Some twenty billion pairs of shoes are made each year globally and most are destined ultimately for the municipal tip. With this in mind, footwear manufacturers have turned to researchers at Loughborough University to help develop a more environmentally-friendly shoe.
Professor Shahin Rahimifard is director of Loughborough's centre for Sustainable Manufacturing and Recycling Technologies, or SMART for short. As he explains, searching for a solution also meant understanding more about the way shoes are manufactured and how best to go about separating their individual components from the outset.
Professor Shahin Rahimifard - Director of Loughborough's SMART centre [SR]
So is it possible, for example, to separate the upper from insole and then look at these individually as a source of material either for reusing or recycling. This proved to be economically not viable so for a more economically sustainable option we considered this automated system based on fragmentation and separation processes.
In other words, after manually sorting the shoes into their various types, the system uses mechanical shredders to literally slash the shoes into smaller fragments, sorting the results automatically.
Typically the separation processes are based on density of the material and there you have things like vibrating tables or you have air separators; you've got air cyclones, you've got air zigzag separators. They kind of exploit the density and the size of the particle to separate the waste particles from one another. The air cyclones used to extract all of the very lighter particles.
After that the sorting becomes harder because materials like leather and foam barely differ in density so that the following stages took rather more design effort.
Then the particles are introduced to the zigzag separator and here you are kind of exploiting the terminal velocity of these particles, which are introduced from the top, and as they are falling down you are introducing some sort of air jet from the side where all of the lighter material are more or less taken to a different dropping zone and all of the heavier particles just fall down. The result of that then goes into a vibrating table which uses the typical process of sieving and using different mesh sizes and through the vibration you are separating the smaller particles form the bigger particles.
So Shahin, we come to the end of the line, if you like, but this is the end product that we are looking at. Just describe what we have in front of us.
Right, we have a sample of different waste particles that have been separated. So here you see all of those, what we refer to as fluffs, which were part of the fabrics, the leathers and the lighter material that came together. We have now constituted this into kind of slabs; they are kind of used as insulators within the construction industry.
Here you actually see various polymers that have been separated with similar material properties to provide the type of recycled material that you could use either in footwear manufacture or for a variety of other uses; whether it is for surfacing of playing grounds or, in fact, as an underlay for carpets which is the other use that we are making it.
Then you have examples of leathers that we've managed to achieve 85 per cent purity which is good enough for lots of applications like reconstituting it in artificial leathers and using it for handbags and in the furniture industry, car industry and so on.
Having completed their first run of recycling experiments, the team then studies the quality of the materials produced which helps them determine more accurately the cost effectiveness of the process used and which application it might be best suited for. The system was developed and tested at Loughborough University's Innovative Manufacturing and Construction Research Centre, whose ten year research programme was funded by the Engineering and Physical Sciences Research Council.
The SMART team at Loughborough, perhaps unsurprisingly, have now had huge interest from shoe manufacturers worldwide. With this in mind, Shahin Rahimifard's team is now looking at how manufacturers can design shoes to be wholly recyclable, where the idea of environmentally friendly footwear is simply the norm.
At the moment, we are going through all of these challenges of improving recycling technologies because of the poorly designed footwear when it comes to recycling. So, clearly, if we want to make future recycling more successful then we've got to think about the design of future footwear and how we can improve that to make its recycling simpler. The only way that we can sustain our lifecycle is this ability of doing more with less. I believe the shortage of resources, cost and access to resources is going to force us to do things differently in the future.