Development of Polyamide 6 (PA6)/Polycaprolactone (PCL) Thermoplastic Self-Healing Polymer Blends for Multifunctional Structural Composites

Round 1

Reviewer 1 Report

 

This work detailed investigated the structure, thermal, mechanical, and healing properties of polymer mixed with PA6 and PCL. The manuscript should be accepted after minor revisions.

 1.       Table I should be deleted.

2.       As an academic manuscript, the language in the paper should be more concise.

Author Response

1. Table I should be deleted.

The authors thank the reviewer for the comment. The authors have inserted the sample denomination in the text and thus Table 1 was deleted.

2. As an academic manuscript, the language in the paper should be more concise.

The authors thank the reviewer for the comment. The authors have revised all the text and have tried to be more concise.

Author Response File: Author Response.docx

Reviewer 2 Report

I checked “Development of polyamide  (PA6) / polycaprolactone (PCL) thermoplastic self-healing polymer blends for multifunctional  structural composites” title and applsci-2029577 manuscript number.

In this manuscript, because the healing capability agent PCL has the ability to healing capability in thermoset matrices, PA6 / PCL blends were prepared by melt coupling by using Polyamide PA6, which is important for the automotive and aircraft industries Rheological, morphological, chemical, thermal and mechanical characterization processes were performed on PA6 / PCL composites.

On PA6/PCL blends the rheological, the morphological, the chemical, the thermal and the mechanical characterization processes were performed. At the same time, thermally repaired the composites  broken in mechanical tests , healing efficiency, fracture toughness (KIC) of virgin and healed are given by comparing

 

The manuscript  could be accept after minor revision 

I have some comments:

1.     The axes of Figure 7 are confused. Figure 7 can be improved by separating a, b, c.

2.     The originals of the FTIR spectra should be given in the SI.

3.     It would be better to give the original DSC thermograms and TGA thermograms of the PA6/PCL blends in Figure 7 in SI and write the mass losses corresponding to the temperatures in Table 3.

4.     The comment should be added to 3.3 Thermal properties section about ΔH_{m_PCL} and ΔH_m__PA6.

5.     In Figure 9, Elastic modulus, ultimate tensile strength, elongation at break data should be given in a table and an explanation should be given by giving numerical values ​​in the conclusion section.

6.     Critical stress intensity factor (KIC) values ​​and critical strain energy release rate (GIC) values ​​, critical stress intensity factor (KIC) values in Figure 10 ​​should be given in table form.

Author Response

Referee 2

1. The axes of Figure 7 are confused. Figure 7 can be improved by separating a, b, c.

The authors thank the reviewer for the comment. The authors have provided an improved version of Figure 7, following the suggestion provided.

2. The originals of the FTIR spectra should be given in the SI.

The authors thank the reviewer for the comment, but they preferred to maintain the FTIR spectra in the main text, as they clearly show the positions of the peaks associated to the different functional groups, highlighting thus the immiscibility of the prepared blends.

3. It would be better to give the original DSC thermograms and TGA thermograms of the PA6/PCL blends in Figure 7 in SI and write the mass losses corresponding to the temperatures in Table 3.

As requested by the reviewer, the authors separated the DSC thermograms in Figure 7 in three different figures (i.e., a, b, c). The authors decided to maintain the TGA thermograms in the main text, as they highlight the different degradation stages in the blends, highlighting thus their immiscibility. As requested by the reviewer, the authors have inserted in Table 3 (now Table 2) also the values of m_{D_PCL} = residual mass associated to the degradation temperature of PCL, and m_{D_PA6} = residual mass associated to the degradation temperature of PA6.

4. The comment should be added to 3.3 Thermal properties section about ΔH_{m_PCL}and ΔH_m__PA6.

The authors thank the reviewer for the comment. However, the authors have thoroughly discussed the melting phenomena of both PCL and PA6 phases, and further comments on both ΔH_{m_PCL} and ΔH_{m_PA6} were not inserted, also because a more detailed analysis of these data lies outside the main focus of this paper.

5. In Figure 9, elastic modulus, ultimate tensile strength, elongation at break data should be given in a table and an explanation should be given by giving numerical values ​​in the conclusion section.

The authors thank the reviewer for the comment, but it has to be considered that these experimental data were modeled applying different theoretical approaches, and the representation of these data in graphical form is thus necessary to have a direct comparison between experimental results and theoretical predictions. The authors agree with the referee on the need to insert the most important numerical results of the mechanical tests in the conclusions, and this section was thus enriched with these informations.

6. Critical stress intensity factor (KIC) values ​​and critical strain energy release rate (GIC) values, critical stress intensity factor (KIC) values in Figure 10 ​​should be given in table form.

The authors thank the reviewer for the comment. The authors have decided to replace Figure 10 with a table (now Table 3) for improving the readability of the manuscript.

Author Response File: Author Response.docx

Reviewer 3 Report

Figure4(d) and Figure5(a)

Can you tune the brightness or contrast?

It seems darker than the others.

 

Figure6

Would you show which side is 100% transmittance and 0%?

 

 

Figure6(c)

If you discuss only three peaks, you do not need to show under 1400cm-1

 

Figure11

Can you show them in the same brightness or contrast?

 

Figure12 and somewhere around

I am not sure it good to use the word "healing" for legends or experimental parameters.

Because some process show no healing effect so it sounds weired.

I suppose just "heating" would be more suitable.

 

Figure13

Can you show them in the same brightness or contrast?

 

Author Response

Referee 3

Figure4(d) and Figure5(a). Can you tune the brightness or contrast? It seems darker than the others.

