Improving Hydrophobicity and Water Vapor Barrier Properties in Paper Using Cellulose Nanofiber-Stabilized Cocoa Butter and PLA Emulsions

Response to Reviewer 1 Comments

1. Summary

Thank you very much for such kind words and for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted in red in the re-submitted files.

2. Point-by-point response to Comments and Suggestions for Authors

Comments 1: Title should be more concise and focused for better readability.

Response 1: Thanks for your suggestion. The title has been changed to “Improving Hydrophobicity and Water Vapor Barrier Properties in Paper Using Cellulose Nanofiber-Stabilized Cocoa Butter and PLA Emulsions.”

Comments 2: Is the coating adequately resistant to peeling off, or are there potential concerns regarding its durability in this aspect?

Response 2: Thank you for your comment. The peeling resistance of the coating has not been evaluated in this study, but it is an important aspect that will be considered in future work. At this stage, our research has focused on the emulsion's impact on the hydrophobicity and moisture resistance of paper. Durability aspects, such as resistance to peeling, will be relevant for our next paper.

Comments 3: Data in Figure 5 were overlapped. Please modify it.

Response 3: Thank you for pointing this out. Changes have been made accordingly.

Comments 4: What do the arrows in Figure 3 represent? Please indicate it

Response 4: Thank you for your comment. The arrows in Figure 3 indicate the fibers and pores present on the surface of Bond paper after the coating application. A brief description of this was included in the figure caption to avoid any further confusion.

Response to Reviewer 2 Comments

1. Summary

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted in red in the re-submitted files.

2. Point-by-point response to Comments and Suggestions for Authors

Comments 1: In the introduction add also a sentence about the fact that polylactic acid and CB are safe to be in contact with food.

Response 1: Thank you for the comment. Therefore, a short sentence was added in line  82 “Moreover, both PLA and CB are recognized as safe for use in food contact applications [1],  making them ideal candidates for sustainable packaging development”.

Comments 2: Explain what happens with the excess of DCM and its impact with food, if it is approved to be in contact with food products.

Response 2: Thank you for your comment. Dichloromethane (DCM) was used as a solvent in the preparation of the emulsions but was completely evaporated during the process. In particular, during the pressing of the paper, temperatures of 160°C were reached, as mentioned in line 161, which is well above the boiling temperature of DCM (around 40°C), ensuring that no residual solvent remains in the final coating. Since DCM is not approved for direct food contact, this process was carefully controlled. In a future work it is interesting to evaluate if there is a residual content of DCM and its quantification by gas chromatography.

Comments 3: You did not present the coating stability in different pH environments, some foods are more acidic like jus others more basic.

Response 3: Thank you for your observation. At this stage, our research has focused on the emulsion's impact on the hydrophobicity and moisture resistance of paper. For this reason, we did not evaluate the coating stability using different pH environments in this study, it is an important aspect, particularly for food applications where pH can vary. This could be addressed in future research with a more specific focus on the microstructure of a multilayered package for food-related applications.

Comments 4: For a future packaging most likely also the air permeability must be known.

Response 4: Thank you for your suggestion. We agree that air permeability is a critical factor for future packaging applications. While this study is primarily focused on the impact of the coating on paper water permeability, testing for air permeability would be a valuable addition in future work to further assess the coating’s suitability for packaging purposes

Response to Reviewer 3 Comments

1. Summary

Thank you for your thorough feedback. We appreciate your interest in the topic and acknowledge the areas for improvement. Regarding the methodology, we provided additional details to ensure clarity and completeness. As for the title, we agree that it can be refined to better reflect the focus on the use of emulsions for paper coating and was revised accordingly.

While our study primarily focused on the hydrophobic effects and paper permeability, we recognize the importance of exploring other aspects of emulsion stabilization, such as thermal stability, and freeze-thaw behavior. These are crucial parameters that could be addressed in future studies to further validate the performance of the emulsions.

