Study on Aging and Recover of Poly (Lactic) Acid Composite Films with Graphene and Carbon Nanotubes Produced by Solution Blending and Extrusion
, Polya Angelova 1, Todor Batakliev 1, Verislav Angelov 1, Rosa Di Maio 2 and Clara Silvestre 2,*Round 1
Reviewer 1 Report
This paper presents the Study on aging and recover of poly(lactic) acid composite films with graphene and carbon nanotubes produced by solution blending and extrusion. The experiments have been precisely certified with the proper characterization and the results are analytically discussed. However, there are certain technical points that need to be addressed before publication. Hence, I want the authors to revise the following comments before publication.
Comments:
1- Abstract: Keeping in view the previous literature, emphasize the main idea and the novelty of the proposed research in a single sentence or two.
2- Introduction: It is essential to narrate the importance and the scope of the study, especially the aging process, which is missing. Also, concisely explain the most important research findings in the last paragraph of the introduction section.
3- Figure 1 and Figure 2: The scale bars are not clearly visible. To give Figure 1 and 2 a professional outlook, provide a clear and concise scale bar inside the Figures for readers' understanding.
4- Improve the overall quality of the graphs in Figures 3, 4, 5, 6, and 7. At times, the information provided in the insets is vague. For readers' convenience, I encourage the authors to label the graphs such that the graphs be distinguishable in the black and white copy of the manuscript. Also, if possible, change the font style in all figures and increase the inset panel size.
5- Rather than narrative, the conclusion should be analytically epitomized for readers' understanding.
Author Response
Authors thanks vary much for the comments and suggestions of the Reviewer #1.
The answers and corrections in the manuscript related with the comments of Reviewer #1 are marked in blue background.
Comments and Answers:
Comment 1- Abstract: Keeping in view the previous literature, emphasize the main idea and the novelty of the proposed research in a single sentence or two.
Answer 1: Lines 24-28 - corrections in the text of manuscript
The paper underlines that the properties of the nanocomposites under investigation are influenced not only by the composition, chemical nature of the added filler and processing condition, but also by the aging processes which are on turn depending on the type of nanopartcles added to PLA and the compositions. The paper provides valuable information for selection of material and processing conditions.
Comment 2- Introduction: It is essential to narrate the importance and the scope of the study, especially the aging process, which is missing. Also, concisely explain the most important research findings in the last paragraph of the introduction section.
Answer 2. Lines 81-90 - corrections in the text of manuscript
It is well known that the selection of polymers for use as specific materials requires the consideration of how these will withstand the environmental conditions to which they will be subjected. This is particularly true for PLA- based materials as this polymer, if cooled during the processing to below their glass transition, presents a high amount of amorphous material that can undergo small-scale relaxation processes causing a significant change in macroscopic properties at room temperature. A wide range of materials are affected by this aging at room temperature and extensive studies have been carried out on homopolymers and copolymers. Contrary to this, less attention has been devoted to the change in properties of polymer nanocomposites due to the aging process. This paper is devoted to fill this gap by investigateing……
Comment 3- Figure 1 and Figure 2: The scale bars are not clearly visible. To give Figure 1 and 2 a professional outlook, provide a clear and concise scale bar inside the Figures for readers' understanding.
Answer 3: Fugures 1 and 2 are corrected. in the manuscript
Comment 4- Improve the overall quality of the graphs in Figures 3, 4, 5, 6, and 7. At times, the information provided in the insets is vague. For readers' convenience, I encourage the authors to label the graphs such that the graphs be distinguishable in the black and white copy of the manuscript. Also, if possible, change the font style in all figures and increase the inset panel size.
Answer 4: Fugures 3, 4, 5, 6 and 7 are corrected according to the Comment 4.
Comment 5- Rather than narrative, the conclusion should be analytically epitomized for readers' understanding.
Answer 5: Lines 360-383 – corrections, marked in blue are made in the Conclusions
Reviewer 2 Report
This paper reports the effect of introducing graphene and carbon nanotubes on aging, annealing, and reprocessing of PLA films produced by a single-screw extruder. TEM, DSC, TGA, and nanoindentation methods were employed to characterize the films. The authors concluded that the presence of the nanoparticles in the matrix prevented the degradation process of PLA. Annealing of the aged films was reported to improve their crystallinity, however had no effect on hardness and Young’s modulus.
There are some issues that must be addressed prior to making the final decision on publishing this manuscript in Coatings.
