Surface Characterization of Fracture in Polylactic Acid vs. PLA + Particle (Cu, Al, Graphene) Insertions by 3D Fused Deposition Modeling Technology

Round 1

Reviewer 1 Report

Dear Authors,

my comments bellow.

1. Line 37: Could you explain what do you mean by great mechanical properties?
2. Results: Could you, after each section give an explanation? The obtained data are presented in the table 1, however in 3. the text should be explanations of presented results.
4. Discussion: The first paragraph of the presented discussion doesn't contain presented results but overall: literature, PLA materials etc. Should be removed.
5. Line 227: This is not the way how references should be present.
6. Lines 227-229: What do you mean?
7. Discussion: the second paragraph is about an application. Where is the discussion about the obtained results?

Author Response

Answer to the reviewer We modify all the paper, as it follows:

1. The title was changed

2. The abstract was improved

3. Introduction was improved by completing the references from the chapter “discussions” and updating.

4. The chapter “materials and methods” was improved by adding the image for layer deposition, completing with data concerning microscopy and adding the aspect of the tensile testing sample.

5. In chapter “results” the table 1 is deleted. A new figure was made, containing three aspects: a- tensile stress, b- L, c- fiber height versus PLA and PLA + particle insertion printing parameters.

6. In figures 3, we added error bars, for each experiment making 5 samples in same conditions.

7. We modify the font scale of each image in order to be better seeing.

8. We reorganize the images, putting the most relevant aspects of printing, and only one situation for comparison.

9. We improve the discussion for our results.

10. We complete the chapter “discussion” with critical comments concerning our data with other three more researches, suggested by the reviewer.

Author Response File: Author Response.pdf

Reviewer 2 Report

1. The current study investigates the surface quality of fractured Polylactic acid (PLA) against PLA particle insertions manufactured using AM. For this the authors evaluate the filling density, ultimate tensile strength by varying the filling percentage from 60-100% as well as corelating the results with filament angle deposition. The authors did not mention what were the findings and conclusions in the abstract.
2. The abstract is not well written and needs updating. Please consider reviewing the abstract and highlight the novelty, major findings and conclusions.
3. Line 20 check the issue beenchosen
4. Please consider revising the title of your manuscript, from reading the abstract my understand is that the study is a comparison study PLA vs PLA with particle insertions so it is better to specifically mention this in the title of your work. Saying Different Polymeric Composites is vague and does not clearly tell the readers what is being done in your paper.
5. Line 28-60 this is good review, but it is very generic about PLA which is somewhat well known facts in the open literature. When I look at the rest of the introduction, there is still lacks critical literature review which reports on previous studies similar to yours, mentioning what they did and what were their main findings and how does your current work bring new knowledge and difference to the field.  The literature review in the introduction must be improved to better reflect on past literature similar to this work, 
6. At the end of the introduction please answer the following question: What is the research gap did you find from the previous researchers in your field? Mention it properly. It will improve the strength of the article.
7. Section 2 materials must be improved. The authors should add more details of the materials tested and equipment/test setup used for the study. For example add photos for the machines used, the samples which were tested before and after the test..etc this is an experimental study and it is important to showcase everything with images and figures in details to enable others to better understand your work.
8. Results and discussion sections are poorly presented and need significant improvement. First of all please consider combining them together in one section and call it results and discussion.
9. Line 105 according with [14] I am not clear what does this mean, if you are comparing your work against this work then perhaps give us more details about it so we know what they did in their work as well.
10. Please avoid writing smaller paragraphs, consider combining smaller ones together to form larger paragraphs.
11. Extensive editing of English language and style required especially in the results and discussion sections
12. Sections 3.1-3.3 please use a more appropriate naming for them, saying: Regarding… is not a good practice for use as a section title. The recommendation here is just to remove the three sections and just keep the text, we can clearly know when you talk about fracture strength or elongation …etc.
13. Line 126-128 what about past studies in the open literature, did they report on similar findings like yours or different. In both cases please discuss your findings in more details and relate them to similar studies from the literature.
14. 124-135 the way the results are presented here is in very poor quality. Please consider updating all the writing style and way of presenting your findings in a more scientific style. As it is now it more reads like bullet points from a lab report.
15. Line  how do these fibre break, please give more information here it reads incomplete.
16. Figure 1 which one is a and which one is b. please make sure to put more effort in tidying and organising the manuscript.
17. Error bars are needed for all figures
18. How many times the testing for each sample was repeated?
19. Please reduce the size of Table 1 it is way too big, use small line spacing to achieve that if possible.
20. In the table intertwined fibers/ fig.3a, fig. 8a use capitals for fig so it should be Fig.
21. Figure 2 please add some arrows and text to show the readers what they are looking at here.
22. Scale bar is not clear at all in Figure 2-9.
23. There are way too many figures with similar pattern. Perhaps add one from each of the figures for the sake of comparison then add the rest of them in an appendix. For now the manuscript does not read well with all these microscopic images of the samples.
24. Figure 6-9 I am not sure what is the importance of showing us the layer thicknesses using microscope images, if you measured them then just add them all in a table it will save you a lot of space.   
25. Figure 10 Y axis have some red underline please check this
26. Figure 10 please add some text and arrows to highlight the region of interest in each of those SEM images.
27. The results are merely described and is limited to comparing the experimental observation. The authors are encouraged to include detailed discussion and critically discuss the observations from this investigation with existing literature.

