Synthesis and oxidative stability of phenolic antioxidants immobilized by cellulose nanocrystals

Antioxidants are immobilized by attaching them as functional groups to cellulose nanocrystals. The synthesis route includes a carboxymethylation step followed by covalent grafting of di-tert-butylphenol moieties (first product). To improve solubility within non-polar polymeric matrices additional octadecyl groups are added (second product). Both products are fully characterized using FT-IR, solid-state NMR, and thermogravimetric analyses. The degree of substitution in each functionalization step is determined by conductometric titration. The syntheses are successful, with moderate degrees of functionalization due to limited accessibility of the hydroxyl groups, which correlates with the geometric shape of cellulose nanocrystals. The stabilization effect is determined by oxidation induction time measurements in squalane. Further, the influence of additional octadecyl moieties grafted to cellulose nanocrystals is assessed.