Cellulose nanocrystals (CNC) fillers have been shown to significantly improve the performance of polymer composites and hydrogels by introducing strength and toughness. Commonly, the filler-matrix interactions are non-covalent hydrophobic or electrostatic interactions. A third option is the covalent grafting of the matrix to the filler. Such products are superior to composite materials with non-covalent filler-matrix interactions, as the strong bonding enables more efficient load transfer and prevents the disassembly of the compounds. However, the superior interactions come at the expense of laborious synthesis approaches. Popular “grafting-from” approaches by surface-initiated polymerizations such as atom transfer radical polymerization (ATRP) or ring-opening polymerization (ROP), require the introduction of an initiators onto the filler surface or suffer from the need for anhydrous conditions and exact stoichiometries to succeed. While effective and allowing for excellent control of the polymerization, these strenuous procedures limit the attractiveness of these strategies. Conversely, “grafting-to” approaches suffer from the limited reactivity of macromolecules with nanoparticles. Instead, we present a simple water-based modification of CNC by epoxidation to introduce vinyl groups onto the filler surface, followed by free radical polymerization in the presence of hydroxyethyl methacrylate (HEMA) in a grafting-through approach to obtain covalent CNC-reinforced pHEMA composites. Given the excellent biocompatibility of pHEMA, such composites find various applications ranging from bone tissue engineering and wound healing to dental adhesives and contact lenses, illustrating the need for controlling desired mechanical properties. As such, the water-based modification approach, omitting the need for intermediate drying and redispersion of the nanocellulose, coupled with the straightforward free radical polymerization allows for a simpler, cheaper production of the desired composites.

Simple free-radical copolymerization of vinyl-modified CNC for reinforced pHEMA composites

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