adhesion, how many samples did you use for hardness measuring and how many for abrasion resistance?
Answer: The coatings were coated by a paint film fabricator. 3 repeats were performed for each test.
7. Veneer is thin layer of wood usually thinner than 3 mm so I recommend using the term wood sample since your wood sample was 10 mm thick. Coating thickness of 60 µm is thickness of wet coating or dry coating?
Answer: Ok. The coating thickness of 60 µm is the thickness of dry coating.
8. The methods of measuring surface hardness, adhesion and abrasion resistance should be briefly described in order to make the results understandable.
Answer: Ok. And the standards are also listed in the reference list as GB/T 6739-2006 Paints and varnishes-Determination of film hardness by pencil test; Standardization Administration of the People`s Republic of China: Beijing, China, 2006; pp. 425-428. (In Chinese). GB/T1768-2006 Paints and varnishes-Determination of abrasion resistance by rotary rubber grinding wheel method; Standardization Administration of the People`s Republic of China: Beijing, China, 2006; pp. 429-433. (In Chinese). GB/T4893.4-2013 Test of surface coatings of furniture-Part 4: Determination of adhesion-Cross cut; Standardization Administration of the People`s Republic of China: Beijing, China, 2013; pp. 1-9. (In Chinese).
9. Why do you mention the standard for gloss measurement when the results of gloss measurement are not mentioned in the paper.
Answer: Sorry, the standard has been deleted.
RESULTS AND DISCUSSION
10. Line 237: This sentence is not clear. Why UV-cured waterborne coating? Your coating is not curing by UV radiation.
Answer: The coating used in this paper is two-component waterborne polyurethane coating (2K-WPU). Sorry about the misleading, we already changed the discuss in the introduction part.
11. Line 240: The results in Figure 6 are the average of how many measurements?
Answer: 3 repeats were performed for each test.
12. Line 255: This is not clearly explained and is not visible from Figure 7.
Answer: whether the graphene could be successfully grafted to the surface of CNC to form a chemical bond, it is not enough to analyze from the FT-IR spectra alone. But from figure 5 we could see that graphene (hydrophobic) could evenly disperse in the network structure of CNC (hydrophilic) sol, which mightbe result in the better interface between the Gr/CNC and WPU coating. However, in the TEM image (Fig. 5) it also could be seen that there were still more Gr plate separated in the solution, not on the surface of CNC, which could result in the lower hardness.
CONCLUSIONS
13. Line 312: The pencil hardness was increased to 6H compared to what. Adhesion did not change comparing to what? What is your basis for comparison. The reader should be able to answer the question: relative to what?
Answer: Sorry about that, its pencil hardness and wear resistance were also improved to a certain extent when comparing with the control coating sample.
We appreciate for Editor and Reviewers’ warm work earnestly, and hope that the correction will meet with approval. Once again, thank you very much for your comments and suggestions.
Yours sincerely,
Feng Yang and Yan Wu
Author Response File: Author Response.doc
Reviewer 4 Report
Lines 23-26: A vague and too long sentence. Further, clarify what you meant.
Lines 50-56: Here you describe water-based UV-cured coatings, while in section 2.1 Materials you stated that you used two-component waterborne polyurethane coating. Therefore, in Introduction, it should be clarified why the 2K-WPU coatings were investigated in this research.
Lones 90-94: Check if this text applies to Figure1.
Line 95: Explain in the introduction why you chose Basswood as a substrate for coating.
Line 95: According to the definition, a wood veneer can be considered a thin sheet of wood up to 7 mm. This means that samples of wood used in this study are not properly called veneers, simply you can call them only wood samples.
Line 111 (Table 1): Which stands for superscript 1 end of issue 3.
Line 118: What material were the thin sheets of and what was the dry thickness of the coating?
Lines 130-135: Why did you re-describe how to get a CNC / Gr solution if you described it in the section Materials?
Line 135: What FTIR technique did you use, ATR or DRIFT?
Lines 168-173: What is the possible reason for the decrease in absorbance when more than 2% of graphene is added, can you draw a parallel with previous research?
Lines 177-183: In Figure 2, it is not clear what concentration of graphene the FTIR spectra represents. As the whole study is based on examining the effect of graphene concentration on the properties of 2K-WPU coatings, it is necessary to present and comment on FTIR spectra for all samples: 2K-WPU without CNC / Gr, 2K-WPU + CNC / 1% Gr, 2K-WPU + CNC / 2% Gr and 2K-WPU + CNC / 3% Gr.
