Multilayer Granular Recycled Rubber for Its Application to Technical Flooring

Round 1

Reviewer 1 Report (Previous Reviewer 2)

I do not think the authors have improved the scientific soundness of the manuscript. It seems to me that the manuscript looks still like a technical report without making contributions in terms of science.

Author Response

The authors thank the reviewer’s comment and consider that in this case there is a slight line between the scientific research and what can be seen as a technical report.

Having said that, some improvements were made in the first revision in order to make it suitable for publication in the journal as a scientific paper, because the work provides findings in the frame of a research cooperation with a company that manufactures these materials and there is further research in the same field. The investigation in this sense is not finished yet, what it makes the paper being part of a scientific research more than a closed work for the company.

The authors expect that this point is considered.

Reviewer 2 Report (Previous Reviewer 4)

1. 'The surface layer is the one manufactured with cured rubber and the bottom layer in contact to the ground is made of uncured rubber.' The grounded rubber was also cured before its end-of-life.

2. Due to different thickness of second layer, during bending the upper layer will be subjected to absolutely different strain for the same deflection. This why the results can not be compared.

Author Response

COMMENT 1. 'The surface layer is the one manufactured with cured rubber and the bottom layer in contact to the ground is made of uncured rubber.' The grounded rubber was also cured before its end-of-life.

ANSWER.

The authors thank the reviewer’s comment and agree in that the end-of-life rubber is cured rubber as well. To make it clearer, it should have been expressed in terms of treated rubber (for the surface layer with specific pressure and temperature conditions) and untreated rubber (bottom layer coming from end-of-life tyres).

A sentence has been added to the manuscript to clarify this point (LINE 97-99):

“The surface layer is the one manufactured with treated cured rubber and the bottom layer in contact to the ground is made of untreated rubber from end-of-life tyres.”

COMMENT 2. Due to different thickness of second layer, during bending the upper layer will be subjected to absolutely different strain for the same deflection. This is why the results cannot be compared.

ANSWER.

Indeed, an average elastic modulus of the material composed of two different layers is obtained. This is the result that allows us to predict the behaviour of a mixed material made up of two different layers, with different stresses and different deformations.

The modulus of elasticity obtained is not that of each layer or each material, it is the average elastic modulus of the multilayer material, so we consider an equivalent elastic modulus for comparison.

In the article we have stated this point (LINES 172-174):

Because of the two layers, this test has been conducted only to compare the behavior of the materials. The test can only be considered as an estimate approach, since the modulus of elasticity obtained is not that of each layer or each material, it is the average elastic modulus of the multilayer material, considering it an equivalent elastic modulus.

Reviewer 3 Report (New Reviewer)

The manuscript “Multilayer granular recycled rubber for its application to technical flooring ” refers to properties, especially to dynamic and static mechanical properties of multilayer material produced using recycled rubber shred. The topic of the publication it is not new (the idea of design of recycled rubber fitness flooring products) although it has some practical importance especially for the industry and rubber companies. Also the proposed idea of the use of waste rubber that still generate the environmental problems has practical importance. Although it is rather the description of the properties of the product not a research study of some research problems I find this manuscript interesting and worth publishing. Below there are comments which I would like to point before accepting that work. See attached file.  

Comments for author File: Comments.pdf

Author Response

COMMENT. The manuscript “Multilayer granular recycled rubber for its application to technical flooring” refers to properties, especially to dynamic and static mechanical properties of multilayer material produced using recycled rubber shred. The topic of the publication it is not new (the idea of design of recycled rubber fitness flooring products) although it has some practical importance especially for the industry and rubber companies. Also the proposed idea of the use of waste rubber that still generate the environmental problems has practical importance. Although it is rather the description of the properties of the product not a research study of some research problems I find this manuscript interesting and worth publishing. Below there are comments which I would like to point before accepting that work.

1. A) Abstract.

- is written concisely. I suggest to add here some numerical values confirming that the properties of obtained material based on rubber shred is similar to these used on market.

ANSWER. The authors thank the reviewer’s comment and agree that adding some numerical values might help to confirm that the obtained properties are similar to the used-on market. However, since there are four different parameters studied for the materials, adding numerical values could extend the abstract too much and it might not suit the abstract limitation requirements. Instead, a more specific comment with the most remarkable values has been included related to the results to support the conclusions about these materials being suitable as a substitutes of the most used materials.

A sentence has been added: (LINES 10 and 15 -17)

“The selection will vary for the static and dynamic behaviour, being different materials suitable for different applications. In general, the most suitable material for high stiffness applications is the one that reaches values of 67,3 MPa for static modulus and 72,96 MPa for dynamic modulus of elasticity.”