Author Response

Answer to the reviewer

We modify all the paper, as it follows:

1. The title was changed
2. The abstract was improved
3. Introduction was improved by completing the references from the chapter “discussions” and updating.
4. The chapter “materials and methods” was improved by adding the image for layer deposition, completing with data concerning microscopy and adding the aspect of the tensile testing sample.
5. In chapter “results” the table 1 is deleted. A new figure was made, containing three aspects: a- tensile stress, b- DL, c- fiber height versus PLA and PLA + particle insertion printing parameters.
6. In figures 3, we added error bars, for each experiment making 5 samples in same conditions.
7. We modify the font scale of each image in order to be better seeing.
8. We reorganize the images, putting the most relevant aspects of printing, and only one situation for comparison.
9. We improve the discussion for our results.
10. We complete the chapter “discussion” with critical comments concerning our data with other three more researches, suggested by the reviewer.

Author Response File: Author Response.pdf

Reviewer 3 Report

General comment:

The paper investigates the fracture mechanism of the polymeric composites. The paper requires significant improvement before it can be considered for publication. The reporting of the result is very poorly done. To start with, three different tests were conducted, they are the tensile, FTIR, and microscopy. The conducted tests seem reasonable, but there is no link between the tests. There is no inference drawn from the test results.

Specific comments:

1. The mechanical properties of FFF printed parts, especially the anisotropic behavior of the FFF printed samples have been investigated. Suggest citing:
   378. Ning, F., Cong, W., Qiu, J., Wei, J., & Wang, S. (2015). Additive manufacturing of carbon fiber reinforced thermoplastic composites using fused deposition modeling. Composites Part B: Engineering, 80, 369-378.
   379. Goh, G. D., Toh, W., Yap, Y. L., Ng, T. Y., & Yeong, W. Y. (2021). Additively manufactured continuous carbon fiber reinforced thermoplastic for topology optimized unmanned aerial vehicle structures. Composites Part B: Engineering, 108840.
   380. Naranjo-Lozada, J., Ahuett-Garza, H., Orta-Castañón, P., Verbeeten, W. M., & Sáiz-González, D. (2019). Tensile properties and failure behavior of chopped and continuous carbon fiber composites produced by additive manufacturing. Additive Manufacturing, 26, 227-241.
2. How many samples were tested per condition?
3. Graphs were poorly designed.
4. It is necessary to add error bar in the graphs.
5. Figure 2, the font size of the scale can be larger
6. The authors showed a lot of images of the fracture surfaces without providing the possible reasonable for the phenomenon.
7. “All the samples show almost same absorption peaks as simple PLA, no matter the type of insertion (Cu, Al or Graphene)”So what can we infer from the FTIR spectra? What does it mean if the absorption peaks are similar for the materials? How do we relate it difference in to the mechanical properties?
8. “At all samples the fracture has the same structural feature, respectively cleavage aspect, with wave propagation.” So? What does that mean if cleavage and wave propagation are observed?
9. The purpose of figure 6-9 is to report on the filament dimension? So how would the filament dimension affect the final mechanical properties?

