Effect of Surface Treatment of Halloysite Nanotubes (HNTs) on the Kinetics of Epoxy Resin Cure with Amines.

Vahideh Akbari,Krzysztof Formela,Zahed Ahmadi,Hossein Abdollahi,Mohammad Reza Saeb,Maryam Jouyandeh,Seyed Mohammad Reza Paran,Mohammad Reza Ganjali,Sajjad Habibzadeh,Amin Esmaeili,Ahmad Mohaddespour,Henri Vahabi

doi:10.3390/polym12040930

Abstract

The epoxy/clay nanocomposites have been extensively considered over years because of their low cost and excellent performance. Halloysite nanotubes (HNTs) are unique 1D natural nanofillers with a hollow tubular shape and high aspect ratio. To tackle poor dispersion of the pristine halloysite (P-HNT) in the epoxy matrix, alkali surface-treated HNT (A-HNT) and epoxy silane functionalized HNT (F-HNT) were developed and cured with epoxy resin. Nonisothermal differential scanning calorimetry (DSC) analyses were performed on epoxy nanocomposites containing 0.1 wt.% of P-HNT, A-HNT, and F-HNT. Quantitative analysis of the cure kinetics of epoxy/amine system made by isoconversional Kissinger–Akahira–Sunose (KAS) and Friedman methods made possible calculation of the activation energy (Eα) as a function of conversion (α). The activation energy gradually increased by increasing α due to the diffusion-control mechanism. However, the average value of Eα for nanocomposites was lower comparably, suggesting autocatalytic curing mechanism. Detailed assessment revealed that autocatalytic reaction degree, m increased at low heating rate from 0.107 for neat epoxy/amine system to 0.908 and 0.24 for epoxy/P-HNT and epoxy/A-HNT nanocomposites, respectively, whereas epoxy/F-HNT system had m value of 0.072 as a signature of dominance of non-catalytic reactions. At high heating rates, a similar behavior but not that significant was observed due to the accelerated gelation in the system. In fact, by the introduction of nanotubes the mobility of curing moieties decreased resulting in some deviation of experimental cure rate values from the predicted values obtained using KAS and Friedman methods.

Highlights

The curing reaction of epoxy resin, so-called crosslinking, includes formation of short chains followed by branching until formation of a cross-linked network [1,2,3]
OH groups were formed during the reaction of epoxy on the surface of F-Halloysite nanotubes (HNTs) with amine groups of curing agent by surface modification of HNT with epoxy silane coupling agent, and again a shoulder appeared at higher temperatures
pristine HNT (P-HNT) and alkali surface-treated HNT (A-HNT) assisted curing agent, while functionalized HNT (F-HNT) somewhat compensated the stoichiometry for epoxy resin

Summary

Introduction

The curing reaction of epoxy resin, so-called crosslinking, includes formation of short chains followed by branching until formation of a cross-linked network [1,2,3]. The cure reaction of epoxy and its properties are dependent on the fillers involved in the formulation and the interactions between filler and the matrix [7,8,9]. The morphology of nanoparticles and their content can strongly affect cross-linking reaction of epoxy. Surface modification of cobalt doped Fe3 O4 nanoparticles with ethylenediaminetetraacetic acid enhanced the curability of epoxy nanocomposite because of the reaction between the carboxylic acid anchored to the surface of particles and the epoxide rings [11]

Methods

Results

Conclusion