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Biodegradable Finishes

Rapid development is taking place in the mainstream leather-making processes to ensure that the future of processing will be two-tiered.


· Tier 1

The first tier is the exploitation of a unique feature of leather that lies at the heart of the tanning process: “Tanning renders a material imputrescible,” thus safe-guarding the main reason that most people own a leather article, such as a bag, a pair of shoes, a leather belt, or they sit on a leather car seat. A long-lived article that can serve to displace single-use or consumption-based products repeatedly and end up being more sustainable in the long-run.


· Tier 2

The second tier is the “fast fashion” or products that have a short life-cycle, usually ending with them being disposed of after one or two uses. It was always viewed as a business model that is unsustainable and relied on a commodity product that was cheap to produce.


The “Blue Planet” effect is currently having a major effect on consumer choice, with discerning buyers avoiding single use plastics and a “throw-away” culture. Many manufacturers are looking at towards the Tier 1 long-lived items as the “get-out-jail” card. Deep thinkers look at the lower growth model associated with Tier 1 products and realise that the long-lived items will be a fad as it disregards the need for fashion, and the fact that an item that sells every 10 years is a corporate recipe to bankruptcy. All modern economies rely on a steady trickle of manufactured products from the retailers and the focus of fast-fashion items should centre on environmental sustainability that looks at cradle-to-cradle or cradle-to-grave strategies.


Many people focus on the ethically superior cradle-to-cradle strategy that with snooty air looks down on products that are destined to landfill. That is, until two recent developments show that cradle-to-grave may be just as sustainable. No one is doubting that cradle-to-landfill is unsustainable, but what about cradle-to-compost or cradle-to-energy?


In 2015, the European end-of-life vehicle directive tightened its targets from 85% of the car having to be reused or recycled, to 95% (of which 10% can be energy from waste). For some users this will be a maintenance of the status quo, but for other automakers this has meant a chance to improve those last products performances. Much press has been made about car makers who are heading for biodegradable leathers.

Leathers will degrade given enough time. Tanners who are well studied, know that oil and aldehyde tannages perform the best, metals second, and vegetable tanned materials last in the biodegradable all-stars trials. This research should be repeated ad nauseum, until we know these results are definitive, repeatable, and under what conditions this order could change. Currently, the biodegradability (read composting ability) test is performed using a plastic film standard method and consists of placing a defined weight of leather into a defined compost mixture and measuring its weight change and appearance over 45-90 days.


Finish residue

By-in-large, the only remaining vestige of many modern leathers, left in the compost box, is the leather finish. Finishes have slowly progressed from very natural finishes – that had relatively low endurance – to modern finishes that are focussed on synthetic polymers that can be cross-linked for increasing resistance to destruction. Ultimately the resistance to destruction also means the inability to be broken down in compost.


Figure 1. The test for biodegradability of leather and finish entails placing the leather into a controlled composting scenario.


Plastic eating bacteria have been found, as have plastic eating insects. These vectors could be used as agents in the increased composting ability of systems that could degrade all the leather components, no matter how synthetic their make-up. Leather research into tanning methods, however, focusses on the minimal quantity needed in the leather to ensure the resistance of the leather during its working life and then the ability of that leather to degrade in a “grave” scenario.


New finishes

In 2005 and 2006, a European project was launched looking at the biodegradability of shoe tanning and finishes. The finishes were what the project eventually focussed on and the types of finishes examined were as follows: soluble collagen/gelatin, keratin, chitosan, zein, chitin, and casein. Protein finishes have been around since vegetable tannages were used by the Egyptians and were often used to decorate the leathers with colour and décor.


The basis of protein finishes, that is, the ability to dissolve a protein in water and apply it to the leather surface has ultimately been its weakness. If you can dissolve it in water to apply, then it will be easy to remove with adding a little water later. To get around that weakness, tanners have used the fact that cross-linkers can make a protein insoluble and resistant to rewetting. There are other disadvantages of using proteins, they generally have high gloss, can be vulnerable to darkening when polished or glazed, or could not bind non-film chemicals as effectively as other film formers.


The realm of biodegradable films is not restricted to proteins, plastics such as poly-3-hydroxybutyrate (PHB), polyhydroxyvalerate (PHV) and polyhydroxyhexanoate (PHH). These bioplastics are often formed as by-products of large scale biotechnology fermentations, such as vitamin production. Polylactic acid (PLA), polybutylene succinate (PBS), polycaprolactone (PCL) and the starch derivatives are all technologies the leather industry have never looked at, let alone tested.


Figure 2. A protein based biodegradable aniline finish in development.


Conclusion

Well poised to lead by example, the Southern African industry with its history of protecting wildlife, natural heritage, and a leather industry that has always had a good track record of protecting the environment. The international community are exploring all alternatives to develop biodegradable leathers and finishes. With a very healthy biotechnology industry, the production of bioplastics in South Africa could very well lead the nation into unique leather areas.

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