Measuring the Circularity and Impact Reduction Potential of Post-Industrial and Post-Consumer Recycled Plastics

Round 1

Reviewer 1 Report

This is a good paper that tackles an important subject. The paper has thoroughly covered circularity and the environmental benefits of recycling. My suggestions are as follow:

1. The Abstract should contain recommendations and policy implications.

2. Likewise, Section 4 Conclusion and Outlook should read Conclusion and Policy recommendations

The English is good. Minor grammatical errors can easily be handle using a software for grammar e.g. Grammarly.

Author Response

Dear Reviewer,

Thank you for giving us the opportunity to submit a revised draft of our manuscript titled “Measuring circularity and impact reduction potential of post-industrial and post-consumer recycled plastics” to Sustainability. We appreciate the time and effort that the editor and all reviewers have dedicated to providing your valuable feedback on our manuscript. We are grateful to the reviewers for their insightful comments on our paper. We have been able to incorporate changes to reflect the suggestions provided by the reviewers. We have highlighted the changes within the manuscript as tracked changes version.

Here is a point-by-point response to the reviewers’ comments and concerns. Please notice that if we have cited a line in order to show you our changes and improvements to the text, they refer to the document version with the “track changes” function in Microsoft Word activated.

Point by point response to Reviewer 1:
The suggestions from the reviewer were as follows:

1. The Abstract should contain recommendations and policy implications. 2. Likewise, Section 4 Conclusion and Outlook should read Conclusion and Policy recommendations

Response: Thank you for this recommendation. We have added a sentence about policy implications in the abstract. In section 3.4 and 4 we elaborated a bit more the possible policy embedding and its applicability in companies. Please see lines 753-763, and 898-912.

The main headings are instructed by the Journal of Sustainability. For this reason, we have kept the heading of section 4 "Conclusion and Outlook" in order to meet the requirements of the journal. Most of the policy recommendations can be found in chapter 3.4 (e.g. 771ff). For this reason, we have renamed this section into "3.4 Applicability, limitations, and recommendations". We deliberately omitted the term "policy recommendations" because another reviewer encouraged us to add additional recommendations for the applicability of the indicators in industry as well. We hope to meet both comments here.

2. Comments on the Quality of English Language. The English is good. Minor grammatical errors can easily be handle using a software for grammar e.g. Grammarly.

Response: We did a spell and grammar check with Microsoft Word office and during the revision process we found some minor errors. Unfortunately, our institution's policy does not allow using such software tools that require the upload of an entire manuscript. For these reasons, we have no access to such tools. We will see if the Journal’s editing service can support here. If you have specific comments regarding grammatical errors, you can provide us the line numbers for immediate improvement.

Reviewer 2 Report

It is an excellent work, which presents very important results for the field of study. I accept the article for publication after minor revisions are made.

Keywords:

Delete LCA, it is already written in full. Remove other abbreviations from your keywords. You can use them spelled out. Enviromental assessment is the same as LCA, exclude as well. Delete polypropilene, recycling, climate change, indicator, efficiency, effectivelly. Maybe you can insert "environmental efficiency".

Incluse the "Post-industrial recycling", and post-consumer recycling "

Methods

Include your supplementary material (tables) in the methodology, such as sources originating the calculations for the result and discussion. This will make it easier for other readers to understand your article.

Results

Insert a list of abbreviations into your article. Or insert their full names in the titles of figures and tables, to facilitate our understanding.

Author Response

Dear Reviewer,

Thank you for giving us the opportunity to submit a revised draft of our manuscript titled “Measuring circularity and impact reduction potential of post-industrial and post-consumer recycled plastics” to Sustainability. We appreciate the time and effort that the editor and all reviewers have dedicated to providing your valuable feedback on our manuscript. We are grateful to the reviewers for their insightful comments on our paper. We have been able to incorporate changes to reflect the suggestions provided by the reviewers. We have highlighted the changes within the manuscript as tracked changes version.

Here is a point-by-point response to the reviewers’ comments and concerns. Please notice that if we have cited a line in order to show you our changes and improvements to the text, they refer to the document version with the “track changes” function in Microsoft Word activated.

