Regular readers of this journal will realise it is with trepidation that I will ever criticise a conference again. And indeed, the only criticism I can cast at the Associazione Italiana Dei Chimici Del Cuoio (AICC) is that some of the lecturers went well over their allotted time. Overall, the conference on ‘Quality and Environment: process rationalisation’ was a great success.

Holding it in an old monastery was also an interesting idea, although I did think they were going a bit far in replicating the monastic life in the rooms, which were spartan, without television or a mini-bar. Never mind.

Franco Donati, opening the conference, said: ‘When I thought about a European congress for the first time, I wished that it could be widely shared and supported by our directors and be the beginning of a new course for the tanning sector.

‘The year 2000 is characterised by so many symbols that it should be considered a real starting point. The year 2000 should contain the necessary indications that the tanning industry will have qualitative and quantitative developments to the operators’ and users’ advantage. But this target can’t be easily put into practice and I think it can only be reached through specific studies aimed at enhancing product and operative process quality.

‘Personally, I think a future marked by production processes taking care of the environment is indispensable and primary, and that is the reason for the congress theme.

‘This is the first European congress. It has been organised not only for the reasons I have explained, which all of you share I think, but also to be a voice for those who desire a united Europe, where cultural, commercial and professional exchanges are really free and synergetic.

‘This effort has been a dry run for the biggest future event within AICC, namely the organisation of the world congress in 2005. I am sure the result on that occasion, like today, will be more than positive for the quality and quantity of presented works, as well as for the number of participants; therefore, I invite you to consider the possibility of your participation from now on.’

He was followed by Mario Pucci, international relations manager for ASSOMAC, who thanked the organisers for the invitation to speak and commented that he hoped there would be further ‘common co-operation’ between AICC and Assomac. Dr DiStefano of Unic, who said there was a synergy between the groups and hoped that there would be a continuing dialogue between Unic and AICC, echoed this wish.

In a wide-ranging conference, there were speakers from all over Europe and an interesting mix of topics. The first lecture was given by Prof Adzet from AIICA, Spain, who discussed the ‘Improvements in the environmental impact of cattle hide unhairing’.

He said that cattle contained about 3.5% dried hair on the salted weight of the hide. This actually varies between about 2% and 11% according to the animal breed, age and season of slaughter and a winter coat will yield a higher percentage of hair than a summer coat.

Prof Adzet discussed the various unhairing systems and table 1 lists the environmental advantages of using a mechanical unhairing system, which is a system similar to that for sweating sheepskins.

Collecting the hair this way means it can be used, after washing, dewatering, cutting, drying and grinding. The material produced is of two types. The hydrolysed hair is hygroscopic and the organic content is mainly long chain polypeptide chains and amino acids, which makes it suitable as an animal feed supplement. The processed hair is non-hygroscopic and, when blended with other materials as an agricultural fertiliser, produces good results.

On a similar subject, Karl Heinz Munz, from the Testing Institute for Leather Industry, Vienna, Austria, spoke about ‘Making the most of hides and skins’. He pointed out that when a tanner buys 1,000 kg of hides, he actually only gets 250-300 kg of leather from it. The rest, hair, blood, flesh, dung and curing salts, is thrown away at the tanner’s expense. The question is what can be done to reduce this loss and turn the unwanted parts into saleable items.

Munz said that the possible utilisation of byproducts included fleshings, trimmings, dried hairs and shavings, especially if not chrome tanned. Producing non-chrome shavings usually involves a wet-white process but with the help of tanners from Austria, Germany and Italy, Munz and co-workers have developed a new procedure. Delimed and bated pelts are treated with wasserglass, which is a solution of alkaline silicates with a dry content of 50%. This ‘tannage’ imparts enough stability to enable the hide to be shaved, and yet there is no substantial character to the tannage. The hides can then be tanned with standard tanning agents. Table 2 lists some of the resulting automotive leather properties compared with a wet-white process.

In summing up Munz said that delimed and bated pelts could be stabilised sufficiently for them to be shaved without damage. The shrinkage temperature achieved indicated there was no ‘real’ tannage taking place. The advantage is that the shavings do not contain any tannins and any residual silicates are considered non-toxic so they, the shavings, can be readily utilised.

Dr Naviglio from SSIP in Naples, further discussed this process. He said that the results of a European Craft project concerning the use of sodium silicate showed that the chemico-physical properties of the leather were of at least equal standard to leather produced by conventional methods.

Max May, an independent consultant from Monaco, has developed his brand of efficient eco-tanning for over 20 years. In a paper read by myself, May discusses ‘Efficient ecological tanning: Concepts, strategies and goals’. The key to profitable eco-tanning is the production formulation and software. Recipe implementation requires precise parameters to achieve control and improved recycling techniques such as separation, filtering, sedimentation and precipitation, can all save the tanner money.

Water consumption can be reduced by a third and savings are made on chemicals and time, both important in this just-in-time and environmentally conscious world. The need to highlight leather as an environmentally friendly product is shown by the fact that it is under attack from all sides. Even in Italy, 10% of the shoes produced last year were synthetic and that number is growing!

