2.1. Goal and Scope
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. An attributional (aLCA) approach was applied, consistent with ISO 14044 [
17], ISO 14046 [
18], and the wool LCA guidelines developed by the IWTO [
19].
Impact assessment methods are described elsewhere [
15]. Briefly, the impact assessment included greenhouse gas (GHG) emissions (in CO
2-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].
The functional unit was one garment over its lifetime, with impacts reported per wear event in Europe. Merino wool is used to make a large variety of garments, and knitted sweaters are a major product category. In the present work, a knitted wool sweater made from recycled wool fibre blended with polyester and weighing 300 g was selected as a specific example. Other recycled wool blends are possible; for example, virgin/recycled wool blends are commercially produced, although these are more likely to be used in woven rather than knitted fabrics (e.g., suiting cloths), and recycled wool may be blended with synthetic fibres other than polyester. The manufacturing phase of the supply chain included the fibre recovery, blending and treatment processes of two wool recycling companies. The system boundary was cradle-to-grave (
Figure 1). The virgin wool supply chain (originating in the tablelands of New South Wales and south-western Western Australia) and inventory data were as described previously [
15].
2.2. Inventory Data
The inventory data for a recycled wool blend sweater began with the collection, sorting and transport of donated wool garments to recycling locations. Processing data for the mechanical recycling of wool sweaters were collected from a survey of industrial closed-loop recycled wool processors located in Italy and India, providing inventory for pre-treatment (
Table 1), overdyeing (
Table 2), spinning (
Table 3), knitting (
Table 4) and finishing (mechanical and chemical treatment of the fabric) (
Table 5). Of the recycled wool fibre content, 17.5% was required to go through an over-dyeing process; the remaining 82.5% did not require dyeing. When spinning new yarn, the recycled wool processors used a blend (by weight) of 89.5% recycled wool and 10.5% polyester terephthalate (PET) fibres. For the PET fibre production, a global market process from the ecoinvent v3.6 database [
23] was modified to include Chinese electricity and water consumption, reflective of China being the largest producer of PET globally.
A pre-existing inventory [
15] was used to model knitting (fabric manufacture), garment make-up, warehousing and use phase of the recycled garment, as these stages were considered to be equivalent to that of a virgin pure wool sweater. The freight distance to the point of retail was adjusted to reflect manufacturing steps taking place in India and Italy.
Impacts were modelled according to the PEF (European Union Product Environmental Footprint) circular footprint formula (CFF) and its associated application rules [
24]:
where:
full life cycle impacts for indicator i, emissions and resources associated with the recycling process (described above), and all other terms are described in the following paragraphs.
This approach required estimates of recycling rates at the start (
R1) and end (
R2) of the product life cycle as well as identification of avoided impacts (
). The first two terms of the CFF relate to the impacts of virgin and recycled inputs, respectively. Wool is over-represented in clothing donations [
7] and in closed-loop mechanical recycling. Approximately 22,000 t. p.a. of wool rags are recycled in Prato, Italy [
25]. If annual wool use in apparel is 460,000 t [
26], then approximately 4.8% of wool is close-loop recycled annually in Prato; the global market rate would be higher considering the other regions which recycle wool. To reflect these considerations, a closed-loop recycling rate (
R1) of 5% on a garment mass basis was used as a conservative standard, and a sensitivity analysis was used to assess the effect of setting this value at 0.5, 10 or 50%.
The third term of the CFF relates to recycling of the product at hand. The rate of open-loop recycling at home (i.e., what would have been a specific
R2 value) was set to 0%, as wool garments are not normally used as cleaning rags and alternative home uses (e.g., stuffing, textile or fibre recovery) were considered immaterial. A recent grey literature source suggests the combined open- and closed-loop recycling of clothing, home textiles and footwear could be as high as 23.4% [
27]. Taking a conservative approach, we estimated the open-loop recycling rate
R2 to be 10%, and assumed that this process avoided the primary production of mineral wool (fibrous inorganic material) used as insulation, in line with [
28].
The final terms of the CFF relate to the impacts of incineration and landfill. To remain conservative, a 55:45 landfill:incineration ratio [Annex C of [
24]] was applied to garments not recycled. Energy recovery from incineration (
R3) was modelled using an efficiency of 30%, textile energy content of 24 MJ kg
−1, heat:electricity production of 38:62, process input of 19.32 J kg
−1 mass (
EER), released biogenic 0.5 kg CO
2 kg
−1 mass, and avoided the production of European low voltage electricity and central heat or small-scale natural gas [
23]. Landfill (
) was modelled as municipal solid waste [
23]. Impacts associated with the collection and sorting of textile waste (
ErecyclingEoL) were allocated to the end of life processes on a mass basis.
Burdens were allocated between the source and destination of recycled materials using an
A factor of 0.8 [
24]. The quality ratios (
Q, where subscripts ‘in’ and ‘out’ refer to incoming and outgoing recycled materials) for recycled wool and insulation were set at 0.895 (reflecting blending with PET described above) and 1.0, respectively [
28]. The quality ratios are used in the circular footprint formula to modify the allocation of impacts between the source and destination of recycled materials.
Q < 1.0 is consistent with downcycling.
2.3. Scenario Analyses
A scenario analysis was conducted in which cumulative best practice consumer behaviour was modelled [scenario S6B of [
16]]. Briefly, this included best practice washing frequency (14 wears per wash), washing load (2.1 kg), washing machine efficiency (0.1 kWh/kg, 43 L per load), drying regimes (50% outdoors and 50% in unheated rooms), and 200 wears by the first user (and no reuse). The most important parameter change was the number of wears, which under the standard scenario was 109 wears across first and second users. However, the number of wears by the first user under the best practice use and care scenario were half those modelled previously [
16] in order to reflect the limited information available on consumer behaviours pertaining to garments made of recycled fibres. The garment end of life fates were consistent with those described above for a recycled wool blend sweater.
For the purpose of comparison, the modelling choices described above, both with and without best practice use and care, were replicated on a virgin pure wool sweater.
To assess the sensitivity of impacts to the PEF circular footprint formula and its associated allocation rules, the life cycle of the recycled wool blend and virgin pure wool garments with and without best practice use and care were modelled using a simple cut-off approach. This approach assigned no impacts to R2 pathways of open-loop recycling at home, recycling materials for insulation, or energy recovery. End of life impacts were included for the collection and sorting of textile waste, as well as for landfill.
Within the system boundary, there is a link between sweaters made of virgin and recycled wool fibres via closed-loop recycling (
Figure 1) because recycling relies on an ongoing supply of virgin wool fibre. Comparing virgin fibre with recycled wool without taking this into account would overstate the potential for recycling to reduce impacts. More realistically, a reduction in environmental impacts resulting from closed-loop recycling will the reduce the impact of all wool sweaters in the market containing both virgin and recycled fibres. The environmental impact of an average market product (
MPi) was determined as follows:
where
VPi/FU = impact of the virgin pure wool product per functional unit and
RPi/FU = impact of the recycled wool blend product per functional unit.
For simplicity, it was assumed that there was one recycling event, although multiple recycling events are possible. Values tested were R2 = 0, 0.5, 5, 10 and 50%.