Another tile on the chemical tanning sector. The issue concerns the presence of bisphenols in finished leathers. Since the 1960s these chemicals have been widely used in many industrial sectors and are now subject to restriction because they are potentially harmful to humans. As far as leathers are concerned, in particular, type A, F and S bisphenols, manufacturing brands are now asking to restrict their presence below the expected limit of 200 ppm, without obviously altering the leather quality. The reasons for these requests are related to the proposals for restriction and classification change of the bisphenols concerned submitted to ECHA by Germany and Belgium.
It’s not easy to solve the problem and it reverberates directly on the producers of chemical tanning auxiliaries, as explained by the Italian association UNPAC, which has drawn up a very explanatory note that explains in detail the existing technical difficulties but also the path taken to overcome the current detection limits and develop alternative chemical formulations.
“The presence of bisphenols concerns the replacement of synthetic tannins and, for some of these, the currently planned updates relate to the registration dossiers at Reach according to the evolution of regulatory decisions – explains the note – Let’s also say that currently no phenolic-based synthetic tannins and dihydroxydiphenylsulfone are free of bisphenol F and S”.
The chemical sector has taken steps to reduce the bisphenol content in its products but the road ahead is still long: “Thinking of immediately restricting quantities of these substances is pure utopia, as it takes time to build a new chemistry that allows the creation of synthetic tannins with a lower bisphenol content”.
A significant issue is that there is still no official method to determine the amount of bisphenols present in leather, as well as that found in chemical products and UNPAC thus explains “As soon as possible it is necessary to develop an official and regulated method that allows to obtain repeatable and reproducible results, validated through the steps required by the standardisation process”.
For this purpose, the European Commission for Standardisation for the leather industry, CEN/TC 289, during one of the periodic meetings has put forward a proposal method to determine the total quantity of bisphenols found in leather, which was presented in February 2021, also attended by delegates of the Italian Standardisation Commission.
Subsequently, in the recent meeting in March 2021, UNI decided to organise an Interlab involving both the CT/013 – Leather, Hides and Leather Goods, which deals with leather analysis, and the Working Group CT/013-GL01 which deals with analysis on chemical products, in order to analyse both the leathers and the synthetic tannins used for the retanning phase.
The objective of this Interlab is to verify the effectiveness of the different analytical approaches proposed, useful to determine the total extractable content but, at the same time, essential to understand the correlations between the quantities present in chemicals and in treated leathers.
In the subsequent European CEN meeting on 24 March, the Italian delegation presented the accepted design strategy, which saw the involvement of other European laboratories that gave their willingness to take part in Interlab.
Parallel to the activities in progress on the regulatory technical tables, UNPAC has requested and obtained the collaboration of all 8 European chemical companies producing synthetic tannins of various formulations in a round test, to acquire further technical information useful for evaluating what may be the necessary times to the chemical industry for the development of new generations of retanning agents; it should be pointed out that the chemical industry has already taken steps to reduce the bisphenol content in its products.
“It is important to accept the fact that currently no synthetic tannins based on dihydroxydiphenyl- sulfone and phenolic are free of Bisphenol F and S, as jointly confirmed by all the European chemical industries producing retanning agents which, in this project start-up phase for the definition of a reliable and reproducible analytical method that will have to be brought to standardisation, have fully adhered by giving product samples that will be delivered to the laboratories involved in Interlab and which, over the next few weeks, will allow them to get straight to the heart of the experimentation”.
Some samples of synthetic tannins, of different formulations, will be tested for a series of retanning on wet-blue leathers, which will then be subjected to verification for the quantitative detection of Bisphenols, also considering the results that will emerge from the regulatory Interlab. The identified procedural steps, as well as the methods to prepare the sample to be analysed and the various instrumental techniques were carefully evaluated for the harmonisation of the techniques deemed suitable to identify the correlation between chemical product and leather; in order to scrupulously evaluate that the extraction conditions do not overestimate the total bisphenol content, there will be a comparison between different preparatory and procedural methods and different extraction vehicles, in order to define the most suitable ones.