1. B) The introduction

All aspects and problems connected with studied topic are described in details, the amount of references is sufficient. This part of manuscript is correct but I have one comment, moderate English changes are required to improve this part of the manuscript. I would recommend to re-check the grammar, f.e “Chettah et al. developed an investigation in which recycled rubber granulates are 37 added to damp rectangular tubes.” better is “Chettah et al. investigated recycled rubber granulates added to damp rectangular tubes”.

ANSWER.

The authors thank the reviewer’s comment and agree that re-checking the grammar is convenient. The paper has been reviewed by an English translation company to make it understandable in a correct writing style. Even so, some minor corrections have been made, as the one indicated by the reviewer (LINE 37).

Could authors underline in introduction, at the end of discussion the innovative aspect of this work for the industry, and that it gives the possibility of the replacement of the typical flooring fitness mats with these produced based on the recycled rubber

ANSWER. The authors thank the reviewer’s comment and agree that underlining the innovative aspect of the work will give the possibility to replace the typical flooring fitness mats with these produced based on the recycled rubber.

A sentence has been added (LINE 71)

“The investigation focuses on the possibility of the replacement of the typical flooring fitness mats with these new materials based on the recycled rubber”.

1. C) Materials and methods

After the revision of this part according to the other Reviewers’ comment it is written adequately. Authors added the suggested modifications in used procedures and equipment used to study the properties of designed material. Did authors studied the composition of the recycled rubber used? In fact, the elastomers used during the production of tyres or other rubber products are not only the natural rubber and its synthetic equivalent polyisoprene. The vulcanized rubber material due to the presence of some chemical compound such as: accelerators, plasticisers can have negative impact on human health and the application of rubber wase can be restricted in some areas of application where the materials containing rubber shred have contact with human body.

Of course, only the second layer is based on the recycled rubber material, the contact layer is a new material but to achieve the attest for the production and the commercialization in the industry the new fitness or sport mats based on the recycled rubber this aspect should be taken under the consideration.

ANSWER.

The authors thank the reviewer’s comment and confirm that the suggested modifications in the previous revision were added to the manuscript because they will help to better understand it.

In the previous revision, a comment was stated to explain this aspect:

Regarding this comment, the point is that the studied materials in this research have been provided by a company that manufactures technical flooring mainly with Ethylene Vinyl Acetate (EVA) Panels. The authors of this manuscript have conducted previous investigations to determine the properties of those EVA panels (reference 31). This company started a new line of production of technical flooring with recycled rubber as substitution of EVA panels when possible. Because of that, this is a generic recycled rubber and the specific name has not been provided.

1. D) Results and discussion

- The deeper explanation of the obtained results in this part of manuscript is needed. Could authors underline which composition is the best due to its properties and it is recommended in the selected area of application (flooring mats).

ANSWER

The authors thank the comment and a sentence has been added (LINE 285)

“Finally, considering the results of the studied parameters for all the materials, it can be concluded that the composition T1D3G2 is the most suitable for applications where high stiffness is required”.

- I have one comment, moderate English changes are required to improve this part of the manuscript. I would recommend to re-check the grammar (a, the).

ANSWER.

The authors thank the reviewer’s comment and agree that re-checking the grammar is convenient. The paper has been reviewed by an English translation company to make it understandable in a correct writing style.

Round 2

Reviewer 1 Report (Previous Reviewer 2)

The authors have made many efforts to improve the quality of the manuscript. I think the technical significance of their work has been well highlighted, though the scientific soundness is still not very well. I hope the authors can improve the quality of their drawings and figures before the acceptance of the manuscript.

Author Response

The authors thank the reviewer’s comment and have reviewed the tables, drawings and figures:

• Tables have been modified and the lines between rows have been removed (headlines highlighted).
• Figures 5 and 6 have been improved making the dimensions more visible.
• Graphs represented in Figures 7, 8, 9 and 10 have been modified removing the borders and writing the legend on the left (captions highlighted).

The authors consider that those changes improve the readability of the manuscript in its scientific format.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The authors evaluated multilayer granular recycled rubber for its application to technical flooring. The article is well-structured, well-organized, and well-discussed. And the methods are comprehensive and reasonable. The journal can put it into current archive.

Author Response

The authors thank the reviewer comment.

Reviewer 2 Report

This manuscript reported the mechanical properties of multilayer granular recycled rubber. The data presented here can be contributive to the application of similar materials. However, the current manuscript did not provide much scientific insights. The authors did not analyze what influences the materials’ properties. It is not clear how these materials contribute to sustainability quantitatively. Thus, I have to suggest the manuscript be rejected in its current form.

Author Response

Regarding the reviewer comment, some improvements have been made in the manuscript in order to make it suitable for publication in the journal.

