Polyethylenes and Polystyrenes with Carbazole Fluorescent Tags
, Chiara Costabile 1, Mina Mazzeo 1, Vincenzo Venditto 1, Antonella Caterina Boccia 2, Rosalba Fittipaldi 3, Lorella Izzo 4 and Stefania Pragliola 1,*Round 1
Reviewer 1 Report
This paper is a study of the use of fluorescence for sorting of recycled plastics.
The authors polymerize copolymers with fluorescent moieties and confirm their function.
While there is nothing wrong with the description of the paper itself, such efforts have already been made by many research institutes, especially the PRISM project, which is well known.
Authors should therefore provide more detailed information on the characteristics of their study compared to these previous studies. However, there is no mention of this and it is very unclear what value the contents of this thesis have.
Please re-examine the above points.
Line 98 of MAO on page 4 is the first time this abbreviation appears and needs to be explained in detail.
Author Response
The authors wish to thank this reviewer for their useful comments which contributed to improve the quality of the paper.
The author answers to the reviewer comments are following reported:
Referee: 1
Comments to the Author
This paper is a study of the use of fluorescence for sorting of recycled plastics.
The authors polymerize copolymers with fluorescent moieties and confirm their function.
While there is nothing wrong with the description of the paper itself, such efforts have already been made by many research institutes, especially the PRISM project, which is well known.
Authors should therefore provide more detailed information on the characteristics of their study compared to these previous studies. However, there is no mention of this and it is very unclear what value the contents of this thesis have.
Please re-examine the above points.
Author answer: The authors wish to thank the reviewer for the suggestions. As far as the PRISM project is concerned, we consider it extremely interesting and of significant importance for the development of new technologies concerning the recycling of plastic materials. Therefore, in our work we have added a new reference: 21. Harris, P. G.; Fern, G. R.; Silver J. Method and apparatus for identifying articles with a luminescent marker for recycling. WO2018193261A1, filed 19 April 2018, and issued 25 October 2018.As for previous studies in this field, to our knowledge, although in the recent literature some papers describing the synthesis of fluorescent copolymers containing fluorescent units are reported, none of them have been tested as fluorescent marker of polyolefins so far. The only exception is our recent article, Pragliola, S. et al.Polym. Chem. 2022, 13, 2685-2693. We strongly believe that our copolymers can be excellent fluorescent tracers for polyolefins. They can be prepared using fluorescent monomers which are easy and cheap to synthesize. The polymerizations can be also carried out under the same conditions in which polyolefins are industrially produced. We have already successfully carried out some copolymer synthesis, not reported in this work, under conditions very similar to the industrial ones. Our fluorescent copolymers show chemico-physical and mechanical properties like to those of the corresponding homopolymers, so they are completely miscible with them. Consequently, any risk of different behaviour between polyolefin and fluorescent tracer is avoided both during the entire lifetime of the materials and the recycling process.
Comments to the Author
Line 98 of MAO on page 4 is the first time this abbreviation appears and needs to be explained in detail.
Author answer: We apologize for the mistake. Methylaluminoxane (MAO) was added in the text.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Plastics are widely used in everyday life as a useful material. However, the constant generation of plastic wastes and their disposal generates environmental problems along with economic loss. The reviewed paper (manuscript ID processes-2149483, titled: Polyethylenes and Polystyrenes with carbazole fluorescent tags) presents interesting results in the field of the preparation of fluorescence traceable blends in plastic recycling processes, the process and characterization are presented in detail. I appreciate the effort that the authors have put in performing this study. The content of this study is interesting. In my opinion some of the points must be considered before accepting the article. The following points are given below:
Line 11: make correction: add correspondence author, tel.
Please consider reviewing the abstract and highlight the novelty, major findings, and conclusions. I suggest reorganizing the abstract.
Line 32: make correction – give more recent knowledge about global plastic production, not knowledge from 2020; see e.g https://www.globenewswire.com/en/news-release/2022/04/26/2428757/28124/en/Global-Plastics-Market-Research-Review-2021-2022-An-Analysis-of-Developments-by-Key-Plastics-Manufacturers.html
Line 97: make correction Milano, Italy
Line 300: make correction [26-28,29,31,32,39,40]
Line 349: make correction recycling
All equipment used should be fully defined i.e. type, manufacturer, country ( Line 118, Line 128, Line 137, Line 145).
Conclusion can be expanded or perhaps consider using bullet points (1-2 bullet points) from each of the subsections.
The selection of references is correct and adequate but make correction: Use newer references (not references from 1951, 1964, 1971). Remove double numbering in references, remove only 1, 2 etc. References must be prepared according to the rules for MDPI Journals - Add Digital Object identifier (DOI)
In general, what is the reproducibility of those experiments?
Author Response
The authors wish to thank this reviewer for their useful comments which contributed to improve the quality of the paper.
The author answers to the reviewer comments are following reported:
Referee: 2
Comments to the Author
Plastics are widely used in everyday life as a useful material. However, the constant generation of plastic wastes and their disposal generates environmental problems along with economic loss. The reviewed paper (manuscript ID processes-2149483, titled: Polyethylenes and Polystyrenes with carbazole fluorescent tags) presents interesting results in the field of the preparation of fluorescence traceable blends in plastic recycling processes, the process and characterization are presented in detail. I appreciate the effort that the authors have put in performing this study. The content of this study is interesting. In my opinion some of the points must be considered before accepting the article. The following points are given below:
- Line 11: make correction: add correspondence author, tel.
