Plugs over filters: stopping microplastic fibre release at its source

Synthetic fabrics continuously shed microplastic fibres into our water systems. Today, remediation is the name of the game. But targeting the symptoms doesn’t cure the disease - we need to eliminate the release of microplastic fibres altogether. Which begs the question, why do they shed at all?
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Plugs over filters: stopping microplastic fibre release at its source
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In 2022 I purchased my first house and was immediately inundated by a host of small issues. A portion of my water pipes were lead. The weatherstripping underneath my backdoor was eroded away. A sink in the basement was cracked. At around the same time I was diagnosed with dyshidrotic eczema, an incurable but mild skin irritation on my palms managed with topical steroids. Both life events made me acutely aware of the difference between palliative and curative solutions. My eczema has no cure and I’ll be treating it for the rest of my life. My house troubles, however, presented a choice. Do I fix the problem or treat the symptom? Lead filters are economical and easy to install, whereas replacing plumbing is expensive, time consuming, and requires a City of Toronto formal application. In the end I chose the best solutions for my family and our future, weighing the cost, impact, and risks of both alternatives.

Today, the shedding of microplastic fibres (MPFs) from synthetic fabrics is viewed by the textile industry much like my eczema: it’s incurable, so palliative care is the only viable option. Worldwide this has come in the form of legally mandated washing machine filters that can capture the  MPFs released during laundering1. In environmental engineering lingo this is an end-of-pipe solution that mitigates the emissions through their capture, much like a diesel particulate filter in the exhaust pipe of an internal combustion engine vehicle. And these are not well-established mandates; they’ll come into effect in the near future. But also much like my eczema, I really wish there was a cure rather than a symptom-suppressing solution. I’m still waiting on the world’s medical researchers to pull through, but luckily for the textile industry, Dr. Sudip Lahiri joined my group back in 2021.

Sudip brought the issue of MPF release to my attention, with the key idea of using a fabric coating to try and eliminate the problem. Not fix. But prevent. Antiquate. Cure. This began by questioning why MPFs are released from textiles in the first place. We hypothesized that, as the fibres rub against one another or the body or a laundry machine, they slowly erode away. This led us towards tribology, i.e. the study of interacting surfaces in relative motion. Tribology encompasses the study of wear, friction, and lubrication, and is useful both in understanding how to make things grip and how to design slippery interfaces. We targeted the latter.

Much to our surprise, the evidence connecting fibre friction with MPF release was lacking. Despite this, we pressed on with the simple goal of developing a fabric coating that would reduce fibre friction. We started with nylon. For the past few years my group has been developing replacements for perfluoroalkylated substances2, and had formulated a promising coating for nylon based around my favourite polymer, polydimethylsiloxane (PDMS). Quite unrelatedly, we had recently shown that this coating exhibits low friction in a study aimed to aid in the exploration for extraterrestrial life3. Sudip suggested we apply this low-friction PDMS coating to nylon to see if the reduction in friction could have a positive effect on the release of microplastic fibres. It did not.

Collected microplastic fibres from a nylon fabric

Likely every good study starts with a failed experiment, and ours was no different. While we could deposit the low-friction PDMS onto nylon, the mere act of washing the fabric (in order to evaluate how many MPFs are shed) was sufficient to remove the coating. Sudip then had the brilliant idea to mimic how permanent textile dying is achieved, to strongly tether the coating to the fabric using ionic bonding. This would require an intermediary layer to connect the functional coating with the synthetic fibre, akin to a primer layer applied to help adhere paint to a wall. Sudip developed such a primer for nylon that enabled us to robustly attach our low-friction PDMS to the fabric. The result? A 93% reduction in MPF release, even after many repeated laundering cycles. Further, the coating did not negatively impact the nylon fabric’s other properties; its hydrophobicity, air permeability, and flexibility were retained when coated. So it worked. But did it work for the right reason?

SEM of microplastic fibres filtered from wash water

Around that time, one of my senior doctoral students, Sonia, took an interest in tribology and the measurement of friction. Sonia found a way to measure the friction between nylon and itself (mimicking nylon fibres rubbing against one another), and she expanded this to also include coated nylon. Armed with this capability, Sonia conclusively showed that our PDMS coating was indeed reducing the friction of a nylon/nylon interface, by almost four times. Most insightfully, when we measured the friction of coated nylon without Sudip’s primer layer, the initially low friction gradually increased over the course of the measurement, ending up at a value consistent with uncoated nylon. Sonia and Sudip’s story was gaining clarity. When the low-friction coating was not durably adhered to the fabric, it could easily be removed even when rubbing itself. This explained why a primerless coating shed the same number of microfibres as an uncoated fabric, and also why things like fabric softeners (which lessen fibre/fibre friction) cannot solve the microplastic fibre crisis.

So, what’s next? Well, we’ve got nylon pinned down, so onto polyester. And then spandex and then fibre blends. And PDMS isn’t the only low-friction material on the market. Overall, while end-of-pipe, palliative solutions can capture MPFs once shed, what the world really needs are curative solutions that prevent their release altogether. We need to plug the leak, not filter the fragments. Durably reducing fibre friction is key, and will enable a sustainable synthetic textile industry that erodes neither our conscience nor our garments in the years to come.

This work was conducted at the University of Toronto, on the traditional land of the Huron-Wendat, the Seneca, and the Mississauga of the Credit. Any and all questions should be sent to the study’s lead author, Dr. Sudip Lahiri (sudip.lahiri@utoronto.ca), or me, his supervisor, Prof. Kevin Golovin (kevin.golovin@utoronto.ca).

  1. Erdle, L. M., Nouri Parto, D., Sweetnam, D. & Rochman, C. M. Washing Machine Filters Reduce Microfiber Emissions: Evidence From a Community-Scale Pilot in Parry Sound, Ontario. Front. Mar. Sci.8, 1–9 (2021).
  2. Shabanian, S., Khatir, B., Nisar, A. & Golovin, K. Rational design of perfluorocarbon-free oleophobic textiles. Nat. Sustain. 3, 1059–1066 (2020).
  3. Golovin, K., Khatir, B., Recla, L., Azimi Dijvejin, Z. & Zhao, X. Polydimethylsiloxane brushes and the search for extraterrestrial life. Surf. Topogr. Metrol. Prop. (2022).

 

 

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