Morphological development of cellulose fibrils of a bleached eucalyptus pulp by mechanical fibrillation

This study reports the production of cellulose nanofibrils (CNF) from a bleached eucalyptus pulp using a commercial stone grinder. Scanning electronic microscopy and transmission electronic microscopy imaging were used to reveal morphological development of CNF at micro and nano scales, respectively. Two major structures were identified: (1) highly kinked, naturally helical, and untwisted fibrils that serve as backbones of CNF networks, and (2) entangled, less distinctively kinked (or curled) and twisted "soft looking" nanofibrils. These two major structures appeared in different features of CNF network such as "trees", "net", "flower", single fibril, etc. Prolonged fibrillation can break the nanofibrils into nanowhiskers from the untwisted fibrils with high crystallinity. Energy input for mechanical fibrillation is on the order of 5-30 kWh/kg. The gradual reduction in network size of CNF with time may be used to fractionate CNF.