Role of silanized halloysite nanotubes on structural, mechanical properties and fracture toughness of thermoset nanocomposites

This study investigates the structure/property relationship of thermosetting unsaturated polyester (UPE) filled with pristine halloysite (HNT) and vinyltrimethoxysilane-treated halloysite nanotubes (s-HNT) nanocomposites. The dispersion of particles and morphological structures of the nanocomposites were examined using TEM and XRD analysis as well as Fourier Transform Infrared spectroscopy (FTIR). Thermogravimetric analysis (TGA) and mechanical properties were characterized. The evaluation of stress intensity factor (K-Ic) was measured based on linear elastic fracture mechanics (LEFM) and single-edge notch bending (SENB) geometry to identify the role of silanized halloysites on toughening improvement. It was found that modifying UPE matrix with HNT or s-HNT changed the crystalline structure of the UPE nanocomposites, indicating a high degree of halloysite orientation. Uniform dispersed halloysites are observed in the s-HNT/UPE versus skewed-like clusters in the HNT/UPE nanocomposite. The introduction of HNT or s-HNT up to 5 wt.% induced higher mechanical properties and improved fracture toughness associated with a shift in toughening mechanisms from a highly brittle fracture for neat UPE into matrix shear yielding and zone shielding mechanisms with the presence of halloysite particles in the nanocomposite. (C) 2013 Elsevier Ltd. All rights reserved.