Surface chemistry of halloysite nanotubes controls the curability of low filled epoxy nanocomposites

Abstract

A comparative study was performed on curing potential of low-filled epoxy/amine composites containing pristine halloysite nanotubes (P-HNTs), alkali-activated HNTs (A-HNTs), and silane-functionalized A-HNTs (F-HNTs). A-HNTs was obtained from P-HNTs in NaOH solution, then functionalized with 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane (ETMS) in isopropyl alcohol to obtain F-HNTs. X-ray spectroscopy (XPS) and thermogravimetric analysis (TGA) were employed to receive message from surface and bulk changes in nanoparticles, respectively. TGA results confirmed successful surface functionalization of HNT. In XPS spectra, as expected, Na1s appeared after surface activation. Growth in C1s form F-HNT in comparison with two other nanoparticles further approved successful modification. Harmoniously, oxygen graph was declined due to bonding of hydroxyl groups to the surface. Starting from 1 wt. % of HNTs with substantial aggregated HNTs domains seen in epoxy, we examined 0.5, 0.4, 0.3, 0.2, and then 0.1 wt.% of HNTs in 100 parts by weight of epoxy resin, where 0.2 wt.% loading was below the critical nanoparticle concentration for aggregation. Therefore, nanocomposites containing HNTs, A-HNTs, and F-HNTs were all prepared at such low loading level. Nonisothermal differential scanning calorimetry (DSC) at four different heating rates was performed for qualitative analysis of network formation by the aid of Cure Index dimensionless criterion. It was observed that the presence of low percentage of HNT and F-HNT led to Good cure situation in all heating rates. Whereas in low heating rates A-HNT led to Poor cure, which was compensated for at higher heating rates.