Point by point response to Reviewer 2:

Note: Your suggestions are italicised:

Keywords: Delete LCA, it is already written in full. Remove other abbreviations from your keywords. You can use them spelled out. Enviromental assessment is the same as LCA, exclude as well. Delete polypropylene, recycling, climate change, indicator, efficiency, effectivelly. Maybe you can insert "environmental efficiency". Incluse the "Post-industrial recycling", and post-consumer recycling "

• Thank you for your comment. We have excluded the abbreviations from the keywords. Additionally, we have removed “environmental assessment”, “climate change”, “indicator”, “recycling”, “effectiveness”, and “efficiency”. In turn, we have included the key words: “circularity assessment”, “environmental efficiency”, “post-industrial recycling”, and “post-consumer recycling”.
• We kept the keyword “polypropylene”. As this is the specific type of polymer that is the subject of the case study, we think it has added value for people looking for information on this type of polymer.
• After revision, the keywords of the manuscript are as follows: “Life cycle assessment, circular economy, polypropylene, global warming impact, circularity assessment, environmental efficiency, post-industrial recycling, post-consumer recycling”.

Methods: Include your supplementary material (tables) in the methodology, such as sources originating the calculations for the result and discussion. This will make it easier for other readers to understand your article.

• We are not sure if we understood your comment correctly. The calculations in the sections 2.1 and 2.2 have been developed by the corresponding author and were inspired by preliminary considerations quoted in line 149.
• If your comment refers to the calculations for the case study example in section 2.3.1, we have added footnotes to the existing table summarising the parameters and sources. We deliberately decided to put further details regarding the values used for the calculations in the appendix (below the manuscript). Since the focus is on the methodological development, the calculation of the case study is important, but not essential to understand the indicators. If you want to get a better understanding of the results (including sources), you can find this in the appendix. In line with other reviewer, the manuscript is yet quite long. Therefore, we do not want to include this in the main text. We hope that you agree with our decision here.
• The tables and considerations in section 2.3.2 (especially the life cycle inventory for the calculation of the environmentally-efficient circularity for the case study example) are summarized in the main text, but presented in the supplementary material. This includes three extensive tables that find no place in the main text. For LCA studies, it is common to put the inventories in the supplemental material, so that only those who want to replicate the LCA model can follow it in detail. Nevertheless, we have moved the sentence where detailed information on the life cycle inventory can be found to the beginning of the paragraph in question, namely in the accompanying information.

If none of this addresses your concern, please specify describe what information is needed to improve the understanding of the article.

Results: Insert a list of abbreviations into your article. Or insert their full names in the titles of figures and tables, to facilitate our understanding.

• According to our knowledge, the journal does not allow a list of abbreviations. Therefore, we are now using the full names in the figures and tables or added them in the caption. In this way we want to make it easier for the reader to understand the figures and tables. Please note that we could not implement this for the variables and parameters (only for abbreviations). For example, 2 has the purpose of illustrating the variables of equation 8 to better understand the equation. They are first mentioned in the equation and described directly in the text below the figure.

Reviewer 3 Report

The manuscript by Schulte et al is a very interesting piece of work. I recommend the manuscript for publication provided the author’s willing to include following points in the revised version.

1. Provide a table describing all the indicators for measuring circularity and their limitations. Try to include effective circularity (eC) and environmentally efficient circularity (eeC) in the same table and compare these with the reported/existing indicators.

2. Why the authors chose plastic as the material for study? Is it because plastic is difficult to valorise by chemical and enzymatic methods. Somewhere mention whether other wastes can be included in this study and what should be the approach.

3. How will industries benefit from the proposed research conducted by the researchers?  Please state point wise the significant impact of the research on plastic/polymer industries.

4. Sometimes theoretical studies do not match with that of the experimental results. Are the authors planning to apply the results obtained from this study for experimental purposes? If yes, please mention 1-2 lines about it for the benefits of researchers.

