Reducing the Environmental Impacts of Garments through Industrially Scalable Closed-Loop Recycling: Life Cycle Assessment of a Recycled Wool Blend Sweater

Round 1

Reviewer 1 Report

Dear editor, I have reviewed the paper titled "Reducing the environmental impacts of garments through industrially scalable closed-loop recycling – life cycle assessment 3 of a recycled wool blend sweater".

In my opinion, it is a good manuscript, but it needs to resolve some minor issues. 

• Line 10. "for > 200 years". It does not sound scientific.
• Lùines 10-23. The abstract is too long, it exceeds the maximum words allowed.
• Lines 24. Keywords are too general. Please replace them.
• Lines 78-81.  The numbering is not clear.
• Lines 86-87. Are the authors talking about the functional unit? Please state it!
• Lines 161-162. Please provide more information. Referring to a paper published previously is not enough. Indicate, at least, the calculation method, the impact categories, and the software used.

Author Response

Line 10 - "> 200" replaced with "more than 200"

Lines 10-23 - the instructions to authors 'should be a total of about 200 words maximum'. With the change to line 10 (see above), the word count is 199. No change made.

Line 24 - Keywords "water; land; energy; footprint" replaced with "LCA; closed-loop; circularity". "Wool; recycling" were retained.

Line 82 - Avoided referring to "i) and ii)" in the text. Sentence now reads "The study specifically aimed to i) determine impacts and hotspots of a recycled wool blend sweater, ii) identify the extent to which best practice garment use and care could reduce these impacts, iii) compare the impacts of a recycled wool blend sweater to those of a virgin pure wool sweater, and iv) quantify the effect of recycling on the impact of an average wool sweater in the market"

Line 94 - functional unit now stated in first sentence of paragraph

Lines 89 - 93. Change made and paragraph moved to this location. Paragraph now reads:

Impact assessment methods are described elsewhere [15]. Briefly, impact assessment included greenhouse gas (GHG) emissions (in CO₂-e units using 100-year global warming potentials [20]) and water stress (water stress index) [21], and aggregated inventory results for fossil fuel energy use (in megajoules, using lower heating values) and freshwater consumption (in litres). Modelling was done using SimaPro 9.3 [22].

In addition, the figure labels were updated to replace "Climate change" with "GHG emissions".

Reviewer 2 Report

I think the paper has been well structured and written. It is coherent in style and easy to read. Even though I have not been working with wool before, only with other textile materials, the results are somewhat differing to those we have made with e.g. cotton, thus very interesting. 

I have some minor comments, that either can, but must not be integrated to the study. 

• it is stated that wool has been traditionally recycled, especially in overcoats, military uniforms and jackets. For understanding the bigger picture, it would be interesting to hear what the market impact is, in terms of volume, already now? How much is already recycled, and how much does it substitute for virgin material? What is the potential?
• I understand the use of closed and open loop recycling. I was wondering, that could this be also explained by down- and upcycling, as these also have a order of priority?
• In the goal and scope, could the selected environmental impacts be already disclosed here? I often see this vague "environmental impacts" scope in the beginning, which then is diluted to mere carbon footprint estimation. Since this study already considers several impacts (GWP, water, energy), it might be of added value to explain this already in the beginning.
• This may be just my poor English, but I had trouble understanding what exactly "The supply chain reflected the process followed by two wool recycling companies". What process?
• In the process flow sheet I assumed that also substitution impacts are included in the calculation, should they be included within the system boundaries? Also, are the "closed loop" and "open loop" individual process steps in addition to the "recycling" process? I would probably not name these processes as such, but probably rename them as "secondary raw material production" or take them altogether away, since you have the recycling process already included. 
• I haven't used the PEF circular footprint formula comprehensively yet. However, I probably wouldn't call it "end-of-life" formula, since it also includes the (secondary) raw materials provision, so not only end-of-life in your system. Also, I think the paragraph underneath the formula could be clarified. E.g. the first part relates to primary material LCI, the second part to the secondary material LCI and then the third to the end-of-life of the product at hand. Also the use of closed loop versus open loop is a bit uncertain to me here, could it be rephrased to indicate what the impact is? I mean, open loop could also be upcycling, in which case the quality coefficient would be higher. 
• But with the previous comment in mind, I think the sensitivity analysis to the circular footprint formula is very good.
• Could the best practice scenario be briefly explained and what it quantitatively means? The reference is there, but it might help to fully understand the impact.
• Could you detail the method that was applied to water stress calculation, probably also the geographic areas that were considered? In fact, the LCIA method could be detailed.
• In Figure 2, it would be good to have numbers attached to the bars. Also, it would be good to detail, which are the substitution impacts, in comparison to the other impacts, since these are more speculative. 
• I think the discussion is very informative and good. I would, however, point out that embedding technology to each garment will ultimately also affect the environmental impacts, and use of non-renewable resources, sometimes critical materials. Even though a good idea in general, the use of such technologies should be carefully considered - also in order not to further complicate recycling.

