Eco-Friendly and Biocompatible Material to Reduce Noise Pollution and Improve Acoustic Comfort in Healthcare Environments

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

the paper is not very original.

You should explain better how you made the panels, if there are repeatability in the final product and if the panels are all the same.

you can consult this paper on how they made and performed the measurements on sound-absorbing materials:

Mitrevska, M.J. et al Experimental and Numerical Investigation of Sound Absorption Characteristics of Rebonded Polyurethane Foam. Applied Sciences (Switzerland), 2022, 12(24), 12936

 

Figure 4. Sound absorption coefficient: why don't you report 125 Hz and 250 Hz.

Explain better how you performed the RT measurements in the rooms you considered.

Please explain better what kind of prediction software you used to get the RT, STI and C50 values

There is an error, Figure 4 and Figure 6 Figure 8. Noise: - Frequency.

 

You can also consult this paper:

Iannace, G. et al Use of cork sheets for room acoustic correction. Journal of Green Building, 2020, 15(2), pp. 45–55

Improve the acoustic measurements and compare the sound absorption values ​​with those of other materials of the PET, then see if you can get an evaluation of the theoretical characteristics of your material.

The measured value of the flow resistance is missing.

 

see also:

Alabdulkarem, A. et al Thermal analysis, microstructure and acoustic characteristics of some hybrid natural insulating materials. Construction and Building Materials, 2018, 187, pp. 185–196

Author Response

The authors would like to acknowledge the suggestions made by the reviewer and the readiness for the revision of the work. All suggestions and comments have been considered; modifications made accordingly (red color font text in the revised manuscript).

Comments 1: the paper is not very original. You should explain better how you made the panels, if there are repeatability in the final product and if the panels are all the same.

Response 1: The authors would like to sincerely thank the reviewer for pointing out the necessity of better explaining the preparation of the panels and the repeatability in the fabrication process. Some more details and a list of the international certifications met by the fabricated panels that guarantee both the repeatability and uniformity thereof were added in Section 2.1 in the revised manuscript.

Comments 2: you can consult this paper on how they made and performed the measurements on sound-absorbing materials: Mitrevska, M.J. et al Experimental and Numerical Investigation of Sound Absorption Characteristics of Rebonded Polyurethane Foam. Applied Sciences (Switzerland), 2022, 12(24), 12936

Response 2: The paper suggested by the reviewer was carefully read and is now cited in the revised manuscript.

Comments 3: Figure 4. Sound absorption coefficient: why don't you report 125 Hz and 250 Hz.

Response 3: sound absorption data for these frequencies along with results for samples of the same material having several thicknesses (now 9, 12, and 24 mm) were added to the revised manuscript.

Comments 4: Explain better how you performed the RT measurements in the rooms you considered.

Response 4: Some more details were added to the description of the RT measurements in Section 3.4.1 in the revised manuscript.

Comments 5: Please explain better what kind of prediction software you used to get the RT, STI, and C50 values

Response 5: The prediction software used to obtain the RT, STI, and C50 values is the same one used for the simulations (EASE). A remark on this point was added in Section 3.4 of the revised manuscript to avoid misunderstanding, along with a more detailed description of the simulation settings.

Comments 6: There is an error, Figure 4 and Figure 6 Figure 8. Noise: - Frequency.

Response 6: Typing errors were corrected in all these figures in the revised manuscript. Thank you very much.

Comments 7: You can also consult this paper: Iannace, G. et al Use of cork sheets for room acoustic correction. Journal of Green Building, 2020, 15(2), pp. 45–55

Response 7: Again, the paper suggested by the reviewer was carefully read and is now referenced in the revised manuscript.

Comments 8: Improve the acoustic measurements and compare the sound absorption values ​​with those of other materials of the PET, then see if you can get an evaluation of the theoretical characteristics of your material. The measured value of the flow resistance is missing.

