UV-Cured Biodegradable Methacrylated Starch-Based Coatings

Round 1

Reviewer 1 Report

Thank you for the opportunity to review the article entitled UV-Cured biodegradable methacrylated starch-based coatings. The article is interesting, but in its current form is not suitable for publication in Coatings journal. My comments and suggestions are presented below:

1. The introduction section is very general. In fact, most of this section relates to starch. The journal to which the article was sent deals with the subject of coatings. I think that the authors should write in this section about various types of coatings obtained on the basis of renewable raw materials or coatings which are susceptible to biodegradation.
2. Figure 1 is very difficult to read. Authors should sharpen it. Why did the authors not provide the chemical structure of the cross-linked coating?
3. The wavenumber values in Figure 2a are hard to read. I think it would be better to put the appropriate chemical bonds instead values of wavenumber.
4. Do the authors not think that the heating rate of 10 °C/min during the DSC test was too high? When I look at DSC thermograms, I am not entirely sure if these T_g temperatures have been marked correctly. A lower heating rate, e.g. 5 °C/min or less, would allow a more accurate determination of this temperature.
5. Did the authors perform thermogravimetric analysis (TGA)?
6. I think that the result discussion should be more broadly supported by literature. Not for the sake of drawing general conclusions, but for comparison with the research of other scientists..
7. Latin names should be written in italics.
8. Conclusion section should be better supported by research results.
9. Author Contributions should be in accordance with CRediT (Contributor Roles Taxonomy).

Author Response

Thank you for the opportunity to review the article entitled UV-Cured biodegradable methacrylated starch-based coatings. The article is interesting, but in its current form is not suitable for publication in Coatings journal. My comments and suggestions are presented below:

1. The introduction section is very general. In fact, most of this section relates to starch. The journal to which the article was sent deals with the subject of coatings. I think that the authors should write in this section about various types of coatings obtained on the basis of renewable raw materials or coatings which are susceptible to biodegradation.

In the revised version of the paper we have added some extra general information on other types of biobased monomers used in coatings.

2. Figure 1 is very difficult to read. Authors should sharpen it. Why did the authors not provide the chemical structure of the cross-linked coating?

We modified the Scheme 1, (wrongly addressed as Figure 1) in order to clarify it, and we added a second image containing the chemical structure of the cross-linked coating.

3. The wavenumber values in Figure 2a are hard to read. I think it would be better to put the appropriate chemical bonds instead values of wavenumber.

We substitute the wavenumber in the Figure 1a (not Figure 2a) as suggested by the reviewer, in order to make the figure more readable.

4. Do the authors not think that the heating rate of 10 °C/min during the DSC test was too high? When I look at DSC thermograms, I am not entirely sure if these T_gtemperatures have been marked correctly. A lower heating rate, e.g. 5 °C/min or less, would allow a more accurate determination of this temperature.

We selected 10°/min in order to have a good sensitivity. In fact, theoretically, an increase of heating rate could increase the sensitivity of thermal events measured by DSC. The DSC output is a function of heat flow (mW) or energy per unit time (J/s). As the heating rate is increased, there is a greater input of energy per unit time and hence the same heat flow occurs over a shorter time frame.  [Foreman, J.; Sauerbrunn, S.R.; Marcozzi, C.L. Thermal Analysis & Rheology Exploring the Sensitivity of Thermal Analysis Techniques to the Glass Transition 109 Lukens Drive New Castle , DE 19720], [Liu, P.; Yu, L.; Liu, H.; Chen, L.; Li, L. Glass transition temperature of starch studied by a high-speed DSC. Carbohydr. Polym. 2009, 77, 250–253, doi:10.1016/j.carbpol.2008.12.027.].

5. Did the authors perform thermogravimetric analysis (TGA)?

The thermal stability of the coatings was not part of our investigations, therefore we did not measured TGA analysis

6. I think that the result discussion should be more broadly supported by literature. Not for the sake of drawing general conclusions, but for comparison with the research of other scientists.

With the aim to extend the conclusions and compare our results with the others reporrrted in literature, we added two references (43,44) in the revised version where the data are compared with our data.

7. Latin names should be written in italics.

The latin name are now written in italics

8. Conclusion section should be better supported by research results.

We have revised the conclusions, also taking into consideration other reviewer comments.

9. Author Contributions should be in accordance with CRediT (Contributor Roles Taxonomy).

The author contributions are now in accordance with CRediT.

Reviewer 2 Report

The authors of the submitted manuscript continue their work on UV-curable biodegradable starch-based coatings. The thermal and mechanical properties of the fabricated UV-cured coatings were investigated and compared with the starch-based uncured casted coatings.