Reviewer 3 Report

This paper investigated the static and dynamic behaviour of multilayer materials manufactured from granular recycled rubber applied to technical flooring. Two mechanical tests, static and dynamic, were carried out under controlled conditions to evaluate the mechanical behaviour by means of its modulus of elasticity and the dynamic stiffness.

Unfortunately, this paper is actually a production quality test report, rather than a research work. Even though the reviewer can see the effort on the experiments, these methods are not innovative at all.

To future improve the quality of the paper, some major revisions are needed.

1. The detailed name and code, or the product number of the tested specimens should be added for the comparison of other similar studies.

2. Figure 2 shows the microstructure of a sample at different scales. The influence of the microstructure on the mechanical properties of the material can be investigated.

3. The basic mechanical properties of the specimens were illustrated in this paper without any further analysis. The effect of these mechanical properties on the specific functions of the material can be studied.

4. The significance and innovation of this paper should be emphasized and illustrated.

Author Response

The authors thank the reviewer comment, and they answer your questions:

1.- The detailed name and code, or the product number of the tested specimens should be added for the comparison of other similar studies.

Regarding this first comment, the point is that the studied materials in this research have been provided by a company that manufactures technical flooring mainly with Ethylene Vinyl Acetate (EVA) Panels. The authors of this manuscript have conducted previous investigations to determine the properties of those EVA panels (reference 31). This company started a new line of production of technical flooring with recycled rubber as substitution of EVA panels when possible. Because of that, this is a generic recycled rubber and the specific name has not been provided.

2.- Figure 2 shows the microstructure of a sample at different scales. The influence of the microstructure on the mechanical properties of the material can be investigated.

The photographs in Figure 2 intend just to show the internal structure in terms of granulometry and porosity.

In points 3.1.1 and 3.1.2 of the manuscript the specific gravity and porosity have been determined and the influence of the two different granulometries (with density and thickness) has been explained in the results.

3.- The basic mechanical properties of the specimens were illustrated in this paper without any further analysis. The effect of these mechanical properties on the specific functions of the material can be studied.

The authors agree with the reviewer’s comment and want to explain that the investigation is about the influence of the physical properties on the dynamic parameters (dynamic modulus of elasticity, dynamic stiffness and impact sound reduction) of those materials by combining the three densities, the two thicknesses and the two granulometries.

Tables 5 to 9 summarize the results of the parameters relating them to the physical properties.

4.- The significance and innovation of this paper should be emphasized and illustrated.

The main contribution in terms of innovation is trying to demonstrate the suitability of these materials in their application to technical flooring as substitutes of Ethylene Vinyl Acetate (EVA) panels.

A sentence has been added to the manuscript to emphasize this fact in the section “5. Conclusions” (line 278).

Reviewer 4 Report

      Review for “Multilayer Granular Recycled Rubber for its Application to Technical Flooring”

Comment 1.

The current study investigates the possibilities of reusing of end of life tires. Different layer thickness, granules density and sizes were involved. The authors analyze mechanical and acoustic properties of these materials.

Comment 2.

It is hard to expect that present paper will be a breakthrough in the modern science. It is just a new small step on long way of knowledge acquisition.

Comment 3.

Notwithstanding this, the manuscript is well organized, and the subject is well presented. The methods used are interesting and the presentation and discussion of results is mainly logical, but applied method of cantilever beam for mechanical testing in present version is unacceptable.  

The manuscript requires major revision to bring it to a level worthy of publication. My recommendations are detailed below:

Comment 4.

The main error in my opinion, is calculating the mechanical properties of samples without considering the neutral axis of your composite (layered) systems. The correct approach will totally change the results, and the equations will be very complicated. (See for example https://doi.org/10.3390/mi8070201)

To avoid these complications, I suggest to use the compression test of your samples for mechanical parameters calculation. Note that everywhere you will have the effective modulus, effective Poisson coefficient, effective stiffness etc., but at least these results could be compared between each other.

Comment 5.

The tables 1 and 2 should be moved in section “results”.

Comment 6.

ASTM D2845-08 was withdrawn in 2017. At least this fact should be mentioned in manuscript and the reason to use it should be denoted.

Comment 7.

In fig. 6 text should be magnified.

Comment 8.

Fig. 8 caption is unclear. Better to use thickness of samples in mm or T1, T2.

Comment 9.

Row 87- “natural and vulcanized rubber” I suppose you mean cured and uncured rubber. It is not correct to compare the natural rubber without curing system, filler, etc., with vulcanized/cured rubber, due to presence of aforementioned components (filler, curatives, accelerators, antioxidants, etc.).

 Comment 10.

