A comparative study of grafting modification on tannic acid pre-adsorbed cellulose nanocrystals by alkyl chains with different lengths to obtain epoxy resin nanocomposite films with high performance

Cellulose nanocrystals (CNCs) with an exceptional sustainability profile have been used as fillers in epoxy resin as a preferable alternative to carbon nanotube or graphene. However, the dispersibility and compatibility of CNCs in epoxy resin remains an unavoidable issue. Here, the grafting modification of CNCs by alkyl chains with different lengths was achieved through Schiff base reaction/Michael addition, which was systematically compared with commonly used esterification reaction method. Especially, the former strategy was performed directly in water. First, tannic acid (TA) was tried to pre-adsorb on CNC surface, and then ethylamine or dodecylamine was grafted onto reaction sites of TA by Schiff base reaction/Michael addition. The success of these two strategies was confirmed by FTIR and XPS analysis. Meanwhile, the water contact angle of CNC samples and their dispersion stability in acetone were also investigated to explore the impact of the above modification methods on the performance of CNCs. Finally, CNC samples were added to epoxy resin to prepare nanocomposite films and their mechanical, optical and thermal properties, especially their rheological behavior before curing were studied in depth. This work demonstrated the performance changes of CNCs modified by above two strategies and their reinforcement effects in epoxy resin nanocomposite films. Meanwhile, this work systematically revealed the action mechanism of the TA in the modification process.