Plasticized Polylactide Film Coating Formation from Redispersible Particles

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript titled “Plasticized polylactide film coating formation from redispersible particles” explores the preparation and characterization of polylactide (PLA) coatings from redispersible aqueous dispersions, focusing on the role of various plasticizers, particularly synthesized epoxidized oleic and linoleic acids, to improve film formation at reduced temperatures. The manuscript needs major revisions before publication and the points of consideration are as follows:

1. The paper primarily focuses on film formation temperature reduction but does not report on mechanical properties or barrier performance, which are essential for practical coating applications. The authors are suggested to include mechanical and barrier testing of films formed with different plasticizers to assess real-world applicability and performance trade-offs.
2. The authors have highlighted concern over low-molecular-weight plasticizer migration but didn’t provide any experimental evidence such as leaching and long-term stability. The authors are suggested to incorporate plasticizer migration under humidity, temperature cycling, and over time to evaluate stability.
3. The film formation stages are well supported by optical and SEM images; however quantitative metrics such as residual porosity, crystallization or viscosity changes are missing. The authors are advised to include DSC, XRD or rheological measurements.
4. PEG-400 is used as a reference plasticizer, but the paper lacks comparison with commercial PLA coatings or dispersions, e.g., acrylics or polyurethanes, in terms of film properties. The authors are suggested to include at least a qualitative comparison of MFFT and mechanical/barrier properties with commercially relevant systems.
5. Dichloromethane is used for dispersion preparation, a toxic solvent with environmental and health hazards. While the paper mentions capturing and regenerating solvent, green alternatives or solvent-free routes would be more impactful.
6. The advised must improve data presentation and clarity, especially in morphology analysis.
7. In the introduction section, the authors have not included the most recent publications on plasticized polylactide film coating formation. It is recommended that they incorporate up-to-date studies, particularly from 2024-2025. Some suggestions are as follows: https://doi.org/10.1016/j.ijbiomac.2025.141428, , https://doi.org/10.1016/j.carbon.2024.119770,

Author Response

Reviewer 1 replies

Dear reviewer, thank you for your recommendations for improving our study. We have made the appropriate corrections to the text and added additional research results (Fig. 10, Fig. 11). We will use some of your recommendations in our further work, which will be a development of the results described in the text of our manuscript.

Comment 1: The paper primarily focuses on film formation temperature reduction but does not report on mechanical properties or barrier performance, which are essential for practical coating applications. The authors are suggested to include mechanical and barrier testing of films formed with different plasticizers to assess real-world applicability and performance trade-offs.

Reply: Dear reviewer, thank you for this comment. For thin films, especially those intended for use in packaging, these parameters are indeed decisive. For coatings on various substrates, their importance is reduced, although, for example, strength indicators remain quite informative for comparing the properties of films obtained from dispersions as well as by solvent evaporation and extrusion. Therefore, following your recommendation, we have included in the text Fig. 10 a comparison of the strengths of films with different plasticizers, and have also added an interpretation of these results to the discussion (Lines 330-336).  Since such coatings contain a fairly high number of defects compared to solvent and extrusion coatings, and this number of defects will vary depending on the conditions of coalescence, this topic deserves more in-depth coverage, which we plan to do in future publications.

Comment 2: The authors have highlighted concern over low-molecular-weight plasticizer migration but didn’t provide any experimental evidence such as leaching and long-term stability. The authors are suggested to incorporate plasticizer migration under humidity, temperature cycling, and over time to evaluate stability.

Reply: Thank you for this recommendation; it is a very good suggestion for developing the results of our work, bringing it closer to practical implementation. This, along with the additional use of more complex composites (e.g., filled, pigmented) to improve properties, will be the subject of the next article, which is included in the plan for our current project. In particular, we plan to conduct long-term leaching tests for all studied plasticizers. However, such tests are long-term and must be conducted under various conditions—immersion in water, humidity, and different temperatures—in order to be informative. It would be more correct to perform them first on intact films (e.g., obtained by extrusion) to characterize the stability of the plasticizer in the polymer, and only then move on to dispersions, where the picture is complicated by the presence of interphase boundaries. Obviously, such studies are beyond the scope of this article, but they are certainly very relevant. We have added this idea to the discussion before the conclusions as a path for future research (lines 367-374).

Comment 3: The film formation stages are well supported by optical and SEM images; however, quantitative metrics such as residual porosity, crystallization, or viscosity changes are missing. The authors are advised to include DSC, XRD, or rheological measurements.

Reply: Dear reviewer, thank you for this valuable comment and recommendation for further research. Indeed, particle coalescence processes depend on the viscosity of the polymer at a given temperature, and the efficiency of film formation can be characterized numerically by porosity values. However, in this study, we limited ourselves to a qualitative description of the material structure, which will serve as the basis for a quantitative description in the future. We also added our data on the melt flow rate of plasticized polymer to the study (Fig. 11), which allows for a quantitative comparison of the viscosity of materials at a given temperature.

