Investigating the interactions between a poloxamer and TEMPO-oxidised cellulose nanocrystals

Cellulose nanocrystals (CNCs) have emerged as promising, sustainable materials, with applications in sensors, coatings, pharmaceuticals, and composites. Their modification with block copolymers such as PEO-PPO-PEO triblock copolymers of the Pluronic family has been attempted many times in the literature, with claims that such modification would happen by an anchor(PEO)-buoy(PPO)-anchor(PEO) mechanism. However, there is much disagreement in the literature on this. We herein physically adsorbed Pluronic F127, a nontoxic triblock copolymer poloxamer, comprising hydrophilic polyethylene oxide (PEO) and hydrophobic polypropylene oxide (PPO) blocks, onto the surface of TEMPO oxidised CNCs by simple mixing in an aqueous medium. The adsorption of F127 onto the surface of these CNCs was successful and persistent even after solubilisation. The thermal stability of modified TOCNCs increased (by ~19 °C) compared to their neat and oxidised counterparts. F127-TOCNC suspensions exhibited comparable viscosity to their neat and oxidised counterparts without premature gelation of F127. NOESY NMR observations showed that PPO blocks are more proximal to the TOCNC than the PEO blocks. AFM and QCM-D analyses supported the formation of a rigid, thin layer of block copolymer surrounding the TOCNC. A degree of modification (7 %) was achieved, even after washing, proving that adsorption is persistent and mainly irreversible.