A bio-based material with unique properties
Leather, the raw material of the tanning industry, is a material recovered from another production chain: the food industry.
More specifically: leather is an ABP – Animal By-Product (under Reg. UE 1069/2009)- recovered from tanneries and transformed into a high potential material, thus avoiding disposal in landfills as waste.
Almost all of the leather harvested and processed in the world (i.e., 99%) is a by-product from the meat industry, from the supply chains of cattle, sheep, goats and pigs. None of these animals are bred and slaughtered for leather.
Leather is thus a circular, renewable, durable and biodegradable material: in short, it is sustainable and bio-based by nature. But it is too often perceived by the public as unjustifiably negative due to the ’bad legacy’ of the past and the fake news spread by ideologically opposed animal production extremists.
The term hide, on the other hand, refers to leather which, after undergoing physical, chemical and mechanical treatments – namely the tanning process (click here to learn about all the different main types of tanning) – becomes a rot-proof material that the manufacturing industry can use to produce an endless list of items, for example: footwear, leather accessories, garments, furniture products and interior design complements, car interiors, technical objects. It is a unique material in terms of both its nature and characteristics that has always been highly appreciated by consumers for its technical and sensory performance. This appreciation is a value that must be transparently protected, including from the point of view of commercial terminology (click here to learn more about correct leather terminology and the regulations in force in this regard).
Consumer choices are shifting towards increasingly less impactful materials according to the current climate and environmental context.
With this in mind, bio-based materials, i.e., materials derived from renewable sources or plant or animal biomass and which, for obvious reasons, differ from materials that are fossil-based and petroleum-derived, have gained considerable interest. One such example is synthetic materials.
Given its origin, leather is instead a bio-based material in its own right, and the analysis contained in the publication ’Material Circularity: A Novel Method for Biobased Carbon Quantification of Leather, Artificial Leather, and Trendy Alternatives” scientifically proves this. The study was published in MDPI – Coating Journals, is authored by the research company Ars Tinctoria, academics from the University of Florence, and researchers from CNR-INO and LENS. It analysed radiocarbon via SCAR spectroscopy to verify the incidence of biobased carbon in material samples (leather, synthetic and self-styled plant alternatives) to discern their composition. The range of results recognises that the naturalness of leather is higher than that of the alleged green alternatives. In tanned leather, the bio-based carbon content varies between 65% and 96% depending on the type of processing performed, unlike ’leather alternative’ materials claiming bio-based origins, where the majority component is derived from fossil sources.
Click here to view the complete study
Both bio-based and fossil-based materials are carbon-based.
There is basically no difference between carbon from biomass or from fossil sources in terms of structure; the difference between these materials is seen when they are disposed of at the end of their life.
The most widespread practice, which also affects recycled materials, is incineration, the result of which involves the emission of the carbon atoms constituting the material into the atmosphere in the form of CO2-.
Carbon dioxide (CO2) is one of the greenhouse gases (GHGs) that most contributes to global warming. Its presence in the atmosphere therefore needs to be balanced as much as possible.
For the purposes of atmospheric CO2 balance, that deriving from the incineration of bio-based materials is neutral, since it is carbon dioxide that was already present and, based on the carbon cycle, was removed from the atmosphere, trapped in plants and, through feeding, assimilated by the animal’s metabolism. Following the disposal of the material at the end of its life – in this case, the leather – the CO2 is released back into the atmosphere.
CO2 emission from disposal of high percentage bio-based materials
CO2 absorbed = CO2 generated
The CO2 from the disposal of fossil fuel-based materials, on the other hand, is extra CO2 that is released into the atmosphere: in this case, they are carbon atoms that have been enclosed in oil for millions of years and now enter the atmosphere again, increasing their concentration in the atmosphere. In other words, in the case of synthetic materials, 0% CO2 is absorbed and 100% CO2 is generated.
CO2 emission from disposal of materials from fossil sources
CO2 absorbed = 0% ; CO2 generated =100%
The inimitable characteristics of leather and its ’imitations’
Leather is composed of at least 85% collagen fibres, a fibrous protein that reacts directly with substances used in the tanning process.