Response 8: We agree that additional results including other PET materials or prediction models that rely on flow resistance data such as those proposed by Delany and Bazley or Miki would be useful for comparison purposes. In fact, the authors of the current work have implemented similar approaches in the past, see for instance:

2019. Carbajo, A. Prieto, J. Ramis, L. Río-Martín. A non-parametric fluid-equivalent approach for the acoustic characterization of rigid porous materials. Applied Mathematical Modelling 76, 2019.
2020. Carbajo, T. V. Esquerdo-Lloret, J. Ramis, A. V. Nadal-Gisbert, F. D. Denia. Acoustic properties of porous concrete made from arlite and vermiculite lightweight aggregates. Materiales de Construcción 65, 2015.
2021. Ramis, R. del Rey, J. Alba, L. Godinho, J. Carbajo. A model for acoustic absorbent materials derived from coconut fiber. Materiales de Construccion 64, 2014.

However, the main aim of our work was to develop an eco-friendly and biocompatible material showing its potential capabilities for its use in healthcare environments, and the requested analysis is to the authors believe beyond the scope of the current work. Thank you for your comprehension.

Comments 9: See also: Alabdulkarem, A. et al Thermal analysis, microstructure and acoustic characteristics of some hybrid natural insulating materials. Construction and Building Materials, 2018, 187, pp. 185–196

Response 9: This reference was also cited in the section dealing with thermal conductivity and thermal resistance tests (Section 2.3) in the revised manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

This paper conducted an experimental test and simulation of the noise reduction effect of eco-friendly and biocompatible material. This is an interesting paper and has scientific value for the application of eco-friendly and biocompatible material. What is even more commendable is that the authors provided simulations of the application of the above materials in different room scenarios, which can help us better understand the actual noise reduction effect of the above materials in specific application scenarios. Therefore, I recommend publishing this article after minor revision.

1. The last three paragraphs in the Introduction seem to be from the template, not from the authors' input. Please check them.

 

2. The description of simulation settings in Section 3 is not detailed enough. All detailed content such as software used, grid type, grid size, acoustic boundary conditions, and calculation settings should be introduced to demonstrate the accuracy of the simulation.

Author Response

The authors would like to acknowledge the suggestions made by the reviewer and the readiness for the revision of the work. All suggestions and comments have been considered; modifications made accordingly (red color font text in the revised manuscript).

This paper conducted an experimental test and simulation of the noise reduction effect of eco-friendly and biocompatible material. This is an interesting paper and has scientific value for the application of eco-friendly and biocompatible material. What is even more commendable is that the authors provided simulations of the application of the above materials in different room scenarios, which can help us better understand the actual noise reduction effect of the above materials in specific application scenarios. Therefore, I recommend publishing this article after minor revision.

Comments 1: 1. The last three paragraphs in the Introduction seem to be from the template, not from the authors' input. Please check them.

Response 1: Indeed, the reviewer is correct, and these three paragraphs correspond to the template used by the Editorial Office in the copy-editing process after submitting our document.

Comments 2: The description of simulation settings in Section 3 is not detailed enough. All detailed content such as software used, grid type, grid size, acoustic boundary conditions, and calculation settings should be introduced to demonstrate the accuracy of the simulation.

Response 2: Indeed, the reviewer is correct, and these simulation settings should be introduced to demonstrate the accuracy of the model. More details were added in Section 3 of the revised manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript titled «Еco-friendly and biocompatible material to reduce noise pollution and improve acoustic comfort in healthcare environments» describes the standardized properties of recycled PET panels.

The manuscript looks like a test report with valuable and interesting data, rather than a scientific article.

I would like to discuss the acoustic part of the manuscript.

1.       The sound absorption coefficient presented in Section 3.3 is only measured in the frequency range ~300-4000 Hz (Fig. 4). There is no information about low frequencies, but it is crucial for predicting acoustic comfort.

2.       The sound absorption class defined by ISO 11654 used for acoustic test is not estimated. We do not know the absorption coefficient at 125 and 250 Hz, but a rough estimation of the curve “200 mm plenum” in Fig. 3 suggests that the sound absorption index alpha w is about 0.6 at best. So, the absorption class would  likely be C or D. It means that the studied material is not a highly effective sound absorber.

