Quantitative Determination of Surface Functional Groups of Cellulose Nanofibers Using Toluidine Blue O Adsorption Method

Significance of the Topic

Cellulose nanofibers (CNF) are emerging as a sustainable, high-performance biomaterial due to their light weight, mechanical strength, biodegradability and barrier properties. Quantitative characterization of their surface functional groups is essential for controlling dispersion, reactivity and performance in applications ranging from packaging to composites and electronic materials.

Objectives and Study Overview

This study demonstrates a rapid, sensitive and reproducible method for quantifying surface carboxyl groups on CNF via toluidine blue O (TBO) adsorption coupled with UV-Vis spectrophotometry. It aims to overcome limitations of conductometric titration, which requires large sample masses, long analysis times and is operator-dependent.

Methodology and Instrumentation

• Sample Preparation: A TEMPO-oxidized CNF suspension is diluted to 2.5 wt % and mixed with TBO solution. After 2 h shaking, the mixture is centrifuged and the supernatant is diluted tenfold.
• Adsorption Principle: TBO, a cationic dye, selectively binds to anionic carboxyl groups on the CNF surface.
• Spectrophotometric Measurement: Using a Shimadzu UV-1900i, absorbance spectra from 400 to 900 nm (1 nm interval) are recorded, with a primary analysis wavelength at 628 nm.

Instrumentation Used

• Shimadzu UV-1900i UV-Vis spectrophotometer
• Microcentrifuge and orbital shaker for sample handling

Main Results and Discussion

• The supernatant shows a clear absorbance peak at 628 nm, corresponding to TBO bound to carboxyl groups.
• A calculation formula relates the measured absorbance, initial dye concentration, sample volume and molar absorption coefficient to the surface carboxyl concentration.
• Five replicate measurements yielded an average carboxyl content of 2.07 mmol/g with a coefficient of variation (CV) of 3.24 %, indicating high reproducibility.

Practical Benefits and Applications

• Only a few milligrams of CNF are needed per analysis.
• Rapid throughput: up to 50 samples in approximately 2.5 hours of instrument time.
• Minimal operator influence and straightforward data evaluation via spreadsheet calculations.
• Applicable for routine quality control and research in industries developing CNF-based materials.

Future Trends and Potential Applications

• Adaptation to other surface chemistries such as sulfated or phosphorylated nanocelluloses.
• Integration with automated sample handling and data processing for high-throughput screening.
• Correlation of surface functionalization with morphological and mechanical characterization techniques.
• Implementation in process monitoring and regulatory compliance workflows.

Conclusion

The TBO adsorption method combined with UV-Vis spectrophotometry provides a fast, sensitive and reliable approach for quantifying surface carboxyl groups on CNF. It addresses the shortcomings of conventional titration methods and supports efficient quality control in CNF production and research.

References

• Jun Araki, Cellulose, 28, 7707–7715 (2021).
• Jun Araki, Cellulose, 29, 8489–8490 (2022).
• Jun Araki & Minami Nakajima, Cellulose, 30, 849–855 (2023).