Surface-Functionalized White Sapphire alpha-Al2O3 Platelets as Nanofillers for Vinylester Composites and Heavy Duty Anchoring Systems
Year: 2017
Journal: Macromol. Mater. Eng.
Authors: Huber, MP; Mulhaupt, R
Synthetic alpha-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, alpha-Al2O3 platelets of 200 nm thickness and 510 mu m size are uniformly dispersed in vinylester resins which are cured by free radical polymerization at room temperature. With increasing content of ultrahard alpha-Al2O3 platelets (040 wt%) the Young's modulus of alpha-Al2O3 platelet/vinylester composites increases from 3200 to 9000 MPa. However, 15 wt% 3-methacryloyloxypropyl-trimethoxysilane (MPS) as coupling agent, added to the vinylester resin or preferably used to functionalize alpha-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 alpha-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 alpha-Al2O3 platelets and the polymer matrix.
