Surfactant-free emulsion Pickering polymerization stabilized by aldehyde-functionalized cellulose nanocrystals

Aldehyde-functionalized cellulose nanocrystals (CN) with two aldehyde contents were produced by periodate oxidation and gentle sonication. The aldehyde-functionalized CNCs were shown to be an effective stabilizer in the Pickering emulsion polymerization of acrylate monomers using potassium persulfate (KPS)/metabisulfite redox initiation system at 50 °C without any added surfactant. The effect of CNC content on the particle size, zeta-potential, colloidal stability and film properties were discussed. CNCs with the highest aldehyde content impart better colloidal stability to the polymer dispersion and lower particle size. The stabilization process was explained by the reaction of bisulfite with aldehyde groups borne by CNC, forming an adduct that contributes to the initiation of the polymerization and nucleation of polymer particles. This favors the effective attachment of CNCs onto the polymer particle, which is prerequisite for the effective Pickering stabilization process. The optical and mechanical properties of the nanocomposite films obtained by simple casting of the polymer dispersion and water evaporation were also investigated by transmittance and dynamic mechanical analysis (DMA). Better transparency was observed for films prepared in the presence of CNCs with the highest aldehyde content, while a reverse trend was noted for the mechanical properties.