Enhancement of the technofunctional properties of microcrystalline cellulose via combined natural deep eutectic solvents and ultra-high-pressure homogenization

Heretofore, natural eutectic mixture-based solvents (NADES) have gained popularity in the field of cellulose chemistry. The present work explored the efficacy of combined NADES - ultra-high-pressure homogenization (UHPH) processing to transform microcrystalline cellulose (MCC) into nanofibrillar cellulose (CNF). Eutectic mixtures of choline chloride (ChCl) with glycerol, urea, malic, oxalic, or formic acid were employed for the pretreatment of MCC at 90 °C for one hour. Then, NADES-treated MCC was UHPH processed at 2500 bar for 20 cycles. Cellulose’s morphological and size changes during NADES and UHPH processing were monitored using dynamic light scattering and optical microscopy. The 20-fold UHPH processed CNFs were investigated for their chemical structure, crystallinity, thermal properties as well as the rheological behavior of their aqueous suspensions. DLS and microscopic assessments demonstrated a decrease in cellulose particle size proportional to the UHPH passes number. The ChCl-glycerol and -urea treated cellulose exhibited thinner fibers compared to the others. In contrast, the ChCl-malic and oxalic acid treated celluloses were morphologically closer to CNC, likely due to acid hydrolysis. Following DES pretreatment, the cellulose crystallinity increased, but after UHPH, it decreased, as high pressure effectively disrupted the crystalline regions. In addition, we found that the ChCl-glycerol, -urea, and -formic acid treated cellulose suspensions were more viscous, likely due to lower surface charge and fiber entanglement, while others showed lower but still elevated viscosity compared to pure CNCs at the same concentration. In conclusion, the combination of DES and UHPH is an efficient strategy to produce nanocellulose with good thickening properties. • Microcrystalline cellulose was modified employing combined DES-UHPH processing. • Glycerol, urea, malic, oxalic and formic acid were the HBD of the DES. • DES cellulose pretreatment reduced particle size and facilitated UHPH processing. • DES-UHPH processed microcrystalline cellulose exhibits good thickening capacity.