Modified Polylactic Acid with Improved Impact Resistance in the Presence of a Thermoplastic Elastomer and the Influence of Fused Filament Fabrication on Its Physical Properties

Round 1

Reviewer 1 Report

Please see attachment.

Comments for author File: Comments.pdf

Author Response

Thank you for your comments. Our responses are provided in the attached document.

Author Response File: Author Response.docx

Reviewer 2 Report

The article provides a detailed, well-structured, and consecutive description of a research work on improvement of mechanical properties of a PLA/TPCE blend for FFF-printing applications. The article satisfies the requirements of the Journal of Composites Science and is suggested for publication. However some specification and corrections are recommended.

1. p1 l21 "An increase in the mechanical..." sounds ambiguous, some clarification of this sentence would be nice.
2. p1 l43 "good mechanical and rheological properties" here and further in the text please avoid subjective characterisation of physical values, e.g. "better". Also, in the following sentence you mention "low elongation at break and impact resistance". Does it belong to the good or to the bad? 
3. p1 l43 "...rheological properties". A reference would be nice.
4. p2 l44 "elongation at break" here and further in the text please represent physical quantities with attributed symbols. E.g. E for Young's modulus, etc.
5. p2 l55 "Benwood and Wang confirmed that the mechanical..." if this has been already reported, what is the novelty of some of the reported experiments?
6. p2 l69 "contamination of the materials" what does it mean in this context?
7. p2 l79 Please give a chemical description of TPCE in this passage.
8. p3 l116 Table 1 and further in the text. Please change the cipher of PLA to distinguish between PLA as a material and PLA as your sample. Also, use always sample cipher instead of a free-text description.
9. p3 l128 Table 2. Was there any specific reason for choosing this raster orientation? Would something change, if you print it in e.g. 0/90?
10. p5 l179 "3376 MPa" and further in the text. Why and how so precise? Please give values in respect to the measured accuracy.
11. p5 l188 "Hytrel is under its Tg..." Polymer molecules below Tg possess reduced mobility and the material becomes brittle. What makes you come to an opposite conclusion?
12. p5 l190 Figure 2. The mechanical properties have an obvious maximal behaviour. Why does it happen?
13. p7 l228 Figure 6 and others. Please be consistent in the style of the figures in the article.
14. p9 l263 "crystallinity behavior" maybe crystallization behavior?
15. p9 l268 Figure 8 and others. Wouldn't it improve the readablility of the results, if the data were summarised into one table instead of multiple bar charts?
16. p10 l291 "It depended also on..." Please clarify this sentence.
17. p10 l305 "other factors related to 3D printing" which factors?
18. p11 l334 "the intermolecular diffusion caused by heat conduction" does not make sense. Also, the diffusion of polymers is a very complicated and long process. The whole statement requires a proof.
19. p12 l346 The Conclusions section contains only the summary of the result and doesn't have any conclusive statements correlating with the hypothesis from the introduction.
20. A general recommendation would be to reorder sections in the article. It could be easier for a reader to read the discussions of the structure and morphology first and then the mechanical properties. The improvement of the latter is the aim of this article. Therefore, it would be logical to derive those discussions from the study of the structure.

Author Response

Thank you for your comments. Our responses are provided in the attached document.

Author Response File: Author Response.docx

Reviewer 3 Report

In this manuscript, the authors developed polymer blend of PLA and TPCE with improved impact energy and fracture strain for 3D printing.

In this reviewer's view, although somewhat commonplace and of limited novelty, they achieved good results. However, I think it is not suitable for the publication in "Journal of Composites Science" because the content of this paper was in the field of polymer blends rather than composites. Other Journals such as "Polymers", "Journal of Applied polymer science", "Polymer Engineering & Science" are more suitable for this research. In addition, as written in comment 10 below, it would be better to add mentions about how much better the system of PLA and TPCE blend conducted in this study is, compared to previous studies.

Because of the lack of novelty and the difference of the field, unfortunately the reviewer cannot recommend the publish of this manuscript in composite journals.

The detail comments are described below:

 

1. In 2.1 Materials, L97, I have never heard the polymer called "poly(ether glycol)". It might be poly(ethylene glycol) or poly(tetramethylene ether glycol), I guess. Please check the component of Hytrel and fix it.
   
   
2. What is the composition ratio of PBT and poly(ether glycol) in neat Hytrel.
   
   
3. In 2.4 Characterizations, L162, Please fix "Japon" to "Japan"
   
   
4. In 3.1.1. Mechanical properties, L187, what is the glass transition temperature of Hytrel. I think Hytrel is a multiblock copolymer and it possesses two glass transition temperature. The author should provide the result of DSC or DMA curve of neat Hytrel as a Supplementary.
   
   
5. I think the crystallinity in Table 3 are quite unstable. How many times did you do the DSC measurement for each sample? Standard deviation should be added. As well for Figure 6.
   
   
6. The quality of Figure 6 is bad. Please fix it as other graphs.
   
   
7. The volume measurement using caliper is not accurate at all because it cannot reflect the deflection and unevenness of the specimens made by the 3D printing. When you determine the porosity, specific gravity test should be conducted.
   
   
8. The melting point of PBT is ~230°C, but the authors only show DSC result up to 210°C. The crystallinity of PBT should also have a significant effect on its physical properties, so it would be necessary to take DSC result that reflect the region around 230°C, or XRD results.
   
   
9. In 3.2.3 Porosity, L323, the author insisted that the porosity calculated from X-ray microtomography had the same tendency with that measured from density, but there was obvious difference since the porosities of the samples fabricated at nozzle temperature of 210 and 230 were clearly different (~2 times) when measured by X-ray, while those were almost the same when measured from density. What caused these difference?
10. It seems obvious without testing that increasing the nozzle and bed temperature reduces the porosity of the 3D printed specimens, for any polymers. If the novelty of this study is that the 3D printed specimens with mixture of TPCE showed higher impact resistance and mechanical properties than previous studies, the authors should compare the results of this study with those of other previous ones.

Author Response

Thank you for your comments. Our responses are provided in the attached document.

Author Response File: Author Response.docx

Reviewer 4 Report

See the attachment. 

Comments for author File: Comments.pdf

Author Response

Thank you for your comments. Our responses are provided in the attached document.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

The manuscript has been revised well. I think the manuscript will be acceptable after some corrections have been done.

 

1. For the figures in Supporting information, the captions should be numbered as Figure S1, Figure S2...
2. In Table 3, standard deviations should be added for Tm, Tg, and Tc, as well, not only for the crystallinity value
3. The characters (325 nm etc.) in the SEM images of Figure 5 is too small and unclear. Please rewrite them in clear letters.

Author Response

The authors would like to express their deep gratitude to the editor and the reviewers for their invaluable efforts paid to our manuscript throughout the review process. The comments of the reviewers provided a great help to the authors in order to put the manuscript in the best possible form.

We confirm that all the comments and suggestions of the reviewers were taken into account while preparing the revised manuscript. As the corrections are minor, this time the changes have been highlighted in red on the documents. (or the figure directly modified).

Author Response File: Author Response.docx