Holocellulose nanocrystals: amphiphilicity, oil/water emulsion, and self-assembly

Amphiphilic holoCNCs were derived from rice straw holocellulose by sulfuric acid hydrolysis (64%, 45 °C, 45 min) at 11.6% yield (8.8% of rice straw). HoloCNCs are similar in lateral dimensions (4.1 ± 1.6 nm thick, 6.4 ± 1.8 nm wide), but shorter and more heterogeneous in lengths (113 ± 70 nm long), less negatively charged (0.128 mmol/g) and less crystalline (CrI 84.4%) than CNCs. HoloCNCs were also more thermally stable (Tmax =284 °C), attributed to the presence of residual lignosulfonate, hemicellulose, and silica. Most remarkable, the amphiphilic holoCNCs were more hydrophobic than CNCs, exhibiting distinct surface active behaviors and lowering equilibrium surface tension to 49.2 mN/m at above 0.57% critical aggregation concentration. HoloCNCs not only stabilize 30% more oil-in-water (O/W) emulsion and formed droplets (1.2-1.6 μm) doubled the sizes of those with CNCs, but also self-assembled into highly mesoporous structures with up to 3× higher specific surface (111 m(2)/g) and total pore volume (0.40 cm(3)/g) than that from CNCs upon freeze-drying. The unique surface active, amphiphilic, and less self-assembling properties of holoCNCs offer new desirable characteristics but without additional isolation process nor surface modification of CNCs.