Chemiluminescence for the Early Detection of Weathering Effects of Coatings Part l – Fundamentals

By Volker Wachtendorf , Anja Geburtig

Weathering tests are part of the group of long-term tests designed to characterize the aging of materials. Even after decades of use on thousands of different materials, these tests still are necessary to charac­terize new materials as their outcome is material-specific (hence, conclusions from material A to material B cannot be drawn). There still is no physical-chemical model to characterize the aging process as an alternative to the experimental evalua­tion. Since the aging, in terms of a certain property versus its exposure time, does not run in parallel for different materials, it is not sufficient to improve the initial value of a property.

Only the experimental evalu­ation of the aging curve is able to ensure that the aged value of the property is still within specifications. Advances in the UV stabilization of coatings have resulted in increased ser­vice lifetime. Subsequently, artificial tests of long-term stability need to last longer. At the same time, however, demands to shorten the duration of testing have be­come more stringent. Particularly during the development phase of new coating systems, long testing times are prohibi­tive.

Any method that can shorten the time for artificial tests, therefore, is much in demand. The test duration shortening strategy followed here is to use chemilumines­cence as a sensitive detector for weather­ing effects. This means that weathering (outdoor or artificial) is carried out in the conventional way, but for the evaluation of degradation effects caused by weather­ing exposure, use is made of chemilumi­nescence detection.