PET bottles are conveniently recycled into fibres by remelting and spinning.
How come there is no fibre-to-fibre polyester recycling by re-melt-spinning?
Is it due to degradation by i) hydrolysis or ii) oxidation or other iii) degradation mechanism, or additives such as iv) dyes or v) other additives, or due to vi) difficulties to dry the textile material sufficiently, or perhaps due to vii) oligomeric residues or viii) other reason?
Dear David Oulton , I believe you are absolutely right. As long as the virgin PET is so cheap recycling cannot become economically feasible. That is why we should opt for the most cost efficient route to recycle the PET. I'm convinced that the most cost efficient route is also the one that keeps as much as possible of the added value that the scrapped textiles represents. Finally, we (Azadeh Soroudi ) and I have identified a route to rejuvenate polyester by raising its molar mass, which should have potential to enable re-meltspinning. This is commercially accomplished by SSP of PET bottles today but we cannot find that it has been utilized for textile waste. Have you?
You mentioned already many possible reasons. I think that especially the additives to make the fibre antistatic, the so called spin finishes, do not survive a second melt process. You can add new spin finishes but the degradation products of the old additives are enriched. Perhaps also the high cristallinity of fibers impede recycling. The fibres are drawn at a temperature above glass transion temperature to increase cristallinity. This could make remelting more difficult.
Dear Professor Koehler, Thanks for your reply and the two highly plausible re-melt-spinning impediments. The first parameter seems manageable, at least from a technical point of view, whereas the high edegree of crystallinity is more of a challenge. We have noticed heat of melting values by DSC in the range of 60 J/g for polyester fabrics while heat of fusion reference values for the perfect crystal of 140 J/g is reported. If I interpret you correctly our values are underestimations of the actual degree of crystallinity since the melting is not complete. I'll look into this further. Are you aware of a study that compares DSC with direct methods such as WAXS?
You can find many literature even with google, but you must pay a fee if you want to have new citations as complete pdf. Unfortunately I have no paper which I can send you.
In polyester textile manufacturing process improves the intermolecular attraction and crystallinity. This increases the energy required for remelting in this case as compared to the PET bottles. This causes the degradation by oxidation in textiles and the additives may accelerate this degradation process.
Hi all,
Since here the discussion is about PET recycling, so I have a question about the dyes used in PET textile fabrics.
I've extracted dyes from the post-consumer PET fabrics, now I would like to characterise the extracted dyes and find out what exact dyes have been used in these fabrics.
I've done FTIR and NMR (proton) but it is very difficult to confirm the dye names and types.
I really appreciate if someone can suggest any other analysis to find out the dyes name and type.
Thanks
Raj
In some countries (e.g. Spain), PET from drink bottles are also recycled by ultra-clean post-treatments to be used again in food packaging applications. Since it can impair transparency and some physical properties, contents are relatively low yet. In any case, this certainly represents a more sustainable option.
May I suggest that it is simply a matter of cost. I doubt if any of the quoted alternatives would be anywhere near as cheap.
Dear David Oulton , I believe you are absolutely right. As long as the virgin PET is so cheap recycling cannot become economically feasible. That is why we should opt for the most cost efficient route to recycle the PET. I'm convinced that the most cost efficient route is also the one that keeps as much as possible of the added value that the scrapped textiles represents. Finally, we (Azadeh Soroudi ) and I have identified a route to rejuvenate polyester by raising its molar mass, which should have potential to enable re-meltspinning. This is commercially accomplished by SSP of PET bottles today but we cannot find that it has been utilized for textile waste. Have you?
Thanks Azadeh Soroudi for sharing this article. We are (Worn Again Technologies Ltd, UK) working on textile to textile and bottle to textile recycling. Our ground breaking recycling technology is promising so we are confident that the textile grade virgin PET from textile waste can be commercially produced in the near future!!.
Thanks
Raj
Just to add a "bio-perspective" to this interesting discussion:
the French company Carbios has just announced that they plan to use 42 million tons/year of used polyester textile fibers to produce PET bottles:
https://www.usinenouvelle.com/editorial/premiere-mondiale-carbios-transforme-le-textile-en-bouteilles-a-saint-beauzire.N1030134 (only in French)
Thanks for the link Cristiano Varrone. Do you have any idea about their technology? They must somehow raise the IV of the PET.
They are working with enzyme technology.
In particular, they have engineered a (LCC) cutinase to make it more thermostable and are now able to operate at temperatures close to the glass transition of PET, thus facilitating the enzymatic hydrolysis.
They describe the technology in a paper published in Nature :
Tournier et al., (2020). An engineered PET depolymerase to break down and recycle plastic bottles.
Link: https://www.nature.com/articles/s41586-020-2149-4
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