Author answer: Correspondence author was added.
- Please consider reviewing the abstract and highlight the novelty, major findings, and conclusions. I suggest reorganizing the abstract.
Author answer: The authors wish to thank the reviewer for the suggestions. the abstract has been rearranged and the new text is as follows: “The increasingly intense consumption of plastics and above all, their improper disposal in the environment are causing serious environmental concerns. A great effort has been made for the development of new methods aimed at facilitating and speeding up the identification and sorting of different materials in the plastic recycling process. In this field, new strategies based on fluorescent tagging have been developed. This work concerns the synthesis and characterization of new fluorescent copolymers of polyethylene (PE) and polystyrene (PS) which are among the most produced and consumed plastic materials. The synthesized copolymers are potentially suitable for use as fluorescent markers of PE and PS. Ethylene-co-N-pentenyl carbazole (P(E-co-PK)) and styrene-co-4-(N-carbazolyl)methyl styrene (P(S-co-SK)) copolymers have been prepared by Ziegler-Natta and free radical polymerization, respectively. If excited at 300 nm, both P(E-co-PK)s and P(S-co-SK)s give fluorescence emission resulting optically active. Moreover, due to the low amount of fluorescent units, they show chemico-physical properties like to those of the corresponding homopolymers (PE and PS). P(E-co-PK)s and P(S-co-SK)s have been also tested as fluorescent markers of PE and PS. The experimental results demonstrate that from PE/P(E-co-PK) and PS/P(S-co-SK) blends prepared using only 1% by weight of fluorescent copolymer, distinguishable fluorescent emission can be still detected.”
- Line 32: make correction – give more recent knowledge about global plastic production, not knowledge from 2020; see e.g https://www.globenewswire.com/en/news-release/2022/04/26/2428757/28124/en/Global-Plastics-Market-Research-Review-2021-2022-An-Analysis-of-Developments-by-Key-Plastics-Manufacturers.html
Author answer: The authors wish to thank the reviewer for the suggestions. Reference 1 of the manuscript was replaced with: “Global Plastics Market Research Review 2021-2022: An Analysis of Developments by Key Plastics Manufacturers. Available online: https://www.globenewswire.com/en/news-release/2022/04/26/2428757/28124/en/Global-Plastics Market-Research-Review-2021-2022-An-Analysis-of-Developments-by-Key-Plastics-Manufacturers.html.“ The sentence: It is expected that the global plastics production, estimated to be 390.7 million metric tons in 2021, will continue to grow in the next decades, was added in the manuscript (line 34-36)
- Line 97: make correction Milano, Italy
Author answer: The text was corrected.
- Line 300: make correction [26-28,29,31,32,39,40]
Author answer: The text was corrected.
- Line 349: make correction recycling
Author answer: The text was corrected.
- All equipment used should be fully defined i.e. type, manufacturer, country (Line 118, Line 128, Line 137, Line 145).
Author answer: type, manufacturer, country of used instrumentation were added.
- Conclusion can be expanded or perhaps consider using bullet points (1-2 bullet points) from each of the subsections.
Author answer: The authors wish to thank the reviewer for the suggestions. the conclusion has been rearranged and the new text is as follows: “P(E-co-PK) and P(S-co-PS) copolymers containing a low amount of fluorescent units (PK and SK) were prepared to obtain fluorescent PEs and PSs, respectively. P(E-co-PK)s were synthesized by Ziegler-Natta polymerization using the homogeneous catalytic system rac-dimethylsilylbis(1-indenyl) zirconium dichloride/MAO, while P(S-co-SK)s were prepared by free radical polymerization using BPO as initiator.
NMR analysis allowed to identify all copolymer microstructures presenting isolated fluorescent units interspersed in long non fluorescent comonomer homosequences. Due to the low amount of fluorescent units, never higher than 4%, both P(E-co-PK)s and P(S-co-PS)s have chemico-physical properties very similar to the corresponding non-fluorescent homopolymers (PE and PS, respectively). In particular, they have the same thermal stability. Contextually, P(E-co-PK)s and P(S-co-PS)s are optically active showing the typical fluorescence of the carbazole group.
Thus, P(E-co-PK) and P(S-co-PS) copolymers were tested to verify if they could be suitable as fluorescent markers of the corresponding non fluorescent homopolymers (PE and PS, respectively). P(E-co-PK)/PE and P(S-co-SK)/PS polymer blends containing 1% by weight of P(E-co-PK) and P(S-co-SK), respectively, were prepared and analyzed by fluorescence spectroscopy. Both P(E-co-PK)/PE and P(S-co-SK)/PS polymer blends result homogeneous and fluorescence traceable.
Taking into account that the mechanical plastic recycling processes usually involve high temperature treatments and therefore, thermally stable fluorescent markers are required, our fluorescent copolymers should be particularly suitable for application of methods based on plastic fluorescent tagging.”
- The selection of references is correct and adequate but make correction: Use newer references (not references from 1951, 1964, 1971). Remove double numbering in references, remove only 1, 2 References must be prepared according to the rules for MDPI Journals - Add Digital Object identifier (DOI)
Author answer: All DOI were added to the references.
- In general, what is the reproducibility of those experiments?
Author answer: Every experiment was replicated three times, and the results were the same.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Nothing