One of the positive points about the conference was the number of experts attending. The next paper ‘Considerations and observations about the wet treatment of leather: ecological points’ was given by Giorgio Martignone, who has 40 years of tanning experience behind him. He is also the author of ‘Manuale de Pratica Conciaria’.

He spoke about the impact of the beamhouse processes on the environment and discussed the alternative methods to reduce the effluent load. These included speculative processing, such as cutting the hair to facilitate enzymatic unhairing from the grain side, and simple techniques that all tanneries should use, such as lime fleshing to reduce the use of chemicals. He also suggested oxidative liming with enzymes to eliminate the need for deliming and bating.


While the majority of pollution from the industry is caused in the beamhouse, the post tanning processes are also important ecologically because this is where the tanner can save money by reducing chemicals and improving performance.

Eric Poles, Silvachimica, presented work carried out by his company and Chimes. They were investigating the possibilities of a hybrid extract of chestnut and tara for the production of light leathers with good light and heatfastness. They found that the best results, in terms of getting fastness to heat and light, involved treating the vegetable tannins with a small amount of chemicals that gave excellent colour clarification. The leathers produced with the new hybrid extract have the characteristics of the chestnut extract but with the lightfastness of the tara. Articles produced were ‘remarkably lighter and more stable to light’, Mr Poles commented.

Dr Andrew Hudson from BLC Leather Technology Centre, UK, said that the expected quality of leather products has risen during recent years, with consumer pressure requiring textile like specifications. He went on to say that one of the most difficult specifications to attain is that of colour fastness.

While the reasons for this are multitudinous, the combination of high dye offers for deep shades with the limited availability of dye active sites leads to a low level of overall fastness. He then described a novel technique, involving amino functionalised silanes, to increase the number of dye active sites, without adversely affecting the handle of the leather.

The technique results in an increase in dye fixation and resistance to removal from the leather. Table 3 highlights the effect of adding aminosilane to reactive black 5. Although the washfastness is only slightly improved, the colour strength increases (lower L values) significantly.

Chrome (VI)

The formation of hexavalent chromium has taxed many researchers since Nickolaus first suggested that chrome (VI) could be formed in leather in a paper given at the IULTCS congress in 1995.

Since then numerous reports have proposed mechanisms as to how chromium (VI) is formed. Volkan Candar, Cognis, presented work that his company have carried out. They investigated ways of avoiding the eventual formation of Cr (VI) in leathers.

Candar said that the oxidation of chromium in leather is believed to occur via auto-oxidation. Initially, oxygen reacts with double bonds from different auxiliaries used in the post tanning processes, giving rise to the formation of unstable and highly reactive peroxide moieties. Formation of such free radicals can favour the conditions for oxidation of Cr (III) to Cr (VI).

Candar presented work that looked at the influence of the following parameters:

influence of free Cr(III) depending on the type of chrome retanned wet-blue

Using chromium as a retannage is asking for trouble, with levels of Cr (VI) detected significantly higher than without chrome retannage. However, Candar showed that if, after the retannage, the chrome could be better fixed the amount of Cr (VI) detected could be reduced. They found that adding a complex active surfactant reduced the concentration of the hexavalent chromium.

Influence of neutralisation pH

The influence of high pH levels caused by neutralisation has long been understood to cause chromium (VI) formation. Candar suggested a ‘reductive’ neutralisation by adding products such as sodium metabisulfite and sodium sulfite. The results were inconclusive, but did point to the idea that products binding to collagen have a positive effect on the impact of chromium (VI) production.

Problems due to fatliquors

Unsaturated fats have been highlighted many times as influencing the formation of hexavalent chromium. Candar suggested a novel way of reducing their effect, without removing them completely. His leathers were produced with fatliquors chemically bound with a ‘free radical capturing agent’. These so called protected fatliquors definitely reduced the Cr (VI) concentration, table 4.

Influence of retanning agents

The effects here agreed with previous works. The addition of vegetable tannins such as tara, chestnut and valonia significantly reduced the chances of chrome (VI) production. Cognis have also developed a new product, Garmin CR6, which while reducing the chrome (VI) levels to that of pyrogallic vegetable tannins does not affect the handle of the leather.

effect of final washing in a reductive salt bath

The idea of adding sodium metabisulfite to the final wash also produced results that were encouraging.

Fatty spues

One of the age-old problems that tanners have is spue on the leather. Yet, remarkably, investigations of the causes of spue are few and far between. According to Dr Naviglio of SSIP, Naples, the last published results were 40 years ago from work at BLMRA, in the UK. To update this, the group at SSIP used high-resolution gas chromatography (HRGC) to study the mechanism of the formation of fatty spue on leather.

The paper serves two purposes. One, it highlights a new application for separating the components of fats. This may prove useful for a variety of applications involving fatliquors or natural grease distribution. Secondly, the results of the work provide indirect evidence of a biological nature to the problem.

The fatty spues tested show an approximate 1:1 ratio of palmitic: stearic. This led the workers to conclude that the modification concerned the unsaturation in the oleic acid, which undergoes hydrogenation to produce its saturated homologue, stearic acid. This they allocated to an enzymatic mechanism. However, further work is needed to investigate these ideas.

The AICC will be organising the IULTCS congress in 2005 and with this ‘test run’ the congress will be in safe hands – with or without the monastic life and surroundings.