Recycling of Pretreated Polyolefin-Based Ocean-Bound Plastic Waste by Incorporating Clay and Rubber

Round 1

Reviewer 1 Report

The article “Recycling of Pretreated Polyolefin-based Ocean-bound Plastic Waste by Incorporating Clay and Rubber” by Martey and coworkers contributes to the field of plastic waste, reusing and recycling. In a world that currently is in need to solutions to address the extensive plastic pollution, a new approach to recycle and reuse ocean-bound plastic waste at low cost is a necessity.

In this study, the authors have compounder ocean-bound plastic waste with various additives and studies the thermal, chemical and mechanical properties of the resulting materials.

First, I would like to note that the manuscript is very well written, the goals, methods and results are clearly detailed and the conclusions are appropriately supported.

It’s been a challenge to find shortcomings in this study and therefore my comments will be short and concise:

1. Figure 1: Since the labels are clearly established, the lines can be continuous which will help with readability.
2. There needs to be more details about the printed dogbones: size, thickness and tip diameter used. Are the compression molded samples comparable in size and thickness?
3. Can the authors comment on the potential applications of the described compounded materials? From the manuscript, I understand that applications requiring some flexibility are considered.
4. Finally, I would not disregard samples that are compression molded. One can find applications that could still bring significant value: fencing posts, playground surfacing and other low flexibility applications.

Author Response

To Recycling Editors and Reviewers,

Thank you for your letter regarding our manuscript “Recycling of Pretreated Polyolefin-based Ocean-bound Plastic Waste by Incorporating Clay and Rubber” (Recycling - 1665474). We are grateful for the constructive feedback you have provided. We have carefully reviewed your feedback and have made changes to the manuscript item by item to address all your comments.  Please find the proposed corrections in the attachment. 

Author Response File: Author Response.pdf

Reviewer 2 Report

Interesting work with high potential impact, on a highly relevant environmental topic. I have some comments to improve the manuscript’s quality before it is accepted:

Intro: The only introduction to the general environmental issue that underpins the whole study, is condensed in a single short sentence: “Most plastic waste streams contain a mixture of different polymers.”, which is true but vague and could be slightly and shortly expanded, e.g. with some up-to-date references on key areas (Atlantic, Mediterranean, India, China) and pollution-affected natural sanctuaries, as for instance:

• Giarrizzo et al., “Amazonia: the new frontier for plastic pollution”, Frontiers in Ecology and the Environment 17, 6, Pages 309 - 310, 2019
• Cincinelli et al., A potpourri of microplastics in the sea surface and water column of the Mediterranean Sea, TrAC - Trends in Analytical Chemistry 110, Pages 321 - 326, 2019
• Admin et al., Microplastic ingestion by zooplankton in Terengganu coastal waters, southern South China Sea. Marine Pollution Bulletin 150, 2020, 110616
• Devi et al., First report of microplastic ingestion by the alien fish Pirapitinga (Piaractus brachypomus) in the Ramsar site Vembanad Lake, south India. Marine Pollution Bulletin 160, 2020, 111637
• Galafassi et al., Plastic sources: A survey across scientific and grey literature for their inventory and relative contribution to microplastics pollution in natural environments, with an emphasis on surface water, STOTEN 693, 2019, 133499

Intro: “The small entropic gain during mixing makes most polymers immiscible.”, please add ref and/or expand.

I particularly appreciated that the authors discussed the blending and compounding issues with references to the physical-chemistry of the processes, e.g. interface energies, polymers gyration radii, and other relevant parameters. I was expecting some of those parameters to be measured/discussed more deeply in the discussion section, but I could not find much of it; maybe the authors can implement/comment more in that sense.

Figure 1. the authors say that Tg in blends could not be differentiated. However, some changes in the baseline are observable in the curves before the first endo peak, at temperatures compatible with the Tg of PE. Did the authors analyze the first derivative heat flow curve? That could be useful to enhance possible Tg events. Please comment.

Table 4: was the surface tension of these plastic surfaces available/measured? Please discuss and add it if possible.

Final comment: I don’t know if this is the standard format, but finding the Materials section in between the discussion and the conclusions was a bit confusing.

Author Response

To Recycling Editors and Reviewers,

Thank you for your letter regarding our manuscript “Recycling of Pretreated Polyolefin-based Ocean-bound Plastic Waste by Incorporating Clay and Rubber” (Recycling - 1665474). We are grateful for the constructive feedback you have provided. We have carefully reviewed your feedback and have made changes to the manuscript item by item to address all your comments.  Please find the proposed corrections in the attachment. 

Author Response File: Author Response.pdf