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pH related swelling / Richard Daniels in WORLD LEATHER, Vol. 18, N° 4 (06-07/2005)  

[article]  inWORLD LEATHER > Vol. 18, N° 4 (06-07/2005) . - p. 20 Titre : pH related swelling Type de document : texte imprimé Auteurs : Richard Daniels, Auteur ; Walter Landmann, Auteur Année de publication : 2005 Article en page(s) : p. 20 Langues : Anglais (eng) Catégories : Collagène Cuirs et peaux Gonflement (physique) pH Index. décimale : 675 Technologie du cuir et de la fourrure Résumé : Collagen is amphoteric in nature; that is, it can exhibit both cationic and anionic properties. This is due to the presence of both positively charged amino groups and negatively charged carboxyl groups as side chains on the main polypeptide backbone. At the isoelectric point these charges are balanced, leading to a stable and compact structure. If the pH is increased, say, by adding sodium hydroxide to skins in a processing float, hydroxyl ions penetrate the structure. The amino groups lose their positive charge, while the carboxyl groups retain their negative charge. Note de contenu : - Weakening of the electrostatic bond - Osmotic effects - pH related swelling and softness - Swelling control - Panel E3/1 : Charge at the IEP - Panel E3/1 : Charge after introduction of OH- - Panel E3/1 : Swelling of the skin as a function of pH and repression by addition of salt En ligne : https://drive.google.com/file/d/1zU9UtCpsaOBhT__Ddw6Gipg3HTCL2R1U/view?usp=drive [...] Format de la ressource électronique : pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=32374 [article]

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Charge and fixation / Richard Daniels in WORLD LEATHER, Vol. 18, N° 4 (06-07/2005)  

[article]  inWORLD LEATHER > Vol. 18, N° 4 (06-07/2005) . - p. 21 Titre : Charge and fixation : Back to Basics : A framework for leather manufacture Type de document : texte imprimé Auteurs : Richard Daniels, Auteur ; Walter Landmann, Auteur Année de publication : 2005 Article en page(s) : p. 21 Langues : Anglais (eng) Catégories : Agents de tannage Chrome Collagène Complexes métalliques Fixation (chimie) Glutaraldéhyde Liaisons hydrogène Prétannage Réticulation (polymérisation) Tanins végétaux Index. décimale : 675 Technologie du cuir et de la fourrure Résumé : The rate of fixation between the collagen structure and pretanning agents, dyes and many polymeric resins and fatliquors is determined by the charge of the collagen and the charges of the product. An increase in alkalinity causes an increase in negative charge within the skin, due to lesses of amino(+) groups. Under these conditions, if a chemical with a strong positive charge is offered-such as chrome or aluminium salts-there is a very rapid reaction with the surface carboxyl(-) groups and no penetration. Under the same conditions, a product with a negative charge-such as a syntan-will combine slowly and penetrate deep into the structure as there is a reduced number of available amino(+) groups for fixation. Note de contenu : - Panel E4/1 : Charges relating to groups and products - Panel E4/2 : Crosslinking by chromocomplexes: shift to cationic behavior - Panel E4/3 : Crosslinking by glutaraldehyde : shift to anionic behavior - Panel E4/4 : Hydrogen bonding by vegetable or synthetic tannins : shift to anionic behavior En ligne : https://drive.google.com/file/d/16QA5aGRIIVKhSzjDgZd78zp5ZsG158Nb/view?usp=drive [...] Format de la ressource électronique : pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=32375 [article]

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"Formaldehyde-free leather" - a realistic objective ? / Renate Meyndt in WORLD LEATHER, Vol. 18, N° 4 (06-07/2005)  

