Tailored cellulose nanocrystals as a functional ultraviolet absorbing nanofiller of epoxy polymers

Epoxy is an extensively used polymer in several applications such as coatings, adhesives, structural composites etc. However, it is a poor ultraviolet (UV) absorber and suffers from UV-degradation, which usually leads to discoloration and loss of structural integrity. In this study, cellulose nanocrystals (CNCs) conjugated with a UV absorbing molecule were investigated as a functional nanomaterial to enhance the UV absorption of epoxy polymers. The grafting of a UV absorbing molecule, para-aminobenzoic acid (PABA), on the surface of CNCs was confirmed using FTIR, proton NMR, and via elemental analysis. The modified CNCs were then incorporated into an epoxy polymer and their efficacy in mitigating the photo-degradation of epoxy was evaluated. For this, a neat epoxy control, native CNCs and modified CNC based nanocomposite specimens were subjected to controlled UV irradiation and the resulting structure-property changes were assessed. Results of UV absorption and discoloration showed that the neat epoxy was impacted the most as a result of the UV irradiation. While the incorporation of native CNCs displayed some UV absorption and reduction in the UV mediated discoloration of the epoxy polymer, the most pronounced effect was obtained in PABA decorated CNC based epoxy nanocomposites. The use of such tailored CNCs has great potential to mitigate UV induced degradation of a range of polymers that are used especially in outdoor applications where direct exposure to UV is significant.