Managing chrome in leather manufacture / Jürgen Christner in JOURNAL OF THE AMERICAN LEATHER CHEMISTS ASSOCIATION (JALCA), Vol. CVII, N° 12 (12/2012)  

[article]  inJOURNAL OF THE AMERICAN LEATHER CHEMISTS ASSOCIATION (JALCA) > Vol. CVII, N° 12 (12/2012) . - p. 409-415 Titre : Managing chrome in leather manufacture Type de document : texte imprimé Auteurs : Jürgen Christner, Auteur ; Florian Doeppert, Auteur ; Jens Fennen, Auteur ; Jan-Tiest Pelckmans, Auteur Année de publication : 2012 Article en page(s) : p. 409-415 Note générale : Bibliogr. Langues : Américain (ame) Catégories : Additifs Antioxydants Chrome hexavalent Formaldéhyde -- Elimination Polysulfonique, Acide Retannage Tannage -- Aspect de l'environnement Tannage au chrome Wet-blue (tannage) Peau tannée au chrome (le chrome donne une couleur bleue) Index. décimale : 675.2 Préparation du cuir naturel. Tannage Résumé : Chrome Tanning, being still the most used tanning method, has been challenged more and more in the recent past. The main reasons were questions of sustainability and the fact that chromium VI can be formed in leathers tanned with chromium III compounds. From a technical point of view, many solutions exist for using the chrome tanning agent in a most economical and ecological way. In this paper another way is shown for maximizing the distribution of chromium in the cross section of the hide as well as the exhaustion of chromium from tanning float, thus reducing the total chromium emission into the environment. Also the leaching of chrome from wet blue during retanning operations will be considered. The type of chemicals used and the process conditions play an important role in this regard, as well as the type of chrome tannage used to manufacture the wet blue. Various measures and solutions will be discussed in this presentation. The role of chromium VI in tanning is looked at with special attention to the real risks associated with it. Finally the formation of chromium VI will be discussed as well as methods to prevent its formation. A new additive (anti oxidant), which is able to eliminate existing chromium VI and reduce the likelihood of reformation, will be introduced. Note de contenu : - Emission of chromium into the environment - Pickling and tanning with polysulphonic acids (PA) - Chromium exhaustion and fixation in the wet-end processes - Strategies for treating chrome containing waste floats - Chromium toxicity, prevention of chromium (VI) in the wet end En ligne : https://drive.google.com/file/d/1ewCz1iVwEd6ahu0z6oJxE-8ks3AUo9Ur/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=16746 [article]

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Molecular modelling of tanning processes / Jens Fennen in JOURNAL OF THE SOCIETY OF LEATHER TECHNOLOGISTS & CHEMISTS (JSLTC), Vol. 82, N° 1 (01-02/1998)

[article]  inJOURNAL OF THE SOCIETY OF LEATHER TECHNOLOGISTS & CHEMISTS (JSLTC) > Vol. 82, N° 1 (01-02/1998) . - p. 5-10 Titre : Molecular modelling of tanning processes Type de document : texte imprimé Auteurs : Jens Fennen, Auteur Année de publication : 1998 Article en page(s) : p. 5-10 Note générale : Bibliogr. Langues : Anglais (eng) Index. décimale : 675 Technologie du cuir et de la fourrure Résumé : During the past decade molecular modelling techniques have been a field of major research. The underlying theory has been refined, modelling programs have become both faster and more reliable, additionally computer power has increased enormously. The main focus and driving force of the application of these tools has so far been in the area of drug design. Although results have not always been up to expectations, molecular modelling can now be considered to be one of the standard tools in pharmaceutical research. With this palette of modelling tools at hand, it seems promising to investigate the chemical nature of tanning processes at a molecular level. Starting from results obtained at the Eastern Regional Research Center, USDA, Philadelphia, the paper presents the development of a model for bovine collagen type I in aqueous medium and its refinement with the m olecular dynamics method. Density functional theory (DFT) methods were used to calculate the structure of a model chrome complex as it is believed to be formed during the process of chrome tanning. The positions of reactive sites in the collagen model are finally compared with the dimensions of the chrome complex model and show a good fit. It will then be discussed what else might be achieved by molecular modelling in the field of leather chemistry after a promising stard and which problems still have to be solved. The question of the size of an appropriate model which should reproduce macroscopic effects will especially be adressed. Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=7935 [article]

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Side reactions from the reduction of azo dyes with dithionite / Alois Püntener in JOURNAL OF THE SOCIETY OF LEATHER TECHNOLOGISTS & CHEMISTS (JSLTC), Vol. 80, N° 1 (01-02/1996)  

[article]  inJOURNAL OF THE SOCIETY OF LEATHER TECHNOLOGISTS & CHEMISTS (JSLTC) > Vol. 80, N° 1 (01-02/1996) . - p. 1-5 Titre : Side reactions from the reduction of azo dyes with dithionite Type de document : texte imprimé Auteurs : Alois Püntener, Auteur ; Jens Fennen, Auteur ; C. T. Page, Auteur Année de publication : 1996 Article en page(s) : p. 1-5 Note générale : Bibliogr. Langues : Anglais (eng) Index. décimale : 675 Technologie du cuir et de la fourrure Résumé : The recently introduced amendment to the Consumer Goods Act in Germany concerns itself with the prohibition of the manufacture, marketing and import of consumer goods dyed with those azo dyes, which by cleavage of the azo bond(s) can liberate certain toxic listed aromatic amines. Inmany laboratory analytical methods the reduction of the azo bond is accomplished by treatment with sodium dithionite. However, using this strong reducing agent more than just the azo groups can be cleaved as specified in ther German Act. In some cases even new amines can be generated which are neither part of the dye structure nor involved in the synthesis of the dye. These additional amines are formed by a side reaction due to the analytical procedure used and can thus lead to incorrect analytical results. The example reported here relates to the formation of 4-aminodiphenyl, when the diazo component is aniline. En ligne : https://drive.google.com/file/d/17QGfHnQspIRDUwVKSRFj5CYbROGA4O0T/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=8192 [article]

