Barrier and Antimicrobial Properties of Coatings Based on Xylan Derivatives and Chitosan for Food Packaging Papers

Round 1

Reviewer 1 Report

I have reviewed the paper by Roman et al. They describe coated papers with modified xylan and chitosan. While I find their results are significant, I find their presentation style lacking. Specifically, it is very hard to follow their number scheme (P0-P13). This scheme detracts from the results of the paper by forcing readers to reinterpret what each of these numbers mean. I invite the authors to come up with a better numbering scheme that quickly converys what each sample is using the number. For eg. P4 could be 75Xy25Ch. This would allow the readers to focus on the results and trends present in these studies. furthermore I would urge the authors to show how their materials compare with commercially available water vapor and oil/grease barriers so that readers can gauge the significance of their findings.

Author Response

Dear reviewer,

Thank you very much for your useful observations, comments and recommendations. We deeply appreciate your evaluation. Your fruitful comments helped us to improve the overall quality of the manuscript.

Please, find bellow, point by point, the response at your comments:

Reviewer comments

I have reviewed the paper by Roman et al. They describe coated papers with modified xylan and chitosan. While I find their results are significant, I find their presentation style lacking. Specifically, it is very hard to follow their number scheme (P0-P13). This scheme detracts from the results of the paper by forcing readers to reinterpret what each of these numbers mean. I invite the authors to come up with a better numbering scheme that quickly converys what each sample is using the number. For eg. P4 could be 75Xy25Ch. This would allow the readers to focus on the results and trends present in these studies. furthermore I would urge the authors to show how their materials compare with commercially available water vapor and oil/grease barriers so that readers can gauge the significance of their findings.

Response

Regarding the codification of tested samples: if we introduce in graph the new it becomes very loaded with data and thus hard to read.  In this context we choose to give the details in the legend of each figure. In this way the readers will focus on the results and trends more easily.

In the revised manuscript in the Sections Results and discussions and Conclusions we introduced values of existing commercial grease proof papers characteristics and new references, also, [42.43].

All the modifications are marked in the revised manuscript with red colour.

The authors

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear Authors

Your manuscript is interesting paper and well organized. It consists of important topic related to biodegradable type of food packaging based on paper, chitosan, xylan, and so on. Some suggestion for improving your article are given in the attached file. Namely, some of the references could be updated with newer ones, English could be revised in the whole manuscript as well, and other minor revisions are also suggested.

I hope that this article will be a good addition to the portfolio of antimicrobial food packaging materials that are very attractive nowadays.

Thanks.

Comments for author File: Comments.pdf

The English is fine in general, but it could be improved.

Author Response

Dear reviewer,

Thank you very much for your useful observations, comments and recommendations. We deeply appreciate your evaluation.Your fruitful comments helped us to improve the overall quality of the manuscript. Please, find bellow, point by point, the response at your comments:

Reviewer comments

Your manuscript is interesting paper and well organized. It consists of important topic related to biodegradable type of food packaging based on paper, chitosan, xylan, and so on. Some suggestion for improving your article are given in the attached file. Namely, some of the references could be updated with newer ones, English could be revised in the whole manuscript as well, and other minor revisions are also suggested.

Response

All of your recommendations were introduced in the revised manuscript and are marked with red colour. The references  [20, 22] were up dated, the producers of base paper was introduced, in the legend of figure 4 the details regarding the blue circles were introduced,  the graph from figure 11 was modified with more readable variant, and some details regarding the molecular weight of chitosan were addressed. The English was revised in whole manuscript. In addition we will pay the English service to the Coatings journal.

The authors

Author Response File: Author Response.pdf

Reviewer 3 Report

The submitted study, "Barrier and antimicrobial properties of coatings based on xylan derivatives and chitosan for food packaging papers," is an interesting study where the author initially derivatized xylan (using alkyl ketene dimer and acetylation), followed by applying it onto a paper (paper coating). The final material was studied for its barrier properties, chemically characterized using IR spectroscopy, surface morphology was characterized with the help of Scanning electron microscopy, and in the end, an application of antibacterial surface was concluded.

There are a few points that need to be addressed by the authors.

1. Figure 1, alkyl ketene dimers were used to hydrophise the xylan. Please specify the R', and R'' groups; what are these? An aromatic, alkyl, or hydrocarbons? Was there more than one alkyl ketene dimer? Please state it clearly. Another aspect of this particular reaction is that "if reactant (alkyl ketene dimers) is a mixture, then it will likely produce various types of hydrophised xylan derivatives (not a single product). Please explain in the result discussion such information.

