What you need to know about formaldehyde

Introduction
Formaldehyde, a tool and a challenge for the leather industry:
Formaldehyde chemistry is interesting but also complicated. This makes communication about this topic between commercial and technical professionals somewhat difficult. Many misunderstandings do exist, sometimes leading to wrong choices. In this article Smit & Zoon try to give an overview that requires only a basic understanding of chemistry. It is the objective of Smit & Zoon to simplify communication about this important chemical topic.

Formaldehyde: a versatile chemical tool in nature and industry
Formaldehyde is a naturally occurring substance, which is produced and used in every living cell of plants, animals and humans. The molecular formula is CH2O (figure 1). In its pure form, at ambient conditions, it is a gas with a strong, pungent smell. Formaldehyde is highly soluble in water and usually supplied as the aqueous product that we call formalin (37–55%).
Formaldehyde is not only readily found in nature, but is also a versatile chemical when manufactured synthetically. The base material is produced from natural gas, via methanol and used as a building block for many polymers and chemical products. It plays an important role in the production of household products, floor panels, furniture, fabrics, shoes, paper, pharmaceuticals, disinfectants, glues, paints, coatings and many other materials.

Formaldehyde: handle with care
At the high concentrations that can occur in the chemical industry and laboratories, formaldehyde is an irritating, reactive, toxic and flammable chemical that should be handled with due care in a professional way. Formaldehyde is broken down by sunlight and bacteria within a few hours and is quickly decomposed in living cells. This is why formaldehyde never accumulates in the human body or in the environment.
Formaldehyde can cause allergic reactions. Some studies have indicated that there might be a risk of developing a rare form of nose cancer, when exposed to high concentrations over a long period. Although the results of these studies are disputed, some institutions and countries have classified formaldehyde as carcinogenic in both high (IARC) and low (EU) classes. Strange as it may seem, these classifications led, in some cases, to standards for exposure levels or concentrations in products that are even below the natural concentration in an apple (20 mg/kg). Although the disputes about these limits and the data behind them still continue, the industry has to make all possible efforts to achieve them.

Formaldehyde: both needed and unwanted in leather
As in other industries, formaldehyde is used as an essential raw material in the manufacture of many leather chemicals. Examples are biocides, syntans, resins, dyeing auxiliaries, fatliquors and finishing products. Under the influence of temperature and humidity, these substances can partly be broken down into their components by a process called hydrolysis. During the hydrolysis of these chemicals in leather, formaldehyde is released. The conditions inside shoes during wear are particularly favourable for the hydrolysis process. This is one of the reasons that leather with low formaldehyde release is a major issue for many shoe manufacturers.

Production of low formaldehyde releasing leather: a real challenge
The production of leather that releases low levels of formaldehyde starts with a careful choice of base materials and leather chemicals. It will be evident that low formaldehyde chemicals will not recover the situation if the hide, wet-blue or crust already contain chemicals with a high formaldehyde release potential, like certain preservatives.
At this point it is essential to understand the difference between the free formaldehyde content and the formaldehyde release potential of chemicals. The free formaldehyde content is the level of formaldehyde gas dissolved in, or weakly bound to, a chemical or a leather. The formaldehyde release potential is the ability of a chemical to produce formaldehyde while falling apart by hydrolysis. The formaldehyde release characteristic of leather is mainly dominated by this potential and to a lesser extent by the free formaldehyde content of the chemical itself. The formaldehyde release potentials and the free formaldehyde contents of leather chemicals differ widely. It is essential to make the right selection in the whole recipe from beamhouse through to finishing. The choice of a chemical with some formaldehyde release potential is not necessarily a problem, as long as other chemicals in the recipe have low potentials.

The selection of chemicals with low formaldehyde release potential
Many chemical products do not contain formaldehyde, are not produced with formaldehyde and cannot possibly develop formaldehyde in leather. It can easily be concluded that this is the case from a basic knowledge of their chemical composition.
For chemicals that are not obviously part of this category, the assessment of their formaldehyde release potential is less easy. The behaviour of a chemical in leather can be measured in no other way than in the leather itself. This means that several test pieces of leather have to be produced with different chemicals and/or concentrations. Using officially approved test methods, the formaldehyde release characteristics of the leather can be measured and compared with the relevant standards.
Testing for formaldehyde in leather
It is essential to choose the most appropriate test method. The method must be followed very precisely; otherwise the results will be meaningless and will lead to wrong choices and decisions. Several test methods for formaldehyde in leather are widely used. Some of these were developed for textiles and thus result in flawed results when applied to leather or leather chemicals. Examples are EN-ISO 14184 and Japan Law 112. In 2008, a new test method for formaldehyde in leather was published as an official international ISO standard. This new ISO 17226 standard specifies two methods for the determination of free and released formaldehyde in leather. Smit & Zoon strongly recommend that ISO 17226-1 should be the only method used for testing formaldehyde in leathers. For automotive upholstery leathers, individual automobile manufacturers’ specifications and standards, such as VDA 275, also have to be used.

Testing for formaldehyde in leather chemicals
Despite the explanation above, it is very understandable that tanners still have a desire to test a leather chemical in its pure form. There is a way to do this, but due care is necessary before turning to it, and even greater care in attempting to translate the results. It is not unlike predicting what the taste and texture of a cake will be by tasting the raw ingredients. In the case of formaldehyde in leather chemicals many mistakes are made and wrong conclusions drawn, even by reputable companies. The greatest and most common mistake is to adopt test methods originally developed for leather or textiles in the testing of leather chemicals. If you want a meaningful result, there is only one suitable method currently available. This method was developed by the leather institute LGR in Reutlingen, Germany, and adopted by the International Union of Leather Technologists and Chemists Societies (IULTCS). The method is currently in the process of becoming an official ISO standard under the name: IUC 26 or ISO/FDIS 27587 Leather – Chemical tests – Determination of the free formaldehyde in process auxiliaries. It must be stressed that with this test method only the free formaldehyde content of a chemical can be measured. The formaldehyde release potential of the chemical is not measured by this technique. It is only by testing leather, not the leather chemical, that the full answer can be achieved. See table 1.

Smit & Zoon launch Safetan
During the 2009 ACLE leather fair in Shanghai which took place in  September, Smit & Zoon launched an innovative and safe retanning range. Next to their current synthetic tanning agent brand names, they have added the new brand name Safetan for this range.
The Safetan brand name reflects a group of innovative, high quality and safe retanning specialities. The products exceed the latest standards concerning free monomers (such as formaldehyde, phenol) and all restricted substance chemicals (as mentioned in restricted substance or RSL lists).

Safetan range philosophy
Smit & Zoon aims to be a dependable and valuable partner for the tanneries and the customers of these tanneries. They have the ambition to supply answers to the increasing challenges that tanners are facing. One of these challenges is to meet the ever increasing requirements in the field of product safety. Meeting these challenges while using existing chemicals often looks like a balancing act around the edges of health and safety requirements. The risk of producing ‘off spec’ leathers is considerable.
The introduction of Safetan products will make a genuine difference. Smit & Zoon R&D use innovative chemical technologies to develop products that exceed the latest requirements in the leather industry by far. The use of Safetan products will enable the tanner to produce safe leathers without balancing acts and without quality compromises.