Recycling of Post-Consumer HDPE Bottle Caps into New Caps for Food Contact
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
The paper is a good contribution to the literature and relevant conclusions are achieved. The authors addressed the potential for recycling post-consumer high-density polyethylene (HDPE) bottle caps into new caps intended for direct food contact. It provides a literature-based assessment of contamination levels and proposes evaluation criteria derived from EFSA guidance for PET and HDPE recyclates. The paper has potential, however some comments must be taken into account before being considered for publication:
- Regarding the keywords, I would suggest to include “Recycling” and “HDPE bottle caps”;
- A paragraph presenting the organization of the paper must be included in the Introduction;
- Introduction can be revised and a new chapter can include literature review, methodological approach and sustainability concerns (Ferreira et al. 2017);
- Novelty of the paper should be highlighted in the introduction;
- In the methodology, the assumed 0.5 mg/kg contamination level is based on milk bottles from curbside collection, not DRS. Can the authors revise?
- Legends of figures can be reduced and add it in the text;
- Regarding the methodology, the model can be better justified, in particular highlighting the strong and weak points;
- Diffusion modeling (AKTS SML) is appropriate but lacks experimental or literature validation. If possible, justify better;
- Clarify that this is a preliminary theoretical evaluation, not a regulatory proof, and experimental verification will still be required by EFSA for Novel Technology status;
- In the discussion, mention analytical challenges of verifying sub-µg/L migration levels (detection limits, uncertainty);
- I was expecting more recommendations for decision makers in the conclusion chapter;
- The references must be homogenized and in line with the author guidelines (for example, some issues are missing).
References:
FERREIRA, S.; CABRAL, M; DA CRUZ, N.; SIMÕES, P.; MARQUES, R. (2017). The costs and benefits of packaging waste management systems in Europe: The perspective of local authorities. Journal of Environmental Planning and Management. Routledge. ISSN: 0964-0568. Vol. 60, no. 5, pp. 773-791.
Jing Guo, Saleem Ali, Ming Xu (2023). Recycling is not enough to make the world a greener place: Prospects for the circular economy. Green Carbon, Pages 150-153.
Author Response
reviewer 1
The paper is a good contribution to the literature and relevant conclusions are achieved. The authors addressed the potential for recycling post-consumer high-density polyethylene (HDPE) bottle caps into new caps intended for direct food contact. It provides a literature-based assessment of contamination levels and proposes evaluation criteria derived from EFSA guidance for PET and HDPE recyclates. The paper has potential, however some comments must be taken into account before being considered for publication:
Author response: Thanks for this valuable comment
Regarding the keywords, I would suggest to include “Recycling” and “HDPE bottle caps”;
Author response: I included HDPE bottle caps and recycling to the keywords
A paragraph presenting the organization of the paper must be included in the Introduction;
Author response: I included the organization of te paper at the end of the introduction.
Introduction can be revised and a new chapter can include literature review, methodological approach and sustainability concerns (Ferreira et al. 2017);
Author response: The manuscript is focused on the consumer safety and possible evaluation criteria of recycled HDPE caps which are recycled into new caps. Costs and benefits of recycling is not topic of this study and including such a chapter into the manuscript would go beyond the scope of this study. Therefore I made no changes into the manuscript according to this recommendation.
Novelty of the paper should be highlighted in the introduction;
Author response: I decided not to highlight the novelty of this study. The study consequently evaluates the existing data, exposure scenarios, and the already published evaluation criteria of EFSA. This is an approach to suggest a first evaluation of HDPE bottle cap recycling without published criteria by competent authorities.
In the methodology, the assumed 0.5 mg/kg contamination level is based on milk bottles from curbside collection, not DRS. Can the authors revise?
Author response: This is already mentioned in line 132, line 156ff and 299ff. Therefore I made no changes into the manuscript according to this recommendation.
Legends of figures can be reduced and add it in the text;
Author response: This is a matter of opinion. In my opinion, the figures should be self-explanatory and understandable even without reading the text, with all the details that contribute to understanding the figure. Therefore I made no changes into the manuscript according to this recommendation.