Overall, and as said already previously, I think the paper was a very good comparison between different end-of-life options for wool garments and it can be accepted - with minor revisions.

Author Response

To compliment a statement in the Introduction (line 10), the reviewer requested information to gauge the size of the market for products made from recycled wool - this information is provided under the Materials and Methods heading (beginning line 136), where it was necessary to estimate closed and open-loop recycling rates. Estimating these rates requires various assumptions and empirical data. To keep the Introduction brief, and to present the recycling rates in a logical place within the text, no change was made to the manuscript.

The relationship between down- and upcycling, and its relevance to closed loop recycling, is now explained at line 55:

"Where these loops produce recyclate of lesser or greater quality and functionality than the original material, the recycling process may be referred to as down- or upcycling, respectively [11,12]. The latter is not applicable in the context of wool fibres, where minimizing downcycling and maximizing closed-loop recycling is partly dependent on maximizing fibre length during the mechanical recycling process [7]."

In response to the recommendation to state environmental indicators under 'Goal and scope', the former 'Section 2.3 Impact assessment' was moved under 'Section 2.1 Goal and scope', line 89.

Line 101 - Sentence starting with "The supply chain reflected the process..." replaced with the following sentence:

"The manufacturing phase of the supply chain included the fibre recovery, blending and treatment processes of two wool recycling companies. "

Figure 1 was fully revised as per the reviewer's suggestions.

Line 130 - Reference to the PEF circular footprint formula pertaining to the end of life was removed. The following paragraph was then subdivided into several paragraphs, each with a topic sentence indicating to what part of the formula the text pertains. Reference was also made to the relationship between the quality ratio and downcycling (line 174).

The reviewer commented that the sensitivity analysis on the circular footprint formula was very good - no change made.

Line 176 - Under Section 2.4, "Scenario analyses", the reviewer suggested we quantitatively explain what 'best practice' means. To this effect, the following sentence was added (line 181):

"The most important parameter change here is the number of wears, which under the standard scenario, was 109 wears across first and second users."

The water stress method is now stated earlier in the manuscript (line 91). To aid the reader's understanding of the geography of the systems, the manuscript now states NSW and WA (line 103) are where virgin wool originates. Reference to manufacturing in India, Italy and China, and an EU use phase were already present.

The reviewer also suggested the impact assessment could be more detailed. We agree, but in the interest of succinctness, we refer readers to our previous work where the IA is clearly explained - no change made.

Figure 2 - numbers added to the bars as per the reviewer's suggestion. The substitution impacts are partially shown already in the form of negative (avoided) impacts in the end of life phase. We agree with the idea of identifying the extent of the substitution impacts - this is why Table 6 was included in the original manuscript - no change made.

Line 356 - comment added as per the reviewer's suggestion re. the impacts of technology embedded in garments to increase their recyclability.