Combined Effect of Poly(lactic acid)-Grafted Maleic Anhydride Compatibilizer and Halloysite Nanotubes on Morphology and Properties of Polylactide/Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) Blends
Round 1
Reviewer 1 Report
This manuscript studies the influence of both poly(lactic acid)-grafted-maleic anhydride (PLA-g-MA) used as the compatibilizer and halloysite nanotubes (HNTs) as a reinforcement on the morphology and properties of blend based on poly(lactic acid) (PLA)/poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx). The title of the article is lovely for readers and practical. The article is well organized, but the following points should be considered.
Abbreviations are allowed if they are defined in the first mention (DMA line 26). You can also use abbreviations for some terms, such as SEM line 17.
The numbering format of the references is inconsistent with the journal format and should be corrected (Lines 34, 44 and 76). The article needs general writing and grammar editing.
The abstract needs significant revision and should be rewritten. The importance of research, the purpose of doing it, and innovation should be explicitly added. Also, the output data should be mentioned quantitatively, and the achievements should be presented in more detail.
The introduction is, at first glance, too long to be shortened. The introduction is very general. Although the introduction is long, it is written superficially in some paragraphs. Also, in the end, a suitable summary of the importance of the present issue should be provided.
Use the following resources to deepen the introduction. Shape memory performance assessment of FDM 3D printed PLA-TPU composites by Box-Behnken response surface methodology. Toughening PVC with Biocompatible PCL Softeners for Supreme Mechanical Properties, Morphology, Shape Memory Effects, and FFF Printability. 4D printing of PLA-TPU blends: effect of PLA concentration, loading mode, and programming temperature on the shape memory effect.
The research method, like the introduction, is also long and is suggested to be summarized using pictures, schematics, or tables.
How has the reproducibility of the results, especially the mechanical properties, been checked? How many times has this test been repeated for each composition?
Why are all the mechanical parameters improved simultaneously with the addition of PLA-g-MA? Are these changes reasonable for all UTS parameters, elastic modulus and elongation? Why are the stress-strain diagrams of this compound not presented as having the highest and best mechanical properties?
In the conclusion section, a summary of the purpose of the research, innovation, and research method should be presented before presenting the highlights.
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Author Response
This manuscript studies the influence of both poly(lactic acid)-grafted-maleic anhydride (PLA-g-MA) used as the compatibilizer and halloysite nanotubes (HNTs) as a reinforcement on the morphology and properties of blend based on poly(lactic acid) (PLA)/poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx). The title of the article is lovely for readers and practical. The article is well organized, but the following points should be considered.
Abbreviations are allowed if they are defined in the first mention (DMA line 26). You can also use abbreviations for some terms, such as SEM line 17.
- Thanks for your remark. Accordingly, this has been corrected in the revised version of the manuscript.
The numbering format of the references is inconsistent with the journal format and should be corrected (Lines 34, 44 and 76). The article needs general writing and grammar editing.
- The grammar as well as the standard quality of the manuscript have been improved and the correction of the numbering format was taken into consideration.
The abstract needs significant revision and should be rewritten. The importance of research, the purpose of doing it, and innovation should be explicitly added. Also, the output data should be mentioned quantitatively, and the achievements should be presented in more detail.
- The abstract has been revised taking into account your comments and remarks. The revised abstract is the following:
«Given the global challenge of plastic pollution, the development of new bioplastics to replace conventional polymers has become a priority. It is therefore essential to achieve a balance in the performances of biopolymers in order to improve their commercial availability. In this topic, the study aims to investigate the morphology and properties of poly(lactic acid) (PLA)/ poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx): 75/25 (w/w) blends reinforced with halloysite nanotubes (HNTs) and compatibilized with poly(lactic acid)-grafted maleic anhydride (PLA-g-MA). HNTs and PLA-g-MA were added to the polymer blend at 5 and 10 wt.%, respectively, and all, processed by melt compounding. Scanning electron microscopy (SEM) shows that HNTs are preferentially localized in PHBHHx nodules rather than in PLA matrix due to its higher wettability. When HNTs are combined with PLA-g-MA, a finer and a more homogeneous morphology is observed, resulting in a reduction in the size of PHBHHx nodules. The presence of HNTs in the polymer blend improves the impact strength from 12.7 to 20.9 kJ/mm2. Further, with addition of PLA-g-MA to PLA/PHBHHX/HNTs nanocomposite, tensile strength, elongation at break, and impact strength, all improve significantly, rising from roughly 42 MPa, 14.5%, and 20.9 kJ/mm2 to nearly 46 MPa, 18.2%, and 31.2 kJ/mm2, respectively. This is consistent with the data obtained by dynamic mechanical analysis (DMA). The thermal stability of the compatibilized blend reinforced with HNTs is also improved than the uncompatibilized one. Overall, the study highlights the effectiveness of combining HNTs and PLA-g-AM for properties enhancement of PLA/PHBHHx blends».
