Long and entangled native nanofibrillated cellulose (NFC) and rod-like nanocrystalline cellulose (CNC) have extensively been exploited in nanocomposites to reinforce for higher stiffness and strength. In some applications, however, competing capability for controlled structural reorganizations may be needed, for example in designing toughness, self-healing, and switchable structures and properties. Nanocellulose films (nanopapers) are based on dense nanocellulose networks, and upon deformations, the cracks typically tend to propagate catastrophically. Here we show that CNCs with polyacrylate side chain brushes, containing ureidopyrimidone hydrogen bonding supramolecular groups suppress uncontrolled crack growth in mechanical deformations (J. McKee et al, Angew. Chem, 53, 5049, 2014). The architecture allows mutual dissipative movement of the CNCs as well as ureidopyrimidone bond exchanges which dissipate fracture energy where the strong ureidopyrimidone-mediated supramolecular interactions still allow promoted cohesion of the material. Our other examples of incorporating supramolecular interactions with nanocelluloses deal hydrogels. In this case CNC is decorated with polyacrylate brushes containing naphthyl moieties. The hydrogel contains also polyvinyl alcohol polymers with methyl viologen side chains and dispersed cucurbit[8]uril supramolecular host molecules that can bind simultaneous the naphthyls and viologens (J. McKee et al, Adv. Funct. Mater. 24, 2706, 2014). The combination of the competing nanocellulose reinforcement and the rapid dynamics of the host/guest binding leads to rapid sol-gel transitions and self-healing even after long storage times. Another concept is based on similar host-guest chemistry of cucurbit[8]uril, where interpenetrating molecular and colloidal level hydrogels show synergistic improvement of the modulus. In addition, the cucurbit[8]uril-mediated molecular level hydrogel allows improved strain levels vs. the pure colloidal NFC hydrogel, this promoting the interconnectivity of the colloidal gel (E. Janacek et al, submitted). Finally, rheological strain hardening is demonstrated in CNC-reinforced methyl cellulose gels, where the adsorption of methyl cellulose on CNC is expected to be crucial to mediate physical interactions (J. McKee et al, ACS Macro Letters, <b>3</b>, 266, 2014). The examples demonstrate possibilities to combine colloidal and molecular level motifs and interactions in balanced ways to combine competing properties.

Functionalization of nanocelluloses by supramolecular motifs to combine competing properties

249th National Meeting (2015)

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