It is widely accepted that the fiber/matrix interface influences the overall mechanical properties and failure modes of fiber-reinforced composites. Fiber manufacturers use multifunctional sizing packages to lubricate, protect, and promote adhesion between the fiber and the matrix. These sizing packages contain a proprietary mixture of film formers, lubricants, adhesion promotors, etc., and the formulations are tailored to the class of matrix being used. Glass fiber manufacturers often use silane-based adhesion promotors, such as (3-glycidoxypropyl)trimethoxysilane (GPS) and (3-aminopropyl)trimethoxysilane (APS) in these sizing packages. A molecular dynamics simulation study predicts the interfacial shear strength (IFSS) can be maximized by applying a monolayer type of coating of these silanes onto the fiber surface [1]. In this study, we investigated the interface architecture’s role on the S-2 glass fiber/epoxy interface by applying a thin coating of GPS or APS using a low-temperature chemical vapor deposition method (CVD) to create an agglomeration-free thin layer. We varied the deposition time to achieve different coverage on the fiber. The S-2 glass fiber/epoxy interface properties were evaluated for these systems using a single fiber pullout method, and the failure surface was evaluated using AFM. By omitting the other components frequently found in a sizing package, we gained insight into the role of the silane adhesion promotors and the interface architecture. The IFSS was successfully varied from 50 MPa to 75 MPa by varying the silane chemistry and deposition time. By understanding the effects of the chemistry and architecture of the interface as well as how to control it, we gained the ability to tailor the interface to optimize the material for the application-specific needs.
1. Chowdhury, S. C. & Gillespie, J. W. Silica–silane coupling agent interphase properties using molecular dynamics simulations. J. Mater. Sci. 52, 12981–12998 (2017).