3.       The panel without the plenum is a poor absorber (red line in Fig. 3).

4.       The case studies given in Section 3.4 do not provide information about the material itself. The acoustic performance depends on various factors such as space geometry, distribution of an acoustic treatment, location and type of sound sources, among others

5.       Figures 6f and 8c are very strange. We can see that the studied material has weak absorption at low and medium frequencies, while the greatest changes in reverberation time occurs at low frequencies. How does this material reduce the reverberation time?

6.       Sound pressure levels are not calculated. So, the conclusions about noise pollution are not proven.

Therefore, I cannot agree with the authors' statement that the presented material demonstrates "good sound absorption performance." Additionally, I cannot recommend accepting the manuscript.

Author Response

The authors would like to acknowledge the suggestions made by the reviewer and the readiness for the revision of the work. All suggestions and comments have been considered; modifications made accordingly (red color font text in the revised manuscript).

The manuscript titled «Еco-friendly and biocompatible material to reduce noise pollution and improve acoustic comfort in healthcare environments» describes the standardized properties of recycled PET panels.

The manuscript looks like a test report with valuable and interesting data, rather than a scientific article.

I would like to discuss the acoustic part of the manuscript.

Comments 1: The sound absorption coefficient presented in Section 3.3 is only measured in the frequency range ~300-4000 Hz (Fig. 4). There is no information about low frequencies, but it is crucial for predicting acoustic comfort.

Response 1: The authors agree with the reviewer that this information is crucial for predicting acoustic comfort. Low-frequency sound absorption results are now shown in the updated Figure 4 in the revised manuscript, which also includes data on two additional panel thicknesses (9 mm and 24 mm).

Comments 2: The sound absorption class defined by ISO 11654 used for acoustic test is not estimated. We do not know the absorption coefficient at 125 and 250 Hz, but a rough estimation of the curve “200 mm plenum” in Fig. 3 suggests that the sound absorption index alpha w is about 0.6 at best. So, the absorption class would likely be C or D. It means that the studied material is not a highly effective sound absorber.

Response 2: The authors would like to thank the reviewer for pointing out the necessity to estimate the sound absorption class defined by ISO 11654. We have included this data in Section 3.3 for all the panel thicknesses and configurations under analysis (w/o plenum and with plenum), showing the high effectiveness of this material as a sound absorber when used in a plenum configuration.

Comments 3: The panel without the plenum is a poor absorber (red line in Fig. 3).

Response 3: We agree with the reviewer on that remark. Nevertheless, the proposed solution, similarly to other well-known passive solutions for sound absorption such as perforated panel absorbers or other acoustic resonators, relies on the use of a backing cavity (i.e. a plenum) to attain a good sound absorption performance. In fact, another of its advantages is that it can be easily perforated (see Figure 1.c) while still preserving its structural strength capabilities, that being also a feature difficult to attain in conventional materials such as fibers or foams if reduced in thickness.

Comments 4: The case studies given in Section 3.4 do not provide information about the material itself. The acoustic performance depends on various factors such as space geometry, distribution of an acoustic treatment, location and type of sound sources, among others.

Response 4: The authors consider that the case studies analyzed served both to show the potential applicability of the biocompatible material in real scenarios and to highlight the improvements both in terms of reverberation reduction and intelligibility enhancement.

Comments 5: Figures 6f and 8c are very strange. We can see that the studied material has weak absorption at low and medium frequencies, while the greatest changes in reverberation time occurs at low frequencies. How does this material reduce the reverberation time?

Response 5: The authors would like to kindly refer the reviewer to the sound absorption data shown in Figure 4 for the respective plenum configurations used in each case study.

Comments 6: Sound pressure levels are not calculated. So, the conclusions about noise pollution are not proven.

Response 6: We completely agree with the reviewer that sound pressure level measurements are recommended to fully assert that noise pollution is reduced. Nevertheless, provided that using the proposed material yields a significant reduction in the reverberation time and an improvement in the intelligibility parameters, it is expected that noise pollution is consequently reduced, being that a task we look forward to performing in future works. Thank you for your comprehension.

Comments 7: Therefore, I cannot agree with the authors' statement that the presented material demonstrates "good sound absorption performance." Additionally, I cannot recommend accepting the manuscript.

Response 7: Again, the authors would like to kindly refer the reviewer to the updated results of Section 3.3 in the revised manuscript.

