Further characterization of cellulose nanocrystal (CNC) preparation from sulfuric acid hydrolysis of cotton fibers

Cellulose nanocrystal (CNC), as a natural/sustainable material, has attracted considerable attention, and its preparation from the sulfuric acid hydrolysis process has attained the precommercial demonstration stage. In this study, the process was further characterized by following the alkali solubility in an 18 % sodium hydroxide solution (S18) and the degree of polymerization (DP) of the cellulosic substrate during the sulfuric acid hydrolysis of cotton fibers. The results showed that the S18 increased as the hydrolysis progressed until reaching a nearly constant level at about 45 min, while the DP exhibited a decrease and approached a nearly constant level at 55 min. The emergence of the constant S18 coincided with the formation/appearance of CNC; thus, a “critical stage” with irregular CNC particle size but high yield was identified during the hydrolysis. The optimization of the CNC preparation process was realized under a shortened reaction time with 41.7 % yield (with a CNC size of <150 nm). Therefore, the amount of S18 can be used as a new characterization method for the preparation of CNC or other cellulose-derived products during the acid hydrolysis process with the advantage of a favorable product yield.