BIOGENIC LEATHER

New carbon (biogenic), that is carbon that was formed in very recent history (<5700 years ago), is a bizarre concept. Nitrogen is converted to carbon in the upper atmosphere at a rate that is equal to the natural conversion of that carbon back (to nitrogen) – this is not the reason for rising carbon in the atmosphere. Rising carbon in the atmosphere is because it is coming from human based activities, especially burning fossil carbon. The amount of carbon in our atmosphere has jumped from 300 ppm to 400 ppm in less than 100 years.

The biogenic carbon being formed is useful though, it allows us to determine the age of things. We know that if a material has more new carbon than fossil carbon then it is something that was recently made - especially natural materials. Plants absorb new carbon out of the air all the time and use it to build their structure. A plant is largely new carbon as are the animals that eat them. Plants and animals can only build their bodies using new carbon that they have taken in. But where does fossil carbon come from?
Carbon that is recently formed is radioactive (it came from nitrogen so will try to get back to nitrogen). It takes a few thousand years, but it will either go back to being nitrogen or it can become just normal (good old) non-radioactive carbon. This type of carbon is typically what scientists see in coal and oil, or any other carbon form that has been around for longer than 5700 years. For example, the plants you had for dinner last night will be mostly new carbon, but old archaeological items like the Taung Child (Australopithecus africanus) which are millions of years old have had plenty of time for the carbon to change to fossil carbon. So scientists just measure the ratio of new to old carbon and that allows them to date how old something is. The principle of carbon dating can also be used to determine if a material is made from new carbon or old carbon.

Taung Child

Test methods
The two most common methods to determine the biogenic versus fossil content of materials are the ASTM D-6866 (2018) and ISO 16620-2. Not many laboratories can test this as they require specialist equipment. The tests are quite inexpensive because the test is quite fast, but the specialists needed to do the test are rare.
A sample of the material is placed in a piece of equipment that will determine the carbon and nitrogen content of the sample. Once the total carbon and nitrogen content is known then another piece of the sample can be changed into carbon and nitrogen gases and those can be separated and measured. The types of carbon and nitrogen atoms are carefully measured and a calculation is performed to determine the biogenic versus fossil carbon content.

Circular bioeconomy (vegan products and leather)
Recently, Ars Tinctoria, a laboratory in Italy, performed this analysis on a range of leathers and vegan alternatives, Carceone et al. (2023). The results were shocking, in that the extent to how much plastic was present in the leather alternatives told a more accurate story - many of them were just simply plastics. They were not even useful plastics that could be technosphere recycled back into plastics that could be infinitely looped - they were fossil carbon plastics that would be singly used. The kicker was also that many of them were marketed as being more sustainable than leather - a previous FILK report (Meyer et al., 2021) has shown that these materials do not even perform well in wear and performance testing. Now the science shows that they come from fossil origins and have poor end-of-life credentials - quite damning.

Greenhouse gases and biogenic carbon
The measurement outlined above allows the leather industry to look forward positively – work to improve the biogenic content of leathers. If the leathers are biodegradable, the gases given off will then be largely biogenic and the carbon cycle will continue with biocircular carbon. For the fossil containing materials the carbon released through combustion, degradation, or biodegradation will be fossil carbon, which will go straight into the atmosphere adding to rising carbon levels.
The worst release of carbon from materials with a high fossil carbon is in the form of methane. Fossil methane is one of the most nefarious culprits being targeted by climate change campaigners. The amount of fossil methane leaking out of landfill sites or from the petrochemical industry has been previously underestimated. Scientists now know that fossil methane (which is more warming than CO2) is a major contributor to global warming. Governments have signed the Global Methane Pledge which targets the decrease of methane for an easy win on slowing the rate of climate change, with fossil methane being a prime candidate - despite protests from the oil industry.

Tanneries and biogenic chemistry
The focus of leather makers should be to strategise towards a substitution of fossil-based chemistry and elevate leather to the gold standard of materials. A 100% biodegradable leather that is 100% biogenic, that can perform well in technical products and that can survive multiple generations (handed down in families) - is the ultimate accomplishment. The marketing story around that is priceless.
Many chemical companies now sell a range of biobased and biogenic chemicals (as they have done for many years). Vegetable tannins are new carbon that when added to leather will be indistinguishable from the other biogenic carbon of the collagen. Likewise, many of the new retanning agents (bisphenol-free) and biobased fatliquors will add to the biogenic credentials. The next step is to ensure that many of the other auxiliaries and finishes are also compliant. Later this year, S&V African Leather will be discussing biogenic dyes which is another important hurdle.

References
Carceone, F., Defeo, G. Galli, I., Bartalini, S., and Mazzotti, D. 2023. Material circularity: A novel method for biobased carbon quantification of leather, artificial leather, and trending alternatives. Coatings 13: 892. https://doi.org/10.3390/coatings13050892.
Meyer, M., Dietrich, S., Schulz, H, and Mondschein, A. 2021. Comparison of the technical performance of leather, artificial leather, and trendy alternatives. Coatings 11: 226. https://doi.org/10.3390/coatings11020226.