1. considering lines 317 to 322, it is not clear which parameter(s) govern the hardness and Young’s modulus of the control aged films, annealed aged films, and melt reprocessed aged films. A minor reduction in crystallinity (around 2-3%) was considered to explain the remarkable reduction of hardness and Young’s modulus of melt reprocessed aged films compared to the control films. In contrast, a significant improvement in crystallinity (around 30%) of annealed films, compared to the control films, had no effect on hardness and Young’s modulus of the samples. If considering that the nanoindentation and DSC characterizations were performed correctly, other parameter(s) (e.g. degradation and molecular weight reduction) or another phenomenon may cause these results which need to be verified.
2. The authors need to justify the remarkable increment of Tg for the “aged” films compared to the “fresh” ones (Figure 3a and 3b).
3. The authors need to discuss the enhancement of Tonset and T10% of the nanocomposite films, especially those containing GNP, compared to the neat samples.
4. Regarding lines 39-41, the references which are mentioned in the text did not perform the original research on HDT. For example, reference 8 has no HDT results and just referred to another publication’s HDT results in the introduction section. The authors need to cite original researches with HDT results.
5. The authors are encouraged to explain the improvement of the dispersion of both fillers by introducing the second filler (i.e. CNT particles).
6. The caption of Figure 1 is not correlated to the individual images presented in this figure.
7. The scale of the TEM images in Figure 1 and Figure 2 are not visible.
8. In the Materials and Methods section, the authors are encouraged to mention how the slow cooling step in “annealed” samples was performed.
9. Why a twin-screw extruder was not employed to make nanocomposite films to take advantage of high shearing forces for better dispersion and distribution of the nanoparticles within the PLA matrix?
10. Some editing of typo mistakes and English language is required throughout the manuscript. For instance, line 64 (resently), line 116 (aluminous), line 173 (warsen), line 319 (some grammatical errors to be fixed), and line 215 (crystallinity of aged neat PLA film is reported 0.4% while Table 1 reports 0.2%).
Author Response
Authors are thankful for the valuable comments and suggestions of the Reviewer #2.
The answers and corrections to Reviewer #2 in the manuscript are marked in yellow background.
Comment 1. considering lines 317 to 322, it is not clear which parameter(s) govern the hardness and Young’s modulus of the control aged films, annealed aged films, and melt reprocessed aged films. A minor reduction in crystallinity (around 2-3%) was considered to explain the remarkable reduction of hardness and Young’s modulus of melt reprocessed aged films compared to the control films. In contrast, a significant improvement in crystallinity (around 30%) of annealed films, compared to the control films, had no effect on hardness and Young’s modulus of the samples. If considering that the nanoindentation and DSC characterizations were performed correctly, other parameter(s) (e.g. degradation and molecular weight reduction) or another phenomenon may cause these results which need to be verified.
Answer 1. Corrections in Lines 342-343, as well as Lines 346 - 353
The results show, that due to relatively high nanofiller content (6 wt%), the polymer crystallinity cannot be solitary parameter influencing the surface nanomechanical properties of the composites. The homogeneity of the nanofiller distribution at the surfaces obviously plays an important role. Thus, the annealed and the control film produced by extrusion are expected to have similar homogeneity of the filler at the surfaces. While the melt reprocessed films are produced by hot pressing, which may lead to weak separation of polymer and filler phases at the surfaces. This obviously affects the nanoindentation results, which are collected at low depth of about 3-4 µm.
Comment 2. The authors need to justify the remarkable increment of Tg for the “aged” films compared to the “fresh” ones (Figure 3a and 3b).
Ansewer 2. Lines 225-229 in the manuscript.
This increase could be associated with the changes of conformation of macromolecules through spontaneous relaxation during the aging to reach the equilibrium state, which bring shrinkage of specific volume, decreases in specific enthalpy and entropy, decrease in molecular mobility and free volume, those are reflected in the increase of Tg (New Ref. [31])
Comment 3. The authors need to discuss the enhancement of Tonset and T10% of the nanocomposite films, especially those containing GNP, compared to the neat samples.
Answer 3. Lines 320-322 in the manuscript.
This could be associated with the large surface area of graphene nanoplatelets and their high thermal conductivity, which facilitate the heat transfer in the composite and thus reduce the initial degradation.
Comment 4. Regarding lines 39-41, the references which are mentioned in the text did not perform the original research on HDT. For example, reference 8 has no HDT results and just referred to another publication’s HDT results in the introduction section. The authors need to cite original researches with HDT results.
