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Degradationskinetik

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Andreas Buder
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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.
Andreas Buder
added a research item
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.
Andreas Buder
added 2 research items
Degradationsreaktionen von oligo- und polymeren organischen Festkörpern, die durch thermooxidative, photooxidative, mechanische und/oder hydrolytische Prozesse bestimmt sind, werden bis heute in Hinsicht auf Reaktionsgeschwindigkeit und -verlauf in unzureichenden Modellen simuliert. Im Widerspruch dazu steht ein wichtiger Aspekt der modernen Konservierungsforschung, die Prognose von Oxidationsstabilitäten.