The Effect of Polymer Waste Addition on the Compressive Strength and Water Absorption of Geopolymer Ceramics

Round 1

Reviewer 1 Report

The article concerns a very interesting topic of utilization of waste from organic polymers in inorganic polymers such as geopolymers. I strongly support this direction and I am glad that such research is carried out and such articles are created.
In my opinion, however, the article requires some corrections that will increase its quality.
The temperatures used to harden the geopolymer are not high. They are lower than the commonly used ones - than those that are most often used because they are usually above 60 oC. But I understand the authors and the translation that lower temperatures can reduce costs.

In Figure 5b, when reporting EDS results, we should avoid specifying the content of light elements such as carbon C (this is not a suitable method for determining carbon content).
The quality of XRD studies is poor. There is no legend for marking eg Q, K, G. No intensity on the vertical line (this information may also be useful). Few peaks in Figure 7b (maybe filters were not applied properly, eg for "background removal"). Please clarify this issue.
The issues of the influence of the addition of LDPE on the compressive strength should be investigated probably on a larger number of samples or on larger batches of these samples. Were the compressive strength tests carried out on standard samples? What were the dimensions of these samples? I have some concerns that the compression press which has been shown to be tested is not suitable for such small samples.
The literature review is also insufficient. Many literary works are older than 5 years. Perhaps it is worth supplementing the review with items on reinforcing geopolymers with organic materials and fibers made of organic polymers, such as:

https://iopscience.iop.org/article/10.1088/1757-899X/416/1/012090

https://www.mdpi.com/2504-477X/4/3/128

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7730310/

I believe the article could be published in Applied Sciences after minor revision.

Author Response

The authors are grateful for the reviewer comments. The comments gave us more directions as to what the manuscript should be and it has improved the manuscript. The comments have been implemented in the manuscript and also responded to comments as attached.

Reviewer 2 Report

 I have some comments for the document 1141127.

1. Page2, Line67: I think that “Metakaolin or metaclay represented by MC and MK respectively.” should be collected to “Metaclay or metakaolin represented by MC and MK respectively.
2. Page2, Line75: Please add the data of compressive strength (MPa) of pure LDPE. I want know that the strength of LDPE is bigger than MC100 and MK100. The geopolymer in this research is a composite of LDPE and MK or MC. Please check and consider the standard theory of “Rule of mixture” which can use to analyze the strength of composite from the data of each volume fraction and strength.
3. Page2, Line84: How did authors select the curing temperatures 30℃, 50℃ and curing time 24 hours. Because, these conditions are sensitive to strength. 
4. Page3, Line91: (figure 3) should be (Figure 3).
5. Page3, Line91: Please clear the meaning of “after 7days”.  
6. Page3, Line95: First letter of equation (1) looks “6”, so should be collect to “σ “.
7. Page4, Line131: Authors only show the result of chemical compositions of MK and MC in Table1. Please discus the deference between MK and MC in terms of chemical composition and strength.
8. Page5, Line141-143: In this research, LDPE is a reinforcement material that is added to MK or MC. Generally, the shape of reinforcement is fibrous, because the fracture occurs across the fiber not occurs in the boundary like Figure 4a. The separation in boundary is no good for reinforce. Do you have some plan to change the shape of LDPE in future?
9. Page5, Figure 4a, Line145: I think the caption of Figure 4a should be change to “------ 100MCGC, 95MCGC, 90MCGC and 85MCGC”.
10. Page6, Figure 4b, Line147: Same to above comment..
11. Page8, Line187: Please add the abbreviation CS like “----- on compressive strength (CS) -----“Because, the author use CS in Table 2 without explanation.
12. Page10, Figure8a: Four data of 100MC without LDPE are difference each other. Authors have to clear the reason of these deference of 100MC. To avoid the question of readers why the initial materials include big difference.

That’s all.

Author Response

The authors are grateful for the reviewer's comments. The comments gave us more directions as to what the manuscript should be and it has improved the manuscript. The comments have been implemented in the manuscript and also responded to comments as attached.

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear Editors and Authors,

 

Here are my comments, questions and recommendations concerning Manuscript.

 

Here are general remarks:

The article is in general well-written, the research design is appropriate although in general, I would prefer a more detailed discussion of experimental results, more detailed conclusions based on the attempts not only to postulate the data but also to try to built a structure-property relationship or made an interpretation of what have been observed by the Authors. 

Two main very significant negative aspects are:

-I could not even understand the reference list, seems there is a mistake in formatting or something like that as I see lots of abbreviations and do not see any Journal names. 

-The discussion section seriously lacks a comparison of obtained data with the literature, it should be definitely added.

Other comments:

-The authors should more precisely specify what difference they mean by comparison of caolin with clay, what is the exact difference in C and K samples?