The study is well performed, the methods are adequately described, the results are clearly presented and the conclusions are supported by the results.

Author Response

The authors of the submitted manuscript continue their work on UV-curable biodegradable starch-based coatings. The thermal and mechanical properties of the fabricated UV-cured coatings were investigated and compared with the starch-based uncured casted coatings.

The study is well performed, the methods are adequately described, the results are clearly presented and the conclusions are supported by the results.

We thank the Reviewer 2 for all the nice comments.

Reviewer 3 Report

Biodegradable methacrylated starch-based coatings were made by UV-Cured method. There are several problems to be addressed before publication:

1. Film thickness is important and should be characterized with SEM imaging to show the film adhesion on the substrate.

2. For the mechanical strength improvement, a detailed explanation is required rather than one sentence: "These results can also be ascribed to the cross linking reaction." 

3. Statistics analysis is required in Fig. 4.

4. A degradation profile with mass/percentage loss should be provided to prove the degradation property. 

5. The conclusion section should be concise, and only the conclusion supported by the data should be presented. 

Author Response

Biodegradable methacrylated starch-based coatings were made by UV-Cured method. There are several problems to be addressed before publication:

1. Film thickness is important and should be characterized with SEM imaging to show the film adhesion on the substrate.

We were not able to perform the SEM imaging, however the film adhesion on the substrate was evaluated with the adhesion test.

2. For the mechanical strength improvement, a detailed explanation is required rather than one sentence: "These results can also be ascribed to the crosslinking reaction." 

It is well known that the crosslinking reaction induces a hinder of the chain mobility, so increasing the Tg and leading to an enhancement of the mechanical properties. This is an expected result and this is the reason why we mentioned that the mechanical properties of the starch films were enhanced by crosslinking reaction.

3. Statistics analysis is required in Fig. 4.

the error bar is already present into the Figure 4.

4. A degradation profile with mass/percentage loss should be provided to prove the degradation property. 

The tested films start to fragment already after 4 days (second time point), it was impossible to purify the fragmented pieces from the saline buffer solution, so we could no calculate an accurate weight loss estimation.

5. The conclusion section should be concise, and only the conclusion supported by the data should be presented. 

We have revised the conclusions and shortened.

Round 2

Reviewer 1 Report

The article has been significantly improved compared to the original draft. However, authors should add more numerical results (not only conclusions themselves) in the Conclusion section.

Author Response

We have revised the conclusion by adding some numerical results, as suggested by the reviewer.  

Reviewer 3 Report

Biodegradable methacrylated starch-based coatings were made by UV-Cured method. There are several problems to be addressed before publication:

1. Film thickness is important and should be characterized with SEM imaging to show the film adhesion on the substrate.

A.1: We were not able to perform the SEM imaging, however the film adhesion on the substrate was evaluated with the adhesion test.

Comment: Why does "The tested films start to fragment already after 4 days (second time point)", considering the good adhesion value? Please provide some imaging to show the degradation/pealing process in the degradation test and adhesion test. Besides, please add the fragment behavior in the appropriate section.

2. Statistics analysis is required in Fig. 4.

A.3: the error bar is already present into the Figure 4.

Comment: Please provide the significance analysis.

Author Response

Dear editor,

We have revised the paper in accordance with the reviewers comments. Concerning the reviewer N.2 we have upload the following answers, but we are not sure the file was uploaded, for this reason, please find below the detailed answers for the reviewer N.2.

Many thanks for your kind attention.

Marco Sangermano

Reviewer 2:

We thank the reviewer 2 for all the extra suggestions.

1. Why does "The tested films start to fragment already after 4 days (second time point)", considering the good adhesion value? Please provide some imaging to show the degradation/pealing process in the degradation test and adhesion test. Besides, please add the fragment behaviour in the appropriate section.

The enzymatic degradation was not conducted on the coating attached to the substrate, but on free-standing sampleas (similar to the ones used in the tensile test). We clarified this point in the text by adding the sample dimensions in the procedure description. We inserted the information on the fragmentation behaviour in the appropriate section (line 286). Here below we attached the image of the sample after 1 day of incubation and after 4 days to show the reviewer 2 the fragmentation. However, we don’t think this image along with the one from the scratch test will enhance the quality of our paper, so we didn’t insert them on the paper itself.

2. Please provide the significance analysis

We apologize for not understanding the question before. The significance analysis has now been added in the Fig.4 along with a brief discussion in the text.