Aqueous-Cellulose-Solvent-Derived Changes in Cellulose Nanocrystal Structure and Reinforcing Effects

Cellulose nanocrystals as reinforcing agents have received considerable interest, and their dimension mainly depends on the original sources of cellulose. We intend to manually modulate the morphology of cellulose nanocrystals by treating them with cellulose solvents so that we can explore their reinforcing capacity. In this work, waste cotton fabric was processed in two aqueous solvents (a sulfuric acid aqueous solution and a NaOH/urea aqueous solution), and the regenerated cellulose was used to produce cellulose nanocrystals using acid hydrolysis. The results revealed that the nanocrystals (RCNC-H) obtained after the treatment in sulfuric acid had a hybrid crystalline structure and a needle-like shape with an aspect ratio of about 15.2, while cotton fabric was completely dissolved in the NaOH/urea aqueous solution, and the regenerated nanocrystals (RCNC-N) displayed a typical crystalline form of cellulose II with a higher crystallinity and a shorter rod-like shape with an aspect ratio of about 6.3. The reinforcing effects of RCNC-H and RCNC-N were evaluated using polyvinyl alcohol (PVA) films as a model, where the addition of RCNC-H resulted in a relatively better tensile strength and oxygen barrier property, and the PVA/RCNC-N films had a slightly lower water vapor permeability. Therefore, this work suggests a new possibility for altering the naturally formed nanostructure of cellulose for different applications.