Processes During Aging in Ultra-thin Epoxy Films on Metals

Chemical Processes During Aging in Ultra-thin Epoxy Films on Metals 

The aging of adhesives and lacquers affects the durability of structural bonds and coatings. It depends on environmental influences such as humidity, temperature, irradiation, the surrounding media, and the network state of the polymer. In addition, the network properties and therefore the aging behavior are influenced by substrates that provoke the formation of an interphase during network formation. The properties of the interphase differ from the bulk and it is often the weak spot of structural adhesive joints. Hence, to improve the lifetime of such a joint it is crucial to understand the chemical processes both in the bulk polymer and in the adhesive-adherend interphase under given envi- 

Adhesion - Current Research and Application. WulfF Possart Copyright 2005 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 3-527-31263-3 

The aging of hulk epoxy networks has been studied by various techniques such as FTIR spectroscopy [1-4], gravimetric analysis [1, 3, 5, 6], mass spectroscopy [1], DSC [2], or XPS [6]. The aging conditions applied vary broadly from thermo-oxidation at elevated temperature (100-250 °C) [1-3, 5, 6] or photo-oxidation [1, 2] to humid or environmental conditions [4, 7]. FTIR investigations [1-4] show the rise of new IR bands at 1660-1670 cm and 1720-1730 cm in an oxidized region near to the sample surface. The bands are explained by amide and carbonyl formation due to radical oxidation mechanisms initiated by the elevated temperature or UV irradiation [1, 2, 4]. Also, backbone cleavage is held responsible for the observed decrease in glass transition temperature [2]. 

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