The tanning industry is using mainly mineral- and fossil-based chemicals to process raw hides and skins into leather. But manufacturing with low environmental foot print is the mega-trend nowadays which requires energy & waste reduction, re- & upcycling and an end-of-life article strategy. Therefore the modern leather industry is increasingly shifting to the use of metal-free and non-petrochemical solutions to answer the raising market requirement of sustainable consumer goods.
TECNOLOGIA WHITE LINE
The majority of metal-free leathers today are pre-tanned with SELLATAN® WL-G Liq, although glutardialdehyde (GA) is considered a hazardous chemical, it can be handled in a safe way in order to eliminate risks to workers, consumers and the environment.
Pre-tanning based on SELLATAN® WL-G Liq is the most efficient metal-free tanning chemistry to turn collagen into leather. Small amounts of about 0,75% GA 100% are sufficient to achieve a significant tanning effect after basification to pH 4.5 with a typical shrinkage temperature of around 72°C. Due to the formation of covalent bonds the tanning reaction is irreversible, and the polymeric nature of the polymerized tanning agent explains the softening and filling effect of glutaraldehyde tanning.
Producing leather involves chemicals and these chemicals are under continued and ever increasing scrutiny concerning their ecological and toxicological profile. The same is true for the final product of this chemical processing, the leather.
An advantage of GA tanning is that it forms an organic bond. The resulting leather can be composted and unlike chromium tanned leather, there is no issue if it is incinerated. On the other hand, GA as a chemical is often looked upon with some uncertainty by tanners. After all, it is an aldehyde, and other aldehydes like formaldehyde are classified as “CMR” substances (carcinogenic, mutagenic, reprotoxic). But the risk potential of aldehydes cannot be generalized. On the contrary, each substance has to be assessed individually, and the type of exposure and the dosage have to be considered as well.
Focussing on GA, the first fact that needs to be emphazised is that it is not classified as a carcinogen or as an in vivo mutagenic or reprotoxic substance. This shows that GA must not be compared to formaldehyde regarding its risk potential.
The leather making process involves many chemicals that need to be handled with adequate precautions due to their irritant or toxic properties. Tanneries have to know how to handle substances like formic acid or even sodium sulphide. Any tannery working under proper conditions is therefore able to take the necessary measures to address the irritant and corrosive nature of GA. The sensitizing properties of the substance are reflected in rather low occupational exposure limits, which are varying from country to country. In general, tanneries will be able to respect these limits, especially if dosing is done automatically.
During application at pH=3, the concentration of SELLATAN® WL-G Liq in the float originally offered is quickly reduced, although the reactivity of SELLATAN® WL-G Liq towards collagen is still relatively limited. The following increase of the bath – pH to 4.5 results in an exhaustion of SELLATAN® WL-G Liq of up to 99%.
The final user of the leather article will of course mainly be interested in residual amounts of GA in the leather article. Since the GA concentration in the crust is negligible, it is therefore not surprising that a clinical epicutaneous test on humans came to the conclusion that “The chromium-free leather is a skin friendly material, with which even skin-sensitive people may come into direct, prolonged skin-contact. The materials have no potentially sensitizing properties”.
Re-tanning of SELLATAN® WL-G Liq tanned wet white requires a substantial amount of replacement syntans, polymeric retanning agents and fatliquoring agents which are often based on fossil chemistry. Wet-End chemicals based on renewable biomass can help lowering the environmental impact of metal-free leather manufacturing and allow the production of articles with a high sustainability profile. For example, MAGNOPAL® Pure A is an environmental friendly, film-forming bio-polymer based on vegetable biomass. It is produced with sustainable chemistry and therefore free of acrylates, formaldehyde, phenol and naphthalene. The renewable content of the active matters in MAGNOPAL® Pure A reaches staggering 93%.
PURE TEC CONCEPT
Pre-tanning with SELLATAN® WL-G Liq is a proven and efficient technology, viable for tanneries equipped with standard machinery. The process is reliable, consistent and economically feasible. There are no restrictions to the use of GA as a tanning agent, and with proper processing there is no detectable GA in the final leather. Consequently, the produced metal-free leather is a skin-friendly material with no potentially sensitizing properties.
The technology is versatile, allowing the tanner to produce a full range of articles which are not only metal-free but are made with sustainable products according to the TFL PURE TEC concept.