MANUFACTURING & MATERIALS INNOVATION

18 WORLD FOOTWEAR | MAY/JUNE 2015

Future of footwearrecyclingT

he world’s first footwearrecycling system wasdeveloped by a team ofresearchers lead by Professor

Shahin Rahimifard at the Centre forSustainable Manufacturing andRecycling Technologies (SMART), atLoughborough University in the UK. Itwas covered in some considerabledetail in the May/June issue of WorldFootwear last year. While the systemhas proved thoroughly practical interms of technology, it needs tooperate on a large scale basis in orderto become commercially viable. Theteam’s attention during the pasttwelve months has therefore been onidentifying what would be required to

do this and what actions to take.As a brief reminder as to what is

involved, this footwear recyclingsystem is able to recover differentmaterial streams from footwearincluding leather, foam, rubber,plastics, and textiles by using variousfragmentation and separationprocesses including granulation, air-based, density-based and size-basedsystems. It currently recoversmaterials that are considered to be‘down-cycled’ and only suitable forlow value applications such asinsulation, construction and surfacingmaterials. Higher quality and purity ofmaterials can be achieved throughrepetition of fragmentation and

separation processes, but thisincreases throughput time and hencethe overall cost of recycling.Researchers at SMART are now

looking at ways of increasing thequality of the recovered materials frompost-consumer products, thusimproving the commercial viability offootwear recycling. This work, inaddition to improving the recyclingtechnologies themselves, is alsofocusing on challenges in earlierstages of product life cycle such asactual design, material preparationand production, based on a proactiveapproach, to reduce the effortsrequired to recycle the footwearproducts at the end of their lives.

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ELIMINATING THE USE OFMETALMetal removal is the most complex

stage of the footwear recyclingprocess. The frequent heavyencapsulation of metal componentswithin the footwear itself means thatautomatic detection mechanisms canoften fail and, as a result, theundetected metal fragments not onlycause damage to the recyclingequipment itself but also severely limitthe application options for theresulting recycled materials. Metalremoval is currently carried outmanually due to the difficultiesassociated with automated processes.This manual recycling is not onlyarduous and hazardous, but alsoincurs high labour costs thus making itunsuitable for the large-scale recyclingof footwear needed to make itcommercially viable.The SMART research team is

therefore actively promoting the totalelimination of metal components in

footwear production and investigatingthe potential of substitute materials,such as carbon-fibre composites,reinforced plastics and fibre reinforcedplastics. Although the metalsubstitutes currently available presenta number of challenges in terms ofmeeting the functional requirementsnecessary such as stiffness andrigidity, decorative and aestheticappearances, these are not seen asbeing insurmountable.

DESIGN FOR RECYCLINGThe innovative ‘Design for

Recycling’ tool produced byresearchers at the Centre for SMARTpredicts the level of materialseparation that would occur during theend of life recycling process based ona pre-selected combination of materialmix. This is achieved throughmodelling the interaction betweenvarious waste materials based on theirspecific characteristics (e.g. densityand terminal velocity) and

consideration for a range of potentialapplications for material reuse. Usingthis information, footwear designersare able to identify and choose themost suitable combination ofmaterials that would reduce therecycling effort needed and improvethe quality of recycled materialsobtained.

MIXED PRODUCTRECYCLINGA substantial proportion of the cost

of footwear recycling is incurred bythe collection and sorting of usedshoes. Within urban areas and largecities, the amount of footwear wastecollected as a feedstock for a potentialrecycling system is great enough tojustify the set-up and operational costsof a recycling facility. However, inother areas where the level offeedstock required to make theprocess economically viable does notexist, collecting and recycling otherend-of-life products with a similar

19MAY/JUNE 2015 | www.footwearbiz.com

MANUFACTURING & MATERIALS INNOVATION

Footwear recycling line at the Centre for SMART.ALL CREDITS: SMART

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20 WORLD FOOTWEAR | MAY/JUNE 2015

Density range of common footwear materials

Leather

PU - cellular

Thermoplastic rubber - compact

EVA

PVC - compact

Vulcanised rubber - compact

Resin rubber

Thermoplastic PU - cellular

Thermoplastic PU - compact

PU - compact

PVC - cellular

Thermoplastic rubber - cellular

Vulcanised rubber - cellular

Crepe rubber

Density kg/m3

Mat

eria

l

0.0 0.5 1.0 1.5

End-of-Life footwear decision support tool.

Typical metallic items found in footwear. Steel shanks moulded into soles are particularly difficult to extract.

Density range of common footwear materials.

materials content to footwear could be worth considering.In this context, SMART researcher Tegan Pringle is

investigating a novel solution referred to as RRS(Reconfigurable Recycling Systems) in which a range ofused products with similar material content can beprocessed. These systems utilise a series of ‘plug and play’interchangeable processes to provide flexibility to therecycling line and have the ability to switch off a process orre-direct waste flow automatically depending on the natureof the products being recycled. This, for example, allows leather footwear to be recycled

on the same line as leather apparel and other leatherluxury goods such as handbags, briefcases, wallets, pursesand travelling bags. Whereas these items may require aslightly different set of recycling processes in order toprovide good material recovery yields, the significantincrease in the scale of waste being processed wouldimprove long-term economic sustainability.SMART’s view is that if we want to embed sustainability

considerations across the value chain for the production

and consumption of footwear, the way products, servicesand businesses are designed and delivered needs to bechanged. This, in turn, will require such considerations tobe systematically and purposefully incorporated withinexisting practice at every stage of a product’s life cycle.As part of an on-going global programme referred to as

‘Global Leather Recovery’, the researchers atLoughborough are engaging with various stakeholderswithin the footwear value chain in order to develop anoverall consensus for future R&D initiatives that could helpto make footwear recycling an accepted and commerciallyviable practice. Those involved so far include footwearmanufacturers and retailers, chemical producers andtanners, as well as designers and consumers. Indeed,SMART would welcome additional input from anyone elsewho might be interested. Professor Rahimifard is keen to stress that such long-

term aspirations and strategies for improving therecyclability of footwear products require globalacceptance and implementation if they are to succeed.

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