Simple Process To Produce High-Yield Cellulose Nanocrystals Using Recyclable Citric/Hydrochloric Acids

Cellulose nanocrystals (CNCs) have great potentials in many applications, such as high-performance nanocomposites. However, there are many challenges in the industrial production of CNCs, such as high cost of acid recovery, acid disposal, low yield, and poor thermal stability. In this study, a simple process to extract CNCs via recyclable acid hydrolysis of microcrystalline cellulose (MCC) is presented. A high yield (up to 87.8%) of carboxylated CNCs was obtained using recyclable citric/hydrochloric acid mixtures compared to the 53.9% yield for sulfated CNCs via recyclable H2SO4 hydrolysis. The mild acid mixtures could be readily recovered and recycled three times and showed a slight effect on the size of CNCs, carboxyl content of citrate CNC surface, zeta potential value, and thermal stability. Both charged citrate CNCs and sulfate CNCs were excellent food Pickering emulsion stabilizers for soybean oil/water emulsion droplets, whose diameter decreased with increasing CNC contents. This work provides a simple and low-cost pathway to recover mineral or organic acids for the sustainable and green production of CNCs with high yield and thermal stability while addressing the environmental issue of acid disposal in large-scale production of CNCs.