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The challenge of manufacturing leather dyes today / C. T. Page in JOURNAL OF THE SOCIETY OF LEATHER TECHNOLOGISTS & CHEMISTS (JSLTC), Vol. 82, N° 2 (03-04/1998)

[article]  inJOURNAL OF THE SOCIETY OF LEATHER TECHNOLOGISTS & CHEMISTS (JSLTC) > Vol. 82, N° 2 (03-04/1998) . - p. 75-77 Titre : The challenge of manufacturing leather dyes today Type de document : texte imprimé Auteurs : C. T. Page, Auteur ; Jens Fennen, Auteur Année de publication : 1998 Article en page(s) : p. 75-77 Note générale : Bibliogr. Langues : Anglais (eng) Index. décimale : 675 Technologie du cuir et de la fourrure Résumé : The introduction in July 1994 bye the German parliament of an amendment to their Consumer Goods Act, which prohibited certain azo dyes, has had consequences world-wide at all levels of the leather industry. The general thrust behind the law has strong support at all levels in the industry but the fine details have caught many unaware of their practical implications. Ther German law makers have found they needed several further amendments to bring even some degree of workability to the legislation. The test institutes world-wide have discoveres an exceedingly lucrative new business niche in chemical analysies. Those in the leather manufacturing chain, from tanners all over the world through to the German retail shops, have had to subject their products to analytical scrutiny at the parts per million level have discovered the limits of analytical methods. The German Act probihits the use of certain azo dyes in defined consumer goods that come into repeated contact with the skin. The azo dyes affected by this legislation are those that after splitting up of the dye molecule at eht azo groups release any of the 20 amines listed in the Act. Those involved in developing the analytical method quickly discovered it is easy to legally define this splitting up of dye molecules, but in practice much more difficult to implement so that only amines from the splitting of the azo group were detected. Dye molecules are happy to split in other ways if the reaction conditions are sufficient. Any type of correlation with the real life in vivo reduction reactions was never considered as the analysts struggled within strict time constraints to produce a German standard test method. The manufacture of a dye today, taking into account all the constraints of the above legislation, can lead to "clean" dyes being labelled as doubtful. The manufacturing process of a dye will be followed to show how such a situation could arise. It is clear that there are still areas of greynes in the Act as it stands, but the rapid expansion of this type of legislation within Europe means that all in the leather industry will have to work with the current political, commercial and analytical compromise situation. Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=7869 [article]

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The sulphide challenge / Jens Fennen in LEATHER INTERNATIONAL, Vol. 215, N° 4836 (11-12/2013)  

[article]  inLEATHER INTERNATIONAL > Vol. 215, N° 4836 (11-12/2013) . - p. 25-27 Titre : The sulphide challenge Type de document : texte imprimé Auteurs : Jens Fennen, Auteur ; Daniel Herta, Auteur ; Jan-Tiest Pelckmans, Auteur ; Jürgen Christner, Auteur Année de publication : 2013 Article en page(s) : p. 25-27 Langues : Anglais (eng) Catégories : Atmosphère -- Pollution Cuirs et peaux -- Industrie -- Aspect de l'environnement Industrie -- Pollution -- Lutte contre Odeurs -- Lutte contre Sulfure d'hydrogène Sulfures Travail de rivière (cuir) Index. décimale : 675 Technologie du cuir et de la fourrure Résumé : Tanneries are often associated with the characteristic and obnoxious "sulfide smell", which is in fact caused by low concentrations of sulfhydric gas, also known as hydrogen sulfide. Levels as low as 0.2 ppm of H2S are already unpleasant for humans and a concentration of 20 ppm is unbearable. As a result, tanneries might be forced to close down beamhouse operations or are forced to re-locate away from populated areas. As beamhouse and tanning are often done in the same facility, smell is actually the lesser problem. Through human errors, this always holds the danger of mixing acidic floats with the sulfide containing beamhouse float and releasing higher amounts of H2S. At a level of 500 ppm all olfactory receptors are blocked and the gas, therefore, becomes unnoticeable and an exposure for 30 min results in a life threatening intoxication. At a concentration of 5,000 ppm (0.5%), the toxicity is so pronounced that a single breath is enough to cause immediate death within seconds. Despite all these problems and risks, sulphide has been the preferred chemical for unhairing for more than a century. This can be attributed to unavailable workable alternatives: the use of organic sulphides has shown to be practicable but not really accepted due to the extra costs involved. Unhairing solely by proteolytic and keratolytic enzymes has been tried over and over again but for the lack of selectiveness was difficult in practice to control. A lot of work has also been invested in oxidative unhairing, but until today it is very limited in its use as it is hard to get consistent results. Note de contenu : - The unhairing process - Soaking is a key factor for efficient unhairing - Low sulphide enzymatic assisted unhairing - A low sulphide, low time hair safe process En ligne : https://drive.google.com/file/d/1LagW96JfoonNNG_1joIQYOLE8LsGPvj2/view?usp=drive [...] Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=20450 [article]

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