A Kinetics Based Models for Environmentally Induced Sealant Degradation
Donald L. Hunston, Christopher C. White
Caulks and sealants are a critical part of any structure that is exposed to the environment. Although they are good materials, they eventually fail, and the failure is often difficult to detect before extensive damage is generated by water ingress or loss of adhesion. To address this issue, many of the major industry suppliers of sealant have joined with NIST to form a consortium whose goal is the development of test methods and models to predict sealant lifetimes. So far in this program 18 different sealant formulations have been exposed to indoor and/or outdoor weathering for various time periods, and 9 have shown signs of degradation. In all but one case, the primary effect of weathering is to lower the rubber modulus which corresponds initially to a decrease in the effective cross-link density. Eventually this leads to the formation and growth of cracks and debonds. This similarity in behavior is surprising since the materials represent a wide range of chemistries and formulations. On the other hand, it suggests that a common modeling approach might be applicable to a wide range of different sealants. Two approaches were formulated to describe this behavior: one based on zero order kinetics and the other based on first order kinetics. In addition, a variation of the models was developed where not all the effective cross-link points were subject to degradation. This produced the same equation for a zero order reaction but a different relationship for a first order expression. Graphical methods to distinguish the three possible were proposed, and the results were tested with data for a model sealant based on Kraton. The equation for first order kinetics with a limit on degradation was shown to fit the results quite well. The model was then tested with several temperature step experiments, and the results were encouraging.
and White, C.
A Kinetics Based Models for Environmentally Induced Sealant Degradation, Proceedings of the Adhesion Society, St. Petersburg, FL, US, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=922362
(Accessed February 26, 2024)