Lines 187-200: In Figure 3, it is not clear what concentration of graphene the Raman spectra represents. As the whole study is based on examining the effect of graphene concentration on the properties of 2K-WPU coatings, it is necessary to present and comment on Raman spectra for all samples: 2K-WPU without CNC / Gr, 2K-WPU + CNC / 1% Gr, 2K-WPU + CNC / 2% Gr and 2K-WPU + CNC / 3% Gr.
Lines 204-208: In Figure 4, it is not clear what concentration of graphene the XRD spectra represents. As the whole study is based on examining the effect of graphene concentration on the properties of 2K-WPU coatings, it is necessary to present and comment on XRD spectra for all samples: 2K-WPU without CNC / Gr, 2K-WPU + CNC / 1% Gr, 2K-WPU + CNC / 2% Gr and 2K-WPU + CNC / 3% Gr.
Line 212: Did you mean in Figure 5, not Figure 9?
Lines 216-222: In Figure 5, it is not clear what concentration of graphene the TEM images represents.
Line 237: Here again you mention UV-cured waterborne coatings, and in the materials, you describe 2K-WPU coatings.
Lines 270-285: In Figure 8, it is not clear what concentration of graphene the TG curve represents. As the whole study is based on examining the effect of graphene concentration on the properties of 2K-WPU coatings, it is necessary to present and comment TG curves for all concentration of graphene.
Lines 289-299: What is the possible reason for the decrease of thermal conductivity when more than 2% of graphene is added, can you draw a parallel with previous research?
Author Response
Reviewer 4 Comments:
1. Lines 23-26: A vague and too long sentence. Further, clarify what you meant.
Answer: The abstract has been rewritten as “Due to the growing needs of thermal management in modern multifunctional coatings for wood applications, developing advanced composite coatings with both excellent mechanical and thermal properties is highly desirable. The recent development of waterborne wood coatings suggests a promisingthermosetting material with many advantages, including very low volatile organiccontents (VOCs), hardness, and fast curing. In this work, the cellulose nanocrystals/graphene (CNC/Gr) sols have been prepared by one-step method and used as thermally conductive and reinforced modifier for preparing of the high thermal conductivity waterbornepolyurethane (WPU) coatings. The influence of thermal and mechanical properties such as thermal conductivity, abrasion resistance and adhesion on the modified coatings was analyzed and studied. The results showed that the hardness and abrasion resistance of the WPU coatingswere all increased in some degree when CNC/Gr sols were added. The adhesion of the coatings remained at the highest grade (level 1) with different additions of CNC/Gr sols. Comparing with the hardness of the control coating sample (5 H), the hardness of modified coatings was all increased to 6 H. The best abrasion resistanceofmodifiedcoatingwas obtained (0.023g/100r)when the addition of Gr was 3 %.The thermal conductivity slightly increased with the adidition of CNC/Gr sols.”
2. Lines 50-56: Here you describe water-based UV-cured coatings, while in section 2.1 Materials you stated that you used two-component waterborne polyurethane coating. Therefore, in Introduction, it should be clarified why the 2K-WPU coatings were investigated in this research.
Answer: The coating used in this paper is two-component waterborne polyurethane coating (2K-WPU). Sorry about the misleading, we already changed the discuss in the introduction part. Waterborne wood coatings have some dominant environmental and operational characteristics, they have being mainly used in building industrial fields. However, their further applications are limited by some default properties, including water resistance, hardness, wear resistance and stability against strong mechanical forces are poor, and their thermal conductivity needs to be improved in special requirements (such as for heating floor using) [1-2, 8]. Graphene (Gr) has emerged as a revolutionary functional material due to its amazing high thermal conductivity properties (above 3000 W·m·K−1) [33]. Tang et al. [34] found that adding graphene materials into epoxy resin resulted in epoxy resin having its thermal conductivity enhancement factor up to 1900% and yielding greater stability at a high temperature. However, the large specific surface area of graphene-based carbon nanomaterials tends to agglomerate them together when dispersed into other materials as property enhancement agents, thereby causing lower performance of these nanomaterials as property-enhancement agents. Carrasco et al. [35] reported that cellulose nanocrystals as a stabilizer are very efficient for graphite exfoliation through tip sonication and stabilization, resulting in graphene flakes dispersed in aqueous media at a high concentration up to 1 mg/ml. In our former research, we have successfully developed the wood composite by impregnating graphene/phenol-formaldehyde resin for heating floor [36]. In this work, the main aim is to further improve the thermal conductivity and mechanical properties of the heating floor....
