Engineering Innovations for Polyvinyl Chloride (PVC) Recycling: A Systematic Review of Advances, Challenges, and Future Directions in Circular Economy Integration

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The review written by Chidara A. and coworkers is focused on PVC recycling technologies, policy frameworks, and emerging innovations within the context of the circular economy (past, present and future). In my opinion, the work's central theme is more aligned to environmental sustainability and materials science than with machinery or mechanical engineering. The discussion on manufacturing processes is marginal and rather basic—it resembles "Wikipedia's" knowledge (Chapter 5) rather than a scientific analysis. As such, it may be more suitable for journals focusing on sustainability, the circular economy, or materials recycling. In my opinion, publishing this paper in this journal would require a special adaptation of the content to emphasise the engineering and machinery aspects of PVC recycling. In order to align better with the Machines journal, the work could focus more on machinery innovations, detailed mechanical engineering solutions dealing with PVC recycling challenges (material degradation/contamination) and/or integration with technologies like AI or digital twins, which are barely mentioned in the current version. More importantly, the text has errors in its merits. Right at the beginning - in the first line, the Authors state that "PolyVinyl Chloride (PVC), a synthetic thermoset polymer…" - is not true - PVC is a thermoplastic polymer. Moreover, similar content errors appear throughout the manuscript, indicating a rough understanding of the subject. I have the impression that too much attention has been paid to the concept of the paper itself rather than to its actual content. The accompanying illustrations are often random graphs from the literature - they are definitely not necessary for understanding the topic (extruder illustration/ 3D printing production process workflow) - they only increase the volume of the work. I also find the use of a number of screenshots unconvincing, as they are often unclear and accompanied by minimal discussion. 

In my opinion, the submitted article, in its current form, does not fulfil the criteria for publication in a high-level journal like Machines. The text itself needs to sound a bit more scientific. Currently, this is more like a preliminary draft.

Author Response

Dear Reviewer, 

We sincerely thank you for the detailed and constructive comments provided during the review of our manuscript. We have thoroughly revised the manuscript to address all points raised and believe the changes have significantly improved the scientific quality, scope alignment, and clarity of the work.

Please find attached a document below a point-by-point response to each comment, outlining the specific changes made and justifications where applicable. Many thanks.

Kind regards

Alex

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript titled "A Systematic Review on PVC Recycling and Its Circular Economy Perspectives: Past, Present, and Future" appears too simplistic, lacking significant advancements. The authors should consider incorporating the latest developments in PVC recycling. The paper may be reconsidered after major revisions.

1. The title seems simple; consider providing the full name of PVC (Polyvinyl Chloride).
2. The country information for Author 1 is missing.
3. The authors have provided three corresponding authors, they should mark the corresponding author(s) with an asterisk (*).
4. The authors should focus on a more advanced topic in PVC recycling and provide a comprehensive review. There are already many existing reviews on PVC recycling.
5. Use short and precise keywords.
6. Clarify the meaning of "RQ1–RQ5." While initial part of the manuscript.
7. There is no copyright permission provided for all figures, please ensure proper permissions are obtained.
8. The content appears similar to book/book chapters. Kindly refine the paragraphs to be more concise, engaging, and insightful rather than presenting general statements (e.g., pages 11–18).
9. Table 3 appears too simple, please refine and improve its presentation.
10. Figures 22–29 are unclear, provide larger and clearer images.
11. The citation format does not align with MDPI journal requirements, revise accordingly.
12. The section on future directions is minimal, please elaborate further.

Comments on the Quality of English Language

Can be improved

Author Response

Dear Reviewer, 

We sincerely thank you for the detailed and constructive comments provided during the review of our manuscript. We have thoroughly revised the manuscript to address all points raised and believe the changes have significantly improved the scientific quality, scope alignment, and clarity of the work.

Please find attached a document below a point-by-point response to each comment, outlining the specific changes made and justifications where applicable. Many thanks.

Kind regards

Alex

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Manuscript ID machines-3527826 entitled "A Systematic Review on PVC Recycling and Its Circular Economy Perspectives: Past, Present and Future."

The manuscript is unsuitable for publication in its current form due to the review does not conform to the standard manuscript format. The information and figures have been extracted from a dissertation or thesis, and the manuscript was submitted in that manner. It includes excessive unabridged (irrelevant) information, 45 figures and tables that could be better formatted to occupy less space, and a total of 45 pages, which is quite substantial for a current review. It is recommended that the authors review the styles and formats for a journal review, presenting new, relevant information in a summarized manner without excessive pages, tables, or figures, and resubmit the manuscript.

 

Specific comments:

1. Keywords should be reviewed and amended. Some are not actual keywords, such "energy-resources efficient production" and "artificial intelligence (AI) in waste management"

2. The references in the manuscript are not cited correctly. All references need to be reviewed and amended in accordance with the journal's guidelines.

