Second generation Cr-free

Ancient civilisations were known to make a chromium-free leather using aluminium in a process called tawing, producing a softer, more water-resistant form by adding egg yolks and flour. Simultaneously, ancient peoples had perfected the use of vegetable tanning with Egyptian and Hebrew records showing vegetable tanning use in 700BC. Aldehydes were the next chromium-free iteration with the earliest chromium-free aldehyde tannage being the use of rancid oils (especially fish oils), followed by formaldehyde and glutaraldehydes in the 20th century.
Other aldehydics started to appear in the 1990s with Trumpler’s oxazolidine and phosphonium salts which all produce a chromium-free white/off-white material, which as an intermediate would be called wet-whites.
Other chromium-free metal tannages such as zirconium, titanium, iron had also galvanised by the latter part of the 20th century and continue to be useful additions in the tanner’s toolbox.
The sulfur tannage that made use of sodium thiosulfate (or any sulfur-containing chemistry that could release colloidal sulfur) as a pre- or post-tannage was also a chromium-free combination tannage that could also be put into the first generation grouping - providing the industry with a favourable spongy leather with high internal softness. All of these could be classified as first generation wet-white technology.

The change into the new millennium heralded the realisation that Pandora’s box had been opened on chromium. A much-loved technology, that could be easily controlled by tanners and effluent plant managers, had fallen prey to the vagaries of the chemical politicians who were determined to cleanse the leather supply chain of toxic chemistry without regard to the actual science and toxicology.

Generation 1.5
The leather industry’s chemical sector responded with some really incredible technology. Stahl’s Easywhite, a modified di- or triazine, produced a beautiful wet-white intermediate that could reliably replace chromium tannages. The polycarbamoyl sulfate, X-tan, a technology patented in the 1970s, but readied for market in the early 2000s, joined Easywhite. Shortly afterwards, Smit and Zoon released the modified zeolite, a brilliant white tannage that produces very tight, easily dyed leathers. The cross-linked phenolic (e.g., condensed or sulfone) synthetic tanning agent (syntan), the acrylic, polyurethane, melamine, and dicyandiamide polymers were also popular wet-white technologies that could be used in this grouping.
Glutaraldehyde, simple aluminium tannages (aluminium sulfate, aluminium chloride, potassium aluminium sulfate -potash), and oxazolidine survived through into parallel use while these early millennial chemistries were put into action. The distinction between first and first (and a half) generation can be summarised as the following: pre-2000s technologies that are easily grouped as first generation (renowned as key innovations that disrupted the chromium and vegetable tannage dominance); and generation 1.5 chromium-free leathers that were post 2000s technologies, that added to chromium-free knowledge and allowed new branches of future chemical development. A further characteristic of generation 1.5 technologies is that they were produced from starting materials that are either derived from the petroleum industries or synthesized from minerals or feedstocks that cannot be regarded as waste materials.
Nevertheless, generation 1.5 and tenacious, unregulated, first-generation chromium-free chemistry continued to be useful chemicals in a currently demanding industry. None of the chromium-free technologies as yet were able to be produced as intermediate, that could be transported as such, globally, in the fashion seen in wet-blue.

Second generation
Is there a second generation of chromium-free technology? Yes, Succuir, a triose sugar (from Schill+Seilacher) can comfortably be heralded as a second generation of chromium-free chemistry. The reason for this is that it embraces the ideals of a new generation of chemists. Green chemistry is a hot buzz word in the chemical industry. The idea that chemicals will be manufactured and used with complete regard to the highest sustainability principles and will especially focus on renewability and a minimum negative impact on the environment.
Of course, other generation chromium-free chemicals will continue to serve the industry and will be equally valued as tools that help to move the industry away from chromium. The point of a distinction into second generation chemistry is to acknowledge what the new chemistries have managed to achieve - a novel circularity.
The mineral based chromium-free chemistries rely on a mining activity - in principle the renewability of mined resources is finite. Mining activity is energy intensive and can be impactful, in some instances, with regard to land and water changes. Minerals can be infinitely recycled so could effectively be part of the circular economy once collected. A useful character of some of these chromium-free mineral tannages is they could be added to unsplit cattle hides.
Non-mineral, first and 1.5 generation chemistries do rely on the petroleum industries. Glutaraldehyde is directly sourced from the petroleum industry and cannot be regarded as a renewable resource. Other chromium-free technologies will have identical credentials as glutaraldehyde which makes their use (say in next 250 years) doubtful - their feedstock will eventually run out.
Triose is plant-based, and is directly sourced from a biogenic waste product - glycerol. Sourced from plant oils, the biorefinery will break the triglycerides into biogenic glycerol and three fatty acids. The fatty acids will then enter biodiesel production and the glycerol will be actively promoted to any company looking for a waste feedstock for any application.
A chemical company can take the glycerol, convert it into triose for use in the tanning industry. The carbon footprint of that triose is then automatically lower than most other chromium-free chemistry due to them being a waste product. ISO 14044 requires that environmental footprints from upstream processes cannot be allocated to waste products, so triose only starts accumulating footprint the moment it is transported to the triose biorefinery. Another major attribute of these second generation wet-white technologies is the green chemistry credentials of their production. Low energy inputs, benign adjunct chemistry, minimal steps, recycled catalysts (e.g., enzymes), minimal effluent, solvent-free, and safe for chemical workers are green chemistry aspiration. The industry’s plenary second generation chromium-free chemistry, the triose, meets these aspirations.
The future is also positive. The industry will continue to use desirable (regulation permitted) first and 1.5 generation chromium-free chemistry, together with a growing number of second generation wet-whites. Of course, 1.5 generation chemistries will be developed and will be used as long as they are available. Future second generation chromium-free will expand the sugar domain, will exploit a wealth of cellulosic waste feedstocks, but the game changer will come through the breakthrough of using carbon out of the atmosphere.
Third generation chromium-free will come from carbon capture and conversion into organic chemistry and the industry has a palpable excitement in waiting for this.

In the next issue: What is happening to meat? Are markets eating more or less since covid, and how does that affect hide and skin supply in Southern Africa and globally? As a by-product of the meat industry, hides and skins will need to be thrown away if the leather markets cannot handle increasing raw material supply.