Figs. 7 and 8 it will be nice to have on one graph, in order to have the possibility of easy comparison.

Author Response

The authors thank the reviewer comment, and they answer your questions:

Comment 1.

The current study investigates the possibilities of reusing of end of life tires. Different layer thickness, granules density and sizes were involved. The authors analyze mechanical and acoustic properties of these materials.

The reviewer’s comment is right.

Comment 2.

It is hard to expect that present paper will be a breakthrough in the modern science. It is just a new small step on long way of knowledge acquisition.

This reviewer’s comment goes in the same line as the comment 4 of Reviewer 3:

The main contribution in terms of innovation is trying to demonstrate the suitability of these materials in their application to technical flooring as substitutes of Ethylene Vinyl Acetate (EVA) panels.

A sentence has been added to the manuscript to emphasize this fact in the section “5. Conclusions” (line 278).

Comment 3.

Notwithstanding this, the manuscript is well organized, and the subject is well presented. The methods used are interesting and the presentation and discussion of results is mainly logical, but applied method of cantilever beam for mechanical testing in present version is unacceptable.

The manuscript requires major revision to bring it to a level worthy of publication. My recommendations are detailed below:

The authors understand that this comment continues in Comment 4…

Comment 4.

The main error in my opinion, is calculating the mechanical properties of samples without considering the neutral axis of your composite (layered) systems. The correct approach will totally change the results, and the equations will be very complicated. (See for example https://doi.org/10.3390/mi8070201).

To avoid these complications, I suggest to use the compression test of your samples for mechanical parameters calculation. Note that everywhere you will have the effective modulus, effective Poisson coefficient, effective stiffness etc., but at least these results could be compared between each other.

The authors completely agree with the reviewer’s comment as it is a well-known fact that the correct approach considering the neutral axis of the layered system would change the results. Being aware of this fact, the authors have conducted the cantilever beam test in its usual way because of two main reasons:

• The first one is that the properties of the two layers are quite similar. The surface layer is the same rubber (cured) just manufactured with different pressure and temperature. The mechanical behaviour is similar and there are no significant differences between the 2 layers. Of course, this is an approach.
• The second one is that the main purpose of the tests is to compare the behaviour between the materials, it is a comparative study. So, we consider that it is an estimate approach for the comparison purpose.

In this sense, a sentence has been added to clarify this point (lines 161, 162).

Comment 5.

The tables 1 and 2 should be moved in section “results”.

The authors appreciate the reviewer’s comment and have reviewed this possibility. Still, we conclude that tables 1 and 2 are more related to the comprehension of the materials and they contribute to a better understanding of the materials studied in this research.

In the section “Results” there are the obtained values for each one of the tests.

The authors have reflected about that and consider this way well structured.

Comment 6.

ASTM D2845-08 was withdrawn in 2017. At least this fact should be mentioned in manuscript and the reason to use it should be denoted.

The fact of using the ASTM D2845-08 is because the authors started the line of research with rubbery materials for their application to technical flooring in 2015.

At that moment it was a good option to follow the recommendations of the standard that was being applied to those tests. Later on, we have been using this standard with high reliability.

A short explanation has been added to make this point clear in section “3.3. Dynamic modulus of Elasticity. Ultrasounds Test” (line 169 - 170).

Comment 7.

In fig. 6 text should be magnified.

Authors have improved the reading of figure 6 (and figure 5 as well).

Comment 8.

Fig. 8 caption is unclear. Better to use thickness of samples in mm or T1, T2.

Reviewed and extended to figures 9 and 10 as well.

In the manuscript, these captions have been highlighted (lines 227, 240 and 259).

Comment 9.

Row 87- “natural and vulcanized rubber” I suppose you mean cured and uncured rubber. It is not correct to compare the natural rubber without curing system, filler, etc., with vulcanized/cured rubber, due to presence of aforementioned components (filler, curatives, accelerators, antioxidants, etc.).

According to this comment, the authors have added a new photo to Figure 1 to avoid confusion. The uncured (natural) and cured (vulcanized) rubber are not to be compared.

It is that the materials have been manufactured with two layers. The surface layer is the one manufactured with cured rubber and the bottom layer in contact to the ground is made of uncured rubber.

Comment 10.

Figs. 7 and 8 it will be nice to have on one graph, in order to have the possibility of easy comparison.

That is an interesting option to compare graphically some results. In this case, the authors have considered more convenient to compare the two parameters (static and dynamic modulus) for the two thicknesses. And to compare the results, Table 9 includes the columns with the obtained values in figures 7 and 8.

The authors have reflected about that and consider the current form is quite clear for comparison. Still, this change could be made if considered necessary for understanding.