[article]  inWORLD LEATHER > Vol. 18, N° 4 (06-07/2005) . - p. 23-27 Titre : "Formaldehyde-free leather" - a realistic objective ? Type de document : texte imprimé Auteurs : Renate Meyndt, Auteur ; Heinz-Peter Germann, Auteur Année de publication : 2005 Article en page(s) : p. 23-27 Langues : Anglais (eng) Catégories : Cuir -- Teneur en formaldéhyde Cuirs et peaux -- Analyse Formaldéhyde Produits chimiques -- Consommation -- Réduction Vieillissement Index. décimale : 675 Technologie du cuir et de la fourrure Résumé : There is an increasing demand for "formaldehyde-free" leather. No legal regulation presently exists for this chemical in the EU, but in many areas of application the amount of formaldehyde contained in leather is limited by technical specifications or eco-labels. Formaldehyde is used in large quantities as a starting material for the production of synthetic aromatic and resin-tanning agents. During the production of these compounds formaldehyde acts as a condensation agent, helping to develop larger molecules. The resulting condensation products have different levels of hydrolytic stability, so are potential sources of formaldehyde. In addition, some dyeing auxiliaries, fatliquors and finishing products are also able to release formaldehyde. However, high quality leather requirements cannot be met unless a wide range of tanning and retanning agents, dyeing auxiliaries and fatliquors are used. It therefore appears necessary to develop a leather-producing technology that meets high quality demands and guarantees a minimal risk of formaldehyde release from the finished product. Attempts to bind free and releasable formaldehyde in leather with scavenging compounds have been reported and the modification of some technological steps has also been investigated. However, another way to reduce the formaldehyde content of leather is to select the recipe components on the basis of their potential to release formaldehyde. Even so, an adequate analytical method to determine the free formaldehyde in tanning agents and auxiliaries had not been previously developed. Within this investigation the development and validation of such a method was therefore essential. Furthermore, it was important to take into account that the interaction between chemicals and the leather matrix might generate synergistic effects. Also the ageing process of leather could involve formaldehyde release. Finally, several compounds needed testing regarding their suitability as formaldehyde scavengers. Note de contenu : - A test method for the determination of free formaldehyde - Materials for assessment and scope of the investigation - The production of formaldehyde-free leather - The influence of product selection - Determination of free formaldehyde in tannins and auxiliaries - The production of formaldehyde-free leather - The influence of product selection - The influence of ageing - Panel 1 : The release and collection of formaldehyde from leather making products - Panel 2 : Free formaldehyde in different product classes - Panel 3 : Inorganic compound: effect of sodium disulphite (chrome tanned leather) - Panel 4 : Inorganic compound : effect of Auxiliary A (chrome tanned leather) - Panel 5 : Organic compound: effect ofAuxiliary B (chrome tanned leather) - Panel 6 : Efficiency of the tested scavengers (VDA 275, chrome tannage) - Panel 7 : Development of recipes for low formaldehyde release (chrome tannage) - Panel 8 : Development of recipes for low formaldehyde release (chrome-free tannage) - Panel 9 : Artificial ageing parameters - Panel 10 : Results of artificial ageing experiments on chrome tanned leather - Panel 11 : Results of artificial ageing experiments on chrome-free leather - Panel 12 : Chrome tanned leather : Variation of formaldehyde content during storage - Panel 13 : Chrome free leather : variation of formaldehyde content during storage En ligne : https://drive.google.com/file/d/1_OebkuER7Ocv7ObV5t4-vhLMPJrsUl1a/view?usp=drive [...] Format de la ressource électronique : pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=32463 [article]

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Fillers : valuable components in the retanning of leathers / André Spier in WORLD LEATHER, Vol. 18, N° 4 (06-07/2005)  

[article]  inWORLD LEATHER > Vol. 18, N° 4 (06-07/2005) . - p. 28 Titre : Fillers : valuable components in the retanning of leathers Type de document : texte imprimé Auteurs : André Spier, Auteur Année de publication : 2005 Article en page(s) : p. 28 Langues : Anglais (eng) Catégories : Charges (matériaux) Cuirs et peaux Protéines Retannage Index. décimale : 675.2 Préparation du cuir naturel. Tannage Résumé : The use of protein-based fillers in the retanning process can play a valuable part in the production of good quality leathers. This type of product is in wide use, but sometimes not applied in the right way. Accordingly, their full benefits are not always achieved or appreciated within the final leather. Almost all the major chemicals used in the leather tanning processes carry charge so their use involves chemical reactions with collagen. In contrast, protein-based fillers have limited or absolutely no chemical reaction with the protein structure. These products need using selectively, and not all types or leathers need Hers. For example, heavily vegetable re-tanned leathers, or thin leathers may not require this kind of product. However, where selective filling is needed it is easy to see the benefits that can be gained, and this applies to most leathers. Note de contenu : - Why use fillers as opposed to charged retanning agents ? - The location of fillers within the fibre structure - The application of fillers - Fig. 1a : a typical cross section of the dense fibre structure within the butt area of a raw hide - Fig. 1b : The structure in the belly-parts. Although modified in processing before retannage, the forger voids in the flanks, belly and shoulders remain. A selective filling can help make the overall structure more uniform En ligne : https://drive.google.com/file/d/1XluuokWm2EvAWCJo7nqX2hSqRnY0eHHm/view?usp=drive [...] Format de la ressource électronique : pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=32464 [article]

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A practical evaluation of acrylic resins and the development of a materials evaluation method / M. Bientinesi in WORLD LEATHER, Vol. 18, N° 4 (06-07/2005)  

