The Italian Leather Research Institute (SSIP) has recently published the results of a survey on the possible development of phosphine in metal-free tanning systems based on phosphonium salts, or tanning products based on tetrakis (hydroxymethyl) phosphonium sulfate (better known by the acronym THPS). As experts well know, this type of tanning represents one of the most promising alternatives to chrome tanning, but the concern regarding the possible formation of phosphine, a highly toxic gas, during the processing phases had conditioned its large-scale diffusion.
But now science says a clear word. The analysis edited by Dr. Gianluigi Calvanese – Head of Laboratories and Business Services Area at SSIP – presented clear conclusions: “The results of the tests have shown that there is no development of phosphine in tanning liquors and neither in leathers obtained from THPS”, the study reads.
To carry out the survey, laboratory-scale tests were conducted and a tanning system investigated, but in none of the cases phosphine was produced. The system analysed is in fact the one developed over the last few years by KLF Tecnokimica of Castelfranco di sotto (Pisa) which uses two organic products for the production of chrome and glutaraldehyde-free leathers. “Finally some light has been shed on this – comments Marco Frediani, owner of KLF Tecnokimica – The processing system and the final product resulting from the use of phosphonium salts are absolutely risk-free for both workers and consumers. Tests carried out by the Italian Leather Research Institute have established that no toxic gas is developed in this type of tanning, dispelling a heavy suspicion that was holding back the use of an effective and advantageous process”.

The results of the investigation have been published in the newsletter of the Italian Leather Research Institute N° 38/21 of 15 October 2021 and are available at the following address