16 June 2022
Leather chemicals manufacturer Silvateam is working with a series of partners in Italy on a project to develop chemically modified natural tannins (CMNTs) to produce leather, writes Leatherbiz.
Aims of the project are to make adjustments to the ways in which natural tannins are usually prepared for use in leather manufacturing to achieve lower chemical hazards, sustainable costs, reduced waste and improved circularity compared to conventional tanning processes that use chrome, synthetic tannins or aldehydes. The partners have said they believe these modified tannins will allow leather manufacturers to produce “eco-friendly, high-quality leathers use of innovative, sustainable.
They have said the process will use natural tannins from sources such as chestnut and quebracho. These tannins will go through an intense filtration process. This will result in concentrated purified natural tannins, with residue material that is not suitable for use in tanning going for use as additives to animal feed.
Next, the concentrated, purified natural tannins go through a chemical reaction to produce the CMNTs for tanners to use. Off-cuts and trimmings from hides tanned using CMNTs will be suitable for use in agriculture as organic fertiliser.
The partners have also referred to the resulting products as ‘innovative modified natural tannins, giving rise to the project’s name, IM-TAN. Work on IM-TAN began in September 2021 and will run for three years. It has the support of the European Union’s LIFE programme.
They have acknowledged that more than 85% of the leather produced worldwide is tanned with chromium salts owing to their low cost, versatility and capacity for producing high-quality finished leather. They say, however, that some users of leather prefer to avoid the use of heavy metals, and point out that concerns about the capacity for chromium salts to oxidise into chrome VI have not gone away.
Synthetic tannins and aldehydes give finished leather inferior physical and mechanical characteristics compared to chrome tanned leathers, according to the IM-TAN partners, and also presents “some health and environmental issues”.
They express a preference for natural tannins but acknowledge that, typically, these generate high chemical load in wastewater in terms of chemical oxygen demand (COD) and biological oxygen demand (BOD) owing to the presence of non-tanning low molecular weight substances (LMWS). They believe that this is where IM-TAN can make improvements.