Chiral Self-Assembly Behavior of Carboxylated Cellulose Nanocrystals Isolated by Recyclable Oxalic Acid from Degreasing Cotton
Chunxiang Lin, Ping Wang, Yifan Liu, Yuancai Lv, Xiaoxia Ye, Minghua Liu, J. Y. Zhu
Abstract
Carboxylated cellulose nanocrystals (OA-CNCs) isolated by aqueous recyclable oxalic acid hydrolysis from degreasing cotton were used to observe its self-assembly behavior and chiral nematic properties. The oxalic acid here served as the sole catalyst to esterify and hydrolyze the degreasing cotton. The results indicated that the obtained OA-CNC suspensions were spontaneously phase-separated into a chiral nematic mesophase above a critical concentration, and the occurrence of chiral self-assembly is highly dependent on the aspect ratio and the surface charge of the OA-CNC suspension. Scanning electron microscopy images of the cross section of OA-CNC solid films revealed a periodic ordered multilayer structure. The residual OA was easily recovered through simple re-crystallization method after reactions with a high recovery rate of at least 90%. The recycled OA (ROA) had excellent performance in terms of ROA-CNC yield even after reusing for five cycles. Moreover, the resultant ROA-CNCs from recycled OA could also form chiral nematic ordered phases with little change in the critical concentration and pitch, suggesting excellent suitability for sustainable OA-CNC production for photonics and other specialty applications.