- "microstructure was analyzed by SEM and FTIR" - in my opinion, FTIR is not a method that we can specify as analysis of microstructure, rather it provides information about chemical structure or composition

-typo "Kolinite clay (RC and RK)"

-Formatting of formula 1 and 2 is inconsistent (not in one style)

-"The surface chemistry of geopolymer ceramics were characterized using 120 FT-IR Nicolet IS5 269-263200" - again I do not think that FTIR is a good approach to characterize "surface chemistry"

-typo X-ay (XRF)

-Table 1: typo "Of MC" and what is "LOI"?

-The legend of Fig.4 is too small so the scale can be hardly seen thus it is hard to compare the data

-Fig. 5 should be discussed in a more detailed way:

• the caption for fig. 5a and b is identical thus it is not obvious what is the difference between them;
• -what does the symbol “K/k” mean near the elements notation?

-FTIR data should be discussed in a more detailed way:

• when authors explain the assignment of characteristic bands of raw minerals at list several references should be mentioned;
•  The scale of axes on fig. 6 is not optimal: maybe a break should be introduced in X direction where no characteristic bands are observed; and in Y direction the intensity is too low to correctly compare the data.

-Interpretation of fig. 7a data, especially in the identification of phases, also seems to be made on the basis of some literature sources which are not provided.

-Do the values in table 2 and 3 have similar standard errors as shown on fig. 8? Were they measured?

-Caption of fig. 8 should be better formulated as histogram, not a plot

Author Response

The authors are grateful for the reviewer's comments. The comments gave us more directions as to what the manuscript should be and it has improved the manuscript. The comments have been implemented in the manuscript and also responded to comments as attached.

Author Response File: Author Response.pdf

Reviewer 4 Report

• In the introduction, it is better to give a brief definition of geopolymers.
• The authors' contribution to the scientific literature regarding geopolymers should be better underlined.
• One or two supplementary phrases can be given in the introduction explaining the evaluation of compressive strength and water absorption.
• Line 74 > was cured
• Lİne 80 : Geopolymer activator should be explained in detail.
• Line 80 : How was the mixing performed? It should be explained. It is important in terms of the homogeneous distribution of the matrix and reinforcements.
• Line 91: After 7 days of water intake ?
• Line 93 was?
• Line 94 error > deviation
• Table 1 : LOI long for should be given in the text or under the table with an asterisk*
• Images of Figure 4a can bu enumerated.
• Micropore in Figure 4a is not visible.
• Line 137, a porous structure is not evident on the contrary to the authors claim.
• Images in Figure 4 and 5 seems like non polished surfaces? Are you sure about your claim on polishing?
• Line 151: "arrested" is not a proper verb
• Line 152: microcracks suggesting improved toughness >> that sounds like a speculation without proofs.
• EDS micrographs given in Figure 5 normally indicates chosen specific points on the specimen surface.
• It can be better to give percentage differences in Table 3.

The authors presented their experimental results on an interesting topic. Various experimental tools were used in this research. However, obtained results were not discussed in detail with respect to the cause and effect relationship. In my view, this manuscript requires fundamental changes for the publication.

Author Response

The authors are grateful for the reviewer's comments. The comments gave us more directions as to what the manuscript should be and it has improved the manuscript. The comments have been implemented in the manuscript and also responded to comments as attached.

Round 2

Reviewer 3 Report

Dear Editors,

In general, I approve all the corrections provided by the authors except for two points:

-In my opinion,Conclusion section is still written not sufficiently detailed: it is very brief although the authors operate with a large amount of experimental data obtained with different experimental methods for various sample compositions. Still, it does not contain enough summarization or found trends or any other information that can give practical merit for the reader. 

-maybe fig. 8a and b should be replaced to Supplementary section, as they both demonstrate rather flat trend and do not show significant dependency of mechanical properties with sample composition. 

Author Response

The authors appreciate you. The review added so much value to the paper. Thank you so much. The response to the review is attached.

Author Response File: Author Response.pdf

Reviewer 4 Report

• Line 59 "are generally"
• Last sentence of the introduction should be corrected by eliminating grammatical mistakes. Also, the original part of the study should be more highlighted in the last paragraph of the introduction.
• Line 112 were
• Porous structure is not evident on the contrary to the authors.

 

The authors did studied an interesting topic and presented important experimental results in significant value. In the first review, many modifications and corrections were recommended to the authors for the sake of the improvement of their manuscript in terms of the presentation of the results. However, a major part of the modifications were not completed. In addition, it would be better to submit the final form of the manuscript after accepting all the changes done by means of "track change". In the current form, in my view it is aesthetically improper. 

Author Response

The authors appreciate you. The review added so much value to the paper. Thank you so much. The response to the review is attached.

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

Dear Editors and Authors,

I approve rewriting of Conclusions sections and if the Authors insist on the high level of importance of fig. 8a and b, then it is up to them and they can leave it in the main text. The new scale of these figures is much more informative for the readers.