Author Response

Answer to the reviewer

We modify all the paper, as it follows:

1. The title was changed
2. The abstract was improved
3. Introduction was improved by completing the references from the chapter “discussions” and updating.
4. The chapter “materials and methods” was improved by adding the image for layer deposition, completing with data concerning microscopy and adding the aspect of the tensile testing sample.
5. In chapter “results” the table 1 is deleted. A new figure was made, containing three aspects: a- tensile stress, b- DL, c- fiber height versus PLA and PLA + particle insertion printing parameters.
6. In figures 3, we added error bars, for each experiment making 5 samples in same conditions.
7. We modify the font scale of each image in order to be better seeing.
8. We reorganize the images, putting the most relevant aspects of printing, and only one situation for comparison.
9. We improve the discussion for our results.
10. We complete the chapter “discussion” with critical comments concerning our data with other three more researches, suggested by the reviewer.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear Authors,

Comparing to previous version of this paper you put lot of effort in it. Now the paper is more attractive, however, minor English changes are required.

Author Response

Dear Reviewer,

Thank you very much for your appreciation and valuable comments. We hope now the paper is according to your expectation.

We read the paper one more time and wrote again some parts that did not sound good. If there is something wrong, please help us to improve.

The revised manuscript is uploaded.

Thank you very much.

Reviewer 2 Report

All questions were answered just add arrows and text on figure 11 to show us what is it about. also some figure quality can be improved 

Author Response

Dear Reviewer,

Thank you very much for your appreciation and valuable comments.

We have inserted arrows and shapes in  figure 11, in order to highlight the cleavage aspect and the specific particles (Cu, Al and Graphene). The comments are inserted in text after figure 11.

Reviewer 3 Report

1. what does 2 ÷ 5% mean? 2 divided by 5? if you mean 2 to 5%, you should use 2-5%. check for similar error and make necessary corrections.
2. line 161, instead of saying "as one may see", you may use "As observed".
3. i still don't get what we can tell from the FTIR analysis. you have made two observations(from line280 to line 283. so what do these two observation tell us? would they have similar material composition? similar mechanical behavior? some inference should be drawn from the observation.

Author Response

Dear Reviewer,

Thank you very much for your appreciation and valuable comments. We hope now the paper is according to your expectation.

1. ” what does 2 ÷ 5% mean? 2 divided by 5? if you mean 2 to 5%, you should use 2-5%. check for similar error and make necessary corrections.”

Answer: We corrected the errors in all manuscript, including abstract and conclusions.

2. ”line 161, instead of saying "as one may see", you may use "As observed"”.

Answer: We repleaced the words, as your suggestion.

3. ”i still don't get what we can tell from the FTIR analysis. you have made two observations(from line280 to line 283. so what do these two observation tell us? would they have similar material composition? similar mechanical behavior? some inference should be drawn from the observation.

Answer: With the FTIR analysis we performed the identification of PLA material. This is the reason of this test. This analysis does not identify metallic particles, but helps us to observe the similiar aspect (regarding the material compostion) of the experimental samples. This point of view is shown in FTIR spectra, where the peaks are in the specific areas, but with small different heights.  

Thank you.