Extrusion-Based Additively Manufactured PAEK and PAEK/CF Polymer Composites Performance: Role of Process Parameters on Strength, Toughness and Deflection at Failure

Round 1

Reviewer 1 Report

PAEK is a family of polycrystalline thermoplastics with high temperature stability and high mechanical strength. Their processing is quite difficult and requires the use of appropriate machines and tools. The authors in the manuscript undertake such a study. The authors in the manuscript undertake such a study. The selected method of manufacturing products is quite interesting and fits in with the current trends in additive technology. Particularly noteworthy is the machine that is able to work at such high temperatures.

The aim of the work formulated in the introduction is correct. The analyzed literature is a bit poor, it also includes older items. However, this does not diminish its value.

The adopted methodology is correct.

The manuscript should be organized in accordance with the recommendations, as there is a slight chaos associated with the arrangement of tables and figures.

The engravings are heavily focused and not entirely legible.

The descriptions of tables and figures should also be redrafted.

It is worth supplementing with a table with the results of the static tensile test, it is worth specifying how many samples were tested, and some statistics of the results, measurement uncertainty, standard deviation.

Conclusions are correctly formulated.

Author Response

Please see attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript entitled “Extrusion based additively manufactured PAEK and PAEK/CF polymer composites performance: role of process parameters on strength, toughness and deflection at failure” by Sharafi et al. discusses the feasibility of producing neat and fiber reinforced PAEK parts for high performance applications using the fused filament fabrication modality of additive manufacturing. Based on a multiscale modeling study, the authors systematically investigated the effect of the processing parameters on the mechanical properties of the printed parts through a design of experiments approach. The results highlight that the strength and toughness in the printed parts can be designed by carefully tuning the print parameters. In line with multiple previous reports, the properties were found to be strongly dependent on the raster angle and presence of fiber reinforcements. The work performed is original and might be of significant scientific interest to the broad readership of the journal. However, there are several major issues associated with the current manuscript, as outlined below, that need to be addressed before it can be considered for publication in the Journal of Composites Science.

Comments to the Authors:

1.     The authors miss a lot of relevant references related to extrusion-based AM of high temperature, high performance thermoplastics. The Introduction section of the paper is missing a lot of relevant background references. These can be utilized to provide details regarding the state-of-the-art in high-performance thermoplastic printing as well as to compare the results from the current study with respect to what has been reported in literature. A non-exhaustive list of such references is provided below:

a.     https://0-doi-org.brum.beds.ac.uk/10.1016/j.diamond.2021.108421

b.     https://0-doi-org.brum.beds.ac.uk/10.1016/j.addma.2020.101218

c.     https://0-doi-org.brum.beds.ac.uk/10.1007/s00170-022-09983-7

d.     https://0-doi-org.brum.beds.ac.uk/10.1016/B978-0-12-819535-2.00003-X

e.     https://0-doi-org.brum.beds.ac.uk/10.1016/j.dental.2019.11.017

f.      https://0-doi-org.brum.beds.ac.uk/10.1016/j.addma.2022.102733

g.     https://0-doi-org.brum.beds.ac.uk/10.1016/j.addma.2021.101843

h.     https://0-doi-org.brum.beds.ac.uk/10.1016/j.compscitech.2022.109839

2.     It is understandable that the authors did not include bed and nozzle temperature (in the offline study); however, it is important to characterize the crystallization behavior and viscoelastic properties of the printed parts. This will help tie back how the process-controlled morphology/structure evolution is affecting the mechanical properties in a more controlled manner.

3.     Polymer rheology is of paramount importance in the FFF process. This has largely been ignored within the current manuscript. A few recent review articles (provided below) have looked at the implications of polymer rheology on the interdiffusion timescales and weld formation in printed parts. Such characterizations are very pertinent when the authors are comparing the interlayer strength and adhesion in neat vs. reinforced polymer prints.

a.     https://0-doi-org.brum.beds.ac.uk/10.1122/1.5037687

b.     https://0-doi-org.brum.beds.ac.uk/10.1021/acsapm.0c01228

c.     https://0-doi-org.brum.beds.ac.uk/10.1122/1.5022982

4.     The multiscale modeling approach taken by the authors is a novel concept and this reviewer strongly feels that it should be included in the manuscript in more details to make a stronger case for publication.

5.     Table 2: Do the authors mean to say, “Deflection at failure”? Also, please provide details regarding how this was measured. Why was the deflection chosen as the parameter against which the sensitivity analysis was performed (as opposed to say strength at failure)?