The introduction is, at first glance, too long to be shortened. The introduction is very general. Although the introduction is long, it is written superficially in some paragraphs. Also, in the end, a suitable summary of the importance of the present issue should be provided.
- Thank you for your comments. Indeed, the introduction has been changed in the revised version of the manuscript. Some sentences have been removed, while the originality as well as the objective are well clarified.
Use the following resources to deepen the introduction. Shape memory performance assessment of FDM 3D printed PLA-TPU composites by Box-Behnken response surface methodology. Toughening PVC with Biocompatible PCL Softeners for Supreme Mechanical Properties, Morphology, Shape Memory Effects, and FFF Printability. 4D printing of PLA-TPU blends: effect of PLA concentration, loading mode, and programming temperature on the shape memory effect.
- As suggested, 02 references were added in the introduction part. They are as follows:
[8]. Rahmatabadi, D.; Soltanmohammadi, K.; Pahlavani, M.; Aberoumand, M.; Soleyman, E.; Ghasemi, I.; Baniassadi, M.; Abrinia, K.; Bodaghi, M.; Baghani, M. Shape Memory Performance Assessment of FDM 3D Printed PLA-TPU Composites by Box-Behnken Response Surface Methodology. International Journal of Advanced Manufacturing Technology 2023.
[10]. Rahmatabadi, D.; Ghasemi, I.; Baniassadi, M.; Abrinia, K.; Baghani, M. 4D Printing of PLA-TPU Blends: Effect of PLA Concentration, Loading Mode, and Programming Temperature on the Shape Memory Effect. Journal of Materials Science 2023.
The research method, like the introduction, is also long and is suggested to be summarized using pictures, schematics, or tables.
- In the experimental part, no need to summarize the procedures using pictures, or schematics, etc., because, the procedures used are conventional ones and they are well known in the open literature. However, we put Table 1 to provide the data on the formulation codes and compositions used in the study.
How has the reproducibility of the results, especially the mechanical properties, been checked? How many times has this test been repeated for each composition?
- A multi-stage process was applied to assess and guarantee the reproducibility of the mechanical properties recorded. This process included rigorous selection of samples after manufacture, pre-test conditioning procedures and determination of the number of tests performed for each formulation. Each mechanical test was repeated between five and seven times for each composition.
Why are all the mechanical parameters improved simultaneously with the addition of PLA-g-MA? Are these changes reasonable for all UTS parameters, elastic modulus and elongation?
- The simultaneous improvement in various mechanical parameters when PLA-g-MA is added to the PLA/PHBHHx/HNT nanocomposite is well expected because, we believe that this compatibilizer may interact with both the nanofiller, i.e. HNTs through OH groups-MA bonding, on one hand and on the other hand, the affinity that may exist between the PLA chains of the matrix and PLA segments.
Why are the stress-strain diagrams of this compound not presented as having the highest and best mechanical properties?
- We have chosen to highlight mechanical properties such as tensile strength, elongation at break and impact strength as the main mechanical characteristics. This decision stems from the fact that presenting mechanical properties as numerical values enables direct quantitative comparisons between different formulations or materials. This facilitates rapid understanding and evaluation of performance without the need for in-depth analysis of stress and strain curves. However, this does not undermine the significance of stress-strain diagrams. They offer an additional and intuitive depiction of mechanical behaviors.
In the conclusion section, a summary of the purpose of the research, innovation, and research method should be presented before presenting the highlights.
- This points has been added to the text.
