Leather-making is a science rooted in craftsmanship. Despite its artisan image, there's a good case for arguing that leather-making is simply applied chemistry. Especially today, when tanners and chemical specialists invest vast amounts of time and money in researching, improving and perfecting the chemistry of leather making.

Originally, leather tanning occurred naturally or was done by man using natural resources in a process that was the precursor of today’s ‘vegetable tanning’. But leather production has always looked for more efficiency and better performance. Since 1840, chemistry has taken over the role of tanning agent from traditional tannins, alum and oils. In old footage and reports, you’ll often find stories about the downsides of chemicals, but today, this is a very different story.

Chemicals and leather production

Much of the contemporary research by chemistry suppliers and tanners focuses on minimizing the impact of chemicals on human health and the ecology. Over the last three decades, safe chemical management and sustainability have become the hallmarks of a responsible tannery with high-quality products.

For chemistry management within leather production, one of the major challenges is the diversity of methods. The process steps may be broadly the same, but each type of leather application and industry require different technologies. Chemicals, either aqueous or spray, are used to clean the hide, modify its structure and add the desirable characteristics to the final leather. The craft side of the industry further complicates things, as each tannery follow its own distinct processes and recipe. An automotive tanner will not use the same methods for its leather as a shoe-leather tanner or automotive competitor. This makes perfect sense, as each tanner relies on their signature look and feel for their product.

There are three main tanning systems in use today, namely:

  • Wet blue tanning (chromium-based)
  • Wet white tanning (alternative tanning solutions)
  • Vegetable tanning (tanning based on plant-based technologies).

Industrial tanning methods have, for a long time used Chromium (III), which is a highly effective tanning agent (chrome tanning often takes less than a day). It’s use is tightly controlled to avoid and eliminate any formation of Chromium (VI). Chromium (III) is a non-toxic material that is found in many every day items such as stainless steel cutlery. Aldehydes, aluminum or other compounds are used in wet white tanning, which yields softer leather. In recent years, a big switch to biotechnology, using natural oils and other food by-products as resources, has emerged to enable more circular processes.

Salt and water

Water is used ubiquitously in the leather tanning process, and salt is increasingly avoided in favor of “green” hides that are transported short distances and processed very soon after arrival (removing the use of preservatives). Historically, both salt and water were used extensively in the tanning process. Sourcing hides locally helps to reduce the amount of salt necessary or even eliminate it. To reduce their usage of freshwater, premium automotive tanners often have circular processes in place, where wastewater is purified and filtered. This enables them to use the same water over and over or discharge it safely, as clean as it was before. Many of these automotive tanners go even further in making processes more sustainable and environmentally friendly.

An automotive tanner will not use the same methods for its leather as a shoe-leather tanner

Lowering the chemical impact 

Within the methods above, there are still endless options in what chemicals to choose. Yet, in the recent decades, a significant shift has occurred in tanning technology and todays’ tanners actively monitor for and remove chemicals that pose a threat to our health and the environment.

Industry-wide initiatives, such as the Zero Discharge of Hazardous Chemicals, are part of a global push for more sustainable chemistry. Research and process development has embraced this as its focus, developing non-hazardous and bio-based alternatives. The goal is to reduce workplace exposure and health and safety risks, enhance process efficiency, make more efficient use of processing water and reduce emissions and waste that may damage the natural environment.

The automotive industry drives leather technology development

The automotive industry holds exceptionally high standards for leather quality and chemical-management. After all, we expose ourselves to the interiors of our cars for extended periods of time. Increased awareness of the chemical impact on materials, both in contact and emission, has prompted a search for alternatives. That new car smell? You won’t find that anymore in modern cars with leather seating, as VOC-emitting solvent-based surface chemistry is severely limited today. But this is just one example in how the automotive industry has become one of the biggest users of leather and a driver of leather chemistry research. As our use of mobility is changing, with the arrival of electric vehicles and shared mobility the demands for more durable and sustainable interiors are changing. This prompts further development of leather chemicals and what they can achieve. Tomorrow’s cars will need even more advanced material properties, with soft-touch, squeak-free premium surface technologies for automotive leather.

As tanners look for ever more responsible technologies, chemical suppliers develop solutions that enable higher uptake rates in the leather, which reduces waste and emissions. Next-generation chemicals will improve bonding, dyeing and coloring processes, and improve resistance for even more durable leathers. The impact of these changes can already be felt. Thanks to new chemical technologies, certain tanners have vastly reduced the carbon footprint of their production already. Data collected by European Leather Industry members show a reduction in the average value of chemicals used per square meter of finished leather of 6.2% between 2010 and 2011, from 2.09 kg to 1.96 kg. With a new survey coming up, the future results are expected to be even better.

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