Improved resistance of chemically-modified nanocellulose against thermally-induced depolymerization

Area of Science:

• Materials Science
• Polymer Chemistry
• Nanotechnology

Background:

• Nanocellulose is a promising biomaterial with diverse applications.
• Its thermal stability is a critical limitation for many uses.
• Thermal degradation involves depolymerization and discoloration.

Purpose of the Study:

• To investigate the effect of benzoylation and pivaloylation on nanocellulose thermal stability.
• To assess the impact of these modifications on depolymerization and discoloration.
• To evaluate the role of α-hydrogens in thermal degradation pathways.

Main Methods:

• Esterification of nanocellulose with benzoyl (BNZ) and pivaloyl (PIV) groups.
• Thermal treatment of modified and unmodified nanocellulose in nitrogen and air.
• Viscometry and gel permeation chromatography (GPC) to determine changes in degree of polymerization (DP) and molecular weight distribution (MWD).

Main Results:

• BNZ and PIV nanocellulose esters, lacking α-hydrogens, exhibited higher DP and narrower MWD after thermal treatment compared to pure bacterial cellulose and esters with α-hydrogens (acetyl, myristoyl).
• Suppression of depolymerization correlated with reduced thermal discoloration.
• Resistance to depolymerization inhibits the formation of reducing ends, which are active sites for discoloration.

Conclusions:

• Benzoylation and pivaloylation significantly improve nanocellulose resistance to thermally-induced depolymerization.
• These esterification methods effectively reduce thermal discoloration by preventing the formation of degradation byproducts.
• Benzoylation and pivaloylation are excellent modification strategies for enhancing nanocellulose thermal stability.