6.     Are the authors printing PAEK or PEEK? Table 3 presents data for PEEK. I am assuming this is a typo and this is indeed a study on PEEK then there is a huge precedence of such work in the current literature and the manuscript is not novel at all.

7.     The 1 mm/min strain rate is a bit slower than what most researchers use to characterize the tensile properties of the printed parts. Are the authors following any ASTM standards here? If not, please provide the rationale behind this selection.

8.     Please provide the details regarding the source of the filaments; otherwise, it becomes impossible to independently reproduce the reported results. As the authors doubtlessly know that manufacturers often add processing aides to help with the printing process and even slight variation in the filament grades can lead to widely different results.

9.     Section 5, Lines 172-174: Yes, it is true most studies look at the effects of print temperature and speed on the mechanical properties of printed parts and there is a lack of literature looking at layer design parameters. But could the authors comment on the relative impact of the differences in speed/temperature vs. layer design optimization on the tensile properties?

10.  Figure 2 resolution needs to be improved; it is difficult to read in its current form.

11.  Page 6, Lines 213-221: The weld line arguments can be substantiated by SEM micrographs of the tensile fractured samples.

12.  Quality of Figures 4 and 5 needs to be improved.

13.  A major criticism of the paper is the level of exposition into the results. In the current form, Section 5 reads as a long list of obtained results and trends without providing many insights into the fundamental physics governing the process. What is expected is a better understanding of how these 10 layer design parameters change the associated thermal history (and crystallization kinetics/half times) during printing and how that in turn affects the print properties.

14.  Have the authors considered annealing their prints and evaluating its effect in property improvement? There is a strong precedence in literature about annealing semicrystalline polymer prints.

15.  The current version of the manuscript is too phenomenological; they performed these optimizations on a particular grade of material using a single printer. Printed part properties obtained from different material grades and/or printers even at same printing settings have been found to be drastically different. Therefore, this reviewer has some reservations about the universality of the framework proposed in this work. Can this approach be used to explain process-property relationships during FFF of semicrystalline polymers?

16.  Since the authors performed a DOE; is there a reason why an ANOVA-type analysis of the results was not presented in the manuscript? That will help in reinforcing some of the claims made in this paper.

Author Response

Please see attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The manuscript sent after corrections is significantly supplemented. The introduced corrections explain the purpose of the work. Despite some chaos in the layout of the manuscript. It should be prepared in accordance with the requirements of the journal. In general, the work is acceptable provided that the layout of the manuscript is thoroughly redrafted.

Author Response

• The manuscript sent after corrections is significantly supplemented. The introduced corrections explain the purpose of the work. Despite some chaos in the layout of the manuscript. It should be prepared in accordance with the requirements of the journal. In general, the work is acceptable provided that the layout of the manuscript is thoroughly redrafted.

Thank you. The new version is made based on layout of the Composite science journal.

Reviewer 2 Report

The authors have significantly improved the manuscript and the response is well articulated. They have incorporated a large number of suggestions and have improved the manuscript considerably in this revision. However, there are a couple of minor issues, as listed below, that need to be addressed prior to publication.

1. Figures 8-10: The Y-axis should have axes label as well as the units. Also, the captions should explain the X-axis labels in Figure 10. Please also make sure that the formatting is consistent across the different figures.

2. The experimental data in Figure 5 and Table 1 should have error bars.

3. Please present the TGA data with temperature in the X-axis rather than time.

4. Please make sure that the formatting is consistent in Table 3.

5. Please plot the data in Figure 1 in a different software. It is very hard to follow the data as presented from the instrument software.

6. Could the authors comment on if size of the printed parts and localized thermal history play a role in controlling the mechanical properties? For example, if they were to print a different ASTM standard specimen will the conclusions from this study hold? There are some recent works from Bryan Vogt (Penn State) and Mike Bortner (Virginia Tech) on polypropylene that look into such details. This reviewer is intrigued if the same thing happens for the high performance semicrystalline PAEK.

7. In response to one of the reviewer comments, the authors state that reporting the standard deviation is similar to performing the ANOVA analysis. Not sure if this reviewer agrees with the statement but for the scope of the current manuscript that might not be required.

Once again, the authors are thanked for revising their manuscript and this reviewer recommends publication as soon as these small changes are made.

Author Response

See attached file

Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

The introduced corrections and additions significantly improve the value of the manuscript. Of course, there are still minor shortcomings. However, they do not diminish the value of the work. The explanations provided by the author are also satisfactory.

Reviewer 2 Report

The manuscript can be considered for publication; the authors have incorporated the suggested changes in the revisions. Please make sure that the formatting of the references is consistent with the journal requirements since this reviewer spotted a few irregularities.