Abnormally High Graphitic Crystallization of Cellulose Nanocrystals

Area of Science:

• Materials Science
• Nanotechnology
• Polymer Chemistry

Background:

• Cellulose nanocrystals (CNCs) are abundant, sustainable materials with potential in energy storage and nanocomposites.
• Cellulose typically yields hard carbon upon carbonization, but abnormal graphitization in CNCs has been observed.
• Understanding the structural development during CNC carbonization is crucial for tailored material properties.

Purpose of the Study:

• To investigate the carbonization behavior of amorphous and crystalline phases of cellulose nanocrystals (CNCs).
• To differentiate the structural evolution of CNCs using spray-freeze-drying (SFD) and subsequent carbonization.
• To correlate CNC phase structure with the resulting carbon material properties (hard vs. soft carbon).

Main Methods:

• Utilized spray-freeze-drying (SFD) to process cellulose nanocrystals (CNCs).
• Performed carbonization studies on SFD-treated CNCs.
• Employed high-resolution transmission electron microscopy (HR-TEM) for morphological analysis.
• Conducted reactive molecular dynamics (RMD) simulations to study structural development.

Main Results:

• Morphological analysis revealed that amorphous CNC phases form hard carbon, while crystalline CNC phases form soft carbon.
• Reactive molecular dynamics (RMD) simulations indicated fewer carbon ring structures in amorphous cellulose, consistent with hard carbon formation.
• The crystalline cellulose phase exhibited higher density and thermal stability, promoting the formation of highly graphitic soft carbon structures.

Conclusions:

• The phase structure (amorphous vs. crystalline) of cellulose nanocrystals significantly dictates the type of carbon formed upon carbonization.
• The SFD method enables the differentiation of hard and soft carbon derived from CNCs.
• This finding offers insights into controlling carbon structures from biomass precursors for advanced applications like energy storage.