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In this study, hydrolyzable tannins (commercial chestnut, valonea and tara extracts), condensed tannins (commercial quebracho and mimosa extracts) as well as calf leathers produced using these vegetable tanning agents were characterized by thermal decomposition methods using slow and high heating rates. Calf gelatin obtained by heating calf pelt in water at 70 ˚C was chosen as a reference material. Thermogravimetry/mass spectrometry (TG/MS) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) experiments were performed on the tannin and leather samples. The evolution profiles of the decomposition products as well as the thermal stability of tannins and leathers were studied by TG/MS. A net difference was observed in the thermal behavior of hydrolyzable and condensed tannins. The condensed tannins produced the highest char yield, while the hydrolyzable tara extract released the most volatile products. The tannins of higher reactivity produced more stable leathers as it results from their higher decomposition temperature. The composition of both vegetable tanned leathers and vegetable tanning agents was characterized by the pyrolysis product distribution measured by Py-GC/MS method. Resorcinol and its methylated derivative (orcinol) were found to be characteristic decomposition products for both condensed tannins, i.e. mimosa and quebracho. It was identified among the pyrolysis products of the mimosa and quebracho tanned leathers, as well. Characteristic decomposition product, a bisphenol derivative was identified among the pyrolyzates of hydrolyzable tannins and the leathers tanned with the hydrolyzable tannin agents.

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The dose dependent effect of gamma irradiation on collagen in vegetable tanned leather was studied by the MHT method. Examination of the irradiated samples at 3 months after the irradiation treatment revealed variations of the main shrinkage temperatures and intervals. Up to 25 kGy, the shrinkage temperature does not vary while the total shrinkage interval decreases suggesting cross-linking as the main process. At higher doses, the decrease of shrinkage temperature is accompanied by the increase of the total shrinkage interval indicating that peptide chain scission becomes predominat. Quebracho-tanned sheep leather shows to be the less resistant to the deterioration effect of gamma radiations, while both mimosa-tanned goat leather and quebracho-tanned calf leather better withstand the destabilization effects.

ABSTRACT. The dose dependent effect of gamma irradiation on collagen in vegetable tanned leather was studied by unilateral nuclear magnetic resonance (NMR). Examination of the irradiated samples after 1 week of treatment revealed variations of both spin-lattice (T ) and spin-spin (T ) proton relaxation times. To evaluate 1 2 the long-term effects of gamma irradiation, the irradiated samples were further exposed to accelerated ageing at 40°C and weekly alternate 30% and 75% relative humidity (RH) for 12 weeks. The synergistic action of temperature and relative humidity caused distinct variations of both T and T relaxation times suggesting 1 2 distinct modifications within the collagen fibril structure. Structural variations were attributed to cross-linking, the prevalent pattern at 25 kGy dose, while polypeptide chain scission was shown to be prevailing at higher doses. KEY WORDS: collagen, vegetable tanned leather, gamma irradiation, unilateral NMR STUDIUL EFECTULUI DOZEI DE RADIAÞII GAMMA ASUPRA COLAGENULUI DIN PIELEA TÃBÃCITÃ VEGETAL UTILIZÂND SPECTROSCOPIA RMN REZUMAT. S-a studiat efectul dozei de iradiere gamma asupra colagenului din pielea tãbãcitã vegetal prin rezonanþã magneticã nuclearã unilateralã (RMN). Examinarea probelor iradiate dupã 1 sãptãmânã de tratament a indicat variaþii atât ale timpilor de relaxare a protonilor spin-reþea (T ), cât ºi a celor spin-spin (T ). Pentru a evalua efectele pe termen lung ale iradierii gamma, probele iradiate au fost expuse în continuare la îmbãtrânire acceleratã la 40°C ºi s-a alternat sãptãmânal umiditatea relativã (UR) în intervalul 30%-75% timp de 12 sãptãmâni. Acþiunea sinergicã a temperaturii ºi umiditãþii relative a produs modificãri distincte ale timpilor de relaxare T ºi T , sugerând modificãri distincte în structura fibrilelor de colagen. Pânã la doze de 25 kGy mecanismul predominant a fost reticularea, în 1 2 timp ce la doze mai mari a predominat scindarea lanþului polipeptidic. CUVINTE CHEIE: colagen, piele tãbãcitã vegetal, iradiere gamma, RMN unilateralã L'EFFET DE L'IRRADIATION GAMMA SUR LE COLLAGÈNE DU CUIR À TANNAGE VÉGÉTAL EN UTILISANT LA SPECTROSCOPIE RMN RÉSUMÉ.On a étudié l'effet de la dose d'irradiation gamma sur le collagène du cuir à tannage végétal par la résonance magnétique nucléaire unilatérale (RMN). L'analyse des échantillons irradiés après 1 semaine de traitement a montré des variations des temps de relaxation des protons spin-réseau (T ) et spin-spin (T ). Pour 1 2 évaluer les effets à long terme de l'irradiation gamma, les échantillons irradiés ont été davantage exposés à un vieillissement accéléré à 40°C et on a modifié chaque semaine l'humidité relative (HR) entre 30% à 75% pendant 12 semaines. L'action synergique de la température et l'humidité relative ont produit des changements distincts dans les temps de relaxation T et T , ce qui suggère des changements distincts dans la structure des fibrilles de collagène. À la dose de 25 kGy le mécanisme 1 2 prédominant était la réticulation, tandis qu'aux doses plus élevées le clivage de ...