Improving UV-stability of epoxy coating using encapsulated halloysite nanotubes with organic UV-stabilizers and lignin

Abstract

Epoxy coatings are used in a wide variety of applications due to their excellent chemical, thermal, and mechanical properties. However, their susceptibility to UV degradation has limited their use in exterior applications. Usually, organic UV absorbers and stabilizers are added to epoxy systems to improve their UV stability, but their performance decreases over time due to the degradation and loss of organic UV-stabilizers. In this study, a novel method was developed to encapsulate organic UV stabilizers and lignin (as a natural UV absorber) into halloysite nanotubes (HNTs). To ensure successful encapsulation, the pristine and filled halloysite nanotubes were characterized quantitatively, using a thermogravimetric analyzer (TGA), and qualitatively with X-ray photoelectron spectroscopy (XPS). Then, encapsulated nanotubes (HNTs) were added to an epoxy system (1−3 wt%) and their efficacy was evaluated before and after 840 h of accelerated weathering. Changes in physical, chemical, and thermal properties of coatings were measured using a spectrophotometer, field emission scanning electron microscopy (FE-SEM), electron paramagnetic resonance spectroscopy (EPR), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The results showed that epoxy samples containing 2 wt% HNT-encapsulated with organic UV-stabilizers, and samples containing 1 wt% HNTs encapsulated with lignin had significantly higher UV stability than epoxy resin prepared with the same concentration of these individual components (UV-stabilizers or lignin). This study demonstrates the efficacy of encapsulated HNTs, with UV stabilizers or lignin, in improving UV stability and extending service life of epoxy coatings. Nanoclay (HNT) loaded with lignin, a natural polymer, can be used as an effective UV-absorber to increase the weathering performance of epoxy resins.