The authors agree with the referee and the brightness of these figures was adjusted. 

Figure 6. Would you show which side is 100% transmittance and 0%?

The authors agree with the referee and modifed this figure accordingly.

Figure 6(c). If you discuss only three peaks, you do not need to show under 1400cm-1

The authors preferred to maintain this figure in the present format, to give a more complete information to the readers, especially in the part below 1400 cm-1, that is commonly known as “digital zone”.

Figure 11. Can you show them in the same brightness or contrast?

The authors agree with the referee and the brightness of these figures was adjusted.

Figure12 and somewhere around. I am not sure it good to use the word "healing" for legends or experimental parameters. Because some process show no healing effect so it sounds weired. I suppose just "heating" would be more suitable.

In all the literature references on this topic (reported in the paper), the term “healing” (or repair, or mending) is used, regardless to the healing efficiency shown by the samples. Moreover, a distinction between “healing” and “heating” will probably generate confusion in the reader. Therefore, the authors prefer to maintain the text in the present format.

Figure 13. Can you show them in the same brightness or contrast?

The authors agree with the referee and the brightness of these figures was adjusted.

Author Response File: Author Response.docx

Reviewer 4 Report

This paper aims to develop a polyamide 6 (PA6) matrix with self-healing properties. Polycaprolactone (PCL) was used as healing agent and melt compounded with PA6 to fabricate a self-healing polymer blends which for multifunctional structural composites. PA6/PCL blends were then comprehensively investigated with regard to rheological, morphological, chemical, thermal and mechanical characterization. The fracture toughness of blends was evaluated both in quasi-static and impact conditions. The samples broken in these tests were thermally repaired using a lab made device. Finally, the healing efficiency was evaluated comparing the fracture toughness (KIC) of the virgin and healed materials. The subject under investigation is certainly of interest, but lack of well designing and writing for the scientific significance and purpose. I recommend the manuscript be accepted after problems are revised. More detailed problems are listed as follows:

1.Line 111-112 in “1. Introduction”, It is recommended to elaborate on the reason for using fracture toughness (KIC) as the indicator for healing efficiency of PA6/PCL blends. Citing some researches and references as support is necessary. 

2.Line 113-114 in “1. Introduction”, The expectations of this study is supposed to be placed in the section “4. Conclusion”.

3.Line 137, There is a formatted problem in title of “Table 1”. And the format is inconsistent with later tables. 

4.“3.2 Microstructural and chemical properties”, This section is complicated and informative but lack of clear and fluent descriptions. It is supposed to be further divided into several subsections for managing this section logically.

5.Line 339, There is a formatted problem in title of “Figure 4”. And the format is inconsistent with later figures. 

6.“4. Conclusion”, Conclusion is verbose. It is recommended to revise it to be more concise. Also, conclusions will be more logical and convinced if summarized in several points.

Author Response

Referee 4

1.Line 111-112 in “1. Introduction”, It is recommended to elaborate on the reason for using fracture toughness (KIC) as the indicator for healing efficiency of PA6/PCL blends. Citing some researches and references as support is necessary. 

The authors thank the reviewer for the valuable comment and inserted a comment in the introductive section. The evaluation of the healing efficiency is usually carried out as the ratio of specific mechanical properties of virgin and the damaged samples after healing [1]. One of the possible ways to determine the healing efficiency is through the evaluation of the fracture toughness (K_IC) of the virgin and healed materials, as reported in the literature [2]. By performing the evaluation of the healing efficiency in this way, it is possible to understand the effect of the healing agent in the worst-case scenario, i.e., the complete failure of the component.  

2.Line 113-114 in “1. Introduction”, The expectations of this study is supposed to be placed in the section “4. Conclusion”.

The authors thank the reviewer for the comment. The authors have moved the future expectations of this study in the conclusions section.

3.Line 137, There is a formatted problem in title of “Table 1”. And the format is inconsistent with later tables.

The authors thank the reviewer for the comment but, as requested by the Referee 1, this table was deleted.

4.“3.2 Microstructural and chemical properties”, This section is complicated and informative but lack of clear and fluent descriptions. It is supposed to be further divided into several subsections for managing this section logically.

The authors thank the reviewer for the valuable comment. The authors have splitted 3.2 Microstructural and chemical properties into two different sections: ‘3.2 Microstructural properties’ and ‘3.3 Chemical properties’. The same opertation was performed in the Section 2.3, devoted to the Experimental Techniques.

5.Line 339, There is a formatted problem in title of “Figure 4”. And the format is inconsistent with later figures. 

The authors thank the reviewer for the comment. The authors have now correctly formatted the text of Figure 4.

6.“4. Conclusion”, Conclusion is verbose. It is recommended to revise it to be more concise. Also, conclusions will be more logical and convinced if summarized in several points.

The authors thank the reviewer for the comment. The authors have improved the conclusions, reducing the text and inserting some numerical results.

References

[1] Diesendruck C. E., Sottos N. R., Moore J. S., White S. R.: Biomimetic self-healing. Angewandte Chemie International Edition, 54, 10428-10447 (2015).

https://doi.org/https://doi.org/10.1002/anie.201500484

[2] Dorigato A., Mahmood H., Pegoretti A.: Optimization of the thermal mending process in epoxy/cyclic olefin copolymer blends. Journal of Applied Polymer Science, 138, 49937 (2021).

https://doi.org/10.1002/app.49937

 

Author Response File: Author Response.docx

Round 2

Reviewer 4 Report

My comments have been addressed. The manuscript is now acceptable.