An air-based automated materials recycling system for postconsumer footwear products

The increased option of cheap produced in higher quantities goods, coupled with quickly changing consumer fashion trends has resulted in a sharp upsurge in the consumption of products in many industrial sectors. The worldwide per capita usage of shoes has elevated significantly, from 1 footwear per 12 months for every person in the global globe in 1950 to almost 2.6 pairs of shoes in 2005. In the EU, it is estimated that the amount of waste due to postconsumer shoes could reach 1.2 million tonnes each year. The vision of ‘Zero Waste materials to Landfill’ thus remains among the main issues of 21st century for the footwear sector. This target is very ambitious as presently less than 5% from the 20 billion pairs of shoes produced worldwide every year are recycled or reused. However, increased raw materials costs, producer-responsibility issues and forthcoming environmental legislations are anticipated to challenge what sort of footwear industry deals with its end-of-life products.

It really is argued that in many situations, materials recycling is seen as the utmost suitable means of dealing with discarded sneakers. However, for long-term sustainability of such footwear recovery activities an viable material recycling system should be established economically. In the automotive and electric/digital industries, where European Producer Responsibility directives, such as the End-of-life Vehicles directive and the Waste materials Electronic and Electrical Equipment directive have already been presented, a number of materials recycling value chains have now been founded. This has been feasible because these products typical contain a large percentage of very easily recoverable metallic components to facilitate an economically lasting value chain. However, footwear products include a large combination of materials typically, such as rubbers, polymers, leather and textiles which have low recycled value relatively.

Therefore understanding and developing methods for footwear recycling is of main concern towards the footwear sector and this paper will discuss the introduction of an automated material recycling system for blended postconsumer footwear waste. The first part of the paper begins by introducing the many EoL choices for footwear and outlines the problems of EoL shoes recycling. The paper represents the recycling approach that is developed then, provides a basic economic analysis and outlines some potential applications for recovered materials. The later part of the paper after that presents the outcomes of experimental research with three common forms of footwear products. Further work is certainly discussed and conclusions are drawn finally.

As discussed by Staikos and Rahimifard there are four main EoL options that can be considered for postconsumer footwear products, seeing that illustrated in Fig. 1, they are: landfill, incineration/gasification, recycling and reuse. For each from the EoL choices there are many environmental impacts, economic benefits and specialized requirements that must be considered.

Land-filling is definitely the most undesirable choice, due to the obvious bad environmental effect, depletion of assets, increasing landfill fees and in a few countries the limited option of landfill space. Incineration is still considered a controversial technology with environmental worries over the discharge of polluting emissions. Reuse entails the assortment of put on or undesirable shoes or boots for distribution primarily within developing countries. Charitable organisations such as the Salvation Army Trading Company Ltd. (SATCOL) and Oxfam, as well as local specialists and municipalities are the primary supporters of reuse plans in the united kingdom. However, it really is argued that because the economic power of developing nations grows the demand for second hand shoes may begin to fall. Furthermore, not all shoes which are collected could be reused, because of the poor circumstances, and in such circumstances material recycling sometimes appears as the most suitable option.

Nike happens to be the only shoes manufacturer which is engaged in postconsumer shoes recycling on the commercial range. Their scheme has been labelled the Nike ‘reuse-a-shoe’ program and provides been created to recycle put on and defective shoes. Customers can return any brand of unwanted shoes via Nike's world-wide network of collection points placed within retail stores. The collected sneakers end up in one of two central recycling plants - in america or in Belgium. In these plant life the sneakers are shredded and subjected to some mechanical recycling processes to separate them into three materials channels: Nike Nike Fluff, Nike Foam and Grind. These components are then useful for different sports activities related applications such as for example running track underlay, playground basketball and surfacing court underlay. The Nike ‘reuse-a-shoe’ scheme has been operating for over a decade and Nike promises to get recycled around 25 million pairs of sneakers to date. Nevertheless, the scheme isn't designed to cope with the recycling of various other nonathletic sorts of postconsumer shoes waste. Therefore, a far more common recycling approach as outlined in this paper must deal with various types and varieties of footwear products.

