The silane interphase of composites: Effects of process conditions on γ‐aminopropyltriethoxysilane

Abstract FT‐IR spectroscopy was used to collect spectra of γ‐aminopropyltriethoxy silane (γ‐APS) coupling agent deposited on KBr plates, modeling the silane interphase of composites, to study the effects of heating the γ‐APS film under various environmental conditions. This coupling agent is used in fiber‐reinforced epoxy composites. An aminebicarbonate salt forms when the sample is dried in a moist carbon dioxide environment giving rise to a series of bands from 2800 to 2000 centimeter ⁻¹ (cm ⁻¹ ) and bands at 1637 cm ⁻¹ , 1330 cm ⁻¹ , 696 cm ⁻¹ , and 663 cm ⁻¹ . The primary amine group is split into two bands at 1572 cm ⁻¹ and 1486 cm ⁻¹ in the NH ₃ ⁺ form. Heating removes the aminebicarbonate salt at temperatures above 95°C and condenses the γ‐APS polymer to a polysilsesquioxane film. The aminebicarbonate salt partially reforms if the γ‐APS film is stored in a moist CO ₂ environment. At temperatures above 120°C the primary amine of γ‐APS is oxidized in air to imine groups. In the process of evolving the CO ₂ the polymer is further condensed and the amine groups can be converted to imines if the temperatures exceeds 120°C. Both processes reduce the reactivity of the coupling agent with the epoxy resin. The structure of the silane interphase must be controlled during the processing of the composite to yield materials with maximum properties.