Additionally, we acknowledge the suggestion to evaluate the mechanical performance of the paper after coating. This would indeed provide valuable insights and could be included in follow-up research to expand upon the current findings.

2. Point-by-point response to Comments and Suggestions for Authors

Comments 1: The correct spelling of polymer names is: e.g. poly(ethylene terephthalate) -l. 38-39, poly(vinyl alcohol) – l. 52, and others l. 62, 96, please correct the whole manuscript.

Response 1: Thank you for pointing this out. Therefore, all the polymer names in the manuscript were changed accordingly. 

Comments 2: The abbreviations should be explained when used the first time (see: l. 85).

Response 2: Thank you for pointing this out. All the abbreviations used in the manuscript were explained when needed.

Comments 3: The methodology of obtaining CNF should be provided.

Response 3: Thank you for the suggestion. A brief description of the methodology of obtaining CNF was added to the manuscript, l. 106-114.

Comments 4: The molecular weight of PLA should be provided

Response 4: Agree. Therefore, molecular weight of PLA was included in Materials information according to the data provided by Kmetty et al (2020) [2].

Comments 5: “They they” – please correct

Response 5: Thank you for your observation. Corrections were made accordingly.

Comments 6: The photographs of emulsions should be provided (supplementary information l. 199  -not available).

Response 6: Thank you for letting us know. Thus, photographs of emulsions were provided as supplementary information, and they were summited in an additional document.

Comment 7: Table 1 – what was the unit?

Response 7: Thank you for pointing this out. The units (mm) were included in Table 1.

Comment 8: Fig. 1a – what was the content of CNF?

Response 8: Flow curves presented in Fig. 1a correspond to 1 wt.% CNF suspension. This value was included in Figure caption.

Comment 9: L. 305 “crystallization of triglycerides” – please provide the confirmation

Response 9: Thank you for your inquiry regarding this phenomenon. As a future work, we could conduct complementary characterization studies to verify the crystallization and hardening behavior of triglycerides within the CB droplets. This will provide a more comprehensive understanding of the interactions in our emulsions. However, considering this important recommendation we improved this discussion in lines 321- 324. " Increases in the modulus of CNF/CB can be linked to several phenomena, including the hardening of the cocoa butter droplets associated with the partial crystallization of triglycerides at room temperature [68]. As mentioned by Marangoni et al., cooling cocoa butter produces a solid material with a crystalline structure [69]"

Comment 10: L. 432 “suspension of PLA” and l. 438 “emulsions as suspensions” – confusing

Response 10: Thank you for your observation. Corrections were made accordingly.

1. Summary 

Thank you very much for once again reviewing this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted in red in the re-submitted files. 

2. Point-by-point response to Comments and Suggestions for Authors 

Comments 1: Please also add in the article the answers to comments 2 to 4, explaining that there are aspects that have not yet been addressed (comments 3 and 4). 

Response 1: Thank you for your suggestion. We have included a short sentence referring to comment 2 from the first round of reviews, which has been added in line 164: “Since this step is well above the boiling temperature of DCM (around 40°C), no residual solvent is expected to remain in the final coating.” 

Additionally, a brief reference to comments 3 and 4 has been added in line 453: “However, to ensure the applicability of these coated papers in food packaging, it is important to test them for other properties, such as air permeability, grease resistance, and coating behavior in different pH environments.” 

1. Summary 

Thank you very much for reviewing this manuscript once again. We have improved the discussion in the results and conclusions sections by providing a more detailed analysis and relevant context that enhances the understanding of the implications of our findings. Please find the detailed responses below, along with the corresponding revisions and corrections highlighted in red in the resubmitted files. 

2. Point-by-point response to Comments and Suggestions for Authors 

Comments 1: Please corract also polybutylene terephthalate - l. 44. 

Response 1: Thank you for pointing this out. The name “poly(butylene terephthalate)” was changed accordingly.