Is there still a future for polymer-based fibers for textile applications post COP26?

Plastics in general and PET fibers are not necessarily bad
In recent years there have been many publications appearing explaining how bad the use of PET is for the environment and for public health. Below are the positive points of PET:
•    PET fibers are a very economically friendly (cheap) alternative, when compared to all other man-made and natural fibers.
•    PET fibers have very good technical characteristics compared to many synthetic and natural fibers. It is a strong fiber, with high tenacity, very low shrinkage because of the high melting point, relatively easily dyeable with good color fastness.
•    PET is a fully recyclable product. Post-consumer PET bottles are recycled into PET staple fibers and textile products made from those fibers can again be fully recycled into new fibers using the correct technology.
•    The full environmental impact of synthetic fibers in general and PET more specifically is actually better than those of natural fibers and recycled PET staple fiber is much better placed than all the other synthetic fibers.

Environmental dimensions of materials sustainability
GWP (global warming potential) or carbon footprint as it is commonly known, is a too simplistic approach to describe a product’s full sustainability impact on the environment.
In order to find a way to tackle this, the apparel and footwear industry have since a number of years developed a specific Materials Sustainability Index (MSI) that incorporates 5 environmental impact factors. This Higg MSI or Higg Materials Sustainability Index considers the factors:
•    global warming score
•    eutrophication score
•    water scarcity score
•    fossil fuels score
•    chemistry score.
This index is not perfect because some factors like land-use is not considered, but it does already give an interesting view on total sustainability [1]. If a look is taken at where recycled PET (rPET) would fit into Fig. 1: the GWP of rPET is <30 of="" the="" gwp="" v-psf="" virgin="" pet="" staple="" fiber="" so="" it="" would="" shift="" much="" more="" to="" right="" in="" fig="" 1="" probably="" just="" before="" organic="" cotton="" br="">More specifically on land-use: also, there v-PET has very low impact, certainly when compared to all natural fibers, and definitely also when compared to bio-PET being produced from sugarcane of corn, for instance. (Fig. 2, whereby scenario 0 stands for v-PET compared with all other scenario’s being some form of bio-PET, with scenario 7 for instance being PLA) [2].

Fig. 2: Impact on land-use whereby scenario 0 stands for v-PET compared with all other scenarios being some form of bio-PET, with scenario 7 being PLA (Source: TWE Group)

Carbon footprint impact
Still one of the most discussed environmental impact factors is the GWP or often referred to as carbon footprint. Fig. 3 shows the carbon footprint of several types of fibers.
But how big exactly is the carbon footprint of the entire PET fiber industry vs. the total global GHG (greenhouse gas) emissions?
The total cumulative GHG emissions in 2019 were around 42 billion tons of CO2e (gtons). If we now know that there are 57.7 million tons of PET fibers being produced with 8.1 million tons being rPET, the share of the PET industry is: v-PET fiber approx. climate impact of 4.06 kg CO2e/kg fiber and rPET fiber 0.96 kg CO2e/kg fiber.
Simple math arrives at a total environmental impact for the global PET fiber industry of 210 million tons of CO2e, equaling 0.5 % of the global overall impact, still an impressive number.

Fig. 3: Cradle-to-factory gate GWP of 1 ton staple fiber based on the “cut-off” approach. The error bar shows the results corrected by the “waste valuation” method. The carbon sequestration of bio-based fibers has been taken into account. For “Chem. Recycling (DMT route, POY)”, only the “cut-off” approach was applied. (Source: L. Shen et al.: Open-loop recycling: A LCA case study of PET bottle-to- fibre recycling, Resources, Conservation and Recycling 55 (2010) 34-52)

Mitigation strategies to further reduce environmental impact of PET fibers
As it seems unavoidable that we all will need to try to live with PET fibers used in garments and other textile products for the foreseeable future, we will therefore have to try to reduce the environmental impact of synthetic fibers in order to cooperate with the goals set at the Paris Agreement. Therefore, the following potential mitigation strategies are of great interest:
•    life cycle perspective
•    full circular solution
•    biodegradable PET.

