Effects of hyperbranched poly(ester-silane) as a coupling agent on the mechanical behavior of glass bead filled epoxy resin

Abstract

Hyperbranched poly(ester-silane)s (HPE-Si, including HPE-Si4 and HPE-Si8) were synthesized for glass bead filled epoxy resins. The grafting reaction and the degree of grafting of HPE-Si onto the surface of glass beads were characterized by Fourier transform infrared photoacoustic spectroscopy (FT-IR-PAS) and thermogravimetric analysis (TGA) measurements. The degree of grafting was calculated to be in the range 1.0–4.2% for different HPE-Si treatments. The tensile strength and modulus of glass bead filled epoxy resins were found to increase with increasing filler content. Moreover, HPE-Si4 series have the highest tensile strength and modulus at the same glass bead size and volume fraction in the composites compared with HPE-Si8 series. The fracture toughness (K1c) of specimens with different glass bead sizes (4.8 and 2.0 μm) has the same trend that changes with the filler content and the modification of the surface of glass beads. The investigation of the toughening mechanism using Irwin's model through the yield stress measurements suggest that the toughening mechanism for small glass bead filled resins does not involve matrix plasticity, whereas the toughening mechanism involving matrix shear banding for large glass bead filled resins with higher filler content (up to 10 wt%) was proposed. The morphology of the filled resins studied by scanning electron microscopy (SEM) showed that the interface compatibility between the glass beads and epoxy matrix was greatly improved by the treatment with HPE-Si. Copyright © 2005 John Wiley & Sons, Ltd.