Interactions of ionic liquids with polysaccharides. VI. Pure cellulose nanoparticles from trimethylsilyl cellulose synthesized in ionic liquids

Trimethylsilyl cellulose (TMSC) can be efficiently synthesized with 1,1,1,3,3,3-hexamethyldisilazane (HMDS) by applying the ionic liquids (ILs) 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium chloride, and 1-butyl-3-methylimidazolium chloride as reaction medium, yielding pure biopolymer derivatives with degrees of substitution (DS) up to 2.89. Cosolvents, for example, chloroform, could be used to adjust the viscosity of the system and to achieve the miscibility of the components. During the synthesis of highly functionalized derivatives precipitation of the TMSC occurred, which simplifies the recycling of the IL. The high tendency of TMSC toward the formation of supermolecular structures was exploited for the formation of nanoparticles studying a simple dialysis process. Amazingly, pure cellulose nanoparticles can be obtained by dissolving TMSC in tetrahydrofurane or N,N-dimethyl acetamide and dialysis against water. FTIR spectroscopy confirmed the complete removal of the TMS functions during this process. Scanning electron microscopy, dynamic light scattering, atomic force microscopy, and particle size distribution analysis showed that cellulose particles down to a size of 170 nm are accessible in this simple manner. The nanoparticle suspensions exhibit viscosities in the range of water.