Detailed explanation of the preparation process of acid hydrolysis of nanocellulose

Detailed explanation of the preparation process of acid hydrolysis of nanocellulose

Nanocellulose is a high-performance material obtained by nano-treating natural cellulose, with excellent mechanical properties, thermal stability, biocompatibility and environmental friendliness Among them, . Acid Hydrolysis is a common and mature preparation method, which is particularly suitable for obtaining cellulose nanocrystals ( CNC ) . This process selectively degrades the amorphous region of cellulose through acidic media, thereby retaining the crystalline region and ultimately forming a highly ordered nanostructure.

1. Process principle

The acid hydrolysis method mainly relies on strong acids such as concentrated sulfuric acid or hydrochloric acid to hydrolyze cellulose at an appropriate temperature and reaction time. The acid preferentially acts on the amorphous region of the cellulose, causing it to break and dissolve, while the crystalline region is relatively stable due to its dense molecular arrangement structure, thus retaining it to form nanocrystals. The final nanocellulose is rod-shaped, has high rigidity and uniform size.

2. Preparation process

For raw materials,
you can choose plant-based raw materials rich in cellulose, such as wood pulp, cotton pulp, hemp fiber, sugar cane bagasse, and pretreatment is required to remove lignin and hemicellulose.

The acid hydrolysis reaction
is between controlled temperature ( 4590mins, depending on the type of raw material and the desired particle size.

Immediately after the termination reaction and dilution
reaction is completed, the mixture is poured into a large amount of cold water and quickly diluted to avoid structural damage caused by continued hydrolysis.

Neutralization and washing
by centrifugation and repeated washing with deionized water, the residual acid was removed, so that the pH was close to neutral.

Dialysis and desalting
The nanocellulose suspension was placed in a dialysis bag and dialyzed with deionized water for 3-5 days to further remove small molecule acids and impurities.

Homogenization and ultrasonic dispersion
are obtained to obtain a stable dispersed nanocrystal suspension, which can be subjected to ultrasonic treatment or high-pressure homogenization treatment.

Dry or freezing treatment (optional)
You can choose spray drying, freeze-drying or directly stored as a colloidal solution according to the product purpose.

3. Process parameter control

parameter	scope	Corresponding effects
Acid concentration	60% ~ 65% H₂SO₄	Determine the hydrolysis rate and nanocrystal size
Reaction temperature	45°C ~ 60°C	Increased temperature can speed up the reaction rate
Reaction time	30 ~ 90 minutes	The longer the time, the smaller the particle size, and the lower the yield
Solid-liquid ratio	1:10 ~ 1:20	Influence in the degree of infiltration and reaction efficiency

4. Process advantages and application prospects

Advantages:

The obtained CNC has uniform particle size distribution and high crystallinity;

The surface has a negative charge (sulfate group) and has good dispersion;

The cost is relatively low and is suitable for laboratory and pilot-scale operations.

challenge:

Acid treatment has environmental pollution problems;

Need a large amount of water resources for neutralization and cleaning;

The process needs to be precisely controlled, and slight deviations may lead to structural damage or a decrease in yield.

Application direction:
The CNC produced is widely used in food thickeners, biomedical materials, green packaging, ink coatings, composite materials and other fields, and is one of the green nanomaterials with great development potential.

Conclusion

As one of the classic methods in the preparation of acid hydrolysis nanocellulose , has become a key route in research and industrialization with its high crystallinity, high dispersion and mature operating procedures. With the development of green processes and resource recycling technology, the process will be further optimized in the future to help expand the application of nanocellulose in high-performance materials.