Reviewer 4 Report

Comments and Suggestions for Authors

In current study (buildings-3165001), the authors attained and investigated that entitled:

Eco-friendly and biocompatible material to reduce noise pollution and improve acoustic comfort in healthcare environments.

It’s well-constructed and the paper can be considered for publication with minor comments.

 

-           Abstract: well-constructed with focusing in each parts background of study, problem, research aim, methodology, results, and conclusion.

- Introduction: there is lack of research background information about building materials characters and its better introduction start with this kind of information and explain about some issues based on research scope.

Line 63-65: need some references

Line 70: “A comprehensive review of sustainable materials for acoustic applications can be found in [35].” It’s needed to more explanation and revise the sentence with some important info from reference.

Line 71-74: this content needs proper reference.

Before mention the research outline (Line 80), it’s better improve the research background information with some extra information (one paragraph) about recycle materials usage in construction industry and their rewards and roles in term of sustainability.

 

-        2. Materials and Methods

Line 91, “2. Materials and Methods” it’s the title of second section, correct format.

Line 92-96: these three sentences are not discussed about important information about this research. Please revise it

Line 96-106: Why Authors explained this kind of information here? I think it’s no needed and better to eliminate it.

Figure 1: in the fig explanation, there isn’t part d, change ‘d’ to ‘c’.

In part 2.2. Biocompatibility assessment and 2.2.1. Antifungal resistance: the Authors used and referred more standard tests such as ATCC 6205 without any reference, please check all and prepare more references for all standard tests.

2.2.2. Volatile Organic Compounds (VOC) emission: this part is needed to consider some references, check it.

2.3. Thermal conductivity and thermal resistance tests: this part is needed to consider some references, check it.

2.4. Sound absorption performance assessment: this part is needed to consider some references, check it.

-           Results and Discussion: great analysis and discussion

Line 440: “(Bottalico et al., 2016; Rollins et al., 2019; Taghipour et al., 2020)” what about these references, check it please

-           Conclusion: perfect achievement and explanation

Author Response

The authors would like to acknowledge the suggestions made by the reviewer and the readiness for the revision of the work. All suggestions and comments have been considered; modifications made accordingly (red color font text in the revised manuscript).

In current study (buildings-3165001), the authors attained and investigated that entitled:

Eco-friendly and biocompatible material to reduce noise pollution and improve acoustic comfort in healthcare environments.

It’s well-constructed and the paper can be considered for publication with minor comments.

-           Abstract: well-constructed with focusing in each parts background of study, problem, research aim, methodology, results, and conclusion.

Comments 1: - Introduction: there is lack of research background information about building materials characters and its better introduction start with this kind of information and explain about some issues based on research scope.

Response 1: The authors would like to thank the reviewer for these suggestions and have included this information in the Introduction of the revised manuscript.

Comments 2: Line 63-65: need some references.

Response 2: Some references were added in this part of the revised manuscript.

Comments 3: Line 70: “A comprehensive review of sustainable materials for acoustic applications can be found in [35].” It’s needed to more explanation and revise the sentence with some important info from reference.

Response 3: An explanation with some important information from this reference was added to the revised manuscript.

Comments 4: Line 71-74: this content needs proper reference.

Response 4: Proper references were added in the revised manuscript. Thank you very much.

Comments 5: Before mention the research outline (Line 80), it’s better improve the research background information with some extra information (one paragraph) about recycle materials usage in construction industry and their rewards and roles in term of sustainability.

Response 5: Information about recycled and natural materials was added as in Comments 3 in the revised manuscript.

-        2. Materials and Methods

Comments 6: Line 91, “2. Materials and Methods” it’s the title of second section, correct format. Line 92-96: these three sentences are not discussed about important information about this research. Please revise it. Line 96-106: Why Authors explained this kind of information here? I think it’s no needed and better to eliminate it.

Response 6: These sentences correspond to the template used by the Editorial Office in the copy-editing process after the submission of our document and were deleted in the revised manuscript.

Comments 7: Figure 1: in the fig explanation, there isn’t part d, change ‘d’ to ‘c’.

Response 7: Changed, thank you very much for the correction.

