A facile approach for extracting cellulose nanocrystals (CNCs) was presented through hydrochloric acid hydrolysis of cellulose raw materials under hydrothermal conditions. The influences of preparation parameters, such as reaction time, reaction temperature, and acid-to-cellulose raw material ratio, and different neutralization methods on the yield, microstructure and properties were studied. A high yield of up to 93.7%, crystallinity of 88.6%, and a maximum degradation temperature (T_max) of 363.9 °C can be achieved by combining hydrochloric acid hydrolysis under hydrothermal conditions and neutralization with ammonia, compared with only 30.2%, 84.3% and 253.2 °C for sulfuric acid hydrolysis, respectively. More importantly, good stability of aqueous CNC suspensions can also be obtained due to the existence of ammonium groups, which can easily be removed through simple heat treatment before using the CNCs.

An efficient and low-cost approach to prepare spherical cellulose nanocrystals (SCNCs) is presented through chemical hydrolysis of lyocell fibers in an ammonium persulfate (APS) solution. The as-prepared cellulose nanoparticles were characterized by scanning electron microscopy, atomic force microscopy, laser light scattering particle analysis, wide angle X-ray diffraction, Fourier transform infrared spectrometry and thermal gravimetric analysis. Effects of hydrolysis conditions, such as reaction time and temperature, and APS concentration on the morphology, microstructure, and thermal stability of cellulose nanoparticles are discussed. Moreover, it is found that under mild reaction conditions, cellulose nanoparticles are spherical particles with a narrow diameter distribution, and have a cellulose II polymorphic crystalline structure with surface carboxyl groups. The optimal hydrolysis time was found to be around 16 h for hydrolysis at 80 °C with a 1 M APS aqueous solution.