Life cycle perspective
One of the possible huge impact factors is the life cycle perspective of a textile product, for instance a garment. As the global population is growing very fast and therefore the needs for textiles and especially garments are very large, the lifetime of such garments should be extended, as this will very significantly reduce the environmental impact.
Another very important factor to look at is the spend behavior. We are living in a consumption society with often an unstoppable urge for new things. If the lifecycle of a garment would be extended from 30 to 60 washing cycles, so using the garment twice as long as we used to do, the environmental impact halves.

Full circular solution
A second mitigation strategy would be to go full steam for the circular solution. Within the PET fiber industry, already about 14 % of the total PET fiber supply chain is being recycled, mainly by converting post-consumer PET bottles from the packaging industry into PET flakes, with which rPET fibers can be produced. The rPET fibers produced as such are having very good physical characteristics and are therefore fully comparable with their v-PET counterparts for many different applications, especially in the nonwovens and fiberfill sector.
As the PET packaging market (PET bottles) is increasingly becoming aware of its environmental impact, the supply chain of the rPET fiber industry is coming seriously under strain, as this feedstock chain is slowly but certainly drying up.
As such, significant efforts are currently underway to find new feedstock sources. A very important feedstock source is the post-industrial/post-consumer textile product waste itself.
There are ample examples: recovering used mattress covers, textiles used in the automotive industry, PET carpets could be redesigned, acoustical and thermal insulation products etc. and there are numerous possibilities that will emerge in the coming years. The circular industry will have an influence at the textile industry that will be of increasing importance, making sure at the end, that much less virgin PET will be consumed, with significant positive effects on climate change.

Biodegradable PET
A further solution is to be found in using biodegradable PET fibers going forward. Every material in that is found in nature biodegrades at different paces, and in the case of synthetics and PET more specifically this process takes an awful long time. Depending on the study this half-life of PET varies from several hundreds of years to >2,500 years. In recent times, there are additives available, with which, when added to the melt of PET at minor percentages (typically around 1 %), this makes the PET polymer to decay or biodegrade under specific conditions at a much faster rate, typically >90 % after 3 years or so.
The typical and worldwide accepted standard for biodegradation of polymers is the ASTM D-5511 or similar ISO 15985. This is the standard for anaerobic biodegradation of plastic materials under high solids anaerobic digestion condition.
The TWE Group has been testing biodegradable PET fibers specifically developed according to their specifications for nearly 2 years now, and Fig. 4 shows the biodegradation so far after 435 days, showing a biodegradation of 43.5 % [4].
It is not really possible to extrapolate as there is no guarantee the curve will continue to behave like it has over the past months, but assuming it will, a 90 % biodegradation rate will effectively be reached after 900 days, just 2.5 years.

Fig. 4: Biodegradation of different materials (Source: TWE Group)

The ultimate solution
In order to mitigate carbon footprint as an industry under the best possible conditions, the ultimate goal would be to combine each of the 3 mentioned principles. This could then be described as: “The ultimate solution”. If each company could work on trying to find their own ultimate solution, the world can become a better place, in any case a much more environmentally friendly place, fit for generations to come, to have a great and sustainable life on this beautiful planet Earth.

Conclusion
As there will be no way around using PET fibers in the future, and considering the fact they are a reasonably sustainable product anyway, we can only try to make them even more environmentally friendly by encouraging each industry to find their own “ultimate solution”.
Humanity is resilient enough to cope with the huge challenges lying ahead of us. Together, we can and will succeed!

References
[1]    Higg Material Sustainability Index, Source Lenzing, www.kymo.de/en/, How sustainable are Textiles? – A comparison using the Higg Material Index, posted by Iris 03/09/2021
[2]    Graph on Land-use #polyester fibers, Bio-Based Polyester Fiber Substitutes: From GWP to a more comprehensive Environmental Analysis, Applied Sciences, MDPI, Tijana Ivanovic, Roland Hischier, Claudia Som, 11.2021
[3]    Cradle to Factory Gate GWP of 1 tons of staple based on “cut-off” approach, Elsevier BV, Shen L, et al. Open-loop recycling: A LCA case study of PET bottle-to-fiber recycling. Resour Conserv Recy (2010), doi: 10.1016/1.resconrec.2010.06.014
[4]    Biodegradation of low melt polyester fiber after 435 days, Edenlabs, Sept 2021