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Abstract

Dammar, a natural triterpenoid resin, is widely used as a picture varnish in art technology. Several research workers have recently characterised its composition and oxidative degradation. Due to a lack of sensitivity, conventional thermal methods to characterise oxidation stability (like TGA and DSC) often require a high temperature regime. Chemiluminescence measurements turned out to be more sensitive (temperatures below 100 °C) and simultaneously allowed for better selectivity of the signal, which is directly coupled to the oxidation mechanism. The data collected here will enable an advanced kinetic modelling of Dammar degradation.
... Als direktes Resultat des Forschungsprojektes wurde im Mai 2008 die Firma ACL Instruments AG als Spin-off der BFH gegründet, welche die zweite Gerätegeneration optimieren und erweitern sollte (Forschungsprojekt: Käser/Baumberger 2009). Begleitet wurde das gesamte Vorhaben von kleineren Forschungsprojekten, die vor allem die Anwendung des entwickelten Prototyps zum Inhalt hatten (Forschungsprojekte: Buder /Wuelfert 2008/Wuelfert , 2009/Wuelfert , 2014; (Buder 2008). Abrusci et al. (2007) haben den hydrolytischen Abbau von Gelatine-Proben mit Chemilumineszenz untersucht. ...
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During conservation studies different materials are analysed and tested for their solidity in order to be able to carry out precise conservation and restoration measures and to be able to assess their sustainability. Chemiluminescence is a phenomenon in which an electron is relaxed from an energetical- ly higher orbital into a lower situated condition while simultaneously releasing energy in the shape of photons. As a consequence the stimulated state is caused by a chemical reaction. This process is very specific and occurs during an oxidation reaction among oth- er things. Through the recombination of two peroxides for example a stimulated carbonyl compound is generated which emits its energy as light. This connection between the oxidation of organic substances and the emission of photons determines the main question, whether chemiluminescence can be used as a method for characterisation of materials which are relevant to the research of conservation. As a result of a research project between departments of the Bern University of Applied Sciences BFH it was possible to construct a chemiluminescence measuring device and modify it in a way that it could be used for this work. Within this experiment a standardised method of measurement was tested on different substances, for example adamantylidenadamantan-1.2-dioxetan, and the different im- pacts on the chemiluminescence-signal investigated. Through this process important facts were determined for the concept of measurement, for example precision, proof- and defi- nition perimeters. Based on the solidity of dammar, a triterpene resin, the method could be experimentally verified within the test using a complex example from conservation research. Within that process published results about the oxidation properties of dammar resin were verified. Due to the specific signal, the thermally initiated responses in inert as well as oxidative gas atmospheres could be documented. The results were compared with established methods like DSC, TGA and ESR spectroscopy and the consistencies to the signals logged. The already much discussed influence of stabilisers on dammar resin was tested on non- aged and artificially aged specimens using chemiluminescence. Through these previously suggested formulations, effects of certain synergistic composites were detected and con- firmed. Using the data from the chemiluminescence measurements kinetic calculations about activation parameters were compiled. The identified parameters were used for the prog- nosis of the course of reactions during differently simulated temperature profiles, making a prediction of the materials’ life span possible. Through these results not only the high performance ability of the method became appar- ent but also the potential of the determined measurement data, mainly in connection with the application within the model-free kinetic. However, alongside these possibilities limitations of the method were revealed. These are partly caused by the characteristics of the signal which has yet to be mechanistically fully clarified. Simultaneously, further processing of the measurement data via thermokinetic software makes clear that the quality of the calculations of the reaction process is only as good as the quality of the initial data. This suggests the prognoses about the stability of the material only conveys a concept of their qualities.
