Multiscale investigation of the effect of sizing chemistry on the adhesion and interfacial properties of glass fiber‐reinforced epoxy composites

The objective of the present work is to understand how the main constituents of sizing modify the interfacial strength, the mechanical properties of epoxy composites as well as their durability. In this study, two model interphases between E‐glass fibers and epoxy resin were designed and studied in terms of adhesion and mechanical strength from nano to macroscale. The first one is made from a reactive sizing of APTMS silane coupling agent and DGEBA pre‐polymer film‐former. The other one contains a non‐reactive MTES silane and neutralized DGEBA film‐former. The sizings were evidenced by SEM/AFM observations and XPS spectroscopy. The characterization of the prepared composites by AFM nano‐mechanic mode, micromechanical tests revealed the effect of the sizing chemistry on the interfacial properties between glass fibers and matrix. The interfacial strength is more important for the composites reinforced with APTMS‐DGEBA sized fibers than those prepared with MTES‐BGEA sized fibers. In each case, an interphase area of around 200 nm width is detected at fibers vicinity. In this area, the elastic modulus is more than 25% lower than the bulk matrix modulus. This work demonstrates the effect of sizing chemistry on the adhesion and interfacial properties of glass fiber‐reinforced epoxy composites. The multi‐scale investigation shows that the interfacial strength is more important for the composites with reactive sizing than those prepared with unreactive one.