Surface-Functionalized White Sapphire α-Al2O3Platelets as Nanofillers for Vinylester Composites and Heavy Duty Anchoring Systems

Abstract

Synthetic α-Al2O3 platelets, also referred to as corundum and white sapphire, represent attractive fillers improving the mechanical properties of vinylester-based chemical anchoring systems. Even in the absence of coupling agents, as verified by scanning electron microscopic (SEM) analyses of fracture surfaces, α-Al2O3 platelets of 200 nm thickness and 5–10 µm size are uniformly dispersed in vinylester resins which are cured by free radical polymerization at room temperature. With increasing content of ultrahard α-Al2O3 platelets (0–40 wt%) the Young's modulus of α-Al2O3 platelet/vinylester composites increases from 3200 to 9000 MPa. However, 1–5 wt% 3-methacryloyloxypropyl-trimethoxysilane (MPS) as coupling agent, added to the vinylester resin or preferably used to functionalize α-Al2O3 surfaces in a filler pretreatment step, improves elongation at break (+50%) without sacrificing high stiffness and strength. The X-ray photoelectron spectroscopy (XPS) analysis confirms the successful surface-functionalization of α-Al2O3 platelets by using pretreatments with MPS in toluene, acidified ethanol/water or tetrahydrofuran, respectively. The MPS filler pretreatment simultaneously enhances tensile strength (+22%), elongation at break (+50%), and Young's modulus (+12%) as compared to composites containing unmodified filler. According to SEM analyses of composite fracture surfaces, MPS-mediated functionalization affords significantly improved interfacial adhesion between α-Al2O3 platelets and the polymer matrix.