Answer 4. Lines 44-46 and the new Ref. [8] (Lines 409-411) cited the original research on HDT.
Comment 5. The authors are encouraged to explain the improvement of the dispersion of both fillers by introducing the second filler (i.e. CNT particles).
Answer 5: Lines 184-189 in the manuscript.
It is not easy to explain the improvement of the dispersion of both fillers by introducing the second filler. In order to make an hypothesis the improvement could be related to a repulsive effect between the two fillers that tend to distribute themselves as far as possible each other, in analogy to what was reported for some blends containing a copolymer that were found miscible without any specific interaction because of the repulsion between the two different monomers constituting the copolymer. [30]
Comment 6. The caption of Figure 1 is not correlated to the individual images presented in this figure.
Answer 6. Lines 192-193. The caption of Figure 1 is corrected in the manuscript.
Comment 7. The scale of the TEM images in Figure 1 and Figure 2 are not visible.
Answer 7.. The scale of the TEM images in Figure 1 and 2 is corrected
Comment 8. In the Materials and Methods section, the authors are encouraged to mention how the slow cooling step in “annealed” samples was performed.
Answer 8. Corrected in Line 132-135 .
Two regimes of heating and cooling were applied in order to study the crystallization processes in the PLA-based composites: (i) heating at 20oC/min with subsequent fast cooling at 20oC/min, as well as (ii) heating at 10oC/min and slow cooling at 1oC/min for the “annealed” samples (performed by a controlled vacuum oven).
Comment 9. Why a twin-screw extruder was not employed to make nanocomposite films to take advantage of high shearing forces for better dispersion and distribution of the nanoparticles within the PLA matrix?
Answer 9.. Lines 107-108: Yes, a 10mm twin screw extruder Microlab (Rondol). was used. The error in the text description was corrected.
Comment 10. Some editing of typo mistakes and English language is required throughout the manuscript. For instance, line 64 (resently), line 116 (aluminous), line 173 (warsen), line 319 (some grammatical errors to be fixed), and line 215 (crystallinity of aged neat PLA film is reported 0.4% while Table 1 reports 0.2%).
Answer 10. Corrected in the text and marked in yellow background
Round 2
Reviewer 1 Report
This paper presents the Study on aging and recover of poly(lactic) acid composite films with graphene and carbon nanotubes produced by solution blending and extrusion. The authors have thoroughly reviewed the paper as per the prescribes comments. However, there are a few minor things that need to be addressed before publication. Hence, I want the accept the paper publication after minor revision of the comments provided in the next.
1- Figure 4 and Figure 5: There are small pointed arrows beneath the x-axis bars whose meanings are not explained in the main body of the manuscript. Either explain the meanings of the arrows in the manuscript or delete the arrows if they are just typos.
2- Figure 6 has two y-axis parameters (weight and derived weight) against one x-axis parameter (Temperature). It is not clear that which set of graphs is corresponding weight and which set is corresponding the derived weight? It's better to circle the certified set and use pointed arrows to confirm their relevance.
3- As indicated previously, the graphs are still indistinguishable in the black and white copy of the manuscript.
Author Response
Thank you for the comments.
Comment 1- Figure 4 and Figure 5: There are small pointed arrows beneath the x-axis bars whose meanings are not explained in the main body of the manuscript. Either explain the meanings of the arrows in the manuscript or delete the arrows if they are just typos.
Answer 1. We have deleted the arrows in the X axis of Figures 4 and 5.
Comment 2- Figure 6 has two y-axis parameters (weight and derived weight) against one x-axis parameter (Temperature). It is not clear that which set of graphs is corresponding weight and which set is corresponding the derived weight? It's better to circle the certified set and use pointed arrows to confirm their relevance.
Answer 2: . Arrows are add in Fig. 6. The text under Fig. 6 explain the arrows:
Lines 330-331:
Arrows point the corresponding Y-axis of each set of graphs.
Comment 3- As indicated previously, the graphs are still indistinguishable in the black and white copy of the manuscript.
Answer 3. Improvements have been made in the figures.
Reviewer 2 Report
The reviewer has no additional comment, except a minor correction of the typo mistake in the legend of Figure 7.a ("PLE" to "PLA").
Author Response
Authors thank for the reviewer comment.
The reviewer has no additional comment, except a minor correction of the typo mistake in the legend of Figure 7.a ("PLE" to "PLA").
Answer: The Fig. 7a was corrected
