High-Pressure FDM 3D Printing in Nitrogen [Inert Gas] and Improved Mechanical Performance of Printed Components
Round 1
Reviewer 1 Report
The present work experimentally investigated the mechanical properties of 3D-printed PLA under various environmental conditions and compared them with the injection moulded specimens. It is an interesting work but can literally be seen as a mimic/replication of the author’s previous research (https://doi.org/10.3390/jcs6010016).
Compared with the previous work, this paper considered the Nitrogen [Inert Gas] influence and added an injection moulding sample as a control group. I expected a more in-depth discussion, which is not demonstrated enough in the paper. So my recommendation is a major revision.
My comments are as below,
1. FDM first appears as an acronym in the abstract. Please use Fused Deposition Modelling here.
2. The materials and methods Section is too long, with too many overly detailed and unnecessary introductions. Because the methodology is exactly as same as the previous study, the authors could cite the previous paper.
3. Line 180: ‘coating post-, treatment’, no comma here.
4. Line 193: ‘depicts3’, Figure 3?
5. The authors selected 0 bar pressure (vacuum) as one set. Why not set up one standard atmosphere? Because normally the products are printed in 1 atm environment. Comparison with ambient pressure is more informative and reasonable.
Even if not printing samples under ambient pressure, the authors could find many papers about the mechanical properties of 3D-printed PLA and compare results with them.
6. In Line 247, the authors wrote,’ The specimens 247 are manufactured longitudinal.’ However, later in the results and discussion section, there are results of the specimens with transverse printing direction. This is inconsistent.
7. In Lines 249-251, the authors wrote, ‘so in all the test results to have a better comparison transverse injection molding samples strength was considered’. It is vague and unclear as I can find both longitudinal and transverse comparisons.
8. In the Results Section, I expect a comparison with ambient pressure.
9. The results in this paper are much higher than the author’s previous paper (0 bar and 5 bar compressed air conditions), especially for the transverse printing direction. It is significant to discuss and justify this difference.
10. It’s important to discuss the error bars in each figure. The results of each 3D-printed specimen under the same conditions have huge differences. Please justify.
11. All microscopy images are not clear. Please also add an image for the injection-mould specimen.
12. The authors proposed that the nitrogen gas atmosphere in the chamber inhibits layer oxidation which strengthens the specimen. This justification requires more support from SEM images which could show the oxidation phenomenon. Please add.
Author Response
Dear Reviewer,
Thank you for the constructive review. I have updated it in most places and attached responses in the document, kindly go through it.
Thank you.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The authors presented a study of FDM printing under high pressure and showed the improvement of mechanical properties and density. However, an in-depth analysis of the underlying mechanism and potential benefit in applications is required. In particular:
1. The introduction can be tied to the study a little better. Please explain why the particular approach is important.
2. The description of the experimental process can be simplified.
3. page 7 line 282: load(weight)?
4. in all mechanical tests: how do you define quantitative values e.g. modulus. Please describe how you process the stress-strain/load displacement curves.
5. Microscopy test: how do you see the surface of a PLA sample, supposed thick and opaque, with a transmitted light microscope?
6. How is the density measured: are the samples sectioned into the same dimension and measured? or are they measured with a caliper etc. 3D printed samples has significant surface roughness, please explain how that is taken into account, or taken care of. Besides, please specify the balance used to measure the weight, so the significant figures on the density value make sense.
7. Overall, please provide in-depth analysis of how such structure difference give rise to the mechanical properties.
Author Response
Dear Reviewer,
Thank you for the constructive review. I have updated it in most places and attached responses in the document, kindly go through it.
Thank you.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors revised the manuscript. However, there is no good answer to some of the critical comments. Please make further clarifications or changes based on the below comments.
For Comment 5's Reply:
'Thank you for the point, but we want to compare results with vacuum conditions, so…..sorry.' This is a bad justification to explain the reason for the vacuum condition selection. Please give reasonable justification.
For Comment 11's Reply:
At least the Figures need clear labelling/marking. For example, I cannot identify some values marked in Figure 10. Please reprocess the figures and keep the values visible.
Author Response
Dear reviewer,
Thank you for the remarks. Attached is the response letter.
Regards.
Author Response File: Author Response.docx
Reviewer 2 Report
The authors made significant improvements to the manuscript. A few things remained:
1. The authors claimed that the nitrogen atmosphere prevents oxidation and improves interlayer adhesion. please provide references or direct experimental proof(e.g. spectroscopy) for it.
2. The mechanical properties of both longitudinal and transvers directions improved when using 5bar N2 compared to 5bar air. The interlater adhesion should only play into the z direction. Why is the other direction also improved?
Author Response
Dear reviewer,
Thank you for the remarks. Attached is the response letter.
Regards.
Author Response File: Author Response.docx
Round 3
Reviewer 1 Report
Dear Authors,
Thank you for your reply.
Reviewer 2 Report
Thanks for the clarification.
