IN-SITU EXAMINATION OF WATER DIFFUSION TO THE POLYPROPYLENE-SILANE INTERFACE USING FTIR-ATR

This study investigated the effect of moisture on a model silane coupl ing agent modified adhesive bond. Fourier transform infrared-attenuate d total reflectance (FTIR-ATR) spectroscopy was used to characterize t he transport of moisture to a poly-propylene-silane interphase and mon itor the resulting chemical changes. The FTIR-ATR method offers the ad vantage of in-situ examination of the diffusion process, as well as th e ability to characterize chemical changes that occur due to the prese nce of moisture. Experiments were conducted at ambient and elevated te mperatures. The results of the real-time measurements demonstrated tha t moisture will migrate through the polypropylene to the silane interp hase. The diffusion behavior was described well by a Fickian model. Th e apparent diffusion coefficients for water in the polypropylene-silan e bilayer were on the order of the diffusion coefficients for water in polypropylene at both test temperatures. Furthermore, changes in the spectra were observed during the diffusion experiments. These changes were indicative of hydrolysis of the siloxane backbone in the silane l ayer while buried beneath the polypropylene film. This finding is sign ificant as it presents direct evidence of a degradation mechanism in s ilane-modified adhesive bonds. (C) 1997 John Wiley & Sons, Inc.