[article]  inWORLD LEATHER > Vol. 18, N° 4 (06-07/2005) . - p. 31-35 Titre : A practical evaluation of acrylic resins and the development of a materials evaluation method Type de document : texte imprimé Auteurs : M. Bientinesi, Auteur ; Maurizia Seggiani, Auteur ; Sandra Vitolo, Auteur ; Domenico Castiello, Auteur ; M. Salvadori, Auteur Année de publication : 2005 Article en page(s) : p. 31-35 Langues : Anglais (eng) Catégories : Agents de tannage Cuirs et peaux -- Analyse Essais (technologie) Evaluation Indice des prix Polyacryliques Polymères -- Analyse Retannage Index. décimale : 675 Technologie du cuir et de la fourrure Résumé : This study describes a method for evaluating commercial acrylic resins as used in retannage. By means of in-house tests, this technique can prove useful to tanneries in the selection of resin retanning agents that, from a cost-effectiveness point of view, best suit their purposes. The technique has been used previously in an evaluation of dyestuffs and, furthermore, it is believed that this method can be used as a powerful tool within any manufacturing process as part of product or component evaluation. Note de contenu : - The study - Consistency tests - Determination of the performance index - Determination of the price index - Findings from the investigation - The performance index - The final product evaluation - Findings from the investigation - Fig. 1 : Standard procedure for retanning, dyeing and fatliquoring - Fig. 2 : Weightings attributed to tactile parameters of finished leather - Fig. 3 : Dry solids content of resins - Fig. 4 : Lastometer test results - Fig. 5 : Evaluation of retanned, fatliquored and dyed leathers - Fig. 6 : Price index for resins - Fig. 7 : Final evaluation of resins examined - Panel 1 : Price index calculations for resins En ligne : https://drive.google.com/file/d/1JRiRbDpp1z_yI_qImQR3AimWuGELVlcs/view?usp=drive [...] Format de la ressource électronique : pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=32465 [article]

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An appreciation of rollercoating in WORLD LEATHER, Vol. 18, N° 4 (06-07/2005)  

[article]  inWORLD LEATHER > Vol. 18, N° 4 (06-07/2005) . - p. 37-41 Titre : An appreciation of rollercoating Type de document : texte imprimé Année de publication : 2005 Article en page(s) : p. 37-41 Langues : Anglais (eng) Catégories : Cuirs et peaux -- Finition Enduction au rouleau Index. décimale : 675 Technologie du cuir et de la fourrure Résumé : The technology of finishing leather by rollercoating has now been under development for some thirty years, having originally been transferred from industries coating rigid, board-like materials. The huge advantage of rollercoating over spraying of finishing pigments, oils and lacquers is in economy of application—a rollercoater only applies the finish to the leather surface, and virtually none is lost or wasted. The continuous development of machinery and finishing chemicals now enables us to use rollercoaters to finish the softest, thinnest leathers produced, both in 'synchro' and 'reverse' coating, for impregnation, base pigment coating, design printing and final lacquering ; in fact, we are now at the point of being able to carry out all these operations with a single, multi-purpose machine. Let us briefly review the basic principles of rollercoating machinery as used in the leather industry. Pigment, oil or lacquer is applied to a rotating cylinder with an engraved pattern that can `carry' a thin film of the material. Excess material is wiped from the engraved surface by an angled sprung doctor blade, which also serves to form a small reservoir of material against the rotating cylinder. The coating material is pumped to this reservoir, normally by a pneumatic diaphragm pump, and overflows via weirs and catchment trays at each end back to the material container. Leather is carried beneath the engraved cylinder by a rubber roller or a rubber conveyor belt, so positioned as to give a very small clearance beneath the engraved cylinder. When the leather passes through this 'nip' point, material is transferred from the surface of the engraved cylinder onto the surface of the leather. Note de contenu : - Coping with soft leathers - Sophisticated accuracy - Fig. 1 : A multi-purpose synchro and reverse rollercoater for sides and skins - Fig. 2 : Synchro coating - Fig. 3 : Synchro coater with three engraved rollers in rotary turnet - Fig. 4 : Engraving pattern of a synchro coating roller - Fig. 5 : Reverse coating - Fig. 6 : Original engraving pattern of a reverse coating roller - Fig. 7 : A whole hide reverse rollercoater - Fig. 8 : Introduction conveyor unit, withdrawn from reverse rollercoater - Fig. 9 : Engraving pattern of helically grooved reverse coating roller - Fig. 10 : Three whole hide reverse rollercoaters with driers, linked into a continuous production line - Fig. 11 : Synchro rollercoater with twelve rollers on rotary turret - Fig. 12 : Whole hide multi-purpose rollercoater with automatic changeover from synchro to reverse coating - Fig. 13 : Multi-purpose rollercoater En ligne : https://drive.google.com/file/d/1MLiReWJAh1b7NhVzYG0QVvXvRIoaNkkn/view?usp=drive [...] Format de la ressource électronique : pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=32466 [article]

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