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Water at the Polymer/Substrate Interface and Its Role in the Durability of Polymer/Glass Fiber Composites.


pdf icon Water at the Polymer/Substrate Interface and Its Role in the Durability of Polymer/Glass Fiber Composites. (832 K)
Nguyen, T.; Byrd, W. E.; Alsheh, D.; Aouadi, K.; Chin, J. W.

Durability of Fibre Reinforced Polymer (FRP) Composites for Construction (CDCC'98), 1st International Conference. Proceedings. August 1998, Canada, Benmokrane, B.; Rahman, H., Editor(s)(s), 451-462 pp, 1998.

Keywords:

water; durability; building technology; bonding strength; FT-IR; interface; polymer composite; composite materials

Abstract:

Fiber-reinforced polymer composites are increasingly used in offshore and civil engineering structures. In these applications, composite material are often exposed to aqueous environments. Water can reduce polymer composite durability by affecting the matrix, the fiber, and the fiber/matrix interface. This study investigated the role of the polymer/substrate interfacial water layer on the shear strength of polymer/glass fiber composites. The thickness of the interfacial water layer was measured by Fourier transform infrared-multiple internal reflection (FTIR-MIR) spectroscopy of an epoxy applied to a model siliceous substrate. The shear strength of the composite was determined from the short-beam test of unidirectional composites made of E-glass fiber and the same epoxy matrix. Both untreated and silane-treated siliceous substrates and E-glass fibers were used. Little water was observed at the interface of the silane-treated specimens, but about 10 monolayers of water accumulated at the epoxy-substrate interface of the untreated samples after exposure to water. Shear strength loss of the untreated composite was twice that of the silane-treated material after a 3-month immersion in 60 deg C water. Further, the treated specimens remained transparent but the untreated specimens became opaque after water exposure. Evidence from mechanical and spectroscopic analyses and visual observaton indicated that water at the polymer/fiber interface was responsible for the dfference in the loss of the shear strength of the untreated and surface-treated composites. Data on solubilities and diffusion coefficients of water in the eopoxy for two exposure temperatures and changes of epoxy glass transition temperature and work of adhesion of epoxy/silica due to water are presented.