Molecular engineering of nanocellulose copolymer by grafting from homopolymerization of caprolactone: A revisit to temperature condition

Cellulose nanocrystal (CNC) is valued for their versatile applications, but its hygroscopic nature can limit performance in certain contexts, such as in biocomposites. One effective strategy to mitigate this issue is to enhance the surface hydrophobicity of CNC. Despite advancements in CNC surface hydrophobicity, comprehensive insights into the surface chemistry and physicochemical properties of polymer-modified CNC remain limited. This study investigates the effect of reaction temperature on structure and performance of polycaprolactone-grafted cellulose nanocrystals (PCNC) via ring-opening polymerization. Detailed structural analysis using liquid-state proton nuclear magnetic resonance ( ¹H NMR) reveals a notably high grafting ratio of 12.03 for caprolactone at 130 °C - six times higher than that at 100 °C. Higher reaction temperature yielded increased molecular chain length and substitution degree of grafted PCL, attributed to enhanced caprolactone reactivity. Dispersion tests show that PCNC formed homogeneous and stable colloids in dichloromethane, evidencing an enhancement in surface hydrophobicity. Furthermore, the PCL layer anchored to the CNC disrupted the original crystal lattice, concurrently diminishing its crystallinity and thermal stability. These findings provide critical insights into CNC surface modification, with controlled grafting chain length and tailored polymer behavior, expanding CNC's utility across various applications.