The natural structure formed by these interwoven fibres determines inimitable and non-reproducible aesthetic and performance characteristics and ensures strength, durability, elasticity, flexibility and adaptability to various shapes. Not only that, it is also simultaneously breathable and insulating.
The tanning process enhances these characteristics and the leather becomes incredibly versatile, both functionally and aesthetically, making it ideal for numerous manufacturing uses.
In itself, leather combines tradition and memory of the past with a vision of a future made of natural materials that can be articulated in infinite creations with elevated performance and values that are maintained over time.
For all these reasons, there have been multiple attempts to imitate leather, but none of them replicate its performance or technical and stylistic characteristics.
The alternative to leather has historically always been synthetics, which, as highlighted above, are completely derived from fossil sources, with all the related consequences in terms of sustainability. However, in recent years a wide variety of new materials, known as ’plant-based materials,’ have also come to public attention, whose only (or almost only) slogan for calling themselves green and sustainable has been to declare themselves better than leather in one respect rather than another.
Granted that materials innovation is a key step in the transition to sustainability, almost nothing is known about most of these materials beyond the information used for superficial marketing strategies, with an absolute absence of scientifically supported arguments and transparency with respect to their peculiar technical characteristics.
On the other hand, from the perspective of sustainability, everything is known about leather, its characteristics, performance, and the tanning process.
The first proof of this can be found in the study ’Comparison of the Technical Performance of Leather, Artificial Leather, and Trendy Alternatives’ conducted by FILK (an independent German institute specialising in materials analysis) where the physical and strength properties of leather and materials presenting themselves as its alternatives were evaluated and compared.
The overall results of the study make it clear that none of these ’alternative’ materials possess all of the high performance characteristics of leather, and therefore do not actually represent a viable alternative to it.
The Tanning Process in a Nutshell
Tanning makes the raw hide rot-proof and resistant to moisture.
Depending on the tanning agents used, there are different types of production processes, which take place in drums or tanks depending on the properties of the item to be made.
The three main tanning methods are:
Chrome Tanning
About 85% of the leather produced today is chrome tanned. The process uses trivalent chromium sulphate (Cr III), a tanning agent that is nontoxic and not hazardous to health or the environment.
Misinformation about the leather industry sometimes suggests that hexavalent chromium or Chromium VI (Cr VI), an oxidation state of chromium that is carcinogenic and risky for consumers and operators, is used.
Let it be emphasised as much as possible: CHROMIUM VI IS NOT USED IN LEATHER MANUFACTURING, and well-defined and effective industry practices are in place to prevent its formation in the post-tanning stages.
The chrome tanning process is a modern, widely known and safe process that is constantly updated in order to ensure better absorption and, therefore, less use of any tanning agent -starting with chromium III – and reduced water consumption.
The best chrome tanning practices use half the chemicals required by other methods and produce water emissions below legal requirements. Advantages of this type of tanning also include the ability to completely recycle the chromium used (chromium III sulphate).
The result is there for all consumers to see: chrome tanning produces leather that makes it possible to manufacture shoes, bags, clothes and whatnot that can be used year after year without losing any of their properties.
Vegetable Tanning
Vegetable tanning is the oldest tanning method; its tanning agents are tannins extracted from the wood and nuts of trees and shrubs, which the tanning industry sources from companies that guarantee their origin from sustainable sources. Compared to chrome tanning, this method takes longer, but the result is leather with a distinctive aesthetic and a finish that ages beautifully.
The name and origin of the substances used in tanning make it easy to think that vegetable-tanned leather is more ’environmentally friendly,’ but it is important to consider the balance in the entire process to make a more meaningful comparison with other methods. For example, vegetable tanning uses less tannins – natural, sustainable and renewable raw materials – than those using chromium III. The resulting effluent, however, requires more treatment before it can be discharged.
Chrome-free and Metal-free Tanning
All other tanning methods have different names, but are usually referred to as chrome free. Chrome-free leathers are generally made for specific performance, often for automotive use. The most common is aldehyde tanning, which uses glutaraldehyde. Leathers made with this tanning agent require more chemicals after tanning to improve the properties of the leather, and for this reason the effluent from the chrome-free process requires additional treatment before it can be discharged.