Nanocellulose preparation process: from natural cellulose to high-performance nanomaterials

Nano- cellulose is a nano-scale material extracted from natural cellulose. It has excellent properties such as high mechanical strength, low density, high transparency and biodegradability. It is widely used in composite materials, flexible electronics, Biomedicine and other fields. The preparation process of nanocellulose is the basis of its application. This article will systematically introduce the main preparation methods and process characteristics of nanocellulose.

Classification of nanocellulose

Nanocellulose is mainly divided into three categories:

Cellulose nanocrystals: Rod-like structure with high crystallinity.

Cellulose Nanofibers: a fibrous structure with a high aspect ratio.

Bacterial Cellulose (BC, Bacterial Cellulose): Nanocellulose synthesized by microorganisms with high purity and high mechanical properties.

Preparation process of nanocellulose

1. Preparation of cellulose nanocrystals (CNCs)

Cellulose nanocrystals are mainly prepared by strong acid hydrolysis, and their process steps are as follows:

Raw material pretreatment: Crush, wash and dry natural cellulose (such as wood, cotton, straw, etc.) to remove impurities.

Acid hydrolysis: The pretreated cellulose is reacted with concentrated sulfuric acid (usually 60-65%) at 45-60°C for 30-120 minutes. Acid hydrolysis destroys the amorphous region of cellulose, retains the crystalline region, and forms nanocrystals.

Neutralization and washing: dilute the reaction solution with deionized water and remove the acid by centrifugation or dialysis.

Dispersion and drying: The obtained nanocellulose dispersion is sonicated and finally CNC powder is obtained by freeze-drying or spray-drying.

Process Features:

The product has high crystallinity (usually >70%) and high mechanical strength.

The process is simple, but the use of acid has a certain impact on the environment.

2. Preparation of cellulose nanofibers (CNF)

Cellulose nanofibers are mainly prepared by mechanical methods, and common methods include high-pressure homogenization method, grinding method and ultrasonic treatment method. The process steps are as follows:

Raw material pretreatment: Natural cellulose is subjected to chemical or enzymatic treatment to reduce the degree of polymerization and crystallinity of cellulose.

Mechanical treatment:

High-pressure homogenization method: The pretreated cellulose slurry is passed through a high-pressure homogenizer to dissociate the fibers into nanofibers under high pressure (usually >500 bar).

Grinding method: Use an ultrafine grinder to grind the cellulose slurry multiple times to obtain nanofibers.

Ultrasonic treatment method: Use the cavitation of ultrasonic waves to dissociate the fibers.

Dispersion and drying: The obtained nanofiber dispersion is sonicated and finally CNF powder is obtained by freeze-drying or spray-drying.

Process Features:

The product has a high aspect ratio and high flexibility.

High energy consumption, but environmentally friendly process.

%1. Preparation of bacterial cellulose (BC)

Bacterial cellulose is prepared by microbial fermentation method, and the process steps are as follows:

Strain culture: Select suitable bacteria (such as Acetobacterium leukococcus) for cultivation.

Fermentation and synthesis: Inoculate bacteria into culture medium containing carbon sources (such as glucose) and nutrients, and ferment under static or dynamic conditions for 5-14 days. Bacteria secrete cellulose, forming a network of nanofibers.

Purification treatment: The fermentation product is washed, alkaline treatment (removing bacteria and impurities) and dried to obtain a bacterial cellulose membrane or powder.

Process Features:

The product has high purity, high mechanical properties and high biocompatibility.

The process cycle is long, but the product performance is excellent.

Optimization and innovation of nanocellulose preparation process

To further improve the performance of nanocellulose and reduce the production costs, the researchers have developed many optimization and innovative processes:

Green chemistry method: Use environmentally friendly solvents such as ionic liquids and deep eutectic solvents to replace strong acids to reduce environmental pollution.

Enzyme-assisted method: Pretreat natural cellulose with cellulase to reduce the energy consumption of mechanical treatment.

Compound preparation method: Combining chemical method with mechanical method to improve the yield and performance of nanocellulose.

Continuous production: Develop continuous production processes to improve production efficiency and reduce costs.

Challenges and future development directions of nanocellulose preparation process

Although the preparation process of nanocellulose has made significant progress, there are still some challenges:

Large-scale production: It is necessary to develop efficient and low-cost large-scale production processes.

Process environmental protection: reduce the use of strong acids, strong alkalis and other chemicals, and develop green preparation processes.

Performance consistency: Improve the performance consistency of nanocellulose and meet the needs of industrial applications.

Multifunctionalization: Through surface modification or composite technology, nanocellulose is imparted with more functional characteristics.

In the future, with the advancement of nanotechnology and materials science, the preparation process of nanocellulose will develop in a direction of more efficient, environmentally friendly and more functions, laying the foundation for its application in more fields.

Conclusion

The preparation process of nanocellulose is the core of its application, and the transformation process from natural cellulose to high-performance nanomaterials involves a variety of methods and technologies. Through continuous optimization and innovative preparation processes, nanocellulose is expected to play a greater role in composite materials, flexible electronics, biomedicine and other fields, providing new solutions for sustainable development. With the advancement of technology, nanocellulose will surely become one of the important pillars of future materials science.

References

Klemm, D., et al. (2011). Nanocelluloses: A New Family of Nature-Based Materials. Angewandte Chemie International Edition, 50(24), 5438-5466.

Moon, RJ, et al. (2011). Cellulose Nanomaterials Review: Structure, Properties and Nanocomposites. Chemical Society Reviews, 40(7), 3941-3994.

Isogai, A. (2013). Wood Nanocelluloses: Fundamentals and Applications as New Bio-Based Nanomaterials. Journal of Wood Science, 59(6), 449-459.

ns as New Bio-Based Nanomaterials. Journal of Wood Science, 59(6), 449-459.