Poly(Lactic Acid) (PLA)-Based Nanocomposites: Impact of Vermiculite, Silver, and Graphene Oxide on Thermal Stability, Isothermal Crystallization, and Local Mechanical Behavior

Round 1

Reviewer 1 Report

The manuscript is interesting and fits the scope of the journal; however, before its pubblication, some major revisions are needed.

• Introduction section: the bulleted list (lines 60-65) must be deleted; a space is missing at line 90; the sentence (line 95) must be rewritten is not clear; the introduction must be improved adding more references and better highlithing the main novelties of the work. 
• Materials section: more informations abput the PLA adopted must be added (MFI, density, average molecula weight). Why a 3D printing grade was selected? The choice of this PLA grade must be better explained in the manuscript.
• Section 2.2.4.: A recycling time of 5 min into a Minilab is excessive and not realistic from a pratical point of view. Moreover, a GPC analysis must be done to verify that after this extrusion time the PLA did not degradate (in this case the entire work lose its meaning).
• The quality of the images in Figure 2 must be improved, the images must be enlarged and some indicators must be added . 

Author Response

 

1. Introduction section: the bulleted list (lines 60-65) must be deleted;

A space is missing at line 90;

The sentence (line 95) must be rewritten is not clear;

The manuscript has been proofread with the requested corrections to avoid such errors.

2. The introduction must be improved adding more references and better highlighting the main novelties of the work.

The introduction has been improved  as requested

3. Materials section: more informations about the PLA adopted must be added (MFI, density, average molecula weight).

The requested information about PLA provided by supplier were added to the text, section 2.1.

4. Why a 3D printing grade was selected? The choice of this PLA grade must be better explained in the manuscript.

The prepared PLA composites should be used for preparation of biomedical devices, for example stents which can be easily printed using 3D printing. For that reason the 3D printing grade was used. It is mentioned in Introduction.

5. Section 2.2.4.: A recycling time of 5 min into a Minilab is excessive and not realistic from a pratical point of view. Moreover, a GPC analysis must be done to verify that after this extrusion time the PLA did not degradate (in this case the entire work lose its meaning).

Yes, we know that 5 min is excessive. However, we used this time, to be sure that we reached a good homogenization of fillers in matrices. The molecular weight of PLA foils after the extrusion was checked by GPC; it was of 184,500±700 g/mol. The molecular weight of the original PLA pellets was of 189,000 g/mol. The degradation reached approx. 2.4 %, thus it was from this point of view very low. It was confirmed also by XRD and FTIR analyses, which results were very similar.

6. The quality of the images in Figure 2 must be improved, the images must be enlarged and some indicators must be added .

The Images were improved and scale was added in a readable way.

 

 

Reviewer 2 Report

The manuscript is generally well written, however I suggest to improve the quality of the graph (e.g., use scientific number format for the y-axis and avoid 45°C labels). Statistical analysis should be also included to show significant differences. 

Regarding the indendation tests, it should be indicated how the elastic modulus was calculated. In particular, it should be indicated as apparent elastic modulus since in viscoelastic materials it depends from the applied strain rate (or load rate, in this case).  See for example https://www.liebertpub.com/doi/full/10.1089/ten.teb.2021.0151. Viscoelastic characterisation could be also of interest for these materials, maybe some discussion can be added.

Finally, I suggest to improve the conclusion highlighting how the different properties obtained with different fillers may affect the use of the material in different applications  

Author Response

 

 

1. I suggest to improve the quality of the graph (e.g., use scientific number format for the y-axis and avoid 45°C labels). Statistical analysis should be also included to show significant differences.

The modification has been added as requested corrections

2. Regarding the indendation tests, it should be indicated how the elastic modulus was calculated. In particular, it should be indicated as apparent elastic modulus since in viscoelastic materials it depends from the applied strain rate (or load rate, in this case). See for example https://www.liebertpub.com/doi/full/10.1089/ten.teb.2021.0151. Viscoelastic characterisation could be also of interest for these materials, maybe some discussion can be added.