Author Response

Dear Reviewer,

Thank you for giving us the opportunity to submit a revised draft of our manuscript titled “Measuring circularity and impact reduction potential of post-industrial and post-consumer recycled plastics” to Sustainability. We appreciate the time and effort that the editor and all reviewers have dedicated to providing your valuable feedback on our manuscript. We are grateful to the reviewers for their insightful comments on our paper. We have been able to incorporate changes to reflect the suggestions provided by the reviewers. We have highlighted the changes within the manuscript as tracked changes version.

Here is a point-by-point response to the reviewers’ comments and concerns. Please notice that if we have cited a line in order to show you our changes and improvements to the text, they refer to the document version with the “track changes” function in Microsoft Word activated.

Point by point response to the reviewer 3

Note that your suggestions are italicised:

1. Provide a table describing all the indicators for measuring circularity and their limitations. Try to include effective circularity (eC) and environmentally efficient circularity (eeC) in the same table and compare these with the reported/existing indicators.

• Thank you for this comment. We appreciate the idea of providing a table to compare the effective circularity (eC) and environmentally efficient circularity (eeC) indicators to existing indicators. Since there is a range of indicators, we have selected two indicators that were previously mentioned in the introduction to follow the common thread (the widely applied Material Circularity Indicator (MCI) for PCR only and the Circular Economy Performance indicator (CPI) for PIR). The indicators are presented in a new Table 2, each stating their scope, perspective, unit (of the result), number of material uses considered, life cycle stages, information needed, and their applicability to PIR and PCR (see lines 716-734 including table 2). We think that this table provides an additional value to the manuscript.

2. Why the authors chose plastic as the material for study? Is it because plastic is difficult to valorise by chemical and enzymatic methods. Somewhere mention whether other wastes can be included in this study and what should be the approach.

• Thank you for your comment. We have added a few sentences about the applicability to other materials and waste. Furthermore, we explained why we focused on plastics as follows: In principle, the provided indicators are applicable to all types of waste and materials. The indicators are not only limited for the purpose of assessing recycled plastics. This study focuses on recycled plastics, because the difference between post-industrial and post-consumer recycling is mainly discussed for plastics. The post-consumer recycling of mixed plastic waste often creates higher environmental impacts and suffers from downcycling effects compared to post-industrial recycling from a product perspective. (Lines 748-752)
• It is previously mentioned that measuring quality loss is beyond the scope of this work. We elaborated this in a previous work on recycled plastics (cited in line 747 the article). Therefore, the integration and the influence of the use stage and quality aspects are outlined as future research. In the long term, the use of PCR plastics is essential for a circular economy which has been demonstrated by the case study results (lines 742-747).

3. How will industries benefit from the proposed research conducted by the researchers? Please state point wise the significant impact of the research on plastic/polymer industries.

• Thank you for another useful suggestion, which we have incorporated in lines 753 to 763 as follows: Due to the material perspective, which covers multiple uses of a material, the proposed indicators of this study are primarily relevant for strategic decision-makers at company and policy level. The indicators might also be used by companies that face decisions of whether to use material from post-industrial recycling and post-consumer recycling. If companies solely stick to product LCAs, they might conclude that the environmental impacts of a product are lower when using PIR material compared to PCR material. However, to contribute to closing the loop at the EoL, companies also need other methods and indicators to quantify the environmental advantages along the value chain including multiple material uses. A particularly suitable area of application in industries can also be the monitoring and assessment of closed-loop recycling systems in cases where companies can control the recycling system, which is supported by Figge et al. [42].

4. Sometimes theoretical studies do not match with that of the experimental results. Are the authors planning to apply the results obtained from this study for experimental purposes? If yes, please mention 1-2 lines about it for the benefits of researchers.

• You are right that the results of experimental studies might not match those of theoretical studies such as ours. We have added this limitation in lines 844 to 848. We found the idea quite helpful and think that one could succeed here by testing closed loop systems with a fixed material quantity. We are currently discussing this idea with our industry partners.

Round 2

Reviewer 3 Report

The manuscript can be accepted for publication. 

Minor editing may be necessary.