Intrinsic kink deformation in nanocellulose

Area of Science:

• Materials Science
• Nanotechnology
• Polymer Science

Background:

• Cellulose nanofibrils (CNFs) exhibit sharp bends (kink dislocations) after mechanical treatment, similar to those observed in wood cell walls under compression.
• The non-Gaussian distribution of kink angles suggests underlying deformation behaviors in cellulose nanocrystals (CNCs) during kink formation in CNFs.

Purpose of the Study:

• To investigate the kink deformation mechanism of nanocellulose using molecular dynamics simulations.
• To elucidate the intrinsic deformation modes and structural transitions of cellulose nanocrystals (CNCs) under compression.

Main Methods:

• Molecular dynamics simulations were employed to model the uniaxial compression of nanocellulose.
• Analysis focused on identifying deformation modes, structural phase transitions, and the role of hydrogen bonding in kink formation.

Main Results:

• An intrinsic deformation mode for Iβ cellulose nanocrystals (CNCs) under uniaxial compression was identified.
• Kinked CNCs were found to transition to a metastable triclinic Iα phase, featuring twin boundaries resulting from interlayer dislocation-induced allomorphic transitions.
• A characteristic intrinsic kink angle of approximately 60° was defined based on the geometry of stable kinked CNCs.
• Weakened intrachain hydrogen bonds within twin boundaries expose glycosidic bonds and disrupt hydrogen-bonding networks, initiating kink defects.

Conclusions:

• The study reveals an intrinsic mechanism for kink defect formation in nanocellulose, involving allomorphic transitions and hydrogen bond disruption in cellulose nanocrystals (CNCs).
• The findings provide fundamental insights into the mechanical behavior and defect origins in nanocellulose, crucial for understanding its properties and applications.