Article
Although films of dammar resin cannot be stabilized against photochemical degradation in the presence of ultraviolet light with currently available additives, a remarkable stabilization is obtained with a hindered amine light stabilizer (HALS) if the ultraviolet component of the light source is eliminated. Even in the absence of UV light the effect of HALS can be improved by further addition of a benzotriazole ultraviolet absorber. It is proposed that the UV absorber functions as a radical scavenger under such conditions. Films of dammar containing 2% Tinuvin 292 and 3% Tinuvin 328 remain intact when aged in a xenon arc fadeometer under exclusion of UV light for as long as 3700 hours, while they normally break down in a few hundred hours. After such a period of accelerated aging the original components of the resin are all still intact and the films remain removable with cyclohexane. No yellowing occurs during heat aging after a preceding period of prolonged fadeometer aging. Changes in the films were observed using ultraviolet-visible light and infrared spectrophotometry, gel permeation chromatography, gas chromatography/mass spectrometry and solubility tests. The 'cut-on' wavelength of the UV filter should not be lower than c. 400nm for best results. /// Bien que l'on ne puisse pas protéger les films de résine dammar de la dégradation photochimique due à la lumière ultraviolette avec les additifs courants, un certain type de stabilisation importante peut être obtenu grâce à un stabilisateur de lumière contenant une amine bloquée (HALS), si toutefois le composant UV de la source lumineuse a été éliminé. Même en l'absence d'UV, l'effet du HALS peut être renforcé par l'addition supplémentaire d'un absorbant UV au benzotriazole. On pense que l'absorbant UV agit alors comme un destructeur de radicaux. Les films de dammar contenant 2% de Tinuvin 292 et 3% de Tinuvin 328 restent inchangés après un vieillissement de 3700 heures au fadéomètre à xenon en l'absence de lumière UV, alors que normallement ils se dégradent après quelques centaines d'heures. Après cet essai de vieillissement accéléré, les composants de la résine sont toujours intacts et les films restent solubles dans le cyclohexane. On ne constate aucun jaunissement pendant le vieillissement à la chaleur succédant au vieillissement prolongé au fadéomètre. Les changements dans les films ont été étudiés à l'aide du spectrophotomètre en lumière UV-visible et infrarouge, en chromatographie sur gel, en chromatographie gazeuse couplée au spectromètre de masse, et par essais de solubilité. La longueur d'onde de protection du filtre UV ne doit pas être inférieure à 400nm. /// Derzeit können Dammarfilme durch auf dem Markt erhältliche Zusätze nicht gegen durch UV-Strahlung verursachte photochemische Abbauprozesse geschützt werden. Eine beträchtliche Stabilisierung wird allerdings unter Zusatz eines sterisch gehinderten Amins erreicht, sofern der UV-Anteil des Lichtes herausgefiltert wird. Dieser Effekt kann -- ein fehlender UV-Anteil vorausgesetzt -- durch eine zusätzliche Beigabe von UV-absorbierenden Benzotriazolen noch verbessert werden: Dabei könnte der UV-absorbierende Bestandteil als Radikalfänger fungieren. Dammarfilme mit einem Zusatz von 2% Tinuvin 292 und 3% Tinuvin 328 bleiben unter künstlichen Alterungsbedingungen--(Xenotestanlage, wiederum UV-Anteile ausgefiltert) 3700 Stunden stabil. Normalerweise verändern sich derartige Filme bereits nach einigen wenigen hundert Stunden. Nach diesem Test erweisen sich alle Bestandteile des Harzes noch als unverändert und die Filme behalten ihre töslichkeit in Cyclohexan. Setzt man die Filme nach dem Alterungstest zusätzlich noch einer Wärmebelastung aus, konnte kein Vergilben beobachtet werden. UM ein bestmögliches Ergebnis zu erhalten, sollte die Absorptionskante des UV-Filters jedoch nicht unter 400nm Ilegen. Diese Erkenntnisse Stützen sich auf analytische Ergebnisse, die mittels der UV/VIS Spektroskopie, der Gelpermeationschromatographie, der Gaschromatographie/Massenspektrometrie und durch löslichkeitsvecsuche erzielt wurden.
Article
Derivatization procedures using quaternary ammonium hydroxides are now frequently applied to the gas chromatography/mass spectrometry (GCMS) analysis of paint media and varnishes. This paper compares the results obtained when triterpenoid resins are analysed using different reagents and sample preparation methods. Depending on the reagent and derivatization method used, the quaternary ammonium hydroxides produced multiple derivatives and induced isomerization in a number of the components of triterpenoid resins. This has implications for selecting an appropriate derivatization technique for the analysis of triterpenoid resins such as dammar and mastic.