Postconsumer footwear products certainly are a largely untapped commodity with a substantial prospect of recycling. This highlights environmentally friendly and economic benefit that may double screw extruder be extracted from establishing a sustainable shoe recycling chain. However, current materials recycling facilities and operators are either incapable of dealing with the precise material blend in shoes products or do not provide the best method of recovering optimum value from postconsumer shoes waste. Among the major requirements for establishing sustainable recycling procedures inside the shoes sector is to investigate suitable recycling procedures to successfully independent postconsumer shoes into well-defined mono-fraction material streams. The evaluation of varied postconsumer shoe waste has nevertheless shown the material recycling of combined footwear products can be an incredibly challenging problem. There are two particular issues that present a significant challenge to materials recycling of sneakers, namely the varied range of footwear types with various construction methods and the significant number of different materials used.

The footwear industry employs a multitude of materials to make a diverse selection of different types and styles of shoes. Based on Weib there are around 40 different materials used in the developing of a shoe. Leather, rubber, foam, textile and plastics are between the simple materials most found in footwear manufacture generally, with each materials possessing its specific characteristics. There are also many metallic elements present in footwear products. These include noticeable metallic parts, such as for example metal eyelets, buckles and decorative components and various other metallic elements which are inserted in the footwear for structural purposes frequently, such as metal metallic back heel supports, shanks and steel toe caps. The removal of these steel parts presents a substantial task for the material recycling of footwear - the metals tend to be present as a small percentage of the total shoe by weight and are generally extremely entangled with additional elements and materials. At their easiest, shoes are made up of as few as two parts per pair, for example flip-flops, with foam lone and rubber strap, or can be complicated constructions with 60 or even more elements per pair, such as for example in many modern sports shoes. Nevertheless, most can be described as using a subset of parts and parts that are generally common to all varieties of shoe. These include; higher parts, lower parts and grindery products. A typical footwear product is going to be assembled from a number of elements using a variety of becoming a member of systems, such as gluing, moulding and stitching. Previous analysis shows that because of the difficulty of footwear design and structure it is theoretically difficult and frustrating to manually disassemble and distinct footwear products into usable recycled material channels. It is argued that because of the relatively low material values manual processing in this manner would not become an economically lasting activity for huge scale footwear recycling. Furthermore to full manual disassembly, the authors also have explored the semi-automated parting of shoes components based on slicing or pulling/tearing. However, due to the huge range of shoes designs and sizes these strategies have had only limited achievement with particular sub-categories of shoes. Thus these technology are not considered suitable for the top scale processing of the numerous tonnes of mixed shoes waste currently delivered to landfill.

The complex materials mixture of modern shoes and the wide variety of construction techniques used necessitates the usage of an automated recycling process, based upon feasible and commercially viable recycling technologies technologically. Such highly mechanised recycling systems are currently employed by various other industries because the primary means of recycling end-of-life products in an economically sustainable manner. Recycling products this way generally entails shredding or granulation, such that the product can be split into different parts and/or materials types. After fragmentation following parting machines exploit the distinctions in material properties to supply automated parting into different material streams. Generally speaking these technologies are effective for separating materials such as metal and plastic which have distinctly different properties. However, problems arise when attempting to separate materials with similar properties often, such as the different types of rubbers and polymers that are commonly within footwear products.

