What happens when tyres wear down?

We all know tyres wear down, but never stop to consider where they go. Tyres wear out from friction every time we brake, accelerate or turn a corner. The particles become airborne affecting our lungs. More are swept into our waterways and oceans eventually entering our food chain. In fact, tyre wear emissions account for nearly half of PM 2.5 emission from road transport and are the second-largest microplastic pollutant in our ocean after single-use plastic.

An electric future

Electric vehicles (EV's) and stringent regulations will lower tailpipe emissions in the future. As EV’s are heavier than gas vehicles because of their battery, studies have shown that tyres would wear at a faster rate, increasing tyre wear emissions from 7 kilotonnes in 2015 to nearly 10 kilotonnes by 2030 in the UK. As we transition to EVs, it is crucial to consider the implications of tyre wear, so we are not replacing one pollution source with another. 

Carbon in rubber particles are positively charged as they fly off of the tyre. What started off with rubbing a balloon against a sweater, eventually led to our device that directs and collects charged particles with electrostatics as a guiding principle. Currently, our device collects 60% of all airborne particles. The device is positioned close to where the tyre meets the road. Working with the Imperial Department of Aeronautics we identified this position, to take advantage of airflow and Magnus effect of the spinning wheel.

Closing the Loop

With an aim to create a closed-loop model after collection, these fragments are separated using simple techniques. Particles under 50 microns are small enough to be reused in new tyre walls, and other exciting applications.

Exhibitions

Dutch Design Week 2020
Imperial Lates: Future Commuter 2020, London
Material Driven, Architects@Work, Bilbao
RO Guiltless Plastics Prize Finalist, Milan

Team

Hugo Richardson
Hanson Cheng
Siobhan Anderson

Press

The Evening Standard
BBC Naked Scientists
Designboom
edie.net
Air Quality News
Springwise
Imperial College London
New Atlas
Envirotec Magazine
European Rubber Journal
Energy Live News

We explored various methods like vacuuming and adhesives but our discovery started with an observation—rubbing a balloon against a sweater and watching shaved tyre particles dance. This led us to hypothesise that the rubber itself was charged and that we could use electrostatics to capture it. 

To test our theory we built a rig, spinning a bike wheel against a sprung road to mimic a tyre skidding. Our early prototypes were built in card, foamboard and copper, experimenting with various typologies and configurations of charged plates to maximize surface area and collection efficiency. 

Initially powered by an external power source, we also tested batteries and built our own Van de Graaff generator.
Since the particles are pre-charged we only require a single array of electrostatic plates powered directly from a dynamo, stepping up the voltage as required. 

To validate this problem in the context of London we collected road-sediment samples from different locations and identified a significant presence of tyre wear. To visualise the problem, we tracked TFL busses in realtime and calculated that a single bus produces 336g of tyre wear per day, a pile the size of a grapefruit.