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Making fly-leather

Published: 13th Jan 2022
Author: H Proctor

The product called E-Leather by the company that makes it (it stands for 'leather evolved' or 'engineered leather' - really?) or Fly Leather by Nike, is one of the synthetic products which incorporates leather waste. But the claim that it is therefore more environmentally acceptable than leather doesn't hold up.

Figure 1. Schematic representation of part of the hydroentangled composite materials.

How did the UK trading standards ever approve the names E-leather and fly-leather, considering that the word “leather” is carefully controlled? Quite simply, if no-one raises objections at the time of registration, or if no-one can raise the funding needed to take on big companies in court for infringing your copyright and trademarks. Finally, if the term doesn’t get broad protection under the eyes of the law, then people looking to mislead consumers will exploit legal loopholes as much as they can. Leathers sells – copy it, mislead people about it, and the profits will follow.
Why isn’t it called leather board? It is fundamentally flexible and it isn’t the simple paste together technology that older leather board processes are. It's a low-cost material that makes it into buses, cars, aeroplanes, and the big shoe brands know full well that it is not genuine leather. A bonus is that it uses unwanted leather waste.  
“Waste” is an important point here, because in life-cycle analysis, the protocols do not allow allocation of historical carbon onto wastes - only main products and co-products need to take on footprint from the upstream processes. This means that these “reconstituted" waste-stream products have very low environmental footprints. These products have low footprints as their production impacts are the only things that are considered, up until the supplying tannery begins to take the waste through an end-of-waste scenario – making it a co-product or main product.
The shavings, generally wet-blue shavings, are received from the tannery looking to get rid of their solid waste. The shavings must be processed to get a uniform fibre size that will range anything from 1 mm to 6mm long. The processing of the shavings is then performed to produce a flexible sheet as follows (B&H, 2005):
1. Leather fibres of consistent size are mixed with synthetic fibres (that have meltable layers – outer layers that have low melting point).
2. The mix is then sandwiched between two layers of tissue.
3. The layers are then heated to melt the outer layers of the synthetic fibres to cause the material to fuse (at their intersection points).
4. The fused layers can be transported or stored until needed (Generally stored on a roll).
5. The layers are then placed into the machine that will do the hydroentanglement – during which water jets at high pressure are directed at the fibres to cause entanglement of the fibres. 
6. Multiple passes may be required to optimise the entanglement.
7. The material may show lines after the jets are used, so the entanglement could be repeated when a diffusing screen is used in between the jets and the material itself.
This method has most likely been refined and perfected since then, but it portrays the basic mechanism as to how this technology is carried out. With 5 years of protection left on this patent, it is unlikely that the current licensees of this technology will be using the process outlined above (they are about to lose those restrictions on their technology). Developers of the next generation of materials that are based on this will be using the above process as a starting point.
Figure 1. Schematic representation of part of the hydroentangled composite materials.
Figure 1 then shows the equipment required to get the hydroentanglement. Two further tissues and the fused materials move from the right to the left through the Jetstream. The porous conveyor belt with vacuum suction allows some water to pass through. Fibre and water are collected above the conveyor for recycling.
Finishing or coating
Coatings, or additional layers of synthetic webbing can be applied (as seen Figure 1, left) as needed. The top coating can be applied by roll coating or spray methods to give a top finish that looks and feels like leather. The surface after entanglement will be rough, unfinished, and hard to associate with leather. Like with nubuck or suede, a finisher needs to use a pre-ground or ground coat to seal off the surface layers and start to stick that nap down.
The coats are applied, usually polyurethanes or combinations of polymers, fillers, handle modifiers, gloss modifiers, and colourants. These finishes are built up, with texturization, e.g., embossing or plating, in between.
Some of the claims that are associated with these materials are strong and some of them are weak. Claims that are strong include:  that they have low impacts when compared with leather – until the leather industry starts to take its wastes through an end-of-waste procedure that reclassifies the waste as a co-product. Another strong claim is that they are lightweight when compared with leather. They are reinforced, so can be thinner, and are obviously quite synthetic, so can get away without denser collagen fibres.
Weak claims include that they are leather. Of course, they do not satisfy any of the conditions of leather: largely intact (no bueno), not reconstituted (no), from an animal (yes, in part) and are tanned to render them imputrescible. So as the material is reconstituted and not completely of animal origin it cannot be called leather.
The recycling claim is more complicated. Many of the companies marketing these materials claim it is recycled. They even have recycling certification from Textile Exchange – the so-called Recycled Claim Standard. One first must consider what recycling means to the average user – a material is taken into a circular economy and is cycled (forever!). Like a biodegradable leather being looped through the composting process, soils, plants, cows, leather…forever. These “engineered” materials, composites if you will, are upcycled from leather waste into sheets – that are never taken back to these factories to be used in the next iteration. These are the opposite of the circular economy, greenwashed, linear economies. 
To get the full support of consumers going forward, these companies should develop a circular model that takes their existing products back into the factory for shredding and reconstitution. Everyone knows this is complicated though because they are synthetic blends that are coated, coloured, and are tailored for high performance, such that technosphere recycling is very difficult. Pity.

B&H Research. 2005. Formation of Leather Sheet Material using Hydroentanglement. Authors: Bevan, C. and Quest, B. International Patent - WO 2005/118932. 15 December 2005. 

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