Cellulose nanocrystals (CNCs) are nanoscale, crystalline, rod-shaped particles derived from wood pulp, plants, and other renewable sources. The inherent orientation of cellulose chains in each individual CNC results in an amphiphilic nanoparticle with a hydrophobic edge, a property that allows for CNCs to effectively stabilize emulsions and foams. In this work, we studied the interactions between CNCs and surfactants and their use as stabilizers for mini emulsion polymerization. Anionic CNCs in their acid form, or neutralized to have sodium counterions, and cationic trimethylammonium-modified CNCs were investigated with anionic sodium dodecyl sulfate and cationic cetyl trimethylammonium chloride surfactants. We observed an increase in CNC size and a decrease in absolute surface potential when oppositely charged CNCs and surfactants were mixed, implying electrostatic binding. Colloid probe atomic force microscopy also indicated that the adsorption and structuring of surfactants at CNC interfaces is strongly dependent on the surface charge and counterion. Mini emulsion polymerization reactions were performed in the presence of CNCs and surfactants, with and without hydrophobe, to understand the role of CNCs at the interface during polymerization. Poly(methyl methacrylate) (PMMA) latexes were produced giving PMMA nanoparticles when there was no interaction between the CNCs and the surfactant, and PMMA microparticles when the CNCs and surfactant acted as co-stabilizers (as measured by dynamic light scattering and MasterSizer, respectively). The size and morphology of the latex particles were further confirmed by scanning electron microscopy. Surface potential measurements showed that the charge of the PMMA particle was governed by the location of the CNCs. The glass transition temperature of PMMA remained constant among samples, suggesting that the polymer is not tethered to the CNCs. This work provides new insight into the use of CNCs in surfactant-based systems, such as in mini emulsion polymerization, and may extend CNC applications to new areas including adhesives, coatings, and cosmetics.

Cellulose nanocrystals and surfactants as mini emulsion polymerization stabilizers

253rd National Meeting (2017)

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