Water at the polymer/substrate interface in coatings, adhesives, and fiber-reinforced polymer composites is often the main cause of adhesion loss in these systems. Using experimental data measured in this study, we critically assess the role of interfacial water on the adhesion loss of epoxy/silicon substrate systems (SiOH-covered Si) and epoxy/E-glass fiber composites. Thickness of the water layer at the epoxy/Si substrate interface was measured by Fourier transform infrared-multiple internal reflection (FTIR-MIR) spectroscopy. Peel adhesion and short-beam shear tests were utilized to measure adhesion loss in epoxy/Si substrate systems and epoxy/E-glass fiber composites, respectively. Little water accumulation at the epoxy/Si substrate interface is observed for silane-treated Si substrates, but about 10 monolayers of water is observed at the interface between the epoxy and the non-treated Si substrate following exposure to 24 oC for 100 h. More than 70 % of the initial epoxy/non-silane-treated Si systems peel strength is lost within 75 h of exposure, compared to 20 % loss after 600 h for the silane-treated Si samples. Shear strength loss in epoxy composites made with non-silane-treated E-glass fiber is nearly twice that of composites fabricated with silane-treated fiber after six-month immersion in 60 oC water. Further, the silane-treated composites remain transparent, but the non-silane-treated fiber composites become opaque after water exposure. Evidence from the FTIR-MIR spectroscopy, adhesion loss, and visual analyses strongly indicates that water at the polymer/substrate interface is mainly responsible for the adhesion loss in coatings, adhesives and glass fiber composites, and that FTIR-MIR is a viable technique to reliably and conveniently assess the water resistance of these material systems.
Citation: Journal of Adhesion
Pub Type: Journals
adhesion, ATR, building technology, interface, internal reflection spectroscopy, polymer/glass fiber composites, polymer/substrate, water