Detailed explanation of the preparation process of nanocellulose TEMPO oxidation

1. Overview

TEMPO oxidation method is a highly efficient and highly selective nanocellulose preparation technology, which is widely used in the preparation of carboxylated nanocellulose ( TOCN ). By selective oxidation of the primary hydroxy group at C6 position in natural cellulose molecules, carboxyl functional groups are introduced, so that cellulose has better dispersibility, reactive activity and application functions.

2. Raw materials and pretreatment

Suitable raw materials: wood pulp, cotton pulp, bamboo pulp, agricultural waste and other natural cellulose

Preprocessing steps:

Bleach removes lignin, improves purity and reaction efficiency

Weigh after drying and prepare for reaction

3. Oxidation reaction process parameters (take 1 gram of dry cellulose as an example)

Components	Dosage	effect
TEMPO	0.016 g (0.1 mmol)	Catalyst, initiate free radical reaction
NaBr	0.1 g (1 mmol)	Coordinated catalysis to improve reaction efficiency
NaClO	5–10 mmol	Oxidizing agent, providing active chlorine for hydroxyl oxidation
NaOH	Titration adjustment	Maintain pH 10–10.5
Deionized water	100 mL	Solvent medium

Reaction conditions:

Temperature: 20–25°C

Time: 2–4 hours

Stirring speed: 400–600 rpm

pH control: Adding NaOH dropwise to maintain an alkaline environment

4. Termination of reaction and washing treatment

1. Add ethanol or sodium sulfite to terminate the reaction

2. Centrifuge multiple times with deionized water ( 3–5 times)

3. Use a dialysis bag (molecular weight entrapment for 10,000 Da ) 48to remove residual small molecules

5. Fiber dissociation and dispersion

Oxidated cellulose easily dissociates into single nanofibers due to negative charge (carboxy) on the surface:

Stir and disperse: 30min

Ultrasonic treatment: 20 kHz ，10–15 minutes

High pressure homogeneity (optional): 600–1000 bar

VI. Product performance parameters

Performance metrics	Numerical range
Fiber diameter	3–20 nm
length	Hundreds of nanometers to several micrometers
Carboxylic content	0.5–1.5 mmol/g
Zeta potential (pH7)	–30 ~ –50 mV
form	Gel-like, clear or creamy white
Dispersibility	Stable suspension in the water, without settlement for several months

Structural characterization method

FTIR spectrum : Carboxyl C=O stretching peak at 1730 cm⁻¹ confirms oxidation occurrence

NMR ( 13C CP/MAS ) : The C6 carbon signal is moved left to 175 ppm , indicating carboxylation

XRD : Maintain cellulose type I crystal structure

TEM/AFM : Observe fiber diameter and length

Zeta Potentiometer : Evaluation of Dispersion Stability

8. Parameter optimization and process control

parameter	Enhanced effects	risk
NaClO dosage	Increase the degree of carboxylation	Peroxidation causes chain breakage
Reaction time	Increased carboxyl density	Influences the stability of the crystallization zone
Temperature rises	Accelerate the reaction	Prone to by-products
NaBr concentration decreases	Reduce reaction efficiency	Incomplete carboxylation

9. Industrialization Challenges and Solutions

High catalyst cost : It is recommended to use TEMPO reuse technology or low-cost replacement of catalysts

Heavy burden of water treatment : introduction of membrane separation technology (ultrafiltration / nanofiltration) to reduce waste liquid emissions

Easy to agglomerate when drying : It is recommended that the product be packaged in slurry or freeze-dried powder

10. Application prospects and industry directions

Application areas	Features and Advantages
Medical hydrogels, dressings	Good biocompatibility, controlled release
Food and packaging materials	Degradable, high barrier properties, high safety
Flexible Electronics and 3D Printing	Good rheology and suitable for composite printing materials
Environmental purification	Carboxylic groups can adsorb heavy metals, dyes, etc.
New energy	Can be used in lithium battery separators and conductive composite materials

As a functional green material, With the continuous maturity of low-cost catalysts, green reaction systems and continuous production technologies, this technology is expected to achieve larger-scale commercial application in the future.TEMPO oxidized nanocellulose has shown broad development potential in many high-value-added industries with its excellent dispersion and surface reactivity.