Comments 8: In part 2.2. Biocompatibility assessment and 2.2.1. Antifungal resistance: the Authors used and referred more standard tests such as ATCC 6205 without any reference, please check all and prepare more references for all standard tests.

Response 8: In section 2.2, “Aspergillus brasiliensis (ATCC 9642), Talaromyces pinophilus (ATCC 11797), Chaeto-mium globosum (ATCC 6205), Trichoderma virens (ATCC 9645), and Aureobasidium pullulans (ATCC 15233)” are not references, they refer to the type of organism.

Comments 9: 2.2.2. Volatile Organic Compounds (VOC) emission: this part is needed to consider some references, check it. 2.3. Thermal conductivity and thermal resistance tests: this part is needed to consider some references, check it. 2.4. Sound absorption performance assessment: this part is needed to consider some references, check it.

Response 9: Some references were added in sections 2.2.2 and 2.3 in the revised manuscript, whereas as for section 2.4, the authors consider that the now revised manuscript provides enough references regarding sound absorption performance assessment. Thank you for your comprehension.

-           Results and Discussion: great analysis and discussion

Comments 10: Line 440: “(Bottalico et al., 2016; Rollins et al., 2019; Taghipour et al., 2020)” what about these references, check it please

Response 10: The information on these references is now included in the References section in the revised manuscript. Thank you.

-           Conclusion: perfect achievement and explanation

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

accept

Author Response

Thank you very much for your revision.

Reviewer 3 Report

Comments and Suggestions for Authors

The revised manuscript has no significant changes. I can see the reason to recommend publication.

Once again, the acoustic improvement of any room is not an evidence of the good sound absorption properties of the studied material. For example, we can use a poor absorber at all surfaces of a room and reach a great RT reduction.

To be honest, the studied material has low sound absorption. The authors did not apply any methods or efforts to improve it.

Author Response

The authors would like to acknowledge again the suggestions made by the reviewer and the readiness to revise the revised manuscript. All new suggestions and comments have been considered. We hope that our comments can now meet the reviewer’s requests.

Comments 1: The revised manuscript has no significant changes. I can see the reason to recommend publication.

Response 1: The authors would like to kindly refer the reviewer to the list of changes made in the previous revision and listed below:

+ Research background information on building materials and an extended review of sustainable ones were added in the Introduction together with up to eight new references.

+ A more detailed description of the preparations of the panels and repeatability in the fabrication thereof, including international certifications, was added in Section 2.1.

+ Sound absorption results presented in Section 3.3 were extended to the low-frequency range and for additional material thicknesses (now 9 mm, 12 mm, and 24 mm), along with calculation of the sound absorption class data according to the ISO 11654 both for configurations w/o plenum and with plenum.

+ A more detailed explanation of both the RT measurements (including a plan view indicating the source and microphone positions) and the simulation settings of the prediction model was added in Section 3.4 in the revised manuscript.

Comments 2: Once again, the acoustic improvement of any room is not an evidence of the good sound absorption properties of the studied material. For example, we can use a poor absorber at all surfaces of a room and reach a great RT reduction.

Response 2: Indeed, we agree with the reviewer that the inclusion of a sound absorber in a room would involve an RT reduction in most cases. Nevertheless, the aim of choosing those case studies was to analyze real scenarios in which the use of a biocompatible material as the one proposed constitutes a solution of great importance in terms of healthiness. Besides, it should be highlighted that not only improvements in terms of RT reduction were achieved but also a significant intelligibility enhancement as shown in Tables 3 and 4 for the corresponding indicators (C50, STI, and %Alcons).

Comments 3: To be honest, the studied material has low sound absorption. The authors did not apply any methods or efforts to improve it.

Response 3: Results presented in Figure 4 in the revised manuscript show that the use of the proposed material in a plenum configuration yields a good sound absorption performance (class A for two of the analyzed cases and class B for the other, according to ISO 11654). Its main advantage when compared to conventional solutions based on fibers and foams is that due to its higher density it shows higher structural strength, thus allowing the drilling of perforations to be used as an acoustic resonator system or for ventilation purposes, in addition to the eco-friendly and aforementioned biocompatibility features, these latter being the main goal of the research carried out.