2. The acetylation on xylan at C2 and C3: Is double acetylation equally achieved onto the xylan ring? In my opinion, C2 and C3 are of different reactivities; therefore, getting double acetylation equally on C2 and C3 is a bit challenging, and in most scenarios, only monoacetylation is achieved. To an extent, I agree that assessment of materials can be sufficiently assessed with semi-quantitative methodology; the author needs to be careful when presenting such acetylation reactions as there would be some xylan rings that were only substituted with monoacetylation, and therefore, such chemical interpretations can be challenging to correlate of what is happening at the molecular level. The author could point out such difficulty so that it addresses one of the challenges of chemical reactions in such materials. 

3. The author writes a procedure about coating paper (as a material) by applying their prepared colloidal solutions. However, a schematic representation of layers of this paper coating (as an illustration) would help to understand and improve the manuscript's readability.

Author Response

Dear reviewer,

Thank you very much for your useful observations, comments and recommendations. We deeply appreciate your evaluation. Your fruitful comments helped us to improve the overall quality of the manuscript. Please, find bellow, point by point, the response at your comments:

Reviewer comments

1. Figure 1, alkyl ketene dimerswere used to hydrophise the xylan. Please specify the R', and R'' groups; what are these? An aromatic, alkyl, or hydrocarbons? Was there more than one alkyl ketene dimer? Please state it clearly. Another aspect of this particular reaction is that "if reactant (alkyl ketene dimers) is a mixture, then it will likely produce various types of hydrophised xylan derivatives (not a single product). Please explain in the result discussion such information.
2. The acetylation on xylan at C2 and C3: Is double acetylation equally achieved onto the xylan ring? In my opinion, C2 and C3 are of different reactivities; therefore, getting double acetylation equally on C2 and C3 is a bit challenging, and in most scenarios, only monoacetylation is achieved. To an extent, I agree that assessment of materials can be sufficiently assessed with semi-quantitative methodology; the author needs to be careful when presenting such acetylation reactions as there would be some xylan rings that were only substituted with monoacetylation, and therefore, such chemical interpretations can be challenging to correlate of what is happening at the molecular level. The author could point out such difficulty so that it addresses one of the challenges of chemical reactions in such materials. 
3. The author writes a procedure about coating paper (as a material) by applying their prepared colloidal solutions. However, a schematic representation of layers of this paper coating (as an illustration) would help to understand and improve the manuscript's readability.

Response

1. In the legend of figure 1 it was specified: Note that R’ and R” are typically in the range of C4 – C16 (C₁₄H₂₉). In the reaction was only one alkyl ketene dimer and the one type of hydrophobized xylan was obtained.
2. We are according with your considerations that C2 and C3 from xylan unit are of different reactivities. We conducted the chemical reaction in two stages in the same parameters of time, temperature and molar ratio of acetic anhydride to functional hydroxyl groups.

Regarding both your comments, we mentioned that the objective of this study was to obtain these xylan derivatives and to test their performances in coatings for paper packaging by semi-quantitative methodology. The reaction mechanisms for both xylan chemical modification reactions (hydrophobised with AKD and acetylation with acetic anhydride) will be studied in the future research based on these preliminary findings, and we appreciate a lot your recommendations.

3. A schematic representation of coating process and coating layers was introduced in the revised manuscript (scheme 1: Representation of laboratory coating papers).

The authors

Author Response File: Author Response.pdf

Reviewer 4 Report

The manuscript described the preparation of xylan β-keto ester, using long chain ketene anhydride as the reagent on hydroxyl groups, and acetylation of xylan hemicellulose with the products utilization in the paper coating as the barrier layer against moisture, oil, and bacteria. It is a general unspecific evaluation of paper coating materials for application. Statements in the sections of introduction and discussion were appropriate in the light of functionalization chemistry involved being well-known in the literature. In general, biocidal efficacy on Gram-positive bacteria is much more effective than that of Gram-negative E. coli. Even though a long period of 24 h and 48 h was demonstrated for required cytotoxicity, the manuscript is still suitable for publication at Coatings for purpose of reader’s information.

Author Response

Dear reviewer,

Thank you very much for your useful observations, comments and recommendations. We deeply appreciate your evaluation.Your fruitful comments together with those of other reviewers helped us to improve the overall quality of the manuscript. You will find in the revised manuscript all the modifications marked with red colour.

The authors

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I have reviewed the paper by Roman et al. . The authors have incorporated all comments and I now find the paper suitable for publication.

Author Response

Dear Editor,

Thank you very much for your useful recommendations that helped us to improve the overall quality of manuscript.
We completed and revised the manuscript according to your suggestions. The changes are marked with green colour.

The authors