Phosphorylated cellulose nanofibrils: structure-morphology-rheology relationships

Cellulose nanofibrils (CNFs) are normally available and used as aqueous suspensions. Total understanding of the rheological characteristics of CNF suspensions, however, remains a tremendous challenge. The main objective of this study is to investigate the structure-morphology-rheology relationships for CNFs as a function of phosphorylation duration. For that purpose, phosphorylated CNFs have been produced from jute fibers (Corchorus olitorius) with controlled curing times of the source materials and reported for the first time. The resulting fibers have a width in the range of 21–42 nm. It was observed that the morphological structure, crystallinity, surface charge, surface chemistry, and rheological property of the extracted CNFs were greatly influenced by the phosphorylation. The obtained CNF systems displayed a viscoelastic gel-like behavior because of the formation of highly entangled fibers structure. Results show that all CNF suspensions exhibit shear-thinning behavior. Both steady-state and dynamic rheology revealed that the characteristics of aqueous suspensions strongly changed depending on the phosphorylation. Finally, schematic modeling was proposed to demonstrate the transformation of the gel structure with curing time applied to the CNFs.