Bio-based functionalization of halloysite nanotubes: Rheokinetics and surface modification with epoxidized linseed and soybean oils

Abstract

Halloysite nanotubes (Hal) are among the most important fillers in the polymer industry; nonetheless, their incompatibility with hydrophobic polymers has been challenging. This study investigates the direct modification of Hal using epoxidized linseed oil (ELO) and epoxidized soybean oil (ESBO), focusing on the impact of reaction temperature on functionalization efficiency and kinetics. The chemical interaction between the oxirane groups in ELO and ESBO, and hydroxyl groups on the Hal was monitored using different techniques. Rheokinetics measurements demonstrated a significant increase in storage modulus with temperature, indicating the formation of a crosslinked network between Hal and oils. The reaction kinetics followed an Arrhenius-type behavior, with ESBO-modified Hal exhibiting a lower activation energy (15.50 kJ/mol) than ELO (16.06 kJ/mol). Chemical assessment confirmed a reduction in inner hydroxyl groups and an increase in carbonyl groups at elevated temperatures, while thermal studies revealed a progressive increase in mass loss, indicative of successful functionalization. Microscopy showed morphological changes in Hal upon modification with both oils, with ESBO depicting a higher reactivity despite its lower epoxy content. This study presents a novel approach to modifying Hal while highlighting the influence of temperature. These findings provide sustainable strategies for enhancing the performance of Hal-based polymer composites.