Tuning the Morphology of Microparticles from Spray Drying of Cellulose Nanocrystal Suspensions by Hydrophobic Lignin

Microparticle annular structures resembling "donuts" were obtained from spray drying of cellulose nanocrystal suspensions by addition of lignin. The formation of the donut and its accompanying pit were from the hydrophobicity of lignin that increased water evaporation kinetics during spray drying and decreased ability of water storage inside the microparticles. Indeed, the water inside the microsphere burst the center of the microsphere as verified by fluorescence imaging in which lignin was demonstrated to be concentrated in the center of the annular microsphere; although it was distributed throughout the microsphere, water on the surface of the hydrophobic lignin evaporated faster than on the surface of cellulose nanocrystals (CNC) so that the solid lignin shrank faster than CNC during material aggregation and preferentially concentrated in the center of the microparticle. The particles were modified with a hydrophobic agent, methyltrimethoxysilane (MTMS) and mixed with polydimethylsiloxane (PDMS) to prepare superhydrophobic coatings that greatly depended on the dosage of lignin during particle preparation.