Recycling technologies considered to be technically and economically simple for footwear products consist of: shredding and granulation technology; air-based separation products; liquid-based density separation; and, for recovery from the metallic components, eddy and magnetic current separation and basic sensor based ‘detect and eject’ chutes. Other commercially obtainable recycling technologies such as for example electrostatic parting devices and advanced sensor centered sorters are also considered for footwear recycling. However, there has to be further research into the technical and economic feasibility of such recycling technology for mixed shoes products. At the moment materials separation based upon particle size and fat is just about the most cost-effective, high-capacity process that may be used to automate the parting of footwear waste with an commercial scale. A recycling system based upon fragmentation and air-based separation technologies has hence been developed for the material recovery of shoes products. The procedure is layed out in Fig. 3 and has been designed to process the vast majority of footwear types and styles we.e. sports activities shoes and boots and leather based shoes and boots with rubber soles. In the process you can find three main actions, these are: sorting, metallic removal and material parting. Experimental studies possess derived the typical mass balance and purity of the primary recoverable material fractions.

It is envisaged a business footwear recycling system includes a sorting stage to split up shoes or boots into different groups that will then end up being processed in batches. In this manner the yield and purity of the target material types could be improved. For example, to reclaim foam components in the correct manner shoes that have high foam content material, such as sports shoes, should be recycled from leather based shoes separately. It is because the parting of low density foams from leathers exists a significant problem with the proposed air-based systems.

There are many options which are currently being considered for removing the metallic parts in postconsumer footwear waste. The very first involves removing metal using a manual removal procedure. For example, shoes and boots could be pre-shredded to expose the inserted metal parts, which would then end up being sent to a selecting line for manual sorting and removal of metallic products. However, initial experimentation shows that depending upon the labour cost this manual intervention may not be an economical sustainable activity.

The next option is mechanical separation using specialist metallic separation equipment i.e. shredding followed by induction sensor based, eddy current and magnetic‘detect and ejects’ chutes. When processing metal parts, losing is generally required because granulators tend to be unable to process metals without incurring economically unsustainable use and damage. The shredding procedure does needless to say add further price and intricacy towards the shoes recycling process plan.

Initial experiments have already been conducted with an over-band magnetic separator during shredding trials with commercially available equipment. Although no complete analysis from the separation was conducted, preliminary visual inspection of the waste streams showed great recovery of the ferrous metals when shoes had been shredded to 20-30 mm. As shoes contain both ferrous and non-ferrous metals there will be a certain percentage of non-ferrous metals still present after magnetic separation. A following parting stage is definitely consequently needed to remove these non-magnetic metal particles. This may be finished with an eddy current separator - nevertheless, it really is argued that these separators usually do not supply the most technically or economically feasible means to remove the little percentages of non-ferrous metals present in the waste stream. A cheap means to split the rest of the metals after magnetic parting is to use a sensor structured ‘detect and eject’ chute such as those employed to protect plastic process equipment from international metals parts. However, with this technology, a certain amount of additional material will be ejected combined with the metal parts, which may decrease the overall yield of recycled components.

Aside from specialised metallic parting processes there are other technologies that might be used to remove the metallic parts from shredded footwear waste. Initial tests using a simple sink-float liquid1 based density parting process have tested that it's possible to effectively individual metals from rubber/foam/leather and high light the potential of using a commercial dense media separator like a hydrocyclone to eliminate the metallic content material within shredded footwear waste materials.

However, there are still concerns over the technical feasibility of removing all metallic quite happy with the above mentioned technologies completely. As steel contaminants can reduce the worth of the other recycled components considerably, it is argued that there surely is a dependence on the reduction or even removal of metallic parts at the shoes design stage.

The next stage of separation aims to liberate rubber granulates in the PU and EVA based foams from sports shoes, or for leather based shoes the rubber from leather. A suitable means to provide this separation is really a vibrating air-table. As depicted in Fig. 4b, the air-table uses atmosphere and vibration to split up the heavier rubber that goes up the table through the lighter material that stratifies on top and slides down the desk. Parting performance is definitely highly dependent upon optimisation of various process variables, which include: the position of the vibrating deck; the vibration frequency; the fresh air speed; and the top characteristics from the deck. To ensure maximum separation effectiveness the authors are suffering from a customised air-table that has been specifically made and optimised for the separation of the granulated rubber from foam and leather components in footwear products.

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