3. Lines 90-94: Check if this text applies to Figure1.
Answer: The figure 1 has been changed to the form of bars and the X axis has been changed to “Gr containing solutions”.
Figure 1. Absorbance of graphene with different addition levels at 660 nm
4. Line 95: Explain in the introduction why you chose Basswood as a substrate for coating.
Answer: The Basswood (Tilia) is popular for making wood flooring, which is supplied by Dehua New Material Co., Ltd., China.
5. Line 95: According to the definition, a wood veneer can be considered a thin sheet of wood up to 7 mm. This means that samples of wood used in this study are not properly called veneers, simply you can call them only wood samples.
Answer: Ok, Basswood (Tilia) samples measured 100mm long×100mm wide×10mm thick obtaining from longitudinal, tangential and radial directions, respectively and were obtained from Dehua New Material Co., Ltd., China.
6. Line 111 (Table 1): Which stands for superscript 1 end of issue 3.
Answer: sorry about the mistake, the superscript 1 has been deleted.
7. Line 118: What material were the thin sheets of and what was the dry thickness of the coating?
Answer: The two-component waterborne polyurethane coating (2K-WPU) and the dry thickness of coating is 60 μm.
8. Lines 130-135: Why did you re-describe how to get a CNC / Gr solution if you described it in the section Materials?
Answer: Sorry the repeat, the sentence has been deleted. “The absorbance values of CNC/Gr compound solution were measured on a Lambda 950 ultraviolet spectrophotometer (PE Co., NY, US). The wavelength scanning range of absorbance was 200-800 nm. ”
9. Line 135: What FTIR technique did you use, ATR or DRIFT?
Answer: ATR.
10. Lines 168-173: What is the possible reason for the decrease in absorbance when more than 2% of graphene is added, can you draw a parallel with previous research?
Answer: Yes, this mightbe the more addition of graphene resulted in its incomplete dispersion in the CNC sol, which also could be seen in the TEM image of Figure 5 that there were still more Gr plates separated in the solution, not on the surface of CNC.
11. Lines 177-183: In Figure 2, it is not clear what concentration of graphene the FTIR spectra represents. As the whole study is based on examining the effect of graphene concentration on the properties of 2K-WPU coatings, it is necessary to present and comment on FTIR spectra for all samples: 2K-WPU without CNC / Gr, 2K-WPU + CNC / 1% Gr, 2K-WPU + CNC / 2% Gr and 2K-WPU + CNC / 3% Gr.
Answer: Yes, it`s a good suggestion, in this paper at first we just want to use FTIR to evaluate whether graphene and CNC can former new bonding, which is beneficial for the even dispersion of graphene in the coating. The 3 % Gr/CNC was used in the FTIR test.
12. Lines 187-200: In Figure 3, it is not clear what concentration of graphene the Raman spectra represents. As the whole study is based on examining the effect of graphene concentration on the properties of 2K-WPU coatings, it is necessary to present and comment on Raman spectra for all samples: 2K-WPU without CNC / Gr, 2K-WPU + CNC / 1% Gr, 2K-WPU + CNC / 2% Gr and 2K-WPU + CNC / 3% Gr.
Answer: Yes, it`s a good suggestion, in this paper at first we just want to use Raman spectra to evaluate whether graphene can disperse in the CNC evenly or it can be layered by CNC rod structure. The 3 % Gr/CNC was used in the Raman spectra test.
13. Lines 204-208: In Figure 4, it is not clear what concentration of graphene the XRD spectra represents. As the whole study is based on examining the effect of graphene concentration on the properties of 2K-WPU coatings, it is necessary to present and comment on XRD spectra for all samples: 2K-WPU without CNC / Gr, 2K-WPU + CNC / 1% Gr, 2K-WPU + CNC / 2% Gr and 2K-WPU + CNC / 3% Gr.
Answer: The 3 % Gr/CNC was used in the XRD test.
14. Line 212: Did you mean in Figure 5, not Figure 9?
Answer: Yes, it`s figure 5. Sorry about the mistake.
15. Lines 216-222: In Figure 5, it is not clear what concentration of graphene the TEM images represents.
Answer: The 3% Gr/CNC was used in the TEM test.
16. Line 237: Here again you mention UV-cured waterborne coatings, and in the materials, you describe 2K-WPU coatings.
Answer: Sorry, it`s 2K-WPU coatings. “Fig. 6 also showed the hardness of waterborne polyurethane coatings with and without CNC/Gr...”