Reviewer 2 Report
The manuscript of Nawel Mokrane et al. is devoted to the development of biodegradable composite polymers. The study is actual and is of great interest to researchers in this scientific area. However, the presented results need to be supplemented.
1) The Halloysite nanotubes (HNT) are of key importance in that study. However, in the manuscript had not present the data about this promising but not very common material.There are no supplier information or some standard characteristics (specific surface area, length, diameter, etc.) This material should certainly be given more attention. Authors should pay more attention to this material.
2) The HNT is considered as a nanomodifier, however 5 wt% seems to be quite a large amount. What can you say about the economic feasibility of developing of such compositions? Also, given the research topic (development of biodegradable polymers), what is the toxicity of this modifier?
3) Conclusions about dependence of mechanical properties, flammability properties, etc. are made on the basis of a very small series of polymer compositions (5 samples). Especially, there is a lack of data on the effect of the weight fraction of HNT on the corresponding characteristics of polymer compositions.
Author Response
The manuscript of Nawel Mokrane et al. is devoted to the development of biodegradable composite polymers. The study is actual and is of great interest to researchers in this scientific area. However, the presented results need to be supplemented.
1) The Halloysite nanotubes (HNT) are of key importance in that study. However, in the manuscript had not present the data about this promising but not very common material. There are no supplier information or some standard characteristics (specific surface area, length, diameter, etc.). This material should certainly be given more attention. Authors should pay more attention to this material.
- Thanks for your pertinent remark. This has been changed and completed in the revised version of the manuscript.
2) The HNT is considered as a nanomodifier, however 5 wt% seems to be quite a large amount. What can you say about the economic feasibility of developing of such compositions? Also, given the research topic (development of biodegradable polymers), what is the toxicity of this modifier?
We appreciate your thoughtful question regarding the economic feasibility of using 5 wt% halloysite nanotubes (HNT) in our study.
The decision to incorporate 5 wt.% HNT is indeed the optimal composition obtained after evaluation of the properties of this mixture at rates ranging from 3 to 7 wt.%. While this may appear to be a higher concentration, we have found that this level of nanofiller incorporation leads to significant improvements, particularly in the mechanical properties of the material.
To answer the question of economic feasibility, a comprehensive cost-benefit analysis is required. However, in a broad sense, the cost of HNTs is significantly lower than other biopolymers, which can result in lower costs for the composite. In addition, there is a big mining deposit in Algeria, not really exploited yet.
- The toxicity of halloysite nanotubes (HNTs) is of crucial importance in the development of biodegradable polymers. According to several studies, HNTs in their natural form exhibit no hazardous form according to European Directive N°67/548/CEE. Nevertheless, surface adjustments, coatings and functionalization can modify the potential toxicity of HNTs. Although HNTs show promise in terms of low toxicity, a comprehensive assessment of toxicity under specific conditions remains essential to ensure the safety of the final composite material.
3) Conclusions about dependence of mechanical properties, flammability properties, etc. are made on the basis of a very small series of polymer compositions (5 samples). Especially, there is a lack of data on the effect of the weight fraction of HNT on the corresponding characteristics of polymer compositions.
- We appreciate your pertinent comment regarding the conclusions drawn from our study. Indeed, our conclusions are based on a relatively small series of polymer compositions, comprising five samples. This limitation stems from the global nature of our research, which aims to assess the combined effect of HNTs and ¨PLA-g-MA on the properties of the PLA/PHBHHx blend.
However, we would like to point out that we have already carried out a study on the influence of different weight fractions of halloysite nanotubes (HNTs) on the properties of the blend. We have chosen not to include these data in this article in order to remain focused on the specific results we have presented. Variations in the weight fraction of HNTs and their impact on mixture properties are the subject of a separate study, which could be the subject of a publication in its own right. We would like to thank you for your constructive comments, which reinforce our commitment to comprehensive and rigorous research. Your question prompts us to clarify this aspect and address these results in a more appropriate and detailed way.
Reviewer 3 Report
This manuscript deals with the properties of a polymer blend of poly(lactic acid) (PLA) and poly(3-hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx) : 75/25 (w/w) added with poly(lactic acid)-g-maleic anhydride (PLA-g-MA) and halloysite nanotubes (HNTs) used as a compatibilizer and a reinforcement, respectively. The authors conducted their experiments very carefully, and some of the data presented here seem to be interesting and worthy of publication. The authors are requested to reconsider the following points prior to publication.