Regarding the methodology, the model can be better justified, in particular highlighting the strong and weak points;
Author response: I added a couple of sentences in the discussion sector regarding the applied diffusion model.
Diffusion modeling (AKTS SML) is appropriate but lacks experimental or literature validation. If possible, justify better;
Author response: AKTS SML is only the modelling software. The basic background in diffusion modelling is given in the modelling guide of the joint research centre (JRC). This publication is already cited.
Clarify that this is a preliminary theoretical evaluation, not a regulatory proof, and experimental verification will still be required by EFSA for Novel Technology status;
Author response: This is already included in the manuscript: line 187 and line 402. To make it more clear, I added the following sentence: "The proposed criteria should be understood as a suggestion for a provisional assessment of mechanical recycling processes."
In the discussion, mention analytical challenges of verifying sub-µg/L migration levels (detection limits, uncertainty);
Author response: This is already mentioned in the manuscript. To use migration models instead of experimental migration tests was originally proposed by the EFSA und was adopted in this study.
I was expecting more recommendations for decision makers in the conclusion chapter;
Author response: I revised the conclusions and added more recommendations.
The references must be homogenized and in line with the author guidelines (for example, some issues are missing).
Author response: The literature has been revised and supplemented to the best of our knowledge in accordance with the Author Guidelines.
Reviewer 2 Report
Comments and Suggestions for Authors
Dear Author,
As in conclusion, this manuscript contains important information regarding the recycling of plastics. When plastics are manufactured into virgin pellets, 10 to 30 different additives are added to adapt them to the intended use of the product. Or at the very least, polymerization initiators for polymerizing monomers, as well as unreacted monomers, remain in the product. For this reason, care must be taken when remolding and commercializing recovered products. For example, PET begins to decompose into its raw material monomers after 10 days at 50°C.
The safety of materials ingested by humans is extremely important, and the submitted paper is an essential source of new awareness.
I have a few questions.
- Flake? (p.2 L.83, etc.)
- Proper unit notation throughout: p.3 L.128, 133, 147, 148, etc.)
- No subject (p.10 L.308, 309, etc.)
Please consider.
Sincerely yours
Author Response
reviewer 2
As in conclusion, this manuscript contains important information regarding the recycling of plastics. When plastics are manufactured into virgin pellets, 10 to 30 different additives are added to adapt them to the intended use of the product. Or at the very least, polymerization initiators for polymerizing monomers, as well as unreacted monomers, remain in the product. For this reason, care must be taken when remolding and commercializing recovered products. For example, PET begins to decompose into its raw material monomers after 10 days at 50°C.
The safety of materials ingested by humans is extremely important, and the submitted paper is an essential source of new awareness.
Author response: Thanks for this valuable comment
I have a few questions.
Flake? (p.2 L.83, etc.)
Author response: I changed caps into flakes
Proper unit notation throughout: p.3 L.128, 133, 147, 148, etc.)
Author response: Unfortunately, I don't understand what I'm supposed to change here.
No subject (p.10 L.308, 309, etc.)
Author response: Unfortunately, I don't understand what I'm supposed to change here.
Reviewer 3 Report
Comments and Suggestions for Authors
The manuscript entitled “Recycling of Post-Consumer HDPE Bottle Caps into New Caps for Food Contact” focuses on the recycling of HDPE caps used in food and beverage packaging—an important and timely topic that deserves attention. Although the study appears somewhat incomplete and inconclusive, the results obtained through the literature review and diffusion modeling experiments are interesting and valuable for researchers working in the field of polymer recycling. Therefore, I would like to recommend the manuscript for publication in the Recycling journal.
Author Response
reviewer 3
The manuscript entitled “Recycling of Post-Consumer HDPE Bottle Caps into New Caps for Food Contact” focuses on the recycling of HDPE caps used in food and beverage packaging—an important and timely topic that deserves attention. Although the study appears somewhat incomplete and inconclusive, the results obtained through the literature review and diffusion modeling experiments are interesting and valuable for researchers working in the field of polymer recycling. Therefore, I would like to recommend the manuscript for publication in the Recycling journal.
Author response: Thanks for this valuable comment