For instance, the first paragraph of the introduction:

PolyVinyl Chloride (PVC), a synthetic thermoset polymer, has been a pivotal material since its accidental discovery in 1872. Polyvinyl chloride (PVC) has been widely utilized in various industrial applications since its commercial introduction in the early 20th century. Recognised for its durability, corrosion resistance, and versatility, PVC ranks among the most produced polymers worldwide and ranks as the third widely produced plastic, prized for its corrosion resistance, durability, glossy appearance, and ability to withstand environmental stressors (29; 39). The material's ubiquity in modern life under scores its importance. However, its widespread use presents significant environmental challenges, particularly concerning resource depletion and waste accumulation (47).

 

3. The format and information presented after the introduction are inappropriate for a review manuscript.

 

4. Pages 5 to 9. The methodology section, spanning pages 5 to 9, is excessively lengthy at 4-5 pages and should be condensed to one page.

 

5. In the results section, why do the authors include screenshots as figures? Do they deem these figures relevant to the current review? Figures 16 to 20 and 22 to 29.

 

6. Many figures and tables are not mentioned in the manuscript; they are not cited.

 

7. The conclusion needs to be improved.

 

8. Arrange the references according to the journal's style. Review the references, as they are inadequately formatted. Some lack the journal name, while others are missing the volume and issue number.

Author Response

Dear Reviewer, 

We sincerely thank you for the detailed and constructive comments provided during the review of our manuscript. We have thoroughly revised the manuscript to address all points raised and believe the changes have significantly improved the scientific quality, scope alignment, and clarity of the work.

Please find attached a document below a point-by-point response to each comment, outlining the specific changes made and justifications where applicable. Many thanks.

Kind regards

Alex

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

This review article discusses current methods for recycling PVC. Unlike most engineering plastics, PVC recycling presents greater challenges, particularly in chemical recycling, due to the release of toxic chlorine gas. However, various approaches have been explored to address this issue. This article provides only a brief mention of chemical recycling. Therefore, the authors should include a more detailed discussion of chemical recycling methods.    

Author Response

Dear Reviewer,

We sincerely thank you for the detailed and constructive comments provided during the review of our manuscript. We have thoroughly revised the manuscript to address all points raised and believe the changes have significantly improved the scientific quality, scope alignment, and clarity of the work.

Please find below a point-by-point response to each comment, outlining the specific changes made and justifications where applicable. Many thanks.

Kind regards

Alex

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I believe the article can be published in its current form once substantial amendments have been made.

Author Response

Dear Reviewer, thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections changes and highlighted in the resubmitted files. The manuscript has undergone comprehensive professional English editing to improve clarity and academic tone.

Alex Chidara

Writing on behalf of the authors.

 

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript titled "A Systematic Review on PVC Recycling and its Circular Economy Perspectives: Past, Present, and Future' is unsatisfactory in its current form. It can be accepted after minor revisions. The author should provide clearer images with increased font size. More importantly, all responses are struck out, making it difficult to follow the flow of the manuscript. The author is requested to submit a clean, revised version instead of a strikethrough-marked manuscript.

 

Comments on the Quality of English Language

Can be improved

Author Response

Dear Reviewer, thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections changes and highlighted in the re-submitted files.

Alex Chidara

Writing on behalf of the authors.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

Manuscript ID machines-3527826 entitled "Engineering Innovations for Polyvinyl Chloride (PVC) Recycling: A Systematic Review of Advances, Challenges, and Future Directions in Circular Economy Integration."

The authors made the changes mentioned in the first review; however, additional modifications are needed to enhance the manuscript and make it suitable for publication in Machines.

 

My comments:

1. Table 1 is not mentioned in the text.

 

2. Table 1 requires additional information and should be presented more effectively. For instance, a timeline should encapsulate the most significant details up to the current year, 2024-2025, whereas the table currently only includes information until 2011. Where is the information presented sourced from? References are necessary in the table.

 

3. On page 7, the authors mention "Advanced chemical techniques, such as X-ray fluorescence (XRF) and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), enhance the quality of recycled PVC by eliminating harmful additives [30]." Caution is advised regarding the information presented, as it may lead to miscitation. XRF and FT-IR serve as characterization and supporting techniques for identifying or searching for compounds or materials, but they are not considered recycling techniques or methods for recycling compounds.

 

4. Page 9, in the section "5.1. Innovative Manufacturing Processes for PVC Recycling" The authors present recycling processes. From the list presented, many processes are not recycling processes, so they must be classified correctly. The authors should clarify the differences between reuse and recycling.

I recommend reviewing the following articles, which mentions the difference between reduce-reuse-recycle and includes a diagram of the polyethylene recycling process, which can be applied to or is very similar to that of PVC, indicating the steps for a process to be considered recycled.

https://doi.org/10.1016/j.heliyon.2023.e21374

https://doi.org/10.3390/molecules29020387

References that discuss or explain polymer recycling processes should be cited.

 

5. Most figures are not mentioned in the text. Figures should be mentioned and discussed in the manuscript.

Review the figure numbering for errors.

 

6. References must be in the journal's format or as requested by MDPI. Some references are incorrectly cited, or the journal's name is missing.

Author Response

Dear Reviewer, thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections changes and highlighted in the re-submitted files.

Alex Chidara

Writing on behalf of the authors.

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

Comments and Suggestions for Authors

The authors made the suggested changes based on the reviewers' comments for Manuscript ID machines-3527826. The paper is within the journal's scope, so it is suitable for publication in Machines.