1) In the present study, three samples, i.e., PLA/PHBHHx, PLA/PHBHHx/HNT, and PLA/PHBHHx/HNTs/PLA-g-MA, are compared to find addition effect of HNTs and PLA-g-MA. However, the three-component sample PLA/PHBHHx/PLA-g-MA must also be analyzed to assure the cooperative effect of HNTs and PLA-g-MA. The authors should discuss this point in the text.
2) The formation of the graft copolymer of PLA and PHBHHx was not verified in the presence of PLA-g-MA, although the formation of the latter PLA-g-MA was well analyzed by IR (Figure 1). It should be advised to do solubility test using 1,4-dioxane or 1,3-dioxolane to separate PLA and PHBH. Since PHBH is insoluble in the solvent, the insoluble part from the melt-blend of PLA/PHBHHx/PLA-g-MA should involve the graft polymer, which can be detected by NMR.
3) The following points should also be reconsidered.
L. 150, “2.1 Materials”. The optical purity of PLA sample must be shown. The source of HNTs must be shown together with its size and size distribution. Its morphology should also be explained appropriately.
P. 6, Eq. (1). % AM (%wt) should be % MA (%wt).
L. 203, Wp: weight. Of what?
L. 286, 1600 and 1564 cm-1. These values are different from those noted in Figure 1(b).
L. 288, C=C stretching of anhydride. The double bonds should have been consumed by the grafting reaction.
L. 348-349, a better cohesion is noticed at the interface between PLA and PHBHHx. This feature cannot be well detected from Figure 2. Explain it in detail.
L. 429-, for the second stage of degradation ….. attributed to a hydrolysis phenomenon, which can be explained by several factors. The product of the first degradation must be involved in the degradation of PLA. This feature is also related with the description in L. 476-479.
P. 20, Figure 9. If crosslinking or grafting reaction happens between PLA and PHBHHx, the DMA results should be different in the presence and absence of HNTs and PLA-g-MA. The present data indicated that such reaction had not occur. The authors should discuss this point in detail.
Well documented, but space is missing between the words in several parts.
Author Response
This manuscript deals with the properties of a polymer blend of poly(lactic acid) (PLA) and poly(3-hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx) : 75/25 (w/w) added with poly(lactic acid)-g-maleic anhydride (PLA-g-MA) and halloysite nanotubes (HNTs) used as a compatibilizer and a reinforcement, respectively. The authors conducted their experiments very carefully, and some of the data presented here seem to be interesting and worthy of publication. The authors are requested to reconsider the following points prior to publication.
1) In the present study, three samples, i.e., PLA/PHBHHx, PLA/PHBHHx/HNT, and PLA/PHBHHx/HNTs/PLA-g-MA, are compared to find addition effect of HNTs and PLA-g-MA. However, the three-component sample PLA/PHBHHx/PLA-g-MA must also be analyzed to assure the cooperative effect of HNTs and PLA-g-MA. The authors should discuss this point in the text.
- We appreciate your careful comment and attention to the experimental design of our study. Indeed, you put forward a valid consideration concerning the absence of analysis of the three-component PLA/PHBHHx/PLA-g-MA sample. We agree that analysis of the three-component sample would have contributed to a more in-depth study of additive and cooperative effects in the composite. Unfortunately, we did not include analysis of the three-component sample due to lack of PHBHHx material in the market and unfortunately not available from the Japanese Company Kaneka.
2) The formation of the graft copolymer of PLA and PHBHHx was not verified in the presence of PLA-g-MA, although the formation of the latter PLA-g-MA was well analyzed by IR (Figure 1). It should be advised to do solubility test using 1,4-dioxane or 1,3-dioxolane to separate PLA and PHBH. Since PHBH is insoluble in the solvent, the insoluble part from the melt-blend of PLA/PHBHHx/PLA-g-MA should involve the graft polymer, which can be detected by NMR.
- Your recommendation to perform a solubility test using 1,4-dioxane or 1,3-dioxolane to separate PLA and PHBH is indeed a valuable approach to study the formation of the graft copolymer. However, we regret to inform you that the suggested method using nuclear magnetic resonance (NMR) analysis is not feasible in our case due to the unavailability of NMR equipment for such analyses and the delay given by the editor to supply a revised version.
