Aspects of halloysite nanotubes integration in epoxy nanocomposites: curing kinetics and deformation mechanism

Official URL: https://dx.doi.org/10.1002/pc.27120

The curing kinetics of diglycidyl ether of bisphenol A epoxy resin using amine-based hardener in the presence of halloysite nanotubes (HNTs) are investigated by performing isothermal and dynamic differential scanning calorimetry measurements, followed by a detailed analysis of the experimental data via the kinetic free method and three common model-based analysis. Kamal and Sourour model gave the best fit for the experimental data and thus, was further modified by Williams–Landel–Ferry diffusion control equations to calculate the diffusion constants near the glass transition temperature (Tg). The optimized model is used to find the curing kinetics parameters of epoxy/HNTs nanocomposites, and those finding are further validated and explained by performing rheometric measurements. Noncatalytic and autocatalytic curing reactions and diffusion constants are all functions of the amount of HNTs. HNTs shift the curing reaction slightly toward higher temperatures and promote etherification reactions, leading to an increase in the curing enthalpy, as extra bonds will be formed between HNTs and epoxy resin during the polymerization. The combination of acceleration and inhibition mechanisms dictates the complex kinetics of the reactions at high concentrations of HNTs, while the produced local topology of the polymeric network depends highly on HNTs weight ratio. Furthermore, to investigate the mechanical performance of the prepared nanocomposites under flexural loads, three points bending tests are performed in both modes, dynamic and static, followed by a fractography analysis of the fractured surfaces. The mechanical properties have improved by the addition of pristine HNTs without compromising the Tg of the polymer. This study provides a set of observational relationships between various chemical interactions during polymerization and the final topology and performance of the polymer, which in turn aims to bridge the gap in the literature between the curing kinetics of epoxy/HNTs nanocomposites and the performance of these nanocomposites under various thermal and mechanical stresses.