Comment 4: PEG-400 is used as a reference plasticizer, but the paper lacks comparison with commercial PLA coatings or dispersions, e.g., acrylics or polyurethanes, in terms of film properties. The authors are suggested to include at least a qualitative comparison of MFFT and mechanical/barrier properties with commercially relevant systems.

Reply: Thank you for the recommendation! The fact is that there are currently several experimental products—PLA dispersions—that are in the early stages of technological development. Their MFFT is above room temperature, which means that additional heating is required to obtain continuous films. This problem is described in the last two paragraphs before the conclusions of the work. This means that, in terms of quality, such dispersions cannot yet compete with acrylic or polyurethane dispersions, which have an MFFT of around 5 degrees. The problem can be solved, in particular, by reducing the particle size and using plasticizers or coalescents. We have modified the discussion to emphasize this fact more strongly (Lines              349-353).

Comment 5: Dichloromethane is used for dispersion preparation, a toxic solvent with environmental and health hazards. While the paper mentions capturing and regenerating solvent, green alternatives or solvent-free routes would be more impactful.

Reply: Thank you for your suggestion. Dichloromethane is currently the most effective solvent for PLA, but dichloromethane use is problematic for the environment. This issue can be mitigated by replacing conventional solvents with more environmentally friendly and bio-based solvents, such as 2-methyltetrahydrofuran or dimethyl carbonate [https://doi.org/10.1007/978-3-662-43628-8_12, https://doi.org/10.1007/s10853-016-9778-x ].

Comment 6: The advised must improve data presentation and clarity, especially in morphology analysis.

Reply: Yes, we agree that the recommended characterization will be beneficial and will use this approach in our next work.

Comment 7: In the introduction section, the authors have not included the most recent publications on plasticized polylactide film coating formation. It is recommended that they incorporate up-to-date studies, particularly from 2024-2025.  Some suggestions are as follows: https://doi.org/10.1016/j.ijbiomac.2025.141428, , https://doi.org/10.1016/j.carbon.2024.119770,

Reply: Dear reviewer, thank you for the relevant fresh references! We have incorporated them into the text (this one 10.1016/j.ijbiomac.2025.141428 – is in introduction (Line 92) and this 10.1016/j.carbon.2024.119770 is closer to conclusions (Line 373), together with other up-to-date works.

Reviewer 2 Report

Comments and Suggestions for Authors

Myronyuk et al. reported an interesting work on making polylactide films. I think the overall manuscript is sound and can be accepted for publication after the authors addressed the following comments:

1. In line 68, “TM” needs to be corrected as “T_m”
2. In line 72, “eg” needs to be corrected as “e.g.”, same for the other instances throughout the manuscript
3. I can barely read anything from figure 1. In addition, the authors need to specify the NMR solvent used and the field strength of NMR instrument used.
4. (Line 135) Can the authors explain or clarify what does “multiple bonds” mean?
5. Epoxy structure in line 136 needs to be corrected.
6. The authors need to specify the time and temperature the polymer is being held during the removal of air bubbles (lines 235-237)
7. FT-IR spectrum in the appendix needs to be better interpreted in the corresponding main text section, e.g. which signals are evidences for the formation of epoxy oleic/linoleic acid

Author Response

Reviewer 2 replies

Dear reviewer, thank you for your suggestions on how to improve the readability of our text and the overall perception of the work! We have made the appropriate changes to the text.

Comment 1: In line 68, “TM” needs to be corrected as “T_m”

Reply: Thank you. It was corrected.

Comment2: In line 72, “eg” needs to be corrected as “e.g.”, same for the other instances throughout the manuscript

Reply: Thank you. It was corrected.

Comment 3: I can barely read anything from Figure 1. In addition, the authors need to specify the NMR solvent used and the field strength of NMR instrument used.

Reply: We have edited the figure our best. Required info was added (Lines 131-132)

Comment4: (Line 135) Can the authors explain or clarify what does “multiple bonds” mean?

Reply: Thank you for pointing out! It is checked, and now it is “double bonds”.

Comment 5:  Epoxy structure in line 136 needs to be corrected.

Reply: Thank you for your suggestion. The epoxy structure in line 136 was removed to avoid confusion, because showing the epoxy group cyclic structure in text form is difficult.

Comment 6: The authors need to specify the time and temperature the polymer is being held during the removal of air bubbles (lines 235-237)

Reply: Thank you for noticing – we have added the temperature value and time of our sample exposure. In our future work we plan to reinforce this by porosity characterization.

Comment7: FT-IR spectrum in the appendix needs to be better interpreted in the corresponding main text section, e.g., which signals are evidence for the formation of epoxy oleic/linoleic acid

Reply: Thanks for the suggestion. The description for IR spectra was added.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript is improved after revisions and can be accepted for publication in its current form.