17. Lines 270-285: In Figure 8, it is not clear what concentration of graphene the TG curve represents. As the whole study is based on examining the effect of graphene concentration on the properties of 2K-WPU coatings, it is necessary to present and comment TG curves for all concentration of graphene.
Answer: The maximum thermal conductivity of the CNC/Gr/2K-WPU coatings was 1.39 W/m•K, the Gr content was 2 %. we selected this sample as the TG sample.
18. Lines 289-299: What is the possible reason for the decrease of thermal conductivity when more than 2% of graphene is added, can you draw a parallel with previous research?
Answer: After being dispersed by CNC suspension uniformly, the lamellar structure of Gr can be maintained by van der Waals or restoration π-π stacking between adjacent Gr layers [60]. When the content of Gr beyond 2 %, it mightbe aggregate and resulted in the lower thermal conductivity.
We appreciate for Editor and Reviewers’ warm work earnestly, and hope that the correction will meet with approval. Once again, thank you very much for your comments and suggestions.
Yours sincerely,
Feng Yang and Yan Wu
Author Response File: Author Response.doc
Reviewer 5 Report
I found too many grammar errors and therefore I suggest that the article should be rewritten and edited by native English speaker.
Author Response
Reviewer 5 Comments:
I found too many grammar errors and therefore I suggest that the article should be rewritten and edited by native English speaker.
Answer: Ok. The manuscript was rewritten and edited by a native English speaker.
We appreciate for Editor and Reviewers’ warm work earnestly, and hope that the correction will meet with approval. Once again, thank you very much for your comments and suggestions.
Yours sincerely,
Feng Yang and Yan Wu
Author Response File: Author Response.doc
Round 2
Reviewer 1 Report
I think you corrected the paper properly, following my comments and provided me sufficient explanations.
Author Response
Comments and Suggestions for Authors
I think you corrected the paper properly, following my comments and provided me sufficient explanations.
Answer: thanks.
Author Response File: Author Response.doc
Reviewer 2 Report
There appear to be interesting pieces of data in the paper; however the circular writing, with meaningless verbiage, obscures whatever useful content there may be in the paper. The paper needs to be reviewed by a competent expert in the field that also has strong english background. The problem is not just poor language skills, the primary author of the manuscript has not been trained in scientific writing, and it is unclear in many areas of the manuscript what they are trying to communicate. The manuscript is not acceptable in its current form.
Author Response
Comments and Suggestions for Authors
There appear to be interesting pieces of data in the paper; however the circular writing, with meaningless verbiage, obscures whatever useful content there may be in the paper. The paper needs to be reviewed by a competent expert in the field that also has strong english background. The problem is not just poor language skills, the primary author of the manuscript has not been trained in scientific writing, and it is unclear in many areas of the manuscript what they are trying to communicate. The manuscript is not acceptable in its current form.
Answer: the English language of this manuscript has been modified by prof. Jilei Zhang of Mississippi State University, USA.
Author Response File: Author Response.doc
Reviewer 3 Report
The manuscript is better now, but some parts are still hard to understand. The English language should be checked by an experienced expert in the field of coatings.
Author Response
Comments and Suggestions for Authors
The manuscript is better now, but some parts are still hard to understand. The English language should be checked by an experienced expert in the field of coatings.
Answer: the English language of this manuscript has been modified by prof. Jilei Zhang of Mississippi State University, USA.
Author Response File: Author Response.doc
Reviewer 4 Report
The authors did not respond and appreciated most of my comments. I therefore consider that the manuscript is not significantly improved and that it is not adequate for publication.
Author Response
Comments and Suggestions for Authors
The authors did not respond and appreciated most of my comments. I therefore consider that the manuscript is not significantly improved and that it is not adequate for publication.
Answer: the English language of this manuscript has been modified by prof. Jilei Zhang of Mississippi State University, USA. And revised our manuscript again following the reviewer`s comments. Thanks.
Author Response File: Author Response.doc
Round 3
Reviewer 3 Report
I hope that the manuscript will be corrected according to the comments inserted.
Reviewer 4 Report
As can be seen in my previous comments, it is not clear either from the discussion or from the captions in Figures 2, 3, 4, 5 and 8 what concentration of graphene is used and why exactly that concentration was tested, not all three concentrations. It is also unclear how the results presented in Figures 2, 3, 4, 5 and 8 contribute to the understanding of the mechanical and thermal properties of the coatings, which were tested with three concentrations of graphene. Since the authors have not corrected the paper according to these remarks so far, I think that the work prepared in this way is not suitable for publication.
