Accelerated thermal ageing of acrylic copolymers, cyclohexanone-based and urea-aldehyde resins used in paintings conservation
Part of : Mediterranean archaeology & archaeometry : international journal ; Vol.16, No.3, 2016, pages 213-228
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Pages:
213-228
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Abstract:
The monitoring of performance characteristics of resins was always an issue for the conservation community, since the stability of the art objects depends on the service life of conservation materials used. Among the resins commonly applied in the field of paintings conservation, four of the most popular ones, Paraloid B72, Primal AC33 (acrylic polymers), Ketone Resin N (cyclohexanone) and Laropal A81 (ureaaldehyde) were selected to be comparatively studied under accelerated ageing conditions. These resins have been used by the art conservators either as consolidant materials of the paint or as protecting varnishes for the painting surface. The behaviour of the coatings under thermal ageing was investigated following a methodology depositing films of all materials onto different solid substrates (silicon wafers, quartz and simple glass slides) depending on the method of analysis used. Accelerated thermal ageing tests were conducted at 100 oC, for up to 432 hours. The morphological characteristics of the resins films (crack formations and surface alterations, coherence of film layers, thickness and surface roughness) were examined through scanning electron microscopy (SEM). Chemical changes of the resins were studied with FTIR and UV-Vis spectroscopy, while colour properties and thermal-chemical stability were also studied with spectrocolorimetry. It was found that, although all four displayed changes concerning their colour and film thickness, the two acrylic polymers and the aldehyde resin exhibit high stability against chemical degradation compared to the cyclohexanone based resin. Complementary solubility and swelling testing were also applied and significantly aided in supporting the spectroscopy observations. Finally, microscopic examination of most resin films revealed cracking features which may sometimes render them unsuitable for application under uncontrollable conditions.
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Keywords:
conservation, polymers, resins, thermal degradation, chemical stability
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Περιέχει 17 εικόνες και 9 πίνακες
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