Towards Higher Quality of Recycled Plastics: Limitations from the Material’s Perspective

Round 1

Reviewer 1 Report

In this review paper, the authors discussed and summarized the problems that exist in every step of plastic recycling, The authors made a comprehensive discussion about the strategies of contaminants during the plastic recycling. The paper was written clearly and in a good organization. The reviewer has two suggestions for the authors, which may help further enhance the clarity of the paper. 1. The authors should summarize the limitations regarding the plastic recycling with higher quality of the recycling process. The authors use the word "limitations"; however, no relevant statement was given in the abstract, introduction, and conclusion. 2. The authors mentioned "circular economy" in the paper and posed it out as one of two relevant points to the plastic recycling. It is suggested for the authors to give a definition of circular economy first, and then discuss how the plastic recycling exerts a critical impact on the circular economy.

Author Response

1. The authors should summarize the limitations regarding the plastic recycling with higher quality of the recycling process. The authors use the word "limitations"; however, no relevant statement was given in the abstract, introduction, and conclusion.

Response: thanks for this comment, we expanded the concept in abstract (see line 19-22), introduction (see lines 77-81) and re-worked the conclusion (see line 516-520).

2. The authors mentioned "circular economy" in the paper and posed it out as one of two relevant points to the plastic recycling. It is suggested for the authors to give a definition of circular economy first, and then discuss how the plastic recycling exerts a critical impact on the circular economy.

Response: thanks for this comment, we added the definition of CE and blended it in the scope of the paper (see lines 141-155).

 

Reviewer 2 Report

This review paper is focused on the technical limitations for closed-loop recycling of plastics waste, by evidencing the different factors that can affect recycled materials’ quality.

 In the following, the main remarks to be addressed by the authors.

• In which sense the paper represents “a non-systematic literature review”, as written by the authors at page 2, line 82?
• In several points (page 6, line 235; page 7, line 278; page 8, lines 338 and 341) of the manuscript, the authors do not report the numbers of the corresponding literature references within square brackets, but they include them directly within the main text.
• The definition of Design from Recycling (at page 6, lines 209-210) is not completely correct. In fact, as reported by Ragaert et al (Ragaert, K.; Hubo, S.; Delva, L.; Veelaert, L.; Du Bois, E. Upcycling of contaminated post-industrial polypropylene waste: A design from recycling case study. Polym. Eng. Sci. 2018, 58, 528–534) this methodology consists of making recycled polymers fit-for-use in designated products and/or redesigning products specifically for the recycled polymers. In other words, according with this approach, mechanically recycled polymers can be matched to potential new applications, following two design strategies: the first starts from the characteristics of the recycled material and then, based on these ones, defines the possible application; the second kicks off from the fundamental functional properties of the potential product and then selects the recyclate, using it as such or after proper upgrading steps.

Author Response

In which sense the paper represents “a non-systematic literature review”, as written by the authors at page 2, line 82?

Response: differently, from a systematic one, the non-systematic literature review we performed targeted a fraction of the published scientific and non-scientific literature. It does not encompass all of the published literature on the topic. We clarified this in the text (see line 83).

In several points (page 6, line 235; page 7, line 278; page 8, lines 338 and 341) of the manuscript, the authors do not report the numbers of the corresponding literature references within square brackets, but they include them directly within the main text.

Response: thank you, we formatted the in-text references in all instances (see lines 125, 258, 302, 363, 366).

The definition of Design from Recycling (at page 6, lines 209-210) is not completely correct. In fact, as reported by Ragaert et al (Ragaert, K.; Hubo, S.; Delva, L.; Veelaert, L.; Du Bois, E. Upcycling of contaminated post-industrial polypropylene waste: A design from recycling case study. Polym. Eng. Sci. 2018, 58, 528–534) this methodology consists of making recycled polymers fit-for-use in designated products and/or redesigning products specifically for the recycled polymers. In other words, according with this approach, mechanically recycled polymers can be matched to potential new applications, following two design strategies: the first starts from the characteristics of the recycled material and then, based on these ones, defines the possible application; the second kicks off from the fundamental functional properties of the potential product and then selects the recyclate, using it as such or after proper upgrading steps.

Response: thank you, we removed that statement (see lines 230-232).

Reviewer 3 Report

This paper make a good review on plastics recycling, circular economy on plastics and challenges to plastic waste recycling. It is worthy to publish in the Sustainability after minor revisions.

1, If possible, the data in Figure 1 is expected to be updated to 2020.
Resolving the plastic waste problem is a challenge that will require choosing from a 478
2, It's better to present your own points in the conclusion than to quote other literature, such as literature [212].

Author Response

1, If possible, the data in Figure 1 is expected to be updated to 2020. Resolving the plastic waste problem is a challenge that will require choosing from a 478

Response: the latest global figures we could find are dated 2018.

2, It's better to present your own points in the conclusion than to quote other literature, such as literature [212].

Response: we moved the statement to the discussion section and slightly reworded the conclusions (see lines 463-465 and 506-508).