Sustainable preparation of bifunctional cellulose nanocrystals via mixed H2SO4/formic acid hydrolysis

In this work, a sustainable and highly efficient approach for preparing bifunctional cellulose nanocrystals (CNCs) was proposed through a mixed acid system of sulfuric acid and formic acid (FA). It was found that low-concentration (5–10 wt%) sulfuric acid can significantly improve the hydrolysis efficiency of FA (65–80 wt%), which enabled the highly efficient preparation of CNCs, i.e., the maximum yield of CNCs reached up to 70.65%. The obtained CNCs exhibited a rod-like shape with high crystallinity, and good dispersibility in both water and some organic phases. Moreover, the as-prepared CNCs exhibited high thermal stability, which is much higher than that of the traditionally sulfuric acid hydrolyzed ones. In addition, it was demonstrated that the bifunctional CNCs were able to stabilize various oils to form stable Pickering emulsion gels. Thus, this work provides a promising approach for sustainable preparation of bifunctional CNCs, which may find high-end applications in diverse fields. •Mixed H2SO4/HCOOH hydrolysis was established for the preparation of CNCs.•Both sulfate and formyl groups were introduced on the surface of CNCs.•The maximum yield of CNCs can reach up to 70.65%.•The obtained CNCs show excellent dispersibility in both aqueous and organic phases.•The bifunctional CNCs were able to stabilize various organic solvents to form Pickering emulsions.