- PLA-g-MA has been prepared by reactive extrusion to improve compatibility between the polymer blend and the clay nanofillers. We could have purchased it directly, unfortunately, it's not commercially available.
3) The following points should also be reconsidered.
- 150, “2.1 Materials”. The optical purity of PLA sample must be shown. The source of HNTs must be shown together with its size and size distribution. Its morphology should also be explained appropriately.
- These points have been added in the manuscript.
- 6, Eq. (1). % AM (%wt) should be % MA (%wt).
- This has been corrected.
- 203, Wp: weight. Of what?
- Weight of test quantity of purified PLA-g-MA.
- 286, 1600 and 1564 cm-1. These values are different from those noted in Figure 1(b).
- This has been corrected.
- 288, C=C stretching of anhydride. The double bonds should have been consumed by the grafting reaction.
- That the presence of C = C stretching of the anhydride suggests the potential presence of unreacted anhydride groups. This could imply that the grafting reaction may not have fully consumed all the double bonds as expected.
- 348-349, a better cohesion is noticed at the interface between PLA and PHBHHx. This feature cannot be well detected from Figure 2. Explain it in detail.
- This has been change as follows:
« Furthermore, a better cohesion at the interface between PLA and PHBHHx is clearly demonstrated in Figures 2(c) and 3(b). Indeed, a smoother and a more homogeneous transition between the PLA and PHBHHx regions can be observed. The boundaries between these two polymers appear to be less distinct and more integrated, attesting a closer interaction between them. This accumulated cohesion also translates into a more uniform texture at the interface, where the two polymers seem to gradually melt into each other. These SEM images demonstrate the effectiveness of the compatibilizer in reducing interfacial tension and improving adhesion between the blend components».
- 429-, for the second stage of degradation ….. attributed to a hydrolysis phenomenon, which can be explained by several factors. The product of the first degradation must be involved in the degradation of PLA. This feature is also related with the description in L. 476-479.
- This point has been added to the text.
- 20, Figure 9. If crosslinking or grafting reaction happens between PLA and PHBHHx, the DMA results should be different in the presence and absence of HNTs and PLA-g-MA. The present data indicated that such reaction had not occur. The authors should discuss this point in detail.
- This point has been added to the text.
- In light of your comment, we have included a section devoted to the absence of any substantial cross-linking or grafting reaction between PLA and PHBHHx. We have also highlighted the role of PLA-g-MA and HNTs in influencing compatibility and mechanical properties, even in the absence of significant changes in DMA results as follows:
« The absence of significant differences in dynamic mechanical analysis results in the presence and absence of PLA-g-MA suggests that no substantial cross-linking or grafting reaction has occurred between PLA and PHBHHx. It should be noted that the absence of significant changes in the presence of PLA-g-MA does not necessarily negate the overall improvement in mechanical properties or compatibility achieved by other means. The effectiveness of PLA-g-MA as a compatibilizer and the reinforcing effect of HNTs may contribute to the overall improvement in the mechanical performance of the nanocomposite».
- To support our claim, we have already carried out solubility tests using chloroform at 95%, and observed that the compatibilized nanocomposite dissolved completely. This reinforces our argument that no cross-linking reaction took place, as a cross-linked compound would have resisted dissolution in chloroform.
Comments on the Quality of English LanguageWell documented, but space is missing between the words in several parts.
Thank you, the missing spaces have been removed
Round 2
Reviewer 2 Report
The manuscript has been significantly improved and can be accepted for publication in the form presented.
Author Response
Thank you for your answer and the acceptation of the revised version
Reviewer 3 Report
The authors have revised their manuscript by considering the reviewers' comments. The interpretation of the inter-polymer interaction in the presence of PLA-g-MA has been changed based on the DMA results. The present reviewer agree with this change, recommending the publication of this revised manuscript.
Mostly well documented. However, preferably, native check may be needed.
Author Response
Some minor changes have been made about edition of English language:
We have rectified the phrasing in line 36 of the abstract, replacing "than" with "compared to," .
We have ensured that the abbreviation "HNT" is not only explained in the abstract but also elaborated upon in the full text.