Comments and modifications have been added in the discussion section as requested

3. Finally, I suggest to improve the conclusion highlighting how the different properties obtained with different fillers may affect the use of the material in different applications

We explain in the conclusion why we started to study these nanocomposites. An intention is to use them as materials with antimicrobial properties in biomedical applications, for example as a stents.

 

 

Reviewer 3 Report

Authors studied the reinforced PLA nanocomposites based on their morphology, changes in PLA phases, transitions and thermo-mechanical properties. Studies of nanocomposites reinforced with different nanofillers and subsequent characterisation in itself is not novel. If the aim of the research to demonstrate the application of developed nanocomposites for different applications such as biomedical applications or as packaging materials then it should be elaborated and justified with results. Without such results I am afraid that it is just a routine work and no novelty can be justified. 

Author Response

Authors studied the reinforced PLA nanocomposites based on their morphology, changes in PLA phases, transitions and thermo-mechanical properties. Studies of nanocomposites reinforced with different nanofillers and subsequent characterisation in itself is not novel. If the aim of the research to demonstrate the application of developed nanocomposites for different applications such as biomedical applications or as packaging materials then it should be elaborated and justified with results. Without such results I am afraid that it is just a routine work and no novelty can be justified. 

It is described in the conclusion, that materials will be used for next investigation to be used as biomedical implants and devices, sech as stents. The following publication is aimed to an investigation of PLA composites and its antimicrobial effects within the period of 0-6 months. This publication is now submitted. The results obtained in this study are very important results for our future possible application and together with our following results form complex information about the prepared composites. The results describing several materials are summarized, and from practical point of view it can be a benefit of this article. 

 

Round 2

Reviewer 1 Report

The comments have been addressed and now the manuscript can be accepted for pubblication.

Author Response

Thank you for your comment

Reviewer 2 Report

the authors followed most of my previous comments. however, it is not clear what the authors mean with 'In this work, PLA+VMT+HDP exhibits high viscoelastic characterization' since they only performed load/unload tests with a single load rate. As previously suggested i would refer to the elastic modulus as apparent elastic modulus, since it actually  depends from the applied  rate (https://www.liebertpub.com/doi/full/10.1089/ten.teb.2021.0151). 

Author Response

In fact, you are right because we're doing quasi-static work with a unique charge/discharge process; so there's no strain rate change, and no viscous aspect. However, this explanation should provide a better understanding of the effect of adding nanofillers to the PLA matrix and how the shape and size of the nanofillers play a very important role in the structural behavior. In our study, we used different nanofillers with different property characteristics (such as size, concentration, etc.) and compared them with each other. Because of this, each nanofiller helps to vary the concentration level of the PLA polymer based on its limitations. In our study, VMT+HDP appears to contribute to a further increase in viscoelasticity and thus elasticity. Added and adjusted comments in the manuscript as requested based on the reviewers' comments

Reviewer 3 Report

Authors have stated that they can investigate application related to the studied composites for biomedical implants and devices, sech as stents and properties such as antimicrobial effects within the period of of 0-6 months. I recommend that authors include results from those experiments to demonstrate the novelty and broaden the scope of current ms.

Author Response

Comment :

Authors have stated that they can investigate application related to the studied composites for biomedical implants and devices, sech as stents and properties such as antimicrobial effects within the period of of 0-6 months. I recommend that authors include results from those experiments to demonstrate the novelty and broaden the scope of current ms.

Response

Unfortunately, we are not able to publish these data in this article. Indeed, we are currently finalizing this part which will be the subject of our next paper. These data will be published in our next work.

Round 3

Reviewer 2 Report

the author followed all my last comments.

Reviewer 3 Report

Authors clearly need additional experiments to demonstrate the novelty/applicability of current research, otherwise the scope of article is too narrow to be published in J. Compos. Sci